Race car suspension Class

[Ranger Mike]

We raced Mount Lawn with a mini stock years ago. Was an old baseball diamond I think. Equal length arms is the set up with the least camber change. It is the way to go if you have the room.

 

[Ranger Mike]

Performance Trends Circle Track softwarte shows -

Camber- We run camber to maintain the maximum tire tread contact patch. Typical front end specs are right side camber is - 3 ° and left side is + 2.5° Static. The old Sportsman class of Chevelle or Monte Carlo cars go to dynamic of -7.5° right and -1.83° left when in 2 1/2 inch dive and 2° roll.

A super late model will have same -3° rt. and +2.5° left static but this goes to -5.0° rt and -.9° left in a 2 inch dive and 2° roll.
Now look at the camber pic attached. I ran some numbers using Hoosier F tire, 8 inch wide and diameter of 27 inch.
1" offset is 2.1°
1.5" offset = 3.1°
2 inch offset = 4.2°
2.6" offset = 5.3°
3" offset = 6.3°
3.5" offset = 7.4°
No wonder these hard spec tires on a Sportsman, do not grip when the car is rolled over. You are only using 4.5" of the 8 inch tire for grip at max dive and roll. Not really since the tire carcass can move some. But what this does do is cause a heck of a lot of heat. And heat kills tire grip and life span. If the tire sidewall flex can be reduced or eliminated we have more grip and a longer tire life.

All the above use short A-arms on top and longer lower A-arms on the bottom. So if you can keep the tires planted with minimum camber change and the other drivers are twice the camber, you have a real advantage.

 

[Ranger Mike]

BBSS - Bigs Bar Soft Spring set up is really popular and most often half way implemented these days. You really need a track that is not bumpy and prevents the car skirts from sealing air under the car. You need a down force aero package to add front downforce on the right front. This really takes time and money to do correctly and only 10% of the cars I see have this package working as designed. See page 1 index for BBSS.

But every one has gone to the BBSS setup because of one major factor. It is limiting the amount of body roll that causes camber build. A super late model with custom A-Arm design will be half to camber build of the front clip model sportsman. Many times these high speed super lates have four different A-Arm lengths. Not a hot setup for road course cars use but intense for left hand turn racing, maximum left side weight and Minimum Camber build.

 

[Ranger Mike]

Body roll and RC location

Back on Page 14, post # 479 I used an illustration not to scale but relative to the point. The front Roll Center location matters greatly in the performance of the race car. Below illustration has the RC way up there at about 13” above the track. The Center of Gravity is about 16” above the track. Not to realistic. The pic below is a lot more real world with the Roll center up about 3 inch and 3 inch to the right of center. The CG is offset to the left 1 inch as most rules permit it.

Down force quick tutorial - Take a tire ( mounted on the wheel of course) and stand it up on its wide tread. Now facing the wheel Grip both sides like you are going to put it on the wheel lugs. Slide it on the garage floor. Slides pretty easy, right? Now have Lumpy the fat neighbor kid, sit on the tire and try this again. Sliding a 40 pound tire/wheel was easy but sliding a 165 pound tire/wheel/ fat kid set up is way more difficult. This is what happens when you add DOWN FORCE. More grip.

​

Increasing the amount of vertical downforce on the right front tire increases the available traction, but in a non-linear way. When you increase loading on a tire, it will gain traction, but not in constant multiples. Adding 706 lbs down force adds traction but if we double it the results will not double the traction. The amount of traction will be something less than 2 times.

Big Bar and Soft Spring setups - This setup limits body roll in an attempt to place more load on the left-side tires, leading to more equally loaded sets of tires to produce more traction. One major factor is to limit the air under the car and kill off lift. Initially when this set up developed ride heights were about 4 inch track to chassis now it is 3 inch. Everyone is going lower. This and a more aero body adds downforce on the car body to provide tire loading. You still need to take advantage of RC location to properly load the right front tire.

Per attached pic note - IT is not to scale so pay little attention to the appearance as it is not to scale but close approximation.

Left RC has a 5° angle to the right front tire contact patch. The Right side RC has a 7° angle. This is the jacking effect that can lift the left side tire if it is great enough. Remember the sprint cars carrying the left front tire off the ground thru the turns. This happens when the roll center is placed too far to the right of centerline.

Note the moment arm or lever length between the CG and the Rt RC are very close, less than 0.40 " inch length.Now let us look at what happens during cornering. Momentum will continue to travel in a straight line until another force changes the direction. In this case the tires will do this through the suspension linkages.

Now let us look at the MASS that will have Momentum and must be dealt with before the car starts pushing like a freight train. Typical Late Model car min wight limit is 3000 lbs.

Of this, Unsprung weight of quick change, coil overs (50% unsprung weight, sway bar (ARB), upper control arms) amount to 400 lbs. We need to handle 2600 lbs. mass.

On a typical race car the front to rear weight is 52-48%. Caution- the calculations here are not going to be accurate but are close enough to demonstrate the need for proper location of the front roll center. In this example 52% of 2600 lbs is 1352 lbs.

This Mass will continue forward or diagonal once the tires cause opposing force on the MASS. One force vector is from the right front tire to the Roll Center.

If we know the Angle Sine of the left RC has a 5° angle has SIN of 0.087. and we multiply this by the 1352 Mass we have 118 lbs. acting on the tire contact patch thru this vector and the remaining 1234 lbs. moving laterally to the outside of the track. But wait a minute. What also is happening during the cornering process.

The typical late model car has 34” between the front spring upper mounting points. Our left roll center is offset 3 inches to the left which means 42% of the body roll will act on this RC. We have 42% of the Mass moving thru the RC rotating and planting the right front tire with 518 lbs. downforce. The remaining 716 lbs. is moving laterally and pushing directly on the tires.

Now let us look at the Angle Sine of the right RC, 7° angle has SIN of 0.121 and we multiply this by the Mass we have 164 lbs. acting on the tire contact patch thru this vector and the remaining 1070 lbs. moving laterally to the outside of the track. But wait a minute. What also is happening during the cornering process.

The typical late model car has 34” between the front spring upper mounting points. Our right roll center is offset 3 inches to the right. Now we have 58% of the body roll rotating thru this RC. We have 58% of the Mass moving thru the RC rotating and planting the right front tire with 690 lbs. downforce. The remaining 500 lbs. is moving laterally and pushing directly on the tires.

Feature ................................ Left RC......................Right RC

Downforce on rt ft tire......518 lbs...................690 lbs or 25% more downforce

Force lateral thru tire...........716 lbs..............500 lbs or 30% less side load

Jacking force rt ft tire............118 lbs.................164 lbs

I would prefer 25% more down force on the right front tire and handle the momentum with this set up as opposed to the left side roll center method.

 

[mattmueller]

rm have a few questions on my car 2012 port city modified on bumps weighs 2470 the last setup I had in car
sway bar 1-1/8 1% stagger front 1/4 rear 3
lf 695 13in200 1200bump rf536 11in 250 1000bump
lr748 11in175 nb rr484 11in 400 nb
bar angels set with crossmember at 1/4 off ground II
lr 3 degrees top 5 rr 1 degree

I have moved bar angels springs heights and my result is the same every time and cannot get another reaction out of the car but tight and the tight that will try to take the wall down coming out of the corner 3 night this last year it showed up and was the fastest car on track but if you cant put the whole night together your screwed but when it was that way you could load car up and go back next week and it would be a second off i have showed up to track at 48%cross to 58% with the same outcome the 2 things i havent changed that i wanted to try was to shorten the pull bar as it is 6 in behind the cl of rear axle and adding weight other then motor weight witch i have had 2 weeks put my big motor in witch is a dart block and went from 49.7 rear to 48.3 and still had same outcome Iam about at my ends with this car and about to scrap it and start over

 

[Ranger Mike]

hello Matt
I see you are running big bar soft spring setup.
I see you have 58% left side weight. Right on.
Spring package and ARB is close but too much rt rear spring. a 300# would help. Your 400# rt rear spring works for a 3000 lbs. car but too much for the 600 pound lighter car.
I need information from you. On rear of the car,
Now scribe a line around each rear tire at the center of the each tire. This is the center line of the tread. Measure the distance between each center line. This is track width. Measure the top link (3rd link) mounting point to the right side tire center line . Send these measurements to me in this post please.

 

[UFO]

Body roll and RC location

Back on Page 14, post # 479 I used an illustration not to scale but relative to the point. The front Roll Center location matters greatly in the performance of the race car. Below illustration has the RC way up there at about 13” above the track. The Center of Gravity is about 16” above the track. Not to realistic. The pic below is a lot more real world with the Roll center up about 3 inch and 3 inch to the right of center. The CG is offset to the left 1 inch as most rules permit it.

Down force quick tutorial - Take a tire ( mounted on the wheel of course) and stand it up on its wide tread. Now facing the wheel Grip both sides like you are going to put it on the wheel lugs. Slide it on the garage floor. Slides pretty easy, right? Now have Lumpy the fat neighbor kid, sit on the tire and try this again. Sliding a 40 pound tire/wheel was easy but sliding a 165 pound tire/wheel/ fat kid set up is way more difficult. This is what happens when you add DOWN FORCE. More grip.

​

Increasing the amount of vertical downforce on the right front tire increases the available traction, but in a non-linear way. When you increase loading on a tire, it will gain traction, but not in constant multiples. Adding 706 lbs down force adds traction but if we double it the results will not double the traction. The amount of traction will be something less than 2 times.

Big Bar and Soft Spring setups - This setup limits body roll in an attempt to place more load on the left-side tires, leading to more equally loaded sets of tires to produce more traction. One major factor is to limit the air under the car and kill off lift. Initially when this set up developed ride heights were about 4 inch track to chassis now it is 3 inch. Everyone is going lower. This and a more aero body adds downforce on the car body to provide tire loading. You still need to take advantage of RC location to properly load the right front tire.

Per attached pic note -

Left RC has a 4° angle to the right front tire contact patch. The Right side RC has a 6° angle. This is the jacking effect that can lift the left side tire if it is great enough. Remember the sprint cars carrying the left front tire off the ground thru the turns. This happens when the roll center is placed too far to the right of centerline.

Note the longer moment arm or lever between the CG and the Rt RC.

Now let us look at what happens during cornering. Momentum will continue to travel in a straight line until another force changes the direction. In this case the tires will do this through the suspension linkages.

Now let us look at the MASS that will have Momentum and must be dealt with before the car starts pushing like a freight train. Typical Late Model car min wight limit is 3000 lbs.

Of this, Unsprung weight of quick change, coil overs (50% unsprung weight, sway bar (ARB), upper control arms) amount to 400 lbs. We need to handle 2600 lbs. mass.

On a typical race car the front to rear weight is 52-48%. Caution- the calculations here are not going to be accurate but are close enough to demonstrate the need for proper location of the front roll center. In this example 52% of 2600 lbs is 1352 lbs.

This Mass will continue forward or diagonal once the tires cause opposing force on the MASS. One force vector is from the right front tire to the Roll Center.

If we know the Angle Sine of the left RC has a 4° angle has SIN of 0.07. and we multiply this by the 1352 Mass we have 95 lbs. acting on the tire contact patch thru this vector and the remaining 1257 lbs. moving laterally to the outside of the track. But wait a minute. What also is happening during the cornering process.

The typical late model car has 34” between the front spring upper mounting points. Our left roll center is offset 3 inches to the left which means 42% of the body roll will act on this RC. We have 42% of the Mass moving thru the RC rotating and planting the right front tire with 528 lbs. downforce. The remaining 1402 lbs. is moving laterally and pushing directly on the tires.

Now let us look at the Angle Sine of the right RC, 6° angle has SIN of 0.10 and we multiply this by the Mass we have 135 lbs. acting on the tire contact patch thru this vector and the remaining 1217 lbs. moving laterally to the outside of the track. But wait a minute. What also is happening during the cornering process.

The typical late model car has 34” between the front spring upper mounting points. Our right roll center is offset 3 inches to the right. Now we have 58% of the body roll rotating thru this RC. We have 58% of the Mass moving thru the RC rotating and planting the right front tire with 706 lbs. downforce. The remaining 511 lbs. is moving laterally and pushing directly on the tires.

Feature ................................ Left RC......................Right RC

Downforce on rt ft tire......528 lbs...................706 lbs or 25% more downforce

Force lateral thru tire...........1402 lbs..............511 lbs

Jacking force rt ft tire............95 lbs.................135 lbs

I would prefer 25% more down force on the right front tire and handle the momentum with this set up as opposed to the left side roll center method.

Hi RM
I like this site there is a lot of things you bring to light and explain in a way to make it easy to under stand. There is a couple of things in this post don't sound right to me. One is that the BBSS car has more inside load and the only things that can can change load transfer with a given velocity and turn radius is the track width and COG height. There may be a slight change from COG not rising but that is probably controlled more with jacking forces.

The other thing is your explanation of load transfer on front end verses roll center height. This has the same argument as above, RCH, spring rate, and jacking effect can not change load transfer only how fast it takes place and how its distributed. RCH determines how much of the load transfer is handled by geometric forces and elastic forces. Any jacking forces that happen are subtracted from the elastic forces, or the difference of how much the inside spring got lighter and the outside spring got heavier.

So I don't think it matters where you put the roll center height or lateral position the steady state vertical load on the RF tire, in the turn, will not change. The lateral force on the front will be the static weight of the front end times the lateral G force, on a flat track, a little more complicated for banking. Please let me know if you think I have something wrong.

 

[berkeman]

Hey @Ranger Mike are you racing in New Zealand now?

 

[Ranger Mike]

Hmmmmmmmm..could be

 

[Ranger Mike]

Why does the car drive straight to the wall when I give it the gas?

History - Remember back in the muscle car day. The 426-cube engine would torque up the left front. Many motor mount broke as the rubber mount would separate. We had to put a chain on the left side of the motor and chain it to the chassis. Engine torque would twist the car lifting the left side up and and add load to the right rear tire. The car would swerve left when you dropped the clutch at 7000 rpm. Look on a Saturday morning for the rubber tire tracks showing this on any country road after the hot rodders had fun the night before. Tire marks going to the left !
Right rear tire was loaded, the rear left side tire was unloaded, car shot to the unloaded side, instant push under acceleration. Factory engineers realized this and the big cubic inch cars had 7 leaf right rear springs and 6 leaf left rear springs to counter this. Otherwise, you had a built-in push under acceleration to the left. So why does the hot rodders still shoot to the left? They stuff a high horsepower V8 into a grocery getter designed for the 6-cylinder low HP engine without fixing the rear spring situation.

Factory late model chassis builders , great craftsman like Howe, Port City , Left Hander etc. built late model race cars and sold them. A great value but all in all generic as they did not know what track, or the track rules or conditions the car would race. It saved huge time for the small race teams. They had one great a platform to finalize. Here is the problem.
Usually the car was sold with 4 race wheels to accommodate the track rules regarding tire size. You had to race 10-inch tires max, so you got 4 ten-inch-wide tires and appropriate wheel. Makes sense No one is a mind reader. Again, the rules for the cars would vary all over the places different tracks had different rules on engine offset, % left side weight. maximum track width etc.. goes on and on. You got a generic , well built , safe race car that out of the box was pretty darn good.
Discussion
The car probably had 1 inch engine offset to the left as this was pretty universal. The factory car was set up with at most 52% left side weight. This is still the norm, I think. The majority of racers today are running these older chassis unless you have cubic money and buy the latest greatest new chassis. The big problem is your race team decides on where to put the weight and what wheels to use.
Wheels - factory chassis guys like Howe, Port City , Left Hand ship the car with standard wheels on all four corners. Normally the wheel has 4 inch offset measuring from the back of the wheel to the wheel backing plate. Saves money and is a good baseline. If you take the 4-inch offset wheel off the car and put 3 inch offset on the right side of the car and 5 inch offset on the left side of the car you gain left side weight. You can gain 2% more left side weight doing this. Now you are at 54% left side weight. Now you add a 1-inch spacer between the hub and the backing plate so you can get up to 56% left side weight. Some even go radical using 6 inch offset wheels. Next you find out the track has a 58% maximum left side weight rule, so you move weight around to do this. Now you are at the legal 58% left side weight.
The problem
The location of the top link on any factory chassis is about a 52% left side weight set up on the standard 4 inch offset wheels and the tire track width. A very logical and safe starting point. Unless you ordered it with a specific requirement to change these settings. No one does this because no one knows about this Post!

The problem is the 3rd link is mounted at the original 52% weight location and should now be at the 58% location and it is not.
Why is top link mount so critical? The top link is the rear end link that pulls the race car. This top link directs all rear end force to the chassis. The rear tires grip the track and try to pull the rear end to the rear as the trailing arms. On the bottom, the trailing arms push the car to the front and try to climb up under the car.

We are discussing left turn race car where you want a left side weight bias. When in a turn you want the left side weight rolling over to the right side to assist the car with better traction (tire grip). Correct location of the 3rd link mounting is a real help so the tires are pulling on the third link equally otherwise when you step on the gas, one tire will bite more than the other and shoot you toward the outside of the track or the inside.

If the 3rd link is offset to the left more than the right side, the left will have more load and the right rear tire will have less load. Exactly opposite of the muscle car scenario above. What really happens is more force is added to the side of the car the link is biased to. In this case we have more force added to the left rear tire, so we create an on gas, corner exit PUSH condition.

The Cure

Mark each rear tire centerline. Measure the distance between them. This is the track width. Let's say 66 inches so the mid-point is located at 33 inches. Now measure the right-side tire centerline to the middle of the top link. Let's say it is 34 ¼ inches. 34 / 66 = 52% left side weight. If you are scaling at 58% left side weight we multiply the total track width time the % so 66" x .58 = 38 ¼ inches. The top link mount should be at 38 ¼ " so, move it left 4" then the push goes away. It is that simple to fix. ​

See attached photo a forum member, RaceMan12 posted on page 46 post 1602 this post. You can make this happen.​

Look at photo below. Notice the original top link mount was offset about 1 ½ inch to the left of the quick-change housing centerline. The racer relocated it about 4 inches more to the left.See post # 1576 page 46
post 1602 page 46
post 1604 page 46
this explains things in a lot more detail.

 

[Ranger Mike]

Hi RM
I like this site there is a lot of things you bring to light and explain in a way to make it easy to under stand. There is a couple of things in this post don't sound right to me. One is that the BBSS car has more inside load and the only things that can can change load transfer with a given velocity and turn radius is the track width and COG height. There may be a slight change from COG not rising but that is probably controlled more with jacking forces.

The other thing is your explanation of load transfer on front end verses roll center height. This has the same argument as above, RCH, spring rate, and jacking effect can not change load transfer only how fast it takes place and how its distributed. RCH determines how much of the load transfer is handled by geometric forces and elastic forces. Any jacking forces that happen are subtracted from the elastic forces, or the difference of how much the inside spring got lighter and the outside spring got heavier.

So I don't think it matters where you put the roll center height or lateral position the steady state vertical load on the RF tire, in the turn, will not change. The lateral force on the front will be the static weight of the front end times the lateral G force, on a flat track, a little more complicated for banking. Please let me know if you think I have something wrong.

One is that the BBSS car has more inside load and the only things that can change load transfer with a given velocity and turn radius is the track width and COG height. There may be a slight change from COG not rising but that is probably controlled more with jacking forces.Totally Wrong. *I have intentionally not factored in acceleration ( G force is a measure of acceleration). This would complicate the issue. Turn radius, COG height, RC height have no impact on the force of the car going into the turn. When the car gets to the max apex of the turn the only consideration is how to deal with the force of the momentum. Granted, the more Aero downforce you can apply before the turn the more the sprig package will compress. On ½ mile tracks this is a factor.

Only a few things can change inertia or resistance to change of direction. The tire traction, aero drag or the wall. COG height, Roll center height only change when the springs and ARB ( sway bar ) compress.

The other thing is your explanation of load transfer on front end verses roll center height. This has the same argument as above, RCH, spring rate, and jacking effect cannot change load transfer only how fast it takes place and how its distributed.

So, in fact, by your own words, RCH, spring rate, and jacking effect do change load transfer. Glad you acknowledge this.

RCH determines how much of the load transfer is handled by geometric forces and elastic forces.

I see I am making progress here. I assume by geometric forces you mean force vectors. By elastic forces you mean the springs, sway and tire adhesion handle the above forces.

Any jacking forces that happen are subtracted from the elastic forces, or the difference of how much the inside spring got lighter and the outside spring got heavier.

Yes, any jacking effect is subtracted from the requirement this remaining force that must be dealt with by the tires or the wall. This momentum is not going away.

So I don't think it matters where you put the roll center height or lateral position the steady state vertical load on the RF tire, in the turn, will not change.

This is why I seek not to reply much to your questions. Steady state load on the RF tire will not change???? You think body roll thru the roll center does not impact right front tire load ( more traction)?

The lateral force on the front will be the static weight of the front end times the lateral G force, on a flat track, a little more complicated for banking.

*Which is why I choosing to not complicate matters. Yes ,it does and you still must deal with it or hit the wall.

 

[Ranger Mike]

Street Stock or Hobby Stock Rear end width and 4 link problems

3100 pound max weight, 58% left side weight is max. 78” total tire width, must use stock suspension locations and stock brackets, 8 inch wheels, 9 inch tires max width, Ford 9 Inch rear end permitted.

We are talking about Chevelle, Monte Carlo with metric front end clip race cars. Let us look at what we legally can do to gain an advantage over the other racers.

Front track should be considerably wider than the rear track. The wider the front track, the more resistance to diagonal and lateral load transfer. Thus the car will be less likely to push when you nail the throttle on corner exit as the inside rear wheel won't be driving as much. Because the lateral weight transfer formula is - W x gs x H / G x T

where T = track width, H = height of Cg, G= cornering force we can simplify the formula by factoring in 1 G of cornering force to reduce the equation to WH/T so if we got a stock car with CG 20 inch tall, 3000 lbs. weight and 70 inch track width, we have 857 lbs. lateral weight transfer. If we have the same car and reduce the track width by 4 inches, 3000 x 20 / 66 = 910 pounds transferred and
Wider track will reduce the roll angle, weight transfer, and reduce all the ill effects but if we can gain traction by using the 58% rule the small 52 lbs. going lateral is worth it.
Is there an advantage to change the rear end to a narrower track width. Not really in this class.

Let us assume we have managed to get the 58% left side weight through battery and fuel cell location and ballast weight. For this discussion we will not address the front-end suspension and concentrate on how to best hook up the hard spec rear tires with the stock configuration rear end design.

Note the rear end below. We are locked into the 4-link suspension. The two top links are mounted at an angle 5 inch from the centerline of the rear end housing and at 40 degrees to the body and are connected by 10 ½ inch trail arms.

If we have a 70-inch track width the center is 35 inches. If we use the 58% formula, then 70” x 58% = 40.6 inch** should be where the center point is located so each tire gets equal loads. In reality we are pulling at the 35-inch mid-point and adding more load to the right-side tire. Typical top link with the torque spring on a 3-link rear suspension for car of this weight and these tires is 1200 lbs. spring rating. The car is going to load on the right side 14% more (768 lbs. total.) more than the left side (432 lbs. Total) and push the car to the left when you gas it. Build in loose condition.

track width​	Center line​	Ideal location for the 58%**​	Difference​
70​	35​	40.6​	5.6​
69​	34.5​	40.02​	5.52​
68​	34​	39.44​	5.44​
67​	33.5​	38.86​	5.36​
66​	33​	38.28​	5.28​
65​	32.5​	37.7​	5.2​
64​	32​	37.12​	5.12​
63​	31.5​	36.54​	5.04​

Note the rules say you must have Stock components and they must be mounted at the stock locations. Nowhere in the rules does it state you must use stock bolts OR the stock bolt size! It does not say you have to have them connected or hooked up in the factory manner. Removing the right upper arm will help a little but the rear end would sway sideways too much and the pinion angle would change a lot because the rear end would rotate too much. Not the hot setup.

So, what happens when you replace the stock bolt 9/16” diameter bolt with a smaller diameter bolt? And if you do this at both mounting points on the right-side top link you now have over 1/2 Inch of play before anything happens. Again, the rules say you have to use stock components but can substitute bushings. If you decide to leave in place the really worn-out bushings that have a lot of slop and play, you now have about an inch play on the right-side top link. You turn the right-side trail arm into a slider that will stop at the same place every time.

Note photo below- Mark the frame at the 50% track width center point, Mark the frame at the 58% target and you now have the ideal setup. When the rear end is slid to the full play position, project a straight line from the rear end housing centerline to the frame. It should move closer to the 58% target as depicted by the thick black line. The closer the line gets to the 58% target, the better the traction to 50-50 rear tire load. I cannot tell you a specific angle as there are just too many variables but if you do this you can directly measure the actual distance.

In the photo and my half ars depiction, I make the angle to be pulling at 75° angle and the sine is .96 so the force is1200 lbs. time .96 9 sine of 75° = 1152 lbs. and should be spread equally on the rear tires.
Real rough estimate. Cocking the rearend by 15° is a bunch but on exit traction with hard spec tires, it may be worth it.

There is not a lot you can do with the stock setup but make the best of it. This modification will give you an advantage relative to the monkey see monkey do racers out there.

Offset bushings - these can add static angle to the left side top link and give the rear end even more tilt toward the 58% target. On the lower training arms they can add in rear roll over steer. Many options and almost mandatory these days.

 

[UFO]

RM said
Big Bar and Soft Spring setups - This setup limits body roll in an attempt to place more load on the left-side tires, leading to more equally loaded sets of tires to produce more traction. One major factor is to limit the air under the car and kill off lift. Initially when this set up developed ride heights were about 4 inch track to chassis now it is 3 inch. Everyone is going lower. This and a more aero body adds downforce on the car body to provide tire loading. You still need to take advantage of RC location to properly load the right front tire.

Reference: https://www.physicsforums.com/threads/race-car-suspension-class.326355/page-48

UFO said
One is that the BBSS car has more inside load and the only things that can change load transfer with a given velocity and turn radius is the track width and COG height. There may be a slight change from COG not rising but that is probably controlled more with jacking forces.

Reference: https://www.physicsforums.com/threads/race-car-suspension-class.326355/page-48

RM said
Totally Wrong. *I have intentionally not factored in acceleration ( G force is a measure of acceleration). This would complicate the issue. Turn radius, COG height, RC height have no impact on the force of the car going into the turn. When the car gets to the max apex of the turn the only consideration is how to deal with the force of the momentum. Granted, the more Aero downforce you can apply before the turn the more the sprig package will compress. On ½ mile tracks this is a factor.

Reference: https://www.physicsforums.com/threads/race-car-suspension-class.326355/page-48

UFO
You did not explain why I was totally wrong. Your comment had nothing to do with my explanation. Limiting the roll with a big ARB does not place more load on the left side tires. It gets the front a little lower loading the front tires a little more from aero, but equaly, this load is more noticeable at higher speeds at the end of the straights. You have to be more specific, it looks like ererything I said is true

RM said
Only a few things can change inertia or resistance to change of direction. The tire traction, aero drag or the wall. COG height, Roll center height only change when the springs and ARB ( sway bar ) compress.

Reference: https://www.physicsforums.com/threads/race-car-suspension-class.326355/page-48

UFO
Yes tire traction is the major component but traction of one axle is affected by RC height, spring rates, and jacking force. They are used to balance the front axie with the back so you have the most over all traction and don't have one end or the other heading to the wall. There is other things that affect traction like tire pressure, compound, size, camber, and alighnment that aren't pertinant to this conversation. As far as aero I don't think
drag is the right term, I think it should be flat panel aero of the right side of the car and the difference of pressure under and over the car hopefully adding more down force and traction with out inertia.

UFO said
The other thing is your explanation of load transfer on front end verses roll center height. This has the same argument as above, RCH, spring rate, and jacking affect cannot change load transfer only how fast it takes place and how its distributed.

Reference: https://www.physicsforums.com/threads/race-car-suspension-class.326355/page-48

RM said
So, in fact, by your own words, RCH, spring rate, and jacking effect do change load transfer. Glad you acknowledge this.

Reference: https://www.physicsforums.com/threads/race-car-suspension-class.326355/page-48

UFO
Now how do you get that I said they do change load tansfer, when I clearly said they do not. They handle how load transfer is done, not how much is transfered.

UFO said
So I don't think it matters where you put the roll center height or lateral position the steady state vertical load on the RF tire, in the turn, will not change.

Reference: https://www.physicsforums.com/threads/race-car-suspension-class.326355/page-48

RM said
This is why I seek not to reply much to your questions. Steady state load on the RF tire will not change???? You think body roll thru the roll center does not impact right front tire load ( more traction)?

Reference: https://www.physicsforums.com/threads/race-car-suspension-class.326355/page-48

UFO
On this one I did not write what I trying to say, I was refering to a half car sample, the front only. My point is that you can change RC position on the front or the back and it will not change the total load transfer on the car. If you end up with more load on the right front, then you will have less on the right rear, and the total from the inside to the ouside is the same. You can have one set up that does not roll much and another one that rolls a lot, and in the same turn, at the same velocity, the total load transfer is the same, not more because it rolled more.

 

[Ranger Mike]

you state - the only things that can change load transfer with a given velocity and turn radius is the track width and COG height.
This is 2D thinking that ignores everything I have said. Most of your statements are contradicting your statement in the same sentence. I can not help you.

 

[Savem c10]

I m looking to purchase performance trends geometry software what would be recommended as they make a few different versions?

 

[Savem c10]

I’m looking at roll center geometry there two different styles. A traditional or conventional roll center and jacking force which one is more consistent or better on tires and why ?

 

[jack action]

I’m looking at roll center geometry there two different styles. A traditional or conventional roll center and jacking force which one is more consistent or better on tires and why ?

What is a "traditional roll center"? If the roll center is above ground, there is always a jacking force.

 

[Savem c10]

What is a "traditional roll center"? If the roll center is above ground, there is always a jacking force.

With a traditional style roll center they are usually located to the right of the center line with jacking force they are located left of the center line. Maybe Ranger Mike could shed some light on this .

 

[Ranger Mike]

Hello all, caught this before Sunday Mass, will get back to you but for simple use and good RC location and dynamic checks Performance Trends Circle Track analyzer is excellent. The Suspension analyzer to me is for designing a new suspension and great for the design engineer. i have both and use Circle Track Analyzer 90% of the time.
as far as conventional vs other RC locations...too much to address...im late..see you after Services..

 

[Ranger Mike]

see post 1654 above

 

[Savem c10]

see post 1654 above

see post 1654 above

Well RM I am conflicted right now because I’ve measured out my role centers and currently I’m sitting at 2 5/8 left of the centerline and 3 5/8 above ground and I know that you recommend 2 inches to the right of the centerline and 2 inches above ground, but I’ve heard some conflicting arguments about having the role center too far to the right as the car would last like 10 laps and go away versus the role center being to the left and giving the car longevity. Very unsure if I should move them or leave them where they’re at what would you recommend?

 

[Ranger Mike]

Actually, I recommend front roll center to be 2" to 2.5" above the ground and 2.5" to 3" to the right of centerline. This is for traditional or BBSS set up.
Are you using chassis center line of tire track width center line?
Can we agree that your 3 5/8 rc ht is a bit high for a paved track late model on 8 inch tires?
Can we agree that those spec tires need more down force to stick?
do you have tire temps for last long race?

You said -
I’ve heard some conflicting arguments about having the role center too far to the right as the car would last like 10 laps and go away versus the role center being to the left and giving the car longevity. Very unsure if I should move them or leave them where they’re at what would you recommend?

RM life lesson- ifin you want to keep getting what you been getting , stay in your lane and do nothing.
You want to WIN, take the chance, you only live ONCE. Winning is NOT for everyone.

 

[Savem c10]

Actually, I recommend front roll center to be 2" to 2.5" above the ground and 2.5" to 3" to the right of centerline. This is for traditional or BBSS set up.
Are you using chassis center line of tire track width center line?
Can we agree that your 3 5/8 rc ht is a bit high for a paved track late model on 8 inch tires?
Can we agree that those spec tires need more down force to stick?
do you have tire temps for last long race?

You said -
I’ve heard some conflicting arguments about having the role center too far to the right as the car would last like 10 laps and go away versus the role center being to the left and giving the car longevity. Very unsure if I should move them or leave them where they’re at what would you recommend?

RM life lesson- ifin you want to keep getting what you been getting , stay in your lane and do nothing.
You want to WIN, take the chance, you only live ONCE. Winning is NOT for everyone.

Hahahaha Great point RM . I’m going go with your recommendation. Full fab perimeter chassis . Yes 8” tire durometer is around 70 . I’m going say we are bbss but not 100 %. And yes we can agree the tire needs more down force to stick . I’m going re map roll centers and get back to you . Also I will include photos of my work. Thanks for the words of wisdom Rm . Till next time have a beer on me !

 

[Ranger Mike]

Here are your numbers
On a typical race car the front to rear weight is 52-48%. Caution- the calculations here are not going to be accurate but are close enough to demonstrate the need for proper location of the front roll center. In this example 52% of 2600 lbs is 1352 lbs.

This Mass will continue forward or diagonal once the tires cause opposing force on the MASS. One force vector is from the right front tire to the Roll Center.
If we know the Angle Sine of the left RC has a 115° angle has SIN of 0.190 and we multiply this by the 1352 Mass we have 257 lbs. acting on the tire contact patch thru this vector and the remaining 1095 lbs. moving laterally to the outside of the track. But wait a minute. What also is happening during the cornering process.

The Your late model car has 34” between the front spring upper mounting points. Our left roll center is offset 2 5/8 inches to the left which means 49% of the body roll will act on this RC. We have 49% of the Mass (1095) moving thru the RC rotating and planting the right front tire with 460 lbs. downforce. The remaining 635 lbs. is moving laterally and pushing directly on the tires.

Now let us look at the Angle Sine of the right RC, 5° angle has SIN of 0.087 and we multiply this by the Mass (1352) we have 118 lbs. acting on the tire contact patch thru this vector and the remaining 1234 lbs. moving laterally to the outside of the track. But wait a minute. What also is happening during the cornering process.

The typical late model car has 34” between the front spring upper mounting points. Our right roll center is offset 3 inches to the right. Now we have 52% of the body roll rotating thru this RC. We have 52% of the Mass (1234) moving thru the RC rotating and planting the right front tire with 642 lbs. downforce. The remaining 592 lbs. is moving laterally and pushing directly on the tires.

Feature ................................ Left RC......................Right RC
Downforce on rt ft tire......460 lbs...................642 lbs. or 40% more downforce

Force lateral thru tire...........635 lbs..............592 lbs. side load

Jacking force rt ft tire............257 lbs.................118 lbs.

You are running just about 3 times the jacking force with current set up.

I would bet you are running a stiff right rear spring (300#) to keep the left front from lifting. keep an eye on this! may need change.
The side loads are close but on those hard spec tires you need more down force to out corner the other racers to plant the right front tire and pivot the car in the turn.

Finally, have you ever heard of these hard spec tires going away in ten laps? Adding 182 pound down force and taking away 140 pounds jacking force is going to burn a tire in 10 laps...

Granted, this example is NOT for YOUR car. It is an example of RC location and impact on a spec tire car. So take it worth what it is worth. Opinions are is free. nuff said?

 

[Savem c10]

Here are your numbers
On a typical race car the front to rear weight is 52-48%. Caution- the calculations here are not going to be accurate but are close enough to demonstrate the need for proper location of the front roll center. In this example 52% of 2600 lbs is 1352 lbs.

This Mass will continue forward or diagonal once the tires cause opposing force on the MASS. One force vector is from the right front tire to the Roll Center.
If we know the Angle Sine of the left RC has a 115° angle has SIN of 0.190 and we multiply this by the 1352 Mass we have 257 lbs. acting on the tire contact patch thru this vector and the remaining 1095 lbs. moving laterally to the outside of the track. But wait a minute. What also is happening during the cornering process.

The Your late model car has 34” between the front spring upper mounting points. Our left roll center is offset 2 5/8 inches to the left which means 49% of the body roll will act on this RC. We have 49% of the Mass (1095) moving thru the RC rotating and planting the right front tire with 460 lbs. downforce. The remaining 635 lbs. is moving laterally and pushing directly on the tires.

Now let us look at the Angle Sine of the right RC, 5° angle has SIN of 0.087 and we multiply this by the Mass (1352) we have 118 lbs. acting on the tire contact patch thru this vector and the remaining 1234 lbs. moving laterally to the outside of the track. But wait a minute. What also is happening during the cornering process.

The typical late model car has 34” between the front spring upper mounting points. Our right roll center is offset 3 inches to the right. Now we have 52% of the body roll rotating thru this RC. We have 52% of the Mass (1234) moving thru the RC rotating and planting the right front tire with 642 lbs. downforce. The remaining 592 lbs. is moving laterally and pushing directly on the tires.

Feature ................................ Left RC......................Right RC
Downforce on rt ft tire......460 lbs...................642 lbs. or 40% more downforce

Force lateral thru tire...........635 lbs..............592 lbs. side load

Jacking force rt ft tire............257 lbs.................118 lbs.

You are running just about 3 times the jacking force with current set up.

I would bet you are running a stiff right rear spring (300#) to keep the left front from lifting. keep an eye on this! may need change.
The side loads are close but on those hard spec tires you need more down force to out corner the other racers to plant the right front tire and pivot the car in the turn.

Finally, have you ever heard of these hard spec tires going away in ten laps? Adding 182 pound down force and taking away 140 pounds jacking force is going to burn a tire in 10 laps...

Granted, this example is NOT for YOUR car. It is an example of RC location and impact on a spec tire car. So take it worth what it is worth. Opinions are is free. nuff said?

I have to admit RM most of the calculations are you putting forward to me are beyond my pay grade let’s say I’m not too familiar with trigonometry, but I’ve watched a few videos on what sin is and the calculations of it but not 100% confident on understanding of it. i’ve mapped out the role centers and tryed posting a picture for u .ill try again . I bought the Steve smith book u recommend laying the front end just it states in the book . I set the roll center at 2 5/8 off the and 2 5/8 right of the center line as I can move theses a with the upper a frame angles if need be . Figured this would be a good starting point.

 

[Savem c10]

I have to admit RM most of the calculations are you putting forward to me are beyond my pay grade let’s say I’m not too familiar with trigonometry, but I’ve watched a few videos on what sin is and the calculations of it but not 100% confident on understanding of it. i’ve mapped out the role centers and tryed posting a picture for u .ill try again . I bought the Steve smith book u recommend laying the front end just it states in the book . I set the roll center at 2 5/8 off the and 2 5/8 right of the center line as I can move theses a with the upper a frame angles if need be . Figured this would be a good starting point. View attachment 341203View attachment 341203

There some additional line here just figure out different a frame lengths and height I have lower frame set a correct heights . The thing I most curious about is how much migration I will get . I’m assuming I don’t want much .

 

[Ranger Mike]

AN EXCELLEANT START. Racers on this post. Attention! This is how you separate being a car driver and a winner! Understanding handling on YOUR track with YOUR car and what has to be done to change things to win! More on this later but please let me do some research and break it down on the SINE TRIG thing..
Face it people..todays education system in schools can tell you about Earth Day but lack basic educating of students on the friking basics!


C10 Good job. Hold the 2 5/8 " on both for now. Right in the ball park!


btw Earth Day is when I have a huge bon fire to burn the old race car tires and motor oil to celebrate. Batteries go in the river.

 

[Ranger Mike]

More on RC migration later but as long as the roll center stays to the right of the centerline and orbits within 3 inch of original position, you are good.
Next make sure Bump steer is good.
Also look at camber build on right front.
This is a lot of work but camber build and tire patch is critical on right front.
If you get a chance let me know right front dive ( shock travel) as this is the limits you have to work with.
Do not seek perfection as this is a bull ring car and all you need is have a superior set up versus the other racers. One thing I absolutely know is, unless you bought a new chassis from the factory, your car has been beat on and hacked up and no where near specs when it originally shipped.

Savvy?

 

[Ranger Mike]

Regarding Roll Center acting on right front tire contact patch.


Look at the diagram. We have a block placed on a slope. The forces acting on t his block are its Mass and Gravity.


Parallel force can be found using the formula: Fparallel = m * g * sin(θ) where:


Fparallel is the parallel force, - m is the mass of the object, g is the acceleration due to gravity (approximately 9.8 m/s2 on Earth), and θ is the angle of the inclined plane with respect to the horizontal.


For this exercise we can leave out G as gravity will effect both Roll Center setups the same. This leaves the equation Fparallel = m * sin(θ). or W times Sine θ
Note - θ is Theta angle in degrees.


For our race car we have the sprung weight of the car going into the corner and pushing from the Roll Center to the rt ft tire contact patch. If we know the total mass as previously calculated in the above example post # 1674, we have to deal with 1352 lbs. pushing directly on the rt ft tire contact patch at an angle of 11°

Sine of θ from Trig tables -

Sine of 90° = 1


Sine of 45° = 0.70


Sine of 30°= 0.50


Sine of 11°= 0.19


Sine of 5° = 0.08


So you see when you multiply 1352 x 11° angle with Sine of .19 = 257 lbs.


Now compared to 1352 x 5° angle with Sine of 0.08 = 108 lbs.


the smaller the angle, the less force results, everything else being equal.


This is why we always want to apply for at 90° to the object to get maximum applied force!

 

[Savem c10]

Regarding Roll Center acting on right front tire contact patch.


Look at the diagram. We have a block placed on a slope. The forces acting on t his block are its Mass and Gravity.


Parallel force can be found using the formula: Fparallel = m * g * sin(θ) where:


Fparallel is the parallel force, - m is the mass of the object, g is the acceleration due to gravity (approximately 9.8 m/s2 on Earth), and θ is the angle of the inclined plane with respect to the horizontal.


For this exercise we can leave out G as gravity will effect both Roll Center setups the same. This leaves the equation Fparallel = m * sin(θ). or W times Sine θ
Note - θ is Theta angle in degrees.


For our race car we have the sprung weight of the car going into the corner and pushing from the Roll Center to the rt ft tire contact patch. If we know the total mass as previously calculated in the above example post # 1674, we have to deal with 1352 lbs. pushing directly on the rt ft tire contact patch at an angle of 11°

Sine of θ from Trig tables -

Sine of 90° = 1


Sine of 45° = 0.70


Sine of 30°= 0.50


Sine of 11°= 0.19


Sine of 5° = 0.08


So you see when you multiply 1352 x 11° angle with Sine of .19 = 257 lbs.


Now compared to 1352 x 5° angle with Sine of 0.08 = 108 lbs.


the smaller the angle, the less force results, everything else being equal.


This is why we always want to apply for at 90° to the object to get maximum applied force!

That helps RM . I’m taking a short course trig for dummies . Another question I have .,How much travel should we be getting? And if we travel the car to far how badly does interrup the roll center and its ability to plant the Right front tire.How far off the ground should the cross member be when at full travel ?