Automotive Race car suspension Class

[Ranger Mike]

good one droobie...plus dummy weights don't talk back, screw up or drink all your beer...lot of merit in um!

 

[smithdl4]

Ranger Mike, I've been playing with the Perf Trends software. Was interested to know which direction the roll center ought to move on a road racing car. It appears to be easy to get it to move toward the outside wheel, but very difficult to get. It to go toward the inside of the turn. Seems that the further toward the inside of the turn the better. Is that correct?

 

[red0u812]

Great read Ranger Mike. We currently run a legend car on 1/4 mile medium bank asphalt track. Wondering if you had any input as far as spring selection and cross weight on these cars. Also we have a second one on the jig , what would you recommend for the roll center placement. We only have a little room on the inner pivot points to move things around. Thanks

 

[Ranger Mike]

Roll center is that point where the race car body rolls, pivots, tilts, acts etc.… because of cornering force. When racing a left turn oval track we bias everything to help in a left turn. Not so in road racing that has left and right turns. It is most helpful to have the RC located in the cars centerline ( no offset). To offset the RC in this type racing would have a sweet race car turning left but an ugly hand full any time we entered a right hand turn.In the left turn paved round track car set up we offset the roll center 3 inch to the right side to add down force on the right front tire. This adds grip or traction to that tire. Dirt track set up add 4 inch offset to the right side for even more down force. This goes for dwarf and legend cars as well.
Redou8 welcome... what is total car weight? what % left side weight? what is % rear weight? what size ARB? Do you know your motion rate of the A-arms and what is coil over mount angle?

 

[smithdl4]

Understand that statically for road racing RC should be in center but you don' race statically. Everything is moving with the suspension as the car dives, rolls, and turns. Your saying that keeping the RC in the center as the car moves around is optimum? Thanks in advance. Your class has been helpful and inspiring. Please keep it up.

 

[red0u812]

Thanks Mike, here is what we have. The motion ratio is .84, Coilover angle 20.5, there are no sway bars allowed. Car is fast but always loose in.

wheel weights Lf 318 RF 289
Lr 375 RR 346

springs Lf 275 RF 300
Lr 185 RR 200

 

[Ranger Mike]

thank you smithd
yes, try to keep RC migration around center point as much as possible. This takes a lot of time but will pay off as you won't load either side excessively thru body roll.

 

[Ranger Mike]

RedOu
springs seem way to stiff and loose in proves this. good starting pint is
LF 250 Rt ft 275
Lr 150 RR 125
this is for 1,175 # car with driver, am not sure if your scale weight includes driver but the above springs will be softer, may cause a push. We want it to push as this is the other end of the spring rate limit. Now we can start to add stiffer spring to optimize. If this change makes the car neutral we are at that optimum spring rate. time to look at the dampers (shocks).

 

[red0u812]

Thanks Mike for the info. Yes those scale numbers are with the driver. Our race track is basically a big skid pad (no real straightaway) .The car is always hanging on the rr. That was our reasoning on the heavy rr, but I'm excited to give your numbers a shot. If it does push should we go up on the rear rate's.
Thanks again

 

[Ranger Mike]

red, you are correct. If it pushes you are getting too much traction so stiffen the rear springs

 

[FISCH]

Hello all thankyou for all the posts this is the best info i have ever seen on real numbers regarding raceing. My son and i are building a { G BODY} for a 3/8 asphalt oval , not a lot we can do in tuning, the info i have read here has helped greatly.

 

[FISCH]

red, you are correct. If it pushes you are getting too much traction so stiffen the rear springs

Hello all thankyou for all the posts this is the best info i have ever seen on real numbers regarding raceing. My son and i are building a { G BODY} for a 3/8 asphalt oval , not a lot we can do in tuning, the info i have read here has helped greatly.

 

[FISCH]

sorry I am probably not doing this correctly. but i have a? for ranger mike, after many talks with local racers i have more ? than answers about base line settings for front camber caster on a g body, the class is bomber and 99% stock no after market parts can be used if there is such a thing, the track we will be running on is punta gorda speedway in south west FL.

 

[Ranger Mike]

Welcome, Fish...boy are you in for a ride!

I assume you are racing a 1978 – 1988 Monte Carlo or Malibu??
Automatic or manual transmission? Ifin you run an automatic, its not racing..my opinion.
There are several areas you can gain big time on the guys running the bone stock cars and are within the rules.
All it takes is $$$$$
But you will be a front runner.First thing to do is buy Street Stock Chassis Technology by Steve Smith

www.stevesmithautosports.compersonally I would by chassis software from Performance trend like Circle track analyzer.

You will never be able to legally change roll centers to where they will give you maximum advantage but you can tinker enough to get some offset to your advantage.Put your efforts into three areas – reducing height of Center of Gravity – chassis tuning for tire contact – build in rear over steer

COG height -

Seriously consider Lexan windshield

Unbolt inner fenders

Minimum length width fuel cell but one that is tall. You need to know maximum length of longest race and include any yellow flag laps so you can calculate absolute minimum capacity fuel

Go with track approve pipe bumpers.

Can you use a spool in place of welded spider gears in rear end?chassis tuning for tire contact -

Can you replace stock ball joints with after market?

Can you swap out GM spindles?build in rear over steer

you may be limited to stock Z linkage and location and even stock bushings..but you can sure modify those stock bushings to where they yield rear roll over steer because of “ wear “.Do the research and you will get there.

 

[FISCH]

Hi mike thankyou for responding here is a brief sumery of what we have done so far
book on order
1985 regal was a gn
steering box rebuild with 30 lb tortion bar for pos feed back also shifted back 1/8 to reduce bump steer.
the car has 19 wins before we baught it but it sat after wreck for 2 years in fl weather
mini spool installed, all new front end parts and rear arms, and bushings
the tech is a drive threw that barely looks at the car unless you win but stock spindle are a must
as for rear steer the upper right mount was moded to add such .
we can change out ball joints to moog or other.
sheet metal hood and trunk lid.
and our budget is very tite, my son is paying for most of it
i would like to add a taller ball joint to upper right a arm to hopefully reduce the rollover camber that the metric are prone to
and ? set caster at 1.5 left and 3 right
any input would be very helpful and hopefully were in the ballpark
also not trying to build a winning caar yet just a very consistant one.

 

[Ranger Mike]

sounds like a plan.
when you are limited on budget then go after the big chunks of performance. get software to figure out how to get best front end geometry.
Map out the entire car. Maximize tire foot prints on all 4 corners. Measure bump steer, ackermann, camber build. Do not get frustrated with front roll center movement but do try to get best set up.
rear end wise, look at the rear roll steer and idealize it for best results. Stay away from any engine upgrades other than for longevity. Add accusump for bearing life. Realize the stock spec radials will not be best traction option so why seek more horsepower when you can not use it. bbl carb may be too much so think 2 bbl. lexan windshield is a must. Tall fuel cell will also help drop COG. Skin down the car to where you need to add ballast.

 

[FISCH]

also we are running 88 monti md3 front end with 6 inch under spliter 9 lb drums auto trany and 5/16 lexan windsheild
with all inner body removed as per rules and safety .

 

[FISCH]

mike i have ? about the fuelcell i thaught increasing height would raise CG rather than lower CG' we run a 12 g cell that will just get us threw a
night of racing with a little to spare. its mounted as low as we can per rules with 2 tubes running under and across for safety
dry weight 2750 and track weight will be 3000 i have lots of lead to put where i need to optimize cross weight.

 

[FISCH]

sorry looking at CG bassacwards lowering CG will help increase roll for more traction.

 

[Ranger Mike]

you are good to go with that fuel cell set up

btw, when you lower the COG the roll is less. the moment arm between the COG and RC is shorter, thus less sling weight so to speak

 

[FISCH]

thanks mike i had rc confused with cog, I have built remote control airplanes for many years and cog needs to be the same rc or you have adverse rol coupling. I have another ? I have been told that setting castor with 1-2 degrees of split + - it makes the car more forgiving when loose this is my sons first full size V8 car so I would like to understand that better.

 

[FISCH]

hi mike wanted to add a little info, after maping out the front end i found that moving the steering box back, i had 2 degrees of toe when steering left [12 left 10 right , so to chek reason i moved the box back to stock location and i had 0 toe gain so i will move it back where i had it.

 

[Ranger Mike]

castor makes the car turn easier and will add slight wedge when cornering. Set up correctly the car will steer itself thru a turn if castor splits are right.
you don't have a lot of area to get competitive advantage in this series

 

[HowlerMonkey]

Are there tire size limits or can you use the spool and stagger to help the car turn in?

 

[FISCH]

yes and no 70 series we are running 235 on right and 225 on left with a spool, i did the numbers and that stagger should be close if i get the ackerman correct'

 

[VTRacer5]

Thanks to Ranger Mike and everyone else for their great information. I jumped around a bit on the forum but started from the beginning and am half way through all the posts. I'm taking notes but what has really cleared up is the need to map out the suspension geometry. I'll be buying the Street Stock Chassis Technology by Steve Smith.

We also run a Monte. I posted the rules. We are a top runner even though the field of cars is small. There's really only two of us that at this point that are tenths faster than the rest of the field. Whichever one of us is out front first, the other can't get on the outside and make the pass. I realize there has to be so much more in the car and without finding the role center, I'm still in the trial and error phase which is a waste of time, money, and energy. I'll get the measurements shortly but in the meantime, I thought i'd post my setup and get a few thoughts so this all comes together. Tire temps are front last night during practice.

- 3000 lb car
- run 2 to 2 1/4 rear stagger on American Racer 8" slicks (they are used tires that have to be a certain tread depth before allowed to run them).
- Sway bar we run 2 rounds of slack in the bar

Springs
1100 1400
200 175

Some tire temps
138 142 141 202 194 187
154 161 162 206 211 208

 

[VTRacer5]

1/4 mile high banked asphalt track! Forgot to mention.

 

[mikey531]

Ranger Mike, We are setting up our Troyer asphalt modified for big 1/3 mile (measured on the inside) flat low grip moderate banking track. Troyer recommends moving rear radius rods to the middle hole to 4 degrees down on both sides. After we square the rear how will that make any difference? We have them set for a good grip moderate banking 1/3 mile track with the left side middle hole and 2 degrees down and on the right side the bottom hole at 4 degrees down. The only thing I can think of is it is a timing change as to how quickly the rear responds. What am I missing? Thanks !

 

[Ranger Mike]

vtrracer
I bet that car pushes going in and is loose coming out!Springs are a little high.

When you get the Steve smith book you will see his recommendation for 3300# car on 3/8 medium bank track is

LF 900 rf 1000 lr 175 rr 250Tire temps, camber looks good up front right rear is a little high in the center, drop 2 # and re-read

Your averages are

Lf 140 rf 194

Lr 159 rr 208Normally we want the rr to be 10 to 15 degree cooler than the rf you are at 14 degrees hotter, indicates oversteer

Lr tire inside edge is hotter indicating close on stagger but you need more cross weight to add heat into the lr.Front tire average is 167

Rear tire average is 183

LR/right front diagonal average is 176 which is 17 degrees cooler than the rt ft tire,
a little high you want it at about 8 to 10 degrees for neutral set up.You want the rtf tire to be hottest by 10% compared to rt rear so shoot for 18 degree hotter rt ft vs rt rear

The rtf t tire is hottest the lf ft is coolest on the car for ideal,You want lft ft average to be 25 degrees cooler than rt ft avg.

You are at 54 degrees, the lft ft not carrying its share of the load.

You want the average of lr and rr to be within 5 degrees, 2 degrees is perfect.

Step one is put 250# spring in rr to get more heat in lf ft tire. Think about the frt springs..1400# way too big
I bet that car pushes going in and is loose coming out!Springs are a little high.

When you get the Steve smith book you will see his recommendation for 3300# car on 3/8 medium bank track is

LF 900 rf 1000 lr 175 rr 250Tire temps, camber looks good up front right rear is a little high in the center, drop 2 # and re-read

Your averages are

Lf 140 rf 194

Lr 159 rr 208Normally we want the rr to be 10 to 15 degree cooler than the rf you are at 14 degrees hotter, indicates oversteer

Lr tire inside edge is hotter indicating close on stagger but you need more cross weight to add heat into the lr.Front tire average is 167

Rear tire average is 183

LR/right front diagonal average is 176

17 degrees cooler than the rt ft tire , a little high you want it at about 8 to 10 degrees for neutral set up.You want the rtf tire to be hottest by 10% compared to rt rear so shoot for 18 degree hotter rt ft vs rt rear

The rtf t tire is hottest the lf ft is coolest on the car for ideal,You want lft ft average to be 25 degrees cooler than rt ft avg.

You are at 54 degrees, the lft ft not carrying its share of the load.

You want the average of lr and rr to be within 5 degrees, 2 degrees is perfect.

Think about this. One set up was to go withLF 900
RF 850

LR 225

RR 175For a balanced car we need the front and rear roll centers working at the same point in the turn on these hard tires.

A softer Rt ft spring increases corner entry and front roll angle and when we reduce the rear spring splits and reduces the rear roll.

When we reduce the rear roll we reduce the right rear being over worked by roll. The old spring set up overwhelmed the rt rear tire causing loose off or even totally loose.

So running a RR spring softer than the lft rear spring cause opposite effect. The rear would want to roll over more than the front and car would be tight.
typically you see a 250# Lft Rear spring and 200# RR spring

There is an optimum point on spring split with RR softer that will keep the car balanced at entry, middle and exit.

This is one thing you can work on with the sad crappy rules you are forced to use.

 

[Ranger Mike]

mikey5
Not timing as much as adding rear roll steer. Your timing is the same regardless. it is the amount of change to the wheelbase the bottom links make with these changes. i can not tell you what is happening on your set up but i can recommend you measure the current set up for rear roll steer.
Then set up per manufacturer recommendation and measure for rear roll steer again.
i would do the whole process on every hole to see what each setting does to wheel base.

 

[VTRacer5]

Thanks Mike. For any particular setup I run, I balance my tire temps diagonally. LF/RR average temp vs RF/LR average temp. If they come out the same, I know my car is as balanced as that spring/shock setup will allow. In the case above, the car was a little tight and needed less cross. Is this how you process your temps?

I don't believe I've ever gotten my LR within 5 degrees of my RR. I simulated tire temps based on your input above (and trying to keep the diagonal temps the even). I can't get the numbers to work out as the car will be quite tight. Can you throw some simulated temps based on an even setup? I'd like to see how that looks.

 

[Ranger Mike]

your rt ft tire is not the hottest tire the rr tire is, you are spinning the rt rear
your lf ft tire is way too cool not doing the work
regarding averages, ifin your right foot is in the stream and your left foot is in the camp fire, statistically you are ok

 

[VTRacer5]

Understood. It's not ideal. I'll give the spring changes a try and see if I can get some heat back into the LF and LR. If so, watch out! :).

 

[VTRacer5]

Springs are as close as they will be. Lf 900, rf 1000, lr 175, rr 225. Time to go try it out. Did add some more cross as it should take a bit more now. I'll grab some temps and post later tonight.

 

[VTRacer5]

It took both practices to get the car rebalanced. First practice the springs settled and we were 3/4" low on the LF and LR! Got it back to ride height and the cross almost where it needed to be. Lap times were a bit faster than the rest of the field. The car felt like it had great bite. However, it still is a bit tight in the center of the turns.

LF: 150 155 150
RF: 186 180 184
LR: 154 159 162
RR: 186 185 184

Shock travels
LF: 1 9/16
RF: 2 1/2
LR: 1 3/8
RR: 2

A few thoughts on the above and questions.

- Temps seems quite a bit better now. LF and LR have come up quite a bit compared to the right sides. That is a good thing.
- RF is now traveling a ton compared to the rest of the corners. Is that going to be problematic or should that spring rate go up?
- I'm finding the less bar I run, the better the car gets through the corner. I'm running 2.5 rounds of slack in the sway bar now. Is there any issue if I ran 4, 5, or 6 rounds of slack in the bar to keep it from getting tight in the center. I assume I can keep adding cross to the car.

 

[Ranger Mike]

Tire temps.. good direction. making head way.

Left ft. tire pressure too high as middle temp shows crowning, RT ft. tire pressure too low as middle reading is cooler. This means tire contact patch not optimum.

LR temp good, RT rear perfect.

Big thing is the left rear temp is 25 degrees cooler than RT front – not enough cross weight.

The rtf t and RT rear avg. tempos are too close – car on verge of oversteer.
Your phase 2 push -

the first thing to check is stagger.. add more stagger. go up 1/4" and see.

But i suspect there may be Roll Understeer in the chassis. The 2 ½ inch travel is showing this.
ball park street stock shock travel- rt ft. 1 1/2 to 1 3/4"
Rt rear 2 to 2 1/4"
dont forget..shock travel is NOT wheel travel so the right front wheel is doing 3 to 3 1/2 inch travel. This s unloading the lft rear. Hence, more cross weight to plant both.

We have to use the ARB as intended. Try removing slack in ARB (sway bar).

This will add spring rate to the front of the car but will control Roll Understeer.

We will probably have to change out the right front spring as the new non-slack package will be too stiff.

For your weight car the 1000# RT ft. spring is still too stiff and will be worse when ARB is solid and working as intended.

Be prepared for a PUSH on entry.

I would not be surprise to see the rt ft spring end up 850, or 900#.More cross weight will make this worse but we need to get wedge correct.

 

[Ranger Mike]

VT racer

I did a little back of the envelope figuring on the springs for your Monte Carlo.

You all know how I hate the term “weight transfer” but it is short hand for the force generated by Inertia when cornering with regard to the required spring rate to counter the momentum.The formula is

Weight x COG x Gs / track width = “ weight transfer”

For a 3000# car on hard spec tires typical Gs on a short track will be .85 to 1G. We assume the max traction so use 1G. If we are on the low side of Gs, like .85Gs we would require softer springs than the ones calculated here. Assume a 65” track width and assume we use the camshaft center line for the Center of Gravity so 16” above track level. If we have a lower COG, the springs would be softer than the ones calculated here. 3000 x 16 x 1 = 48,000 divide this by the TW we get 738 “pounds “ transferred to the front end.

We subtract the ARB rate which , depending o nthe mounting and attachment points isestimated to be 220#

738 – 220 = 518We need to hande this 518 “ pounds” with the two front springs. 518 / 2= 259As we know, the typical GM A-arm has a motion rate of .54The formula for figuring spring rate is MR x MR x Spring = Spring rate900# spring x .54 x .54 = 262# spring rate1000 x .54 x .54 = 291850 x .54 x .54= 274

So you can see if we have a 1000# and 900# spring we have 553# not the 518# desired and will have slight understeer.These are ball park numbers but you can see how real life trial and error proves out the rough calculations.

 

[FISCH]

hello mike i have a ? i am at the point of mounting the seat and adding some safety bars, the mounts that were in the car only had 2 attachment
points and were rusted also. Do you know of a good source of info for the most safe and strongest mount system. ' that book is great s192'

 

[Ranger Mike]

do not skimp on this area. The book should outline Seat Belt mountings and supports. I have a pet peeve on racing hardware. I hate farm bolts and spiral lock washers. Use as MINIMUM of grade 8 bolts. We use An aircraft bolts in our cars but for street stock grade 8 is ok. If the mount location is rusted, cut it out and reinforce the whole thing. Do not cut corners in this area. sounds like you are going the right way.

 

[FISCH]

thankyou mike we are using grade 8 hardware, the part that i am concerned with is the frame work for the seat, the seat we have is a nascar
style full containment.[ most exp- part in the hole car] i have seen some horible set ups, i would like to make a frame that sort of follows the contour of the seat with cross atachments so it stays with the cage exactly where i put it and can't crush ? i need pics i guess.

 

[mikey531]

Ranger Mike I have a question. We are trying to duplicate our setup when we put tires on at the track. I try to get the same size etc but never seem to get it right. If we have the car parked in exactly the same spot with the old tires and measure the play in the front sway bar, when we put new tires on the sway bar is either looser or tighter. If we adjust the car so the sway bar is the way it was on old tires will we still close to our setup? Thanks Mike

 

[Ranger Mike]

i assume you are using a stagger tape measure to get same size on the tires. Old tire s and new tires should measure the same. Make sure you jounce the suspension ( jump up and down on each corner before you measure. When we scale the race car we unhook front and rear ARB (sway bar). I run all ARB neutral setting with no preloads.

 

[mikey531]

Yes I am using a stagger tape but we put on at least 2 tires each race and even getting the same chalk mark, unmounted tape size and mounted tape size it is still a guess as to what it will come in at. We set our bar neutral at the shop. I was just looking for an easy way to adjust the car if we get a tires that are bigger than what we scaled with even though even we have the same stagger. We had a right sifde tire at 84 3/4 and left at 81 3/4 which was ideal but we scaled with tires that were 84 and 81 that is where I am having a problem. Thanks

 

[Ranger Mike]

Worry about stagger before worrying about a 3/8" height change from the tire. read page 29 post #572 on why i built the heat cycle machine, get nitrogen and use in t he race tires. get a vacuum pump from an old refrigerator and suck out the moisture containing air and replace with Nitrogen.

 

[mikey531]

We do use nitrogen but at some races we have to use their tires and we draw for picking tires well with our luck we seem to always pick last when there is not much to choose from. I was hoping my thought of getting the sway bar back where we had it would work but I guess not. Thanks

 

[mikey531]

Another idea that kinda worked but not really on our asphalt modified. We tried to reduce the rear weight by moving as much as we could to the center leaving us with a rear percent of 51.2 I want to put about 25 pounds of lead behind the fuel cell and see if I can get the rear up to 52% I think this will help with power off the turns. However the car owner says it will act like a pendulum and cause more problems. I did it on a metric chassis and it worked awesome. but can't convince the owner to let me try it. Anyone had success or failure? Thanks

 

[Ranger Mike]

A lot of penalties in NASCAR lately about rear suspensio n components not properly mating to mounting surfaces. These cars use pickup truck trailing arms and “passenger” car differentials. The rear ends are cambered to better contact the track surface when using stagger tires. A shim is placed between the differential and trailing arm to align the drive shaft pinion angle. Car rolls thru the pre race tech inspection and all is well. If you fabricate the shim with a large knurl so that it will grind down over a few laps, the rear end will twist and change angle. You will introduce rear steer into the car.

The rear end moves to the left during the race, wears off the knurl job and the rear end is skewed to the left.
The object is to obtain as much aero side force as you can get. When the right rear quarter panel and spoiler get more air than the other race car, you get more down force and grip. This years NASCAR restrictions call for low down force package.So now you know why some race winners do a 50 mph sprint then throw the car into a violent RIGHT turn for his 360 burn out It is to slam the rear end back into place for post race tech inspection. You will only find this when you take the car apart and check for this “non contact” violation.

Rear steer helps on short tracks but on the long tracks its about Aero downforce.

 

[mikey531]

New question, We have been playing with stagger and last night we had 4 inches of stagger. The car was very fast for the first 20 laps then when tight. We were lucky to hang onto third. We knew the tires would grow to more stagger that we have ever run so we lowered the track bar 1/4 inch to compensate for the increased stagger. Did we go too far on the track bar and maybe should have gone 1/8 inch? The car has never been as fast as it was last night. What are we missing? Thanks

 

[Ranger Mike]

4 inch is huge amount. you may be racing a three legged stool and the right rear burns off too quick.

I would like to see the tire temps. From what you said, you probably have identified the situation. When you change stagger you move the roll center up or down. Too bad you cannot fabricate a hydraulic cylinder to raise the rear panhard bar ¼” from the cockpit. But that may be cheating…
I would like to see the tire temps. From what you said, you probably have identified the situation. When you change stagger you move the roll center up or down. Too bad you cannot fabricate a hydraulic cylinder to raise the rear panhard bar ¼” from the cockpit. But that may be cheating…

 

[mikey531]

4 inch is huge amount. you may be racing a three legged stool and the right rear burns off too quick.

I would like to see the tire temps. From what you said, you probably have identified the situation. When you change stagger you move the roll center up or down. Too bad you cannot fabricate a hydraulic cylinder to raise the rear panhard bar ¼” from the cockpit. But that may be cheating…
I would like to see the tire temps. From what you said, you probably have identified the situation. When you change stagger you move the roll center up or down. Too bad you cannot fabricate a hydraulic cylinder to raise the rear panhard bar ¼” from the cockpit. But that may be cheating…

I will post the tire temps later today. I had thought about an adjustable panhard bar like NASCAR has.

Thanks