Automotive Race car suspension Class

[John LNZ]

Hi Mike, thanks for the reply. Sounds like we are on the same wavelength on the polar moment. We have done some work with the four bar and have found some gains using it. However we find the car is too inconsistent and we are unable to hold a tidy line. In New Zealand Speedway, every track has a referee and within our rules you must hold your line, you can't enter the turn wide, chop the pole line and exit wide. The referee will put you back places at the end of the race if you are seen to inhibit another driver. The sprint car layout with its minimal rear steer gives the cars the consistency and ability to hold their line. There are some guys running 4 bar link and yes, on certain track conditions they are faster, but given we have 104 inch dia 17inch wide right rear and 16 inch wide left rear, what the 4 bar offers does not seem as crucial as to us as the late model with small tyres. I have always used 4 phase's for corner tuning - 1. entry - (brake balance, rotation), 2. next input - (sidebite), 3. mid -turn (stagger) 4. exit (stagger, links).
My further questions are what would be the minimum rear percentage where you would take weight from the centre and put in the rear? and what are the consequences to forward bite by moving the weight up high to achieve more side bite?
Many thanks - John

 

[Ranger Mike]

John - did we not visit this on post 505 on page 26 when you first joined the forum? As far as minimum rear weight and left side weight
i go for the max the rules permit. But there are consequences when setting up an offset car. I will check back in the super late model notes where we had a lot of left side weight and rear weight ( we ran a V6 engine when every one else was using V8s)

 

[Ranger Mike]

as I said I am a firm believer in Polar Moment and adding weight at this point. For the best handling car you should build it as light as possible and add weight only at the polar moment. Weight added behind the rear wheels only if it is your last option. Adding weight in areas outside the wheels wil counter act polar moment.

Stock class that is restricted the left side weight should be 55 to 56% and 51% rear wt. If you go past 56% left side on a flat track you risk having trouble getting side bite at the right rear tire.
If you run more than 52% rear weight it may push going in and coming out. Going with more than 52% cross weight can cause a push on those stock hard tires you have to run.
A super late model with few restrictions and ability to build a good camber curve and wide open on roll center placement and any spindle/ component usage can run:
58% left side weight, 50 to 50.5% on fast 1/2 mile and up sized tracks and 51% to 52% on 1/4 and 3/8 mile tracks rear and 54 to 58% cross weight. On short track 30 lap races you can go as high as 58 to 60% cross weight knowing you are running a three legged race car.
hope this helps a little??

 

[no friends at]

Ranger Mike- My rear coil-overs are mounted outboard of the chassis and set close to the end of axle as i can get. The bottom shock mount is 7" below centerline of axle. I hear the ideal angle for coil-overs is a 20 degree angle. The set up now consists of two angles a 10 degree angle or a 25 degree angle. Which should i choose in a Road Race environment? Or is it back to the drawing board for a 20 degree angle? And a big thanks to you Mike!

 

[Ranger Mike]

read post 305 on page 16 - adding angle reduces damping. typically mount them between 10 and 20 degrees. i would go with the 10 degree mount as long as the shock pushes straight up and down and you have no bind during roll, dive and bump.

 

[Al Johnson]

Sorry if this has been covered before but the thread is very long ...

Is there any formula to calculate the increase in spring stiffness needed to take turn banking into account? For example, if I know that my right side springs will compress one inch under 1G cornering on a flat track and still have 2 inches of available suspension travel to absorb bumps, how can I know the spring stiffness I need to add to keep the same spring compression on a turn banked 10º? In Herb Adam's "Chassis engineering" there is a table with suggested % of additional spring rate for some situations, but there is no explanation of the formula involved in calculating it.
P.D. I'm always talking here just about final wheel rates, of course I know it has to be later recalculated for suspension leverage before knowing the real spring you must mount.

 

[Ranger Mike]

welcome Al,,yes we beat that dead horse pretty hard...i initially explained it on post 19 but came back to revise it after much discussion with some very technical people on this forum..page 30 post 589 started it and is got very in depth. I was trying to find a formula to find proper spring rate at given Gs. I think i got close...

 

[cyclone clay]

Hi Mike
Great thread and have i just finished reading all 40 pages. Just a question about leaf spring mounting angles. I run a imca style car here in australia stock gm front clip and I am wondering how critical the difference between the front leaf spring Mount and the rear Mount height is. Thanks

 

[Ranger Mike]

welcome cyclone..good to hear from you. leaf springs are a good way to control side to side movement of the differential. Leaf spring front mounts can vary in height from the left side to right side BUT..always make sure the leafs are straight and parallel to each other and to the vehicle centerline and perpendicular to the rear end tubes.
Technically, the proper way to mount leaf springs is to have the front eye lower than the rear as seen from the side of the car..You need a down hill angle of 2 to 4 degrees. I don’t like rear steer so I like a square race car but looking at the attached pic you can do some rear steer if you want to. Pic is from Short Track Chassis Set Up by Duke Southard.

Use slider boxes on the rear if you can. Use the Afco leaf spring pivot bushings on the front leaf spring mount to prevent binding.The rear roll center depends on the rear end tube meeting the top of the leaf spring ( half way point) and lowering blocks are used to change this. Don’t go over 2.5 inch tall lowering blocks because things really get hairy when you stack up the blocks.

 

[cyclone clay]

Thanks Mike Yeah I now have a coy of that book ha ha...I have been ready different forms and some day 7 inch difference some say 9 or 10. The question really is if the angle is too great front to rear will the car struggle for forward bite and will this greater difference create a loose condition due to roll steer. I have slider boxes and front pivots. Thanks

 

[Ranger Mike]

After watching the final NASCAR race look for some rules changes. Everyone was pulling out the sheet metal flare on the rear wheel wells during the first pit stop to get more down force on the car. And turn the flare into a tire shredding terror like in Mad Max road warrior or Ben Hur in my day...and crabbing is sneaking back into the mix.
The Nascar techies will have their hands full this next year.
nothing new just coming full circle

 

[Warriorracecars]

ok newbie here, I have read through maybe half of this thread. Very informative!, We are building our first ever complete straight rail super late (asphalt) My son is doing the drawings in solid works. We have developed some front clips here for existing chassis. My question for Mike or whoever wants to chime in is, Location of lower inner pivots. I have noticed that some builders are locating the inner pivots to the left side of the chassis as well as the engine mounts. On our previous clips, we have located the inner mounts to the right, moving tires to the right so to speak while maintaining equal length lower control arms( as per previous rules). New rules do not require equal length LCA. So I'm wondering what your thoughts might be on unequal length LCA and how they might affect camber gain/loss, MC etc. after this I'd like to get your thoughts on 4 link (birdcage) vs. three link for asphalt?
Thanks Guys
Rich

 

[Ranger Mike]

Welcome warriroracers
You are correct. The “ hot setup” on super late model chassis is lots of left side weight. As much as you can get away with. To do this you have to run longer control arms on the right side and shorter control arms on the left side. You can also offset the chassis to the left side from vehicle track width center line. All to get as much left side weight as possible. Since you will be running a radical non symmetrical chassis you need to know what happens in droop and dive so chassis software is a must.

The “ hot setup “ on asphalt is the three link rear suspension. Simpler to hook up and adjust, Bird cage is good for dirt but not required on paved track . 4 link has and too many headaches.

 

[Warriorracecars]

Thank you Mike. to be more specific, Left side weight being equal, other than camber gain/loss dependent on control arm length, can you think of any other reason to favor one style over the other? Moving inner pivot mounting points left would require a bigger split in LCA lengths left to right as compared to moving chassis centerline. Or in other words,, moving the tires to the right by mounting points moving right, which would allow for more equal length of the LCA. As far as droop, these cars are Using considerable amounts of rebound in the front shocks. The chassis stays down throughout once reaching bumpstops. On the rear end I have seen two chassis builders , (senneker and port city)utilizing a modified "birdcage" style of trailing arm configuration. still 3 link but the senneker style utilizes trailing arm mounts that "float" with attatchement point at the axle being centerline rather then from a dropped position under axle tube. same with port city, but the mount for them is solid mounted with a heim. they are calling this "active" rear suspension. Curious about your thoughts.

Rich

 

[Ranger Mike]

I do not understand your question when you say left side weight being equal?
If you are building the car to turn left only ( non road course car) you are going to run a hybrid.
It will not be symmetrical so why try to hide it. Everything will be built or adjusted to turn left.
So go ahead and accept this and build the lower control arms non symmetrical and counter with your spindle heights upper control arm lengths etc...

Yes the front end stays down thru phase two and most of us want it to so it does not unload the right front tire when it needs down force to make it turn. The front end will come up fast enough when you get back on the throttle on turn exit is the shock package is right.
Our old super late model driver developed a bird cage floater mount for his Late Model car that was on aversion you are looking at.
I think he won championship that year. The big thing about this set up is it eliminates a lot of distortion and twist while cornering.
You can tune in the shock / spring package to a higher degree.
Having been in wide open Super Late model series..the car with the widest lowest design with the mostest left side weight will out run a symmetrical car every time...if you only turn left!
One other thing..in this series everything is up for grabs regarding the rule book...you should see ridiculous lop sided concepts on the track.
A racers mind is terrible thing to race.

 

[Warriorracecars]

Lol! there are two approaches that I have seen to accomplishing left side weight. I will try harder to explain. One is the front clip is designed with the motor mounts 2" to the left of center as well as having the lower control arm points moved 1" to the left of center. the second is the way we have designed clips in the past which is the motor is centered in the clip with the lower control arm points moved 1" to the right of center. with a given track width, the first design would have to have a larger variation in lower control arm length as compared to the second design. the second design would allow for more equal length of the lower control arms. I hope this clarifies things a little. My only question has been, other than camber gain changebetween the two different approaches, can you think of other things that might be affected? And also, the cars around here stay down completely. the track here is very flat, 5.6 degrees of banking cars are alway turning. if there is any droop, it is very little.
Thanks
Rich

 

[Spafco46]

Hey Ranger Mike, just curious as to your thoughts of the 3-link rear suspension for asphalt oval racing. Are you referring to a top mounted 3rd link or a conventional torque arm mounted at the chassis, like that of a Troyer. My question is why is the top mounted link better, and whould you suggest a bushing link, spring link, or solid link, and why? We are in the process of building our new chassis and have the option of either or. I have only ever tuned a car with a torque arm, never a top mount. I want to run the top mount as forward bite is always lacking at the local track we race. I am concerned though with the spring link. I hear they are harder to tune, and can cause issues if set-up improperly. Simple is always the best option as far as I am concerned. Any thoughts?

 

[Ranger Mike]

Moving a 350 pound engine 2 inches to the left is a huge advantage vs. centered with clip having LCA mounts extended.
Example – 66 inch track width centered engine means 175 # is left side and 175 # is right side. math is 66 inch width / 2 = 33 inch the engine is located 1/2 way (50%) between the wheels or ( 350 * .5 = 175#).
When you mount the engine 2 inch to the left of center it is mounted 35 inch to the left of right wheel center line or 35/66 = 53% to the left. so 350# * .53 = 185#
Now we have 185 # left side weight and 164 right side weight. This gets magnified once you figure the drive shaft and rear end will fall in line with the same left side percentage.
now you add 200 # quick change, 150# transmission, 20# drive shaft, you have 720# total.
720# * 53% = 382 left side weight and 338# right side weight.
I have to say 53 % left side weight is ok for a hobby stock but a radical full race super late model...may go as high as 62% .
the Main Event Super Late Model series has 60% max left side weight.
I have seen Super Modifides with 68% left side weight.

Now you can add ballast at polar moment to make it legal. Don’t forget your polar moment location changes with the offset.
More left side weight means higher turn speeds. Left side weight tightens the car up and keeps the car from being loose late in the race vs centered weight car.

When you have the engine centered in the clip but different control arm mounts the bottom line is you still have a neutral car ( left side weight wise). This is not an advantage on a round track.
I have to go pick up my turkey pot pie for tomorrow ..will write more later.

 

[Warriorracecars]

I guess I'm still not conveying this appropriately. The center of mass in both situations is still to the left of track. Picture a chassis in mid air with no wheels. now put the 66" track width under it, stick two lower control arms on say 17" each on the wheels(spindles). now slide the 66" track width to the right side. if the lower control arms stay 17" each, then the mounting for them would have to move to the right of the chassis. the relationship of the drive train to the contact patches of the tires would be heavily to the left. The tires move right but the engine stays centered in the clip. The result is left side weight because the the chassis is being held up mostly by the left side tires. in other words, instead of moving mass to the left, we are moving the tires to the right. with this configuration the lower control arms could be equal in length.

 

[Warriorracecars]

and have a great Thanksgiving, enjoy the pie :)

 

[Ranger Mike]

warriorracecars..thank you for the holiday wishes and i like that idea now that i understand it...seems to be the best way to hang left side weight and least hassle on camber build..

 

[Warriorracecars]

we are working on the modified birdgage 3 link for the rear. sounds like you or your buddy have some experience with that. any pointers on shock numbers for this? arm angles , etc.? The chassis will be highly adjustable but I've got zero experience with a set up like this.

 

[Ranger Mike]

Welcome Spafco
Warrioracecar- See post 305 for shock mount angle.

In my opinion, Phase One – turn entry depends on proper loading of the right front tire. Phase 2 middle of the turn problems usually are incorrect shock rates, wrong stagger or wrong cross weight but surprisingly, caused by the DRIVER. Phase 3 or Turn exit is all about the rear end hooking up. Once you get the spring rates close and shock package dialed into handle phase two you can adjust to hook up the car on exit.

When I refer to 3 link suspension it is two trailing arms and a top link. All three are tube steel pieces threaded to accept rod ends ( heim joints).
The one biggest mistake racers make is to mount the top link in the wrong location. You must mount it at the center of mass weight of the car, i.e. 58% left side weight means the top link is mounted 58% of track width to the left of the right tire center line. It is one of the three moment levers reacting to acceleration/braking.
See Page 38 post # 749 for info on top link mounting. Page 16 post 301 to 314 is a lot of rear end mounting info.
post 116 for rear steer, post 81 for top link info, post 253 for 3rd link info and post 261 for 3rd link spring rate. I’ll do a quick summary -
The top link can be a solid tube or it can have a rubber bushing or a spring ( known as the spring loaded torque link). The rubber bushing type is used on E-mods and lighter cars and dirt racing as you can swap in different bushings as the dirt rack changes. I think 90% of the stock class and late models run the spring loaded torque link. The purpose of these two are to prevent anti squat under acceleration. Squat is when the front comes up under acceleration and the rear takes a squat or compresses. Anti squat helps to plant the rear tires to hook up. The 3rd link spring compresses under acceleration to dampen the torque reaction of the tires hooking up. But...you need an axel damper (shock absorber) mounted in conjunction to dampen wheel hop under braking. The mounting angles of both are very important.
One time we ran a top link that was connected to the rear end and the other end was at the firewall. Longer is better as the rear end will have less angular change in bump and roll.

If you replace the right rear solid trail arm with a spring loaded one you now have a spring-loaded radius rod that creates roll under steer under acceleration.
We have run both spring loaded torque link and spring loaded radius rod. I do not like the spring loaded radius rod simply because it can fail and you will waste valuable time trying to locate the handling problem that suddenly appeared due to a broken spring. I am not a big fan of induced roll under steer but it can be made to work. If you have the rear end set up close to correct in the garage, you should be able to dial in the tire hook up with minor changes to the top link mounting angle.

 

[drobbie]

RangerMike, Thank you so much for this forum. It has brought back to me the engineering needed to successfully run a racecar.
I have a question about laterally locating the rear roll center. My car currently has the front roll center nearly 3 in high and 5 inches to the right of centerline and the rear roll center 8.75 inches high and 2.25 inches to the left of centerline.
Would it be beneficial to keep these in line with eac other, is this offset too much, what might be the ideal situation?
Thanks in advance - DR

 

[Ranger Mike]

welcome drobbie
is this a dirt car? setup leads me to believe it is.

Regarding location of rear roll center...it depends...how high is the sky??
There e is no mathematical relationship between front and rear RC that I can determine after much research. There are so many variables I would say if you are ok on phase one corner entry and things settle out mid turn then the Rc you have is ok.. The mass centroid thing on these offset whopper jawed cars does not seem to matter too much. The whole car is non symmetrical on purpose. Just remember that too much left side location may not shift enough to the right front. Seems to me the 2.25” left side location could match up pretty close to the % left side weight and the top link location we discussed on this page. If that is so you are well within the ball park.
I would be more worried about the front RC being too far to the right of Center line. Too much rt side location of ft RC will lift the lf ft tire and load the rt rear tire under throttle. It may run like a bat out of hell for 4 to 6 laps the the right rear will blister.

 

[drobbie]

Thanks for the quick reply Mike,
This is a modified asphalt car, tube chassis, three link rear. The car is 58% LS so the using the what you say, yes it is close to the discussions you mention. As for the Front Rc, that is a work in progress right. Off season is a great time to sit back an reflect on what you had and to make changes going forward. A little more about the car so maybe you could give me some hints. It is asymmetrical by one inch on the lowers (RF lower longer than LF) and the uppers are the same length. Equal height spindle and ball joints. 95 inch wheelbase and 63 inch tread width.
It was my concern the Rc was a little high not so much to the right being an issue. So maybe a little direction of getting corrected would jump start some ideas.
Let me know if you want more info

 

[Ranger Mike]

The 3 inch RC height is right on. You will not get any lower with the stock components you have to use. Try to move it to 3 inch offset from 5 inch. If you can move it to 4 inch you will be running what everyone else is running. 3 to 3.5 is ideal. Do you have suspension software to show RC moving in roll and droop? Do you run flat track or medium banked ( over 10 degrees)? do you know your camber build per inch of bump?
what spindles are you using?

 

[drobbie]

I have access to RC software so I when back an played around with some numbers based on the existing adjustments available on the car. The attached picture is what I came up with. I think it might be more in line with your recommendations. I use stock Mustang II spindles with tubular upper and lower controls arms. It also has a mustang R&P.
I did run it through 1.75 inches of dive and 1.5 degrees of roll and the Rc moved to .9 high and 4.5 to the right.
As for the tracks we run, I race in a touring series so it is anywhere from a small medium banked 1/4 mile to 5/8 high bank with long straights. There are also a couple of 1/3 mile sweeping turn tracks.
Let me know what you think.
-DR

 

[Ranger Mike]

Sounds like you have a pretty good start to a wining season. The software you have is great. You can dial in the front RC with it. You can always swap in a Chevelle spindle that is an inch taller if you have to, Ford pinto spindle may be same as you are running, not sure.
One thing to note- you have a whole range of different tracks from flat sweeping to serious high bank. I would put major effort into charting the correct camber curve for each track. Then set up car for each event with correct camber shim package. A completely flat rack would need negative 1.75 degree camber per inch camber build on the right front and positive camber on the left front 0.5 to 3/4 degree per inch gain . A 10 degree banked track needs neg. 1.5 degree per inch rt. side and left front 0.5 to 3/4 degree pos. camber per inch gain. A high bank track would take 1 to 1.25 degree per inch of bump rt. side and left front 3/4 to 1 degree per inch gain pos. But..use the pyrometer to dial these in. These are ball park settings. I am sure you know the correct springs for 1/2 mile and longer fast tracks. The time you spend in that cold garage this winter, mapping the camber build for each track will pay off big time. Serious race teams do this. Weekend warriors just swap in the bigger springs and change stagger and go race the high banks ( never taking the time to change the camber build). So their contact patch is off pretty much of the time. You will have the advantage of maximum contact patch matched to the track or darn close too it.
One final note- I would concentrate on smoothing things out aero wise on the tracks over 1/3 mile. Granted you can’t do anything about those ugly tires but you can get benefit with small changes to smooth out flow. I have spent days in the garage taping tuffs of yarn on the car and looking at the air flow. That hog barn fan really flows the air but its cooolllddd.

 

[Warriorracecars]

You lost me on this one Mike. The left side camber gain part. The left will go toward negative in dive so could you explain this a bit more? Also have you experimented with Jacking? As in extreme arm angles that utilize the force that is generated in the cornering phase to accomplish vertical loading on a given corner or tire?