Race car suspension Class

[mender]

emccalment, for info on modified cars you might check the SCCA rules to find a class that is close to what you're thinking of running then checking their records to see what cars have been more popular and have been winning over the last ten years or so.

For first hand info, go to a race or two of your selected class, volunteer as crew for a couple of races for one of the better teams if you can to get an insider's view of what it's about and talk to the guys about car choice. If they see you're serious about getting into racing they'll usually help you and maybe even find the right deal for you to get in cheap; there's almost always someone moving up (good) or getting out (maybe not so good) and wanting to sell. As always though, do your own research before throwing down a wad of cash.

A good place to start and another very good learning experience is to be had in autoslaloms, where you run your car through a temporary course (usually on a large parking lot). The good part is that you can use whatever car you have right now, so you can play for very little pay. Some driver coaches consider this a vital first step, as it teaches you to learn the proper line very quickly.

I can attest to that as that's where I started and I have had very little trouble figuring out the fast way around at any track I've been to. That's a major benefit when you get to a strange track late and only have five minutes of practice before qualifying! Yes, I got pole; then the accusations of cheating started!

Seriously, it'll help a lot and can be used as an occasional driver tune-up between races, besides being a nice way to spend an afternoon. Take the time to talk to the fast guys and study how they are driving; most times they'll look slow because they are smooth and blend the car around the course.

If you want to get good value, you might also want to consider doing some oval track racing; almost everything you learn there is applicable to road course racing and will usually be quite a bit cheaper for the same amount of seat time (seat time is King!). Mini-stocks or Pony stocks will get you that seat time for little investment and you can refine your technique without worrying too much about scratching the car. Same plan; get out to the track and talk to the people involved first.

For starters re: your questions on wheelbase, centre of gravity height, etc. I started out years ago with Fred Puhn's book "How to Make Your Car Handle" and have since added many others as they came out. Carroll Smith's books (http://www.carrollsmith.com/books/) are considered a must-have for anyone who is wanting to do more than just circulate at the back of the pack. If you already have these, just ask and I'll list the next bunch.

You should also understand all the major mechanical systems of the car so you can tell when things aren't right and how to fix them.

You're very fortunate that you have such a vast amount of information presently out there to help you. When I started thirty years ago, very few people knew what was going on and even fewer were willing to share that knowledge.

 

[steve09]

hey mike
thanks for the shock numbers and percentages all of these are almost the same as we
use.but i was wondering what compression and rebound numbers you like to see in the
front and rear shocks.we run a 550 pound front sway bar with front spings from 250
to 300.rear springs at lr 185 rr 275.we think there is to much rebound in the front shocks
we have over 700 and are suspension just don't come off the track.we don't have bbss
set up but we are somewhere in between conventional.we just got the shock dyno and
we are going to lower some rebond.but what's a good number to start off with the cars
way to tight in the entry to middle and we adjusted it all night and still to tight.the track
is a half mile with 16 degrees banking.thanks again.

 

[Ranger Mike]

Mender..excellent advice
Steve09

what does your car weigh and what is cross weight?
That is one beefy sway bar you are running!

From my notes on 3200 pound car we ran a lighter front spring/bar package
was LF 350 RF 350 anti roll bar was 220 pounds LR 225 RR 225
i think the reason you are tight is the front spring/sway bar is kicking the weight back to the rear and the rear tires are really hooking up and snow plowing the car to the guard rail.
One thing you can try without changing the whole front package is to up the LF spring rate to take out some wedge..you are right on the shock rebound..maybe try a tie down shock on the RF..but i think you need a smaller sway bar and more equal spring numbers to take the proper amount of weight..and plant the R front tire to assist turning

 

[steve09]

hey mike
are car weight is 2750 and the cross is 56 to 57 % tires are 84 left and 85 on the right
1' to 1 1/2 stager.we have somewhere around 700 on the rebound on the front shocks
and 50 on the compression side 1 3/8 550 pound bar.275 and 250 front springs that
we changed around still pushing.might try a 1 1/4 sway bar and take some rebound
out of the shocks.what do think about the shocks there penske's with adjustments
for compression and rebound with nitrogen canisters.what would you set the comp and
rebound to for are track.thanks again

 

[Ranger Mike]

i def think the smaller sway bar is the way to go..i can not tell you on penske shocks..yet..we run them but got to dig out the data book on them..as you know there are a lot of shim packs available. so many combos i need to know your exact setup.

what model Penske shock is it?

What shim package do you use in the shocks?
I can tell you this about shocks...Look at the graphs of the shock dyno results,,

There are two areas you should look at on a shock dyno graph. the 0 to 10"/sec is critical range for control of body roll and pitch. the 3 to 5"/sec. is the low speed control of weight transfer during corner entry and middle of the turns. The 8 to 10"/sec. range relates to faster weight transfer control like heavy braking, corner exit and small bumps.
A good shock set up would chart out to 0 to 10"/sec. range with quick and smooth rise then the curve would taper off. It should transition into the 12 to 14 " range where it flattens out. The shocks can not be stiff in compression here or they wouldn't allow the tires to hook up on the track over minor bumps, ruts , dips, Too much dampening in the mid ranges will cause the car to "wash out" over the rough areas of the track.

 

[steve09]

hey mike
i'll have to look at the data sheets and get some numbers for you. we have different
shocks on both super late models.all i know is the valve has three dots on the rebound
side and three .o10 shims i think on the shaft.the front shocks are i think 7500 penskes
on one car they came on it with remote canisters.were goint to try the performace
software this weekend and see how the numbers show up.

 

[Ranger Mike]

did you bench mark the suspension points on the car? ( map all the mounting points) what program did you get from performance software?
you know this already ..but for those viewing..make ONE change at a time..like the sway bar...pyro the tires and record the temps..I am very interested to heart where the RC is on the front end..lot of work but..in my opinion..the software will really tell the whole story and instead of bandaiding the car to remedy a poor design ..you can make serious chassis changes relative to the CG and RC then spring it accordingly..
for those new to motorsports..there is a whole lot of superstition ...no green cars..never say good luck...
so i'll say get a checker

 

[steve09]

hey mike
we used the performance trend suspension analyzer and it says the roll center is 12"
to the left.we also used the chassis r&d roll center software that we had and it says
the roll center is 10" to the right i feel a lot beter with the chassis r&d it's easy to use
and i think more accurate.we will try the 400 pound sway bar next race and get the
roll center to the 3 to 4" to the right.and about 3 1/2 " high. we have lots of slugs
so we will change what we need.and maybe take some rebound out of the front
shocks and add back in with the adjustments on the shocks if needed.no luck on the
shock dyno sheets mike? are shocks are penske 7 in the front 9 in back with nitro
canister set to 80psi coil overs revalved by someone else.thanks for all the info.

 

[Ranger Mike]

Steve09- excellent work
until the roll center is where it should be, every thing you do is a band aid,,,but the sway bar change will get you closer to the " ideal " numbers for all the late model race cars noted in my references...use the software and make changes in the upper ball joint heights, mount heights, upper A-arm length to bring in the roll centers. You can tweak the bottom ball joint locations a little but I think the uppers are the easiest. careful measurement is critical so take your time,,rewards are immense,,,meanwhile I am checking with my shock guy on penskes for the 2700 pound car..

 

[steve09]

hey mike
we moved the roll center to 1.82 to the right and 3.68 on the height static and dynamic
it moved to 5.65 to the right and 2.843 on the height.with 1" of dive and 2.5" of roll and
put the 400 lb bar in.reset are bump steer because it changes everytime you change your
roll center.set the right side to bumping out .008 and the left at .000 at 2" of travel next
time we race i'll make sure the tire temps stay good.only thing were not sure on is the
shocks.thanks again.

 

[GPhillips]

Here is my project. I am starting to design a new style front suspension for a dwarf car. For those of you that may not know much about Dwarf Cars they are a scale race car that weighs 1240 lbs, use a 4 cylinder motorcycle engine, and a cut down Toyota rear end. The front end that most of them use is a old style single kingpin set up with long rear struts that go back to the front upright of the roll cage. What I'm wanting to go to is a more modern upper A-Arm/Lower Control Arm set up using heim joints instead of ball joints. My idea is to start with the front end of a Dirt Late model, scale it down, and work form there.

Any and all opinions and thoughts are welcome and as I get more into the project I will post update and pictures.

Thanks

 

[Ranger Mike]

Welcome. It sounds like you thought things out pretty good. When you are finished wit the measurements, send them to me and i will run them thru the software to find the roll centers. What type of rear suspension is on the car? There is a whole lot of work required to glue on a new front end...hopefully you have the time money and tools..thank you for inviting us on this venture andlet me know if i can help..
RM

 

[GPhillips]

Thanks Ranger Mike, the rear suspension on the dwarfs are a solid mounted three-link, some of them are using a rubber biscuit on the right side bar, some are running a solid bar there, and a spring loaded pull bar mounted above the rear end for forward bite. The cars also run a J-Bar/Panhard Bar in the rear.

 

[HowlerMonkey]

You guys run staggered tires and spools to help the car turn in?

 

[GPhillips]

Yes, the cars run anywhere from an 1" to 3" of rear stagger and full or mini spooled rear ends.

 

[rwstevens59]

Cogitating about rear stagger on spooled solid rear axle on a dirt track when we spin it up either throughout the corner for a heavy track or from mid corner out on a drier/slicker track.

The main purpose of stagger on a spooled axle is to match the roll out difference between inside and outside rear tire due to the rear axle track (i.e. inside tire circumscribes a smaller radius arc then the outside tire). We can calculate this all out but it really isn't worth it as we very rarely know the true path radius of the car through the turn. Nor do we know the banking angle for stagger correction.

So what is everyone's opinion about the effect of stagger when we spin up the rear tires. Is there still a stagger effect or not? And if there is what is the effect?

 

[Ranger Mike]

tire stagger simply means one tire is smaller in circumference than the other at opposite end of a solid rear axle. it generally means the left rear is smaller than the right rear. It is used so that both tires rotate at the same speed (solid rear axle only) when going through a corner.The amount of stagger is directly proportional to the turn radius. The tighter the turn the more stagger you need.
On dirt, with a spool. you still need stagger. As you know, a dirt track will change through the night. You can have slurry conditions to hard packed "pavement like" conditions. The 4 link rear suspensions really hook up and you need to know the stagger. Do not forget that the tire will grow and stagger will change as the right rear is loaded and starts to hook up ( spins on turn exit as you nail it). Heat makes the tire grow and you get heat when you accelerate.
You need stagger to control under steer wit ha locked rear differential.

 

[rwstevens59]

tire stagger simply means one tire is smaller in circumference than the other at opposite end of a solid rear axle. it generally means the left rear is smaller than the right rear. It is used so that both tires rotate at the same speed (solid rear axle only) when going through a corner.The amount of stagger is directly proportional to the turn radius. The tighter the turn the more stagger you need.
On dirt, with a spool. you still need stagger. As you know, a dirt track will change through the night. You can have slurry conditions to hard packed "pavement like" conditions. The 4 link rear suspensions really hook up and you need to know the stagger. Do not forget that the tire will grow and stagger will change as the right rear is loaded and starts to hook up ( spins on turn exit as you nail it). Heat makes the tire grow and you get heat when you accelerate.
You need stagger to control under steer wit ha locked rear differential.

Agreed. And I understand stagger and its use. My point was that how stagger effects the car will be different when the car is at a drift angle in the corner with the rear tires spinning. Part of the forward thrust is being utilized to keep the car on the current circular path toward the center of the corner and part is being used to accelerate the car from mid turn off tangential to the corner. This is a different concept then just using stagger to match the different wheel speeds caused by the track width and different radii traversed by the two rear tires such as on asphalt with a spooled rear.

In a spinning mode the larger outside tire will have a slightly higher surface speed than the smaller inside tire at a given axle speed (rpm). So my gut is telling me there is a difference in the effect of stagger when you 'back it in' on dirt as opposed to driving it through on a hard packed or asphalt surface. Thoughts?

 

[Ranger Mike]

good points all..will let others reply whilst i go to the corner carry out for some beer ...and pork rines?

 

[rwstevens59]

Ranger Mike,

I understand your point, for sure. We do that now, keep track of stagger changes and effects on the cars handling. By 'cut and try', which is not a bad thing, you find the range of stagger for a particular car for particular track conditions on a particular size track.

This all came on while standing in turn one at the local 1/4 mile dirt track last Friday night while the track was still loose. I got to thinking about how the flat track motorcycle boys 'do it' and the cars were mimicking that attitude for those particular track conditions. And then of course I started to ask myself, self, do we really understand what stagger is doing in this mode. So far 'self' is confused in finding a link between the two. Or, I may be breathing just a little too much methanol exhaust. :-)

 

[Ranger Mike]

the short answer is that with two rear wheels and a locked differential, you need stagger tuned to the radius of the turn. If you have too much you are loose, not enough and you will push. Motorcycles don't fight this problem. 1/4 mile flat track needs 4 inch stagger.

 

[steve09]

Ranger Mike
thanks for the advice we put the 400lb sway bar in and we run a lot better,and with some
luck on are side,we won on friday and saturday in two different classes.8 sraight in the
limted late model.still would like to no something on the shocks,we think we may have
to much rebound or not enough.in the front are there any books on shiming and valving
shocks,that you no of.we got the roll center good and we are still allitle tight in the middle and on entry,should we try more stager we only run 1" to 1 1/2.with a detroit locker.quick change.

 

[Ranger Mike]

that is good news..you are getting real close.
yes try a just a little more stagger. this will help free up in the middle of the turn.you can add a little sway bar pre load too.
pushing going in ..make sure the brake bias is not too high for the front brakes..back off front bias just a little until the rear brakes start to do more work.
i will check with the guy who has been the SHOCK rebuild "god" for years on the shim package for the penske shocks,

 

[steve09]

Ranger Mike
we have some extra shocks so we dyno them, and the front has about 50 to 60 on compression and 690 on rebound.we will keep them in the car trailer,with springs
on them and change over to them to see what happens.try 2" of stager and check
the brake bias we have a pressure gauge on the brake calipers so we have a good
idea how much rear brake is in the car,thanks for the advice.

 

[Ranger Mike]

steve
from my old notes on shocks
Lft front 76
Rt ft - 76
left rear 946 or 95
rt rear - 94

my open wheel shock genius can rebuild them of $ 125 to $ 150 each but..if you can do it and dyno them save the $$
i am calling old round track guy who specialized in penske rebuild so may have a recommended ship package for you

i can tell you that you need to rebuild each season.these shims will flex and become too weak and the oil with foam and be ineffective dampening the shock action after so many compression/rebound cycles..this happened to us last season as we let this go too long..

steve09 - see private message with cell phone number
for Penske nascar shock guy.
i talked to him and he can rebuild them to recommended half mile specs for $50 each..this is dirt cheap and they will be dynoed..he can change jets to be more compression on fronts and rebound on rears..he needs to know if track is smooth or bumpy, car weight, spring rate on each corner, and track length and banking,,he can turn them around in one day if need be,,once you get these you will have detailed parts list of the jets and shim package and can dyno them and base line each one for next years rebuild..
you should have him do it the first time because he has done it for years and he will keep it confidential..
my opinion
rm

 

[sierra76]

I have really enjoyed reading everyones posts.
We currently run a 4 cylinder dirt track car on mainly 1/4 mile ovals.
Our car runs a fabricated rear with 4 equal radius arms 22in long
Panhard bar mounted to right of chassis
Coil overs mounted on top of diff tubes .Car is limited to road radial on a 7 inch rim.
Always have trouble getting traction and LR always runs cold.
Is it possible to angle top bars up without bird cages to improve drive.
Any ideas would be appreciated.

 

[Ranger Mike]

Thanks..always nice having a fellow racer ,post in..

before you start changing angles, the basic problem is the LR is cold..right..you need to add more cross weight..this will help cool off the right front tire as well..rule of thumb..if the LR is 25 degrees cooler than the right front, you do not have enuff cross weight,,,add more at the LR..do you have scales?

 

[sierra76]

Yes the car has been weighed but we don't see much improvement when we change corner weights.
With the car running parallel bars we probably are not experiencing much anti squat and the car always appears to fall over on the right rear.We have raised the rear roll centre to help with this.
The reason I am concerned is we buildng a new car and not to sure which way to go.
The rules are fairly open regarding suspension.
We are looking at a 3 link with pull bar for 3 rd link as well as a 4 link but have no experience with either of these set ups .
Any ideas would be appreciated.

 

[Ranger Mike]

3 link is easier to learn but the hot set up on dirt is 4 link and i would start there. the question is, will you keep the present set up? if so we need to know a lot more information..if not, then any data regarding set up will not be useable.

 

[THORPE]

This thread has a ton of useful information!
I'm no expert but I'm trying to relate these setuPs to the ones I use on a radio controlled 1/8 scale late model. We have a very competitive class just like the real cars its all about setup.

They are awd buggy based chassis converted to latemOdels. I normally run a 220' run line with med bank and med bite.
Independent front and rear a arms with lots of adjustment.

My first questions are:
Do you always want the roll center located as low as possible and to the right?
Front only or rear too?
What's more beneficial? softer springs toned down with sway bars and adjust the RC to keep from bottoming or stiffer springs with a lower RC? Seems like softer will be better for traction.

We have about 8 lbs total weight to work with so we need all the help we can get to add traction on the things.

 

[THORPE]

Here is a link to a good example of what we run.
http://losi.com/ProdInfo/Files/L8IGHTtuningguide.pdf

 

[Ranger Mike]

thorpe..pretty nice tech racer...
welcome,,i got no clue regarding these cars..stock cars started running sway bars to permit the car to run lower ride height when the speeds started to rise and aero came into play more significantly. The sway bar would add in spring rate during cornering and the softer spring package meant lower ground clearance. In my opinion, softer is always better because you can make use of the SUSPEND.. sion..otherwise you have a giant go cart. I saw a formula car running 1200 pounds springs and two months later the upper arms were cracked..no way..
Roll centers..again my opinion..lower is better until you reach the point it impacts the suspension movement.Same ewith the Rc offset..you need to plant the right front but not too much so you need to balance it..
if these cars are as tech as they look then the principles should transfer and you are on the way to many checkers..

 

[THORPE]

Thanks for the reply and info!

One new thing I'm tryin for the race this sat is limited down travel so the left doesn't lift much ( body roll) which I predict to force the right side to do the work and push the CG lower while cornering.

 

[THORPE]

I appreciate you taking time for me and my toys ranger mike. Lol

The setup and how it affects these cars is as much fun as racing them to me.

 

[Ranger Mike]

not that we ever did this ..but i heard of one racer who used the engine oil pressure to move a hydraulic cylinder that pivoted ballast weights to the left rear during the warm up lap..then locked them into place. on the cool down lap after the checker, he released the lock mechanism and the ballast weight plate returned to its position. the car had to go over the weight scales and always read 56 % left side weight...a small radio activated linear motor and some weights??