Automotive Race car suspension Class

[Ranger Mike]

Thank you and I hope you will have time to review our efforts from time to time...very glad to have you notice our efforts here..
RM

 

[Fahlin Racing]

Vertical laoding creates downfroce on the outside tire so the more vertical loading there is the better the outside tire sticks during cornering.

I haven't read the book you are using here, but I have read Herb Adams', and he states that when Vertical Load gets too high (for whatever design is being used) is not good, in turn reduces cornering efficiency of the vehicle.

Good stuff Mike, albeit, thought I would add that into here to add more to the visualization on VL.

 

[Ranger Mike]

thanks Fahlin...good advice..
that is a classic "Push" developed by over loading the tire CF...thats what gets beginners confused when the front end pushes..is it the rear tires hooking up too much or are the front springs too soft?

When i first started " round tracking" I watched all the old timers hot lap and they would always get out of the car and walk around to the right front tire and put their hand on it to see if it was "hotter" than the right rear tire..tire pyrometers were way too expensive back then..they wanted to " make her loose and then tighten her up"...
it was all guess work back then...we had something like 7 cars racing from one small town of 10,000 people..
these were "Hobby Stocks"..big V8 in 1955-1957 Chevy, Fords were popular...we ran a 1964 Ford Fairlane. too much nostalgia..sorry..

racing is a compromise ..the chassis only really works with one set up at one particular time on one particular track for one unique set of tires at one ambient temperature...constant tuning is required to WIN...

 

[Fahlin Racing]

You can also mistake an under-inflated LF tire (in circle track) for causing a 'pushing-like' situation because the contact patch is very small, if there is one. When the RF is gripping during the turn, the inside is just slipping from poor tread contact from the tire deforming.

Not having a temperature gun in the tool box just makes things more fun I think. Checking tires pressures and by touching the tires themselves after qualifying/heats/features is a good teaching tool for beginners in circle track on what part of the tire is used most. It worked for me, we moved up in the field slightly just by adjusting our air pressures when we first started.

I can't remember exactly, but I think it was in one of Smokey's books (and others I am sure)that you want each tire within a few degrees of each other (hopefully possible in the situation that is present).

 

[missile07]

Mender,

I am very interested in learning more about how the spring rates change when things bind & what exactly that would do?

We still have yet to race due to rainouts & flooding here locally, so I haven't been able to test anything out.

I went back and looked at a bunch of the previous posts & reading and this is a really good forum!

 

[rwstevens59]

Northeast dirt modified chassis stiffness question.

Here we go again. Just read a blurb about a new chassis builder up here in our neck of the woods extolling the virtues of his new chassis one of which is a change made to the bracing design under or around the engine area which provides better 'chassis flex'. These cars are a complete fabrication using no stock parts, think big sprint car with a lot of added sheet metal. Solid axle front and rear.

Now the race engineer in me says flex is bad, torsional stiffness is good. If the chassis has good (high) torsional stiffness it will be more tunable with springs, shocks and anti-roll bars (if you run them). Low torsional stiffness means, to me at least, that I have a large undamped spring of unknown rate for a chassis and it does not respond well to changes. The claims that these cars are 'easy' to tune on may be true only because they don't respond much to normal tuning changes.

So what am I missing? Why do a lot of the dirt car builders feel chassis flex is a good thing?
For me, I just don't get it.

Ralph

 

[Ranger Mike]

Unless i missed something..i am 100 percent in agreement...

flexy flyer chassis theory been around since the straight axle was introduced...

in my opinion..Races are won by the car that gets there first. to do this..it s all about TIRES...period...if you have the best tire contact patch..you will stick better than the other guy and out corner him..given a half way decent engine and all things being more or less equal..
so how do we do this...by dealing with the with transferred when cornering..its going to transfer...nothing you can do about it..so you learn how best to deal with it..one way is to understand where the CG is and where the RC is and modify these as the rules permit,,,next is to calculate the amount of weight transferred and understand where it goes and at what time ..during the cornering process...that is why you have to understand suspensions and how they work ,,and even more importantly..how to make track side changes to deal with each situation...

 

[rwstevens59]

Thanks Ranger Mike, at least I don't feel so alone in the chassis 'woods' anymore, talking to myself. LOL :-)

Now if I could just get these boys to listen to me about those tires you mentioned...

 

[emccalment]

Digging through this forum, you guys post valuable information I'm dying to be able to understand better. While I'm still working on that particular aspect, I have questions that differ greatly from the current discussion thread I was hoping you could help with. Likely beginner questions, but then again, I'm a beginner. :)

Upon return from Afghanistan I'm going to be looking to buy a car for purposes of taking it to the track and really learning how to drive. Wilst reviewing a wide variety of cars I began to wonder not about initial potential for a car and its handling abilities, but for the modified potential of the cars I'm looking at.

My current questions are how the wheelbase, track, weight and center of gravity would effect a car's final performance abilities. To determine said abilities, am I going to have to go further in depth to type of suspension and characteristics of each?

I apologize if I'm asking in the wrong place, but I am enjoying this thread thoroughly.

Thanks,
Ezra

 

[Ranger Mike]

Welcome and thank you for the service to our country. I recommend you consider joining SCCA. Sports Car Club of America is 200,000 member organization for the amateur motorsports fan/driver. You can join a region and enter in the PDX event which is professional driving experience where you are given instruction by SCCA official on driving the actual track like Mid Ohio. A licensed driver from SCCA will sit in the passenger seat and tech you to drive the course..Then they turn you loose. My old car crew member burned out a set of brake pads on his Toyota Camry during one of these. Then if you really want to step it up, you can by something like a Miata and compete..various classes in SCCA have strictly stock all the way to Open Wheel like we run. all types of classes for all types of budget..I seen guys drive to the track, jack up the car and change tires and go racing..super economical..there is always a racer who can help you and all you need do is ASK
btw this is how you learn about understeer (push) etc,,,in a stock car and start to modify from there,,

 

[steve09]

hello everyone .
this fourm has a lot of info on racing all kinds of different car classes,and i,ve been reading
through this fourm off and on.my dad has three late models one limited and two super.
I help out on the weekends and we have recently got a shock dyno.not shure what valves
work the best and shims to use any info.we race a half mile oval asphalt with sixteen deg
banking. coilover shocks with adjustments for compression and rebound.also mike what
do you recommend for a good software program.

 

[Ranger Mike]

welcome..Steve 09 having purchased a shock dyno means you guys are very serious about winning. I bought one a while back. Got to dig my shock note up in the car hauler. What type software are you looking for? Usually the shock dyno has software with it?

 

[steve09]

hey mike
we have all the software for the shock dyno.but were looking for some geomentry
software.were using chassis r&d for the roll center but it's not as good at showing
you what to change as we thought.something more in detail than just roll center.
like what to change on the car when it's to tight in the center.with out hurting your
car out of the corner.kind of fine tuning to keep more consistant through the race.

 

[steve09]

hey mike
also we have been talking with some other race car builders and they all same the
same thing about right front camber gain.they want almost no gain from static to
dynamic.whats your opinion on that and other than changing spindles and uper
control arms is there anyway to slow down the camber change.
thanks for the info.

 

[Ranger Mike]

Software - Suspension Analyzer by Performance Trends
shows dynamic chassis changes in roll/bump...you have to input three axis measurement of chassis mounting points but well worth it..talk to Kevin Gertgen of Performance Trends Software to assist in explaining the math used for various set up calculations ( caster , camber gain, Toe Out etc..)they also have Circle Track analyzer that is a little less dramatic but quick and easy to input

 

[xxChrisxx]

Susprog.
It sounds almost identical to Suspension Analyser. I think you can download a trial to have a look at the interface.

 

[emccalment]

Mike,

I appreciate the quick response, and that is very much what I am looking into. Almost exactly in fact. I'm heavily considering a Miata with the LSx swap. But, I figure straight line speed can be had with almost any engine or through a swap, so handling ability is what I should make the basis of my decision on what to get. I'm not the type of person to swap cars regularly, so I'm trying to base my decision on where to start with handling capabilities. :)

Unfortunately I missed the opportunity to get into racing with a portion of my family that we weren't very close with when I was little. Oh how I regret that later into life, lol. Loving the discussion guys. Very informative.

 

[Ranger Mike]

we were racing Gateway International Race way in St. louis once and they had the "Miata Mafia" there..about 40 door slammers and man did they race...the next morning at the hotel there were all kinds of Miatas with bent sheet metal, mashed in hoods,,,a lot of contact...
this was a national event and miatas had towed from california, Canada, all for a cheap plastic trophy...those guys had a ball..perfect way to learn the ropes...you will NOT have this in regional events when you start out...
when do you ETS?

 

[emccalment]

You're not helping my desire to move away from the Miata a little bit, lol. But, as I'll probably need something relatively cheap to learn in when I get back, it might end up being a Miata anyways.

As for ETS, I'm on the officer side so it's really anytime I want after Q3 2012. Still working out when that will actually be.

 

[Ranger Mike]

being a former Captain of Infantry...watch your 6 and hunker down ..short timer...all the way!

 

[steve09]

Hey mike
I was looking at the performace trend software and it looks like something that will always
help.we just raced last week and won and were still trying to improve on the car. was you
able to come up with anything on the shock dyno,are dyno is a roerig and works real good
with the shocks we have been using.but not shure the valving is right for other tracks with
less banking and speed.

 

[Ranger Mike]

Great..checker always helps..shocks are the final stage of chassis tuning...sounds like you got the correct spring package to handle the weight transfer..

my notes are for 2500 pound late model, 3 point rear 58% left, 50 % rear, 56 % cross weight,
shocks are
LF -76
RF 76
LR-946
RR-95

 

[emccalment]

Do any of you fine gentlemen know where I can go to find any kind of statistics on modified production cars? People tend to use the Nurburgring for benchmark purposes on new cars, but I'm curious about benchmarks for modified cars. Any thoughts?

 

[Ranger Mike]

sorry emccalment ..i got negative knowledge of this..

 

[Ranger Mike]

Race Update- we ran road course on 95 degree F day..oth days..we put Hoosier R45 tires on the car..this is a hard compound..it took 4 laps to get the temps up enough to get half way sticky..

The driver noted the car rolled going in and the tires would snap ( at the limit of CF) and he almost lost it. We had just replaced the 3 way adjustable Penske shocks ..back from rebuild and ran on shock dynometer. To correct this we increased the dampening on the compression adjustment ..went from Number 3 setting to Number 4...more dampening,,number 6 being max. This made the shock stiffer when compressing..this helped but still not getting enough traction..we lowered the rear ride height a small amount and finally got the car to really hook up on the R45s. The tire pyrometer readings were right on the money. Won all three races.
Lesson learned _ the R45 compound is not the ideal compound..for our weight car on this track with this temperature. next time out, we go with R35 compound ( most often used..has a little more wear and is softer. We leave ride height as set and see if the car pushes ( understeers). The tire pyrometer will indicate which way to adjust.
one more thing..zero over heat problem since we added the oil cooler..

 

[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