schwank

Just a random question I am thinking about before heading back to the track this afternoon for a race weekend.

I have a 944 Cup car, running R888's on yellow Konis and delrin bushes all around... no rubber anywhere in the suspension. 450lb springs up front with 31mm hollow torsions out back. Shocks set about 75% stiff up front, half way in the back. Ride height is the lowest legal SCCA IT setting: 5". Guard LSD. 32psi hot pressures... any more and they start to feel really slick.

In trying to find more speed this year I tried some new suspension settings. I dialed in even more negative camber, to -4.1 deg in the front with max caster. The car turns in quite well now, with less push, and indeed I have picked up a decent amount of time. However this has come at the expense of some stability under braking... in both straight line and trail braking the tail likes to wag a bit, particularly as I get the tank towards empty.

Is there any way to counteract the braking instability, or am I simply paying the price for better handling with a more skittish car? Is it better to dial the front back down and work on modifying the rear settings instead?

Next year I will likely be moving to Hoosiers so I will certainly revisit these settings... but wondering what other little tweaks I can do in the last couple race weekends of this year to improve the stability.

Van

Adjust your shocks to compensate for the weight transfer (stiffen the front / soften the rear). Or, raise your front ride height a little to reduce the rake of the car - this will also reduce weight transfer to the front.

What's your rear toe? Maybe put more of that in.

Nader Fotouhi

What kind of sway bars do you have? What is the toe setting? Also, have you revalved the Konis. IIRC, Koni recommended 400lbs max for yellows.

I used to have 400lb F springs with 30 mm effective rate hollow TBs on my S2. The M030 sways made the car handled great without push and I never needed more than -2.5-2.75 camber. Toe setting has a significant effect on braking stability.

M758

32 psi is too low for R888 IMHO and 4 deg of negative camber is too much. I ran close to 3 deg of negative in my 944 spec on R888 at 38-39 psi hot. I am at 3.5 on RA-1 and 38 psi hot.

Even so the best thing to start adjusting is sway bars. You need to take more methodical approach.

Your goal is not a good feeling car. You goal is lower lap times first and then being able run them consistantly If the car is fast for a lap great, if you can't keep it fast lap after lap then the car maybe too hard to drive. I went from an open diff to a factory LSD. The first benefit is the car is not much faster ( maybe 0.5 sec at most), but it is easier to keep on pace. I used to be able to put in 1-2 fast laps, but then slow down. Now I am not much faster, but can run a higher pace long becuase I am not struggling on turn in quite so much. I have not however been able to fully optimize the chassis to use the LSD nor a fully adjusted my driving style. The car has more understeer than before so it is infact slower in places. However it is faster in other spots for a slight net postitive. I still need to work on taking away stability just a touch so that I don't strubb speed with understeer when full throttle. I plan on doing that with alignment settings and sway bar adjustments.

limerocket

I run a similar suspension set-up in my car, but with less negative camber. I also have a balance bar brake set-up and I can easily duplicate the braking characteristics you describe by directing a small amount of bias towards the rear. Ultimately, I adjust bias to tame the rear end under trail-braking to suite my style.

I'm not familiar with the Spec rules, but a quick and effective fix for you might be to simply install a rear pad with a lower friction coefficient if you otherwise like the handling of the car as currently set up. I've been running Raybestos racing pads (ST-43) in Wilwoods and they are the best I've ever used and have many compounds to choose from. Porterfield Ent. sells them and you can check availability and other options through them for your ATE calipers.

schwank

Well that's the issue really I guess... -4 degrees is unquestionably faster than my previous times on -3.5. Toe is -.05 up front and 0 in the rear. Grip is awesome in the corners, however it is more unstable in braking so not as easy to drive consistently. As soon as I allow the 888's to get over that 32psi they get very slick. I have tested those over two years now and that is my conclusion. I've come off track at 35-37 hot and the car is all over the place. I am still dealing with adapting to LSD as well, though mine is a Guard. No question you have to drive it differently. I am less than 1 sec off the pace of some pretty good local drivers who are on Hoosiers so I have to be doing something right. I can drive it consistently at that pace but have to be extremely aware in hard braking... and also not to push the tires too hard.

I run 968 M030 sways so only have adjustment in the rear. I guess I could back it down a notch and see if that makes it a touch more stable but I fear that may increase understeer.

Did not have much chance to test today as I ran on new full tread RA1's in the morning to scrub them in... which was wise as it was a downpour in the afternoon and a complete nightmare to drive in. That was Q1 only... Back out tomorrow for Q2 and the race with the exact same weather forecast. Should be chaos!

Thanks for the thoughts... Joe as usual I have read your posts and indeed my initial suspension settings were duplicates of what you have published in the past. I don't have a bias controller though it is legal in ITS. I have thought about running a weaker pad in the rear to try and control it a little bit. We had great success with that in our ChumpCar 944. Currently I run Porterfield RS-4 all around.

limerocket

I also used to get caught off guard at times under hard braking due to an initial yaw caused by what appeared to be uneven cooling to the front rotors. A bit anecdotal, but it went away once I redesigned the cooling to be symmetrical.

Every adjustment is a compromise and there is a lot to be said for predictability when you're at or near the limit. FWIW I run Hoosiers at about -2.5 all around and front temps indicate that I could use more, but tire wear tells me to run less. Lap times don't lie.

KLR

Try adding a little toe in at the rear. These cars get unstable under straight line and trail braking with zero toe or toe out in the rear wheels. Might not solve all of your problems, but I guarantee that you will feel an improvement.

originalmotorhead

Last weekend at the NASA Autobahn event, I dropped 3 seconds off my lap times from the 1st race to the second race by switching from full treaded RA1's(that had too high of PSI (45)at the end of the race), to some near bald 888's(at psi of 39 at end of the race).

It was a night and day difference for understeer in the tight turns.

I've got 425lb springs up front and when I originaly ran with hoosier slicks it was fine and handled great; but first time I went to toyo's I could hardly keep the car on track. From the looks of it, I'll likely be backing down to 350 or 375 lb front springs because everyone running spec seems to be in that range. I guess the treaded tires just can't take the extra abuse from the stiffer front and thus it pushes. Course my sway bars are also the tiny oem non adjustable ones, so I also need to upgrade that too.

Anyways, just thought I'd mention my experience with improper air pressure in toyo's and having stiff front springs.

if you figure it out, let me know too

Tom

schwank

Yeah based on my evidence there is indeed 3 seconds a lap here in Portland between full tread RA1's in the dry and well worn R888's. Had to run the RA1's this morn due to threat of rain, but went back to my 888's this afternoon and had barely turned in to T1 when the smile came back to my face. Though it may have been the Civic and Miatas I passed on the way through

I might do some tweaks over the next couple weeks as I have my final weekend of the year in my car at Oregon Raceway Park coming up. It is similar to Thunderhill only more total elevation change... lots of off camber blind corners to keep you sharp. Will need a good suspension setup for this even for sure.

M758

Yes full tread fresh RA-1 are not fast. They never have been over the 8 years I have run them. I always shave RA-1 to 4/32 and then "break them in" 5-6 heat cycles before expecting the best from them. Full tread it owuld take 12 heat cycles to break the in, but the did end up just as fast and lasted just as long.


The R888 is much more sensitive to alignment and driving style. It is easy to make those tires go off. If you want to know how much camber to run get a tire temp gauge and start checking. That will tell you. When I ran R888 if I ran RA-1 camber I would over heat the inside shoulder causing the tire to go off faster. Once I back out 0.5 deg camber I got more even tire temps, faster laps and a more consistant grip through out the run.

If you need 4.0 of negative camber to get the car to turn on R888 you have other issues that you are using camber to mask. The only bid difference is you ride height is 1" higer than most 944 spec cars. I am not sure what impact that has on balancne. I know it raises the CG and in theory lowers the overall grip of the car.