QuestionQUESTION: Hi Dan, I have a 93 Ford Probe that I race on a 4/10th mile banked oval. 13 degrees in the corners and 5 on the straights. I am experiencing one of the wildest problems I have ever heard of. When I enter the corner my rear is extremely loose. Then when Im trying to get back on the gas to allow the frt end to pull it straight, the frt end starts pushing like mad and the entire car starts sliding up the track sideways. Measured at the rim I'm allowed 3 inches of camber and im running about 2.5 right now. My struts must be welded to where they are non adjustable and they are welded in place to the same place it was when the car was handling good. So I really do not think thats hurting me. I am allowed to run up to 2 inches of wheel spacers on the right frt and right now im not running any. the car was handling great without any at one time but just wondering if you thought it may help my problem at hand. Right now Im running 195 65 r14 tires in the rear and 185 65 r14 in the frt. 65 is the lowest aspect ratio that Im allowed. The 185 is the tallest tire I can fit on the right frt. Any suggested changes in tire size? What are some good baseline tire pressures to run. What effect will certain changes make? I have heard that limiting the left frt strut from extending would help. Is this true and if so how do I keep it from extending? Okay and I guess the last thing is what is your opinion on running sway bars?
ANSWER: Honestly ?? It sounds like your tires are worn out, and simply not working any longer. Do you have to run street tires ?
Last question first, YES I run sway bars on both front and rear., but a balanced suspension is the important thing. A front sway bar will eliminate the need to "chain" or otherwise limit your LF strut motion, and you'll have the satisfaction of knowing you're doing it the right way. You might want to run slightly softer springs on the rear, and make the RR softer than the LR. If you decide to run a rear sway bar too, it will allow you to run much softer springs, improving grip.
When the car starts to push suddenly when you apply the gas, that's called "Power Understeer" and is unique to FWD cars. If you are jamming the gas down, try being a little softer, you still need ot apply throttle at the earliest possible time, bu tdo so gently, jerky motions have no place in a race car. Your other option is to pput a higher gear in the differential. not fun on those FWD arrangements.
For tire pressures, you need to know the temperatures. They will also tell you about front and rear camber. I'd suggest starting with manufacturer recommendations. But you really need to get a guide book on the subject. I recommend 'How To Make Your Car Handle" by Fred Puhn, Look for it on Amazon or just google the title, you'll find it. I read it about three times before I understood enough of it, but then went to the track and found 2 seconds a lap within 2 hours of testing . (1.6 mile road race circuit). You will need to get one of those infra-red tire pyrometers. Summit has then, so do all the other supply houses.
Finally , a laot of what you hear around local stock car tracks, esepcially in the lower classes,is real caveman stuff. There are better ways than chaining suspension movement, and welding differentials. GEt some books on race preperation and READ them. Then you'll know as much as I do !!
Good luck!
Dan Liddy
Sarasota, Florida
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QUESTION: Yes I must run DOT tires with a speed rating no higher than "T". My tires have most of the tread shaved off. If I ran a new tire with the full tread on it, it would not last one race. The outside of the right frt tire will chunk out and blow before 25 laps are up.
Okay and for the sway bars, on the frt we always ran a longer link on the right frt so the sway bar acts like a left to right torsion bar thus applying more spring pressure to the right than the left. would doing the same to the rear be effective for my problem?? if so which side needs more spring pressure. Also when I first drove this paticular car, it was extremely loose on the exits. I read that increasing the size of your rear bar helps to loosen the car on exits, so since I could not find one smaller than mine I simply disconnected it. That made the car drive like a dream. Now something has changed and I cant duplicate it.
ANSWER: OK the "something has changed " statement makes me think that something has beocme bent or broken. It could be a lower control arm, simply a loose bolt somewhere, or a bent rear suspension. I tagged the wall gently once with a VW Rabbit and the car was loose afterward. It took hours of checking before we found that I had bent the rear solid axle - - but just a little bit. That 1/8th. of an inch made all the difference. So we straightened it and it was better, but never got really right until we chsnged it out.
So you need to start looking for damage of some sort, or a failed part that is probably in the back of the car. Be sure and check the integrity of all suspension bushings, and also the shock settings. A dead shock can cause some strange gremlins. A slightly loose wheel bearing can also wreck havoc, you will need to do a very complete suspension teardown and rebuild. BE sure and check the alignment.
Assymetrical sway bar settings are a black art but the logic of extra spring pressure on the RF is valid and should help . Also if you can raise the LF a little, you'll gain a little LF grip but be sure and check your corner weights. The front should be as balanced as you can get it. Same with the rear, but with a left bias of about 55%
That's all I can think of at the moment, If I come up with any other brain storms, I'll let you know
Again, Good Luck
Dan Liddy
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QUESTION: Hey Dan thanks again. Now that you mention it when it "Changed" it went to pushing like hell up front and i made some changes to loosen the rear to compensate. I think ill set the rear the way it was and focus on the frt. What are some good caster numbers to run up frt??
AnswerThe saying goes: "Caster is faster" . I can't give you numnbers because there are many variables invloved. Remember the book I recommended ? There is a lot of info in there about that. What I usually do is start with about 3 Deg. and work up until I can no longer turn the steering wheel at low speeds. Then move it back until steering doesn't wear me out on track. Try a left bias- - -5 Deg. LF, and 3 Deg. RF.
Before you do that, align the front end and try about 3/16" of toe out (not toe in) test that and watch your front tire temps. Cooler is better to a point. While it's on the alignment rack, make sure you have between 1/16" and 1/8" of rear toe in. Again watch tire temps for the coolest setting . Toe out in the rear will make the car REALLY loose.
It appears that you're getting to the point where basic set-up is critical. Be sure and get that book. Or any book about suspension set up. Caution though. some of those books are for pro race engineers for highly tweaked stuff like Indy cars or Daytona Prototypes. Most of it doensn't make much sense to grass roots people like us. I remember reading an article about dialing in Geoff Brabham's Nissan GTP AT THE TRACK, where they were changing camber by 15 minutes (1/4 degree) , and toe angles by 1/64". Simply not possible for us without portable scales and laser alignment stuff .
