tube80z Posted October 22, 2015 Share Posted October 22, 2015 I started with the tires in the 18 to 20 psi range and the tire temperatures seemed to indicate that was the correct pressure. Unfortunately, the car felt like it was falling over all the time and the tires were rolling under pretty badly. So, contrary to the tire temps, I started adding pressure until the car felt more stable. I've got the car down to 2580 full of fuel with me in it. I have 610 lbs on the right front and 638 lbs on the left front. That's how they are supposed to feel. If you're trying to get them to feel like hoosier radials you'll need more pressure than where they make max grip. The slicks should be about half for your suspension travel when everything is working correctly. It took me a long time to figure that out even when told it was right. Your pressures are high but not completely out of the realm of reason. A good picture head on of the front at max load will show if you need camber or air pressure. I have a favorite place where we run to get these. I can point you to some examples if that would help. If there are properly inflated more camber or more caster might be needed. I would lower the rear of the car until the spring rattles and then bump up the rate to around 550. I ran rear limiters with just a small amount of drag on a 0.40 feeler gauge. If the track was smooth I ran less and less front droop often down to 0.25 inches to control roll and make the car turn in faster. If you have big bumps you may need to limit the same as the rear. I missed the second pick of your car. It looks like it's rolling too much in that photo. I think you tried the limiters in the past but can't recall. I would do that again and see if that helps with the rolling. I'd also be very tempted to increase the springs rather than add front bar. Springs will reduce the amount of pitch and roll compared to just the bar. Your spring rates look close for the car on radials. Quote Link to comment Share on other sites More sharing options...
clarkspeed Posted October 22, 2015 Share Posted October 22, 2015 That looks like a VW Golf trail braking! Dan is running a fairly stiff set up and looks to have a good deal of mechanical grip in the pic. Going stiffer might cure the problem, but always remember every change has a secondary effect. What is the real problem here? Oveall grip? Corner entry understeer or oversteer? Grip levels and getting the handling right are much more important than trying to cure the wheel lift. It works good for a VW, maybe it works for you too! Quote Link to comment Share on other sites More sharing options...
74_5.0L_Z Posted October 22, 2015 Author Share Posted October 22, 2015 Cary, I did run limiters on the front for a while just to keep the springs from getting loose when I jacked it up. I've since raised the front just enough to no longer need them. Clark, I am not having either an understeer or oversteer problem. The car pretty much goes where I point it. It just takes more slip angle to make it change direction. I am still not used to the Bias ply slicks. The car always feels at the limit of traction (even when its not). I am slower on the bias ply than on the radials. I may get used to them and get faster after a bit more time, but I plan to go back to radials. So, I probably won't spend much effort trying to perfect this set-up until I am back on radials. Quote Link to comment Share on other sites More sharing options...
tube80z Posted October 22, 2015 Share Posted October 22, 2015 You can't trail brake effectively that way. So when you put a big splitter on the car and need to keep it flat on the ground in entry that will become important. Dan did mention the car moving too much. Part of that may be too much suspension travel. From the second picture there's too much roll and that has decambered the outer tire. So even if the car feels great there's a higher level to be had. And these spring rates aren't stiff by any means. Starting points for slicks these days should be wheel rate equal to corner weight for no downforce and that can go up to 1.5 or higher. Add XP/EM downforce and numbers over 2 can be used. On radials .8 to .9 seem to be the norm. On track cars running at higher speeds other ideas could be used. Quote Link to comment Share on other sites More sharing options...
clarkspeed Posted October 22, 2015 Share Posted October 22, 2015 It just takes more slip angle to make it change direction. That is a clue. There can be a lot of difference between radial and bias. To dial them in will most likely will require some testing with different pressure, camber and toe settings. The difference in tire spring rates might also require a spring rate change. It takes a little time. You can't trail brake effectively that way. So when you put a big splitter on the car and need to keep it flat on the ground in entry that will become important. Dan did mention the car moving too much. Part of that may be too much suspension travel. From the second picture there's too much roll and that has decambered the outer tire. So even if the car feels great there's a higher level to be had. And these spring rates aren't stiff by any means. Starting points for slicks these days should be wheel rate equal to corner weight for no downforce and that can go up to 1.5 or higher. Add XP/EM downforce and numbers over 2 can be used. On radials .8 to .9 seem to be the norm. On track cars running at higher speeds other ideas could be used. I would expect some oversteer or instability under trail braking in that condition, but none mentioned. That's why I ask. And it didn't look like Dan is running a splitter. I've seen some strange things over the years and what works for some people may not work for others. Sometimes the answer is don't trail brake so much. I think getting the tires to work is most important. If the overall grip is off, and you are "rolling over the tires" rather than "skating on ice", then stiffer is the way to go. I agree with your direction because tires are a lot gripper these days. Either pressure change )1psi = 60-80lbs/in) which you already tried, or spring rates. I wouldn't call 500/425 soft for a production based S30, but you should go higher if the car/tires are asking for it. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted October 22, 2015 Share Posted October 22, 2015 Your car is freaking awesome. Quote Link to comment Share on other sites More sharing options...
socorob Posted October 22, 2015 Share Posted October 22, 2015 (edited) I did a track day last weekend and the guy behind me came over after and said I was almost picking my rear inside tire off the ground in these couple tight fast Essex on the track. He told me I needed a bigger rear bar. I don't have any rear bar. It looks like in the video for the green hornet z that he is fast and his car looks to stay flat and I think I saw a rear bar on it when he was showing undercarriage shots. Would a rear bar help keep both tires more in contact with the ground without causing anything detrimental? And what was the reason Nissan decided to add one on to the Z? Edited October 22, 2015 by socorob Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted October 22, 2015 Share Posted October 22, 2015 A rear bar will make lifting of the inside tire worse. You don't need a bar on back. Don't believe everything the "experts" tell you. To include me. Quote Link to comment Share on other sites More sharing options...
socorob Posted October 23, 2015 Share Posted October 23, 2015 I have no idea. This guy came up and randomly told me this, but I have no idea how much he knows. I know I don't know a whole lot, so just asking questions. Quote Link to comment Share on other sites More sharing options...
G-E Posted October 23, 2015 Share Posted October 23, 2015 I agree with Reb, if you're lifting the last thing you want is a bigger swaybar at the back, you should instead be looking at rollcenter adjustment for the front, or stiffer springs. Just like with pain, sometimes the symptom isn't located near the cause... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 23, 2015 Share Posted October 23, 2015 Back to the FA tires for a second, I think I was running too much pressure. I bled down to 28, looks like they give spring rates for 18-22 psi.http://www.hoosierracingtire.com/ACSSR.htm Quote Link to comment Share on other sites More sharing options...
JMortensen Posted October 26, 2015 Share Posted October 26, 2015 (edited) Just called Hoosier so I have just a little more info: the FACS tires that I have are R35 compound. They stopped making this tire in R25B. I'm quite sure that the guy thought I was a complete moron at the beginning of our brief conversation. I showed him how his tech release pressures shows that my vertical load will be well within what the tire was designed for, and lateral should be about the same too. 1230 * 3 gs = 3690, and 2250 x 1.5 = 3375. So I think by the end there I wasn't AS much of an idiot... He flat refused to speculate on temps, pressures, camber, etc. EDIT--screwed up my math. With 2250 as the min car weight, add my 180 lbs and there you have 2430 x 1.5 = 3645, so it's even more on target. Edited October 27, 2015 by JMortensen Quote Link to comment Share on other sites More sharing options...
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