heavy85 Posted May 22, 2006 Share Posted May 22, 2006 So now that I have some Hoosier slicks (and am really glad I did - huge fun factor) can anyone give some insight on the best way to dial in the air pressure? I started off at 19-20 PSI and haven't really tried anything different - what should I be looking for? Thanks Cameron Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted May 22, 2006 Share Posted May 22, 2006 This is easy. Get on clean smooth pavement, spin em on clean pavement and then get out and see the contact patch on the pavement. Heavy black in the center, too much air. Heavy black at the edges, not enough air. Nice even black all the way across, just right. I run 11 psi in a 9x29.5x15 slick in the z. 19 is way too much even for a 7 inch slick in a 3800 lb car based on my experience with my Monte SS. Quote Link to comment Share on other sites More sharing options...
drzed Posted May 22, 2006 Share Posted May 22, 2006 I don't know about the Hoosiers but my MT ET drags seem to work well at 15psi. I was told to start at about 15 psi and work my way down but it seems to launch well as is. How do you find the far end of the track? My combo seems to hunt and squirm all over the place above 100MPH. Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted May 22, 2006 Share Posted May 22, 2006 called carcass walk, usually means the air pressure is too low. Tire pressure is an individual car thing, not a general guideline. skinnier tires require more air than wide tires, F=P*A. Quote Link to comment Share on other sites More sharing options...
heavy85 Posted May 22, 2006 Author Share Posted May 22, 2006 Sorry, should have been more specific as these are road racing slicks being used for autox so the burnout method will not work too well ... especially on the fronts. Thanks anyway Cameron Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted May 22, 2006 Share Posted May 22, 2006 Get yourself an IR gun. Measure outside, middle, inside. Middle is hotter, too much air pressure Middle is colder, too little. I'm sure someone else has more detailed instructions but thats the gist as I understand it. Dave Quote Link to comment Share on other sites More sharing options...
bjhines Posted May 22, 2006 Share Posted May 22, 2006 I have done autocross for a few years.... I primarily run in HPDE and time trial events though... I have been using pressure rise and wear patterns to determine correct pressure through tire inspection... too little negative camber and poor lateral stability can mislead you when looking at tire wear to determine pressure.... I know that many instructors at autocrosses will tell you that you should start high and work your way down.... I have been told 40PSI for stock sizes on most daily driver cars... I think that is a little high for best grip... I would try marking the edges with a white shoepolish stick(grocery store). Mark the transition from the tread to the sidewall... check the amount of rollover after each run... you want to use all of the tread without getting contact on the sidewall... this varies with different tires and profiles.. so you still have to adjust for feel... Some tires just don't behave.... getting good turn in may be impossible with some of the cheaper high profile street tires. Falken Azenis are a good choice if you intend to drive on the same tires you autocross on... but I would rely on another vehicle on rainy days... Hoosier makes some of the stickiest tires available for less than $200 each. They also have a super sticky autocross specific compound. You don't want to even think about running those tires on the street... I am not sure that the affordable IR temp guns are going to give very good results in an autocross situation... but I have never tried it... I have heard of people getting Azenis so hot during autocrosses that they get "greasy" feeling.. I have a little trouble believing that because I have run Azenis in 90* heat on track for 30 minutes at a time... you can overheat ANY tire on track... and yes they have more limitations than the Toyo RA1s or the S04s or the Victoracers... but I do not think you are going to overheat any tires during an autocross session unless you go around pushing madly around corners.. slower in>> faster out and UNWIND THE WHEEL.... that should fix any overheating problems during an autocross.... You might also try aligning the car with a little toe out in the front... just a hair out... it will help in those sweepers.... but it will eat the hell out of your street tires in the long run... Quote Link to comment Share on other sites More sharing options...
zguitar71 Posted May 22, 2006 Share Posted May 22, 2006 I run from 21 to 25 depending on the temp. I have cantilever goodyears r250 compound (like the r25 hoosier), I do not know the type of tire you have so my pressure might not apply to you. When it is hot out (90+ and sunny) I run 24-25 or the tires get too warm and become greasy. I do not go below 21 even when the temps are cool because the sidewalls start to deform a little. It is a game to see if the tire will not overheat and not deform the sidewall. My best time have been in the 24 to 25 range on warm days. Below 24 on those days the time goes away a little. I use to run 22 -23 on the warm days and tried 25 just because and it worked well. Over 25 and they stop sticking as well. I usually run 1 pound less in the front than the back too, if the course is very tight. Open courses I run them even. Quote Link to comment Share on other sites More sharing options...
bjhines Posted May 22, 2006 Share Posted May 22, 2006 ohh I almost forgot to post a pressure range... I am shooting for 34 PSI HOT... I usually start at 28-30... this is currently on 225/50/15 Victoracers... I have had similar results with Toyo RA1s. Quote Link to comment Share on other sites More sharing options...
tube80z Posted May 22, 2006 Share Posted May 22, 2006 Get yourself an IR gun. Measure outside, middle, inside. IR guns aren't very useful for tires. The surface temps drop too quickly and they have a tendency to even out before you see the real trends. They are very useful in taking track temp measurements. You really need a good probe pyrometer. Just remember for autox you'll never see the core temps that road racers speak about. If a hoosier R25A slick will show you core temps in the 100 to 125 range when it is working good. When you get over that you'll find they are getting greasy. When taking tire temps remember to take 5 tire readings. What I mean by this is start with one tire (always the same one and usually a front), work your way around the car, and then take the temp of the tire you started with. This will let you see how much temps are dropping as you go. You can use this to guage if a tire that you took the temp of later is actually hotter. In general, once I have established that I don't have an outside edge hotter than the middle or inner I will usually only look at the middle and inner for what needs to change. Remember toe-out heats the inside and toe-in heats the outside. This can mask how the tire is used. For autox pressure rise is a better indicator of how the tires are being used, IMHO. Work to get the front and rears to come up the same amount. You'll also have a target hot pressure that you'll find that works best. You'll need to adjust the starting temp based on ambient temp. Always use the driest air you can in tires. Any water that is condensed and turns to vapor will cause an abnormal amount of pressure rise. Adjust pressure in 20% increments to figure out what works best. That will quickly let you see what you need to do. Cary Quote Link to comment Share on other sites More sharing options...
JMortensen Posted May 22, 2006 Share Posted May 22, 2006 I don't know where the point is at which you have to start worrying about debeading tires with low pressure, but I'd be a little cautious about running under 20. I don't know where the danger line really is, but Tune To Win which was written in like 1980 says don't ever go under 18 even with beadlocks. It's nearly 30 years later, so who knows how directly that relates to today's tires, but I'd still be concerned that you're getting down to the point at which debeading starts to become an issue. I always shot for 26-28 hot on my tires. It does vary quite a bit from tire to tire, so my Yokohamas might want more pressure than your Hoosiers. I always got a lot of pressure change, probably because I usually had 2 or 3 drivers, so what I'd do is start about 5 lbs shy of my hot pressure and then bleed off pressure between runs as needed. I must have had a lot of water in my air, because it didn't take more than 1 or 2 runs to get the pressure up there, then I'd still have to bleed off between runs. Quote Link to comment Share on other sites More sharing options...
tube80z Posted May 22, 2006 Share Posted May 22, 2006 I don't know where the point is at which you have to start worrying about debeading tires with low pressure, but I'd be a little cautious about running under 20. I don't know where the danger line really is, but Tune To Win which was written in like 1980 says don't ever go under 18 even with beadlocks. It's nearly 30 years later, so who knows how directly that relates to today's tires, but I'd still be concerned that you're getting down to the point at which debeading starts to become an issue. I think a lot of it depends on tire construction. The FA tires I use on my car seem to work best for me at 18 PSI HOT. I generally start in the 16.5 to 17 range with them cold. I've never had a tire come off the bead but a few of the hoosiers had issues with not holding air. Well after that fact I heard they may have had a construction problem. A lot of this depends on how much your car weighs, etc. If you want to get real tricky you can play a couple of games with your tires. You can paint them with latex and put them on paper to look at how the contact patch changes with pressure, camber, etc. This is best done by using a modified press. Or if you need to see an actual pressure distribution you can use Fuji prescale pressure sensitive paper. Cary Quote Link to comment Share on other sites More sharing options...
Drax240z Posted May 22, 2006 Share Posted May 22, 2006 I always shot for 26-28 hot on my tires. It does vary quite a bit from tire to tire' date=' so my Yokohamas might want more pressure than your Hoosiers. I always got a lot of pressure change, probably because I usually had 2 or 3 drivers, so what I'd do is start about 5 lbs shy of my hot pressure and then bleed off pressure between runs as needed. I must have had a lot of water in my air, because it didn't take more than 1 or 2 runs to get the pressure up there, then I'd still have to bleed off between runs.[/quote'] What yokos are you running Jon? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted May 22, 2006 Share Posted May 22, 2006 A005 250/590/15's. They're Toyota Atlantic front tires. The compound is really too hard for autox, more like a Kuhmo Victoracer tire than a Goodyear or Hoosier autox slick. Quote Link to comment Share on other sites More sharing options...
tube80z Posted May 22, 2006 Share Posted May 22, 2006 A005 250/590/15's. They're Toyota Atlantic front tires. The compound is really too hard for autox, more like a Kuhmo Victoracer tire than a Goodyear or Hoosier autox slick. For what it's worth the swift manual I have recommends 28 PSI when running these tires on an oval using max downforce (3450 lbs) on a ten inch rim. Cary Quote Link to comment Share on other sites More sharing options...
JMortensen Posted May 22, 2006 Share Posted May 22, 2006 Cary, do you think that that info can be extrapolated to using them on a Z? The only other feedback I've been able to get was from Clifton, who used them on his track car and ran right in the same neighborhood with pressures. All I can tell you is that if you went down too far from the 26 the tire would start to feel floppy and if you got over 30 it wouldn't grip. Quote Link to comment Share on other sites More sharing options...
bjhines Posted May 22, 2006 Share Posted May 22, 2006 About those Hoosier failures... These were beaten hard in rental cars and failed quite spectacularly.....My understanding is that too little camber combined with too much heat is what causes this... I would not put Hoosier to blame on this failure.. they are race tires... they grip like hell.. and they can overheat and go to pieces... these tires were run in a 6 hour enduro.. the drivers and crew took a chance and lost.... I balanced his tires and a bunch of others at Sebring during the Jan06 PBOC winterfest.... ME at the balancer.... I really needed sunglasses.... Money shot... Quote Link to comment Share on other sites More sharing options...
heavy85 Posted May 22, 2006 Author Share Posted May 22, 2006 Thanks for the info. By the way these are 9.5 x 15 FA Hoosiers in R35 compound on 15x10 rims. So in general is less (pressure) more (grip) or vise versa? Cameron Quote Link to comment Share on other sites More sharing options...
tube80z Posted May 22, 2006 Share Posted May 22, 2006 Cary' date=' do you think that that info can be extrapolated to using them on a Z? The only other feedback I've been able to get was from Clifton, who used them on his track car and ran right in the same neighborhood with pressures. All I can tell you is that if you went down too far from the 26 the tire would start to feel floppy and if you got over 30 it wouldn't grip.[/quote'] It looks like I wrote before I had all my facts. At max downforce they are running 27 PSI on the inside tires and 33 on the outers. I'm pretty sure an atantic is supposed to weigh 1250 pounds. So when you add in downforce they are well over what a Z would weigh. They are running spring rates 1200 to 1800 range on an oval (according to the swift manual). For road racing they are looking to be at 24 PSI hot. Downforce may be lower at say 1500 lbs depending on speed, which would be similar to the weight of a Z. So my guess is that what you saw would be about normal for these tires. When I took the motec class we had three pro atlantic teams there and they all mentioned the yokohama needed to be worked pretty hard to get any grip out of it. Claude mentioned that the tire was supposed to be about half the suspension on the car (his company engineered Katherine Legge) so I would assume they know what they are talking about. For road racing they are showing rates in the 500 to 600 range. Cary Quote Link to comment Share on other sites More sharing options...
JMortensen Posted May 22, 2006 Share Posted May 22, 2006 Thanks for the info. By the way these are 9.5 x 15 FA Hoosiers in R35 compound on 15x10 rims. So in general is less (pressure) more (grip) or vise versa? As a loose and general statement, I think less pressure is more grip. Reason being you can put more heat into the tire with less pressure. It's been my experience that with a stockish Z you need to run more pressure to keep the tire from folding over and driving on the sidewall when cornering. Once you dial in enough camber to prevent that from happening, you can reduce the pressure and that heats the tire up and that's when the tire really starts working. BTW thanks for that info Cary. Quote Link to comment Share on other sites More sharing options...
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