jbondfl

Okay guys/gals, clear this up for me.....

RULES---- preface your post with either KVF (known verifiable fact) or JMHO (respectably).

My owners manual says if I am going to run at high speeds I should pump my tires to MAX pressure. Seems odd to me, however, my tire dealer verified it. (He actually gave me a very long answer that sounded reasonable but I'll hold the details until I hear from a few of you).

Thoughts?

Werks

You are on the track forum so what you are going to find is what you do on the track is not necessarily the same as what you would do for the street. At the track once you get familiar with your tires you will generally figure out a "preferred" hot tire pressure target. Basically a temperature at which your tires seem to work the best for you. This generally is a little or a lot lower than max pressure. To get to this target pressure there are two ways that you can go about it. You can start off with a low cold tire pressure which when your tires have heated up will reach your target pressure. Using this as an example when I run R888's on the track I like to run them around 35-36 PSI hot to get there I start off the first session at around 27-28psi. I'll take the first couple of laps a little slow to allow the tire carcass to heat up and to not roll the sidewalls (which will damage them). After a few laps the tires are up in the 30psi range and you can really start getting on it. The second way of doing things is start at your target pressure cold (so 35-36psi) and then bleed down when hot. The issue with this is that you end up basically sacrificing your first session because your tire pressures are going to be too high which usually results in the tires feeling greasy. At the end of the first session you come in, check pressure (which will probably be in the 40-45psi range) then bleed down to your target pressure and you should be good for the next session.

The above example is what I do with R compound R888's. Hoosier R6's I start off mid to high 20's and end up around 34-35psi hot. When you get to slicks you usually see advised cold starting pressures in the low 20's i.e. 22-24psi with hot pressure targets in the high 20 to low 30 range depending on tire brand

So to answer your question when tracking your car there are hot and cold pressures that come into play. I could never see you wanting to run max air pressure in a tire cold ever. When hot it is unlikely that you would ever want to run max air pressure either.

franman69

On street tires I would start DE sessions at around 28 cold. I plan on starting my runs on R888 at 26 cold and checking temps across the treads logging data and tweaking in for best cold starting pressure.

blkbrd69

KVF and VMHO tend to be the same

Yes for something like a Texas mile you would start with high pressures, the thought is you will be at warp speeds before pressures have a chance to rise.

For a roadcourse you will start with low pressures and let the tires warm to best level or them, as verified with a pyrometer and my butt.

My experiance with RE-11's or NT-05's "AT THE TRACK" is a starting pressure just above the low pressure warning, IE 26-27 to achieve 34-36 hot. This is at Sebring, the one I think you may be interested in.

jbondfl

I understand the manual doesn't specify how you intend to get to max speed or how long you plan on staying there. It does seem like a pretty generalized statement though.

So,,, to my tire dealer's long comment....... He actually used to road race with a pro-team and his advice was close to some others.. determine how much pressure your tires will increase over the course of your session and set your starting pressure one pound below the cold pressure that will achieve max pressure at the end (if your tires increase 6lb over a session and your max pressure is 38, then set your cold pressure to 31lb. This will achieve a max running pressure 1lb below max and you will be in the safe zone)

sounded reasonable enough.

MarkDFW

I have questions on this as well, so hopefully this will help everyone and not be considered a thread jack:

I started my Kuhmo v710 around 28 psi all the way around the other week. Track runs CCW. When I came off, left tires were both around 36 psi which is pretty good. Right tires were around 39 PSI because track is CCW and lots of hard, left turns so right tires obviously getting more heat in them.

Should I then have come off the track and immediately bleed the right side down to 36 psi so it matches the left tires? Or should I have right tire psi higher for a reason?

TKOGTO

Never run your cold tires @ max on a road course. They will heat up to well over max in 10 minutes or less and become very difficult to handle or worse.

The manual for 2010 says the following "If you will be driving your vehicle at speeds of 175 mph (282 km/h) or higher, where it is legal,
set the cold inflation pressure to the maximum inflation pressure shown on the tire sidewall, or 38 psi (265 kPa), whichever is lower." At 175, I would increase the pressure to 38 but not @ the track.

Word to the wise: do not accept anything about road racing from a dealer. The ones I have dealt with know how the car should operate on the street but have little or knowledge re: the track. Even if they did, they would likely only tell you what is in the manual so as to prevent opening themselves and the deeper pockets @ GM to litigation.

Follow the recommendations above.

MarkDFW

If the manual says that, it is insane. Street tires will go up 6 to 8 psi on the track if you push it hard, and R Comps can go up 10 or more psi when hot. You would be seriously screwed if you took your tires to max psi cold and then went on the track.

TKOGTO

Mark - my experience has been to leave the pressures alone after a session, doing nothing to them except checking, even if they are different side to side. After 30 minutes or so, they will go back down to approx where you set them. This does change a bit throughout the day and will be influenced by how long they sit between sessions and the ambient. I have also noticed the side facing the sun cools down more slowly on a hot day and the pressure do not goes as high in later sessions as they did in earlier sessions.
Once the tires are back down where you set them originally, I suggest you lower the left sides by 1 psi. See how they turn out after the 2nd session. If they are now 2psi higher than rights, lower the lefts by 2psi for session 3. the again by 3psi if necessary. My goal has always been to have the psi's as close to even for as much of the session as possible.
When you are racing or @ the point you are trying to squeeze out the very last 1/10th, the tuning of tire pressures is more sophisticated. Until then, the above should suffice.

MarkDFW

Thanks. I assume you meant to lower the right side and not the left, since the right side is running hotter/higher psi, correct?

This makes sense as it seems on CCW track you would want to actually start with right side psi slightly lower, since the right side tires will get hotter due to extra load and hopefully you even out on all 4 corners once the tires are hot, assuming my logic is correct.

rfn026

I usually back into my tires pressures. I like to be at 32 psi hot. That means I usually start at about 24 to 26 psi cold. Keep in mind that I'm running Goodyear DOT tires though.

Richard Newton
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Bill Dearborn

I am pretty much in line with these comments. When first tracked my C6Z I was on the GY Run Flats. At the Glen I set the pressures at 28 front and 26 rear, hot pressures were about 10 lbs higher. Same goes for NT05s but they tended to get greasy near the end of a session compared to the GYs that pretty much stayed consistent after the first lap.

With Conti Slicks I started with 26 front and 24 rear although this caused issues with the TPMS until the rear tires got above 26 psi. R888s I would run at 28 and 26. With my C5Z I would run my Kumho V700s at 28 and 26 as well.

I plan on being at Sebring at the end of the month running on almost brand new PS2 Run Flats. Not sure what pressure I will start at but will probably shoot for 30 and 28 and then see where the hot pressures come in.

If you have TPMS installed in the wheels you will find that running pressures higher than 32 or 33 cold will give you hot pressures in the 42 or higher range and you will get over pressure warnings on the DIC.

If you are driving at high speed on a highway where speeds are unlimited like certain sections of the Autobahn then you should look at this tire pressure guide on the Tire Rack Web Site:
http://www.tirerack.com/tires/tirete....jsp?techid=72

The report addresses adjusting pressure and derating load rating based on speed.

Bill

BEZ06

As others are mentioning, different tires will work best at different pressures.

As far as Hoosiers, if you plan to run them, here's a good Hoosier Tech Bulletin about stuff such as initial heat cycle, optimum tire temps, camber settings, and of course pressure recommendations:

http://www.racetire.com/products/tctips.htm


C'ya at the track!!

Bob

TKOGTO

Yes, right side lower - my mistake.

BEZ06

If the track is running CCW, it sounds like you were running a roval. Is there significant banking on the track??

If there are significant banked sections, then the right side NEEDS higher pressure!!!

I've run Daytona a number of times, and Bob Woodman Tires supplies tires at a lot of the events there. When Bob talks at a driver's meeting, he always emphasizes that the right side tires do a lot more work when loaded up in a left turn around the high-banked sections, and the pressure SHOULD be higher in the right side tires. He says he has seen many tires fail from flexing too much due to being under inflated, but he has NEVER seen a tire fail from too high pressure.

If you're running a roval course, take a look at the info below about chassis setup and tire pressures:

http://www.hoosiertire.com/pdfs/bankedovalroad.pdf

http://www.tirerack.com/tires/tirete...nd_Feeding.pdf

Bob

ZedO6

Since this thread has evolved into a collection of data points based on personal experience on the track, I'll add mine.

I'm running Nitto 555RII's on my nearly stock C5Z. The Manufacturer was zero help on pressures, but the CF guys suggested 34-36. So...expecting 10 PSI gain from cold to hot tires, I started out with 27 PSI cold. I ran my first session as a warm up with my last few laps as hard as I could, pulling into the hot pits for tire temps and pressures. My son bled each tire down to my requested 36F 33R pressures.

From there, the rest of the pressure changes were in response to wear and grip issues. Remember your tires are springs and oversteer/understeer can be adjusted somewhat with tire pressures.

BTW, cold pressures after the event were different at all four positions. That is why I always bleed down pressures to my target after my first session and check after each session, which is a good safety proceedure as well. Good luck, YMMV

MarkDFW

Not a roval, but perhaps enough camber in those left turns that the right side tires had higher pressure at the end of a session by a good 2 or 3 psi, and I started the tires out even. Tell me what you think:

06goatm6

JMHO - I agree with what most are saying about running track pressures in the hot range of 32-36lbs. However my answer to your original question, or at least information about it is this. The reason you're manual says to inflate to max pressure for running high speeds is that heat can be the biggest cause of tire failure. At high speeds 150+ the tire is turning at 1000s of rpms. The bottom of the tire will squish a little and re-conform for each revolution, the less pressure the more the squish. So when running at high speeds the tire is squishing and straightening out hundreds or thousands of times per second, this creates a huge amount of internal friction in the tire and thus a lot of heat. I believe that's where the statement comes from. Also I believe it was a Porsche I read about that won't actually let you exceed a certain speed untill the tires have warmed and are up to pressure, or unless they are pumped up high enough to begin with.
For what its worth