mmuller

First of all, I never said I had seen one of my tires get a 14 psi delta. But I have seen tires do that.

Why do I get so many HC (and yes a full session for me is a HC)? I don't beat up on tires, I am a smooth driver who works momentum more than mashing the gas and I use very little brake pressure. AND I am happy to adjust my driving to a changing car so I can extract the full life of the tire. Do I always get that many HC? No, but I never get less than 25. I don't buy take off's because I find that I can't make them last as long because the previous owner beat them up to much.

I have run lower pressure's and frankly, the car was not as fast. And the tires where to easy to damage or hurt. I spoke with a Hoosier engineer and he encouraged me to try more pressure. After some adjustment in driving style, I found the car to be quicker. My front's always have more life in them than my rear's.

Sorry this isnt your experience. Before I ran Hoosiers, I ran R888's. I used to get 65 HC out of them and the car would happily be doing 2:05's at WGI.

My point in all of this is, using the manufacturer's guidelines I found the tire to be sticky, last a long time and fast and I don't hurt them. That has been my experience and the same experience for those I have been able to get to move to this thinking and who I have coached their driving to be kinder to the tires whilst maintaining speed. Don't believe me? Feel free to look at some of my video's on Youtube and you will see how fast the car is going.

fatbillybob

We need to look beyond the tires and look at the total package. Rules effect how you have to set up the car to make it work. I don't think Mark will find supporters of low pressures because there is a reason for the "RL group think"... a consensus of what works on porsches. You put a P guy in the Vette forum and a different set of "group think" prevails.

mark kibort

I think many of us are very smooth, but it takes lateral accelerations and linear deceleration's to be fast and as long as you are not slipping, you are being as kind as you can to the tires. i was watching this video.and was wondering if you go through clutches... a lot of partial over revs on your upshift (timing- thing). Just curious.( I dont know for sure if you are driving below, as you might be coachig) What video is a best display of your "smoothness and speed"? also, you bounced back and forth on your description of your GT3, vs the Boxster i imagine.... which car gets the 65 heat cycles on R888s and 55 on R7s? which sizes? Again, remember we are talking about 3000-3400lb cars running the tire described here on this thread. 315x30x18

Anyway, I've always wondered if there was a way to run higher pressures, as it seems that the car might be faster in a straight line too. I'm more than willing to adjust my style to keep the tires under me at the next event and do a test . Also keep in mind, this can be track dependent. (and car dependent) Watkins glen seems like a very flowing track with little requirement for being hard on the brakes, or accelerations. (by the way, i was able to run a 1:46 at laguna with NO brakes at all which is a spec boxster time flat out so yes, i can adjust my driving as well) Contrast that with tracks like Auto club speedway with 130mph to 40mph several times a lap, plus a 160mph to 40mph decel!! Then, try and get more than 4 heat cycles on the tire grinder track like Willow springs. (or sears point ) i can see why you you would get a lot of heat cycles on a track like WG. i dont think its your smoothness, although you are smooth... I think its the track. just so many drivers , that are fast, that just dont share experiences with R7s to get more than 10 heat cycles. Aure they might be round and have tread, but generally they are HC'ed out by then.. at least for tracks on the west coast.

mmuller

I never mentioned anything about my SPB. Everything I have mentioned 100% relates to my GT3. We run Toyo RR's on the SPB. Different tire with different needs.

That's also not my video or my car. That was a customer car I was giving a ride to the customer in to show him that he could go a lot faster in the car as there was much more grip than he thought there was. I drove that session at around 8/10's as I don't drive customer car's flat out.

When I reference HC's, it relates to all the track's I drive. I only drive WGI once or twice a year in the GT3. But it see's 4-5 other tracks in the Northeast all year. It get those HC counts irrespective of what track it runs on. I used WGI as an example as most people know it and can relate to the lap time there.

And no, I don't go through clutches. Never had one replaced in my life.

mark kibort

Got it. so, I'll give it a shot. i have no problem testing out ideas that have worked for someone else... its the reason i started to drive with the lower pressures to begin with. ill let you know how it goes. However, i wonder too, if that technique only works on the R7 vs the A7s which seem to act more like real slicks in many ways. have you tried them and see the same results with your tests/experience? Getting back to your number of heat cycles, Dont discount my experience either. one thing to think about , is when my tires are tossed, at10 heat cycles, they still can turn a lap time within 2 seconds of my best, so i would think and have taken them to 15 -20 heat cycles on occasion many years ago when they were R6, R4s and R3s....i would leave them on as practice tires and drive a LOT of street miles too. the very worst i saw was 4 seconds off a lap, when they were incredibly old. the point is.... the difference of lap time of 10hc, vs 20, vs 30 vs 50 in your case is the real point of this side bar. like the toyos, they fall off a little and were good until the cords. and my car was very easy on tire for wear. anyway, ill give it a shot in a few weeks!

Mk

k722070

adding a meaningless data point to the thread.
this is for a 20yr old 2710lb 911 run in nasa tt, so short 5-9 lap sessions. hoosiers were new for me this season, previously used toyo rs1.
started the season with hoosier's recommended tire pressure, 27F 29R cold targeting 37F 39R hot.
pit lane pyrometer measurements were used to adjust starting pressure(and camber) until front tires became sticky and reached hoosier's recommended hot psi.
currently using cold starting psi 31F 31R to reach 38F 40R measured in the pit lane.
this is still showing too much camber, 25 degree temp spread, and tiny bit low pressure.
it would be very interesting to hear what the pyrometer data from the corvettes using 30psi hot is producing.

I haven't seen any of the grooving or cracking as seen in the pics posted by cre8fun.
but also have not gone through nearly as many tires as others are indicating.

the pyrometer data has also prompted setup changes.
hoosier's instructions are 3 degrees of negative camber, -3F -2.5R for a 911 but this is just a starting point according to their tech guys.
my car is currently -2.6F -1.8R based on pyrometer data, which could be why my car needs the higher starting pressures.

here's the relevant paragraph from hoosier's guideline pdf

Chassis Setup Recommendations
For optimum performance the Hoosier P-Metric radial tires require about 3 degrees of negative camber. There will be a trade off in maximum performance to maximize wear.
Generally, 1/2 degrees less than optimum will result in the best compromise for wear and speed. Less than 2.5 degrees negative can result in excessive wear on the outer shoulder junction.
Higher pressures are needed when the vehicle has limited negative camber.
The Hoosier tires typically offer better performance with spring/shock rates higher than previous brands you may have run.
Traditionally, Hoosier tires have often required higher pressures than other brands. Hoosier recommends a starting minimum cold pressure of 26 psi on all DOT radials.

mark kibort

what we see in pit lane pressures and temps in the hot pits , is near 180F across the tire, going from 180, loosing 5 degrees to the center and 5 more degrees to the outer edge, being 170. pressure is 30psi... (and by the way, i showed that that pressure stays pretty close to the same, even after 15mins when tire temps go down greatly as it sits in the pits.. so no need to rush to take pressures, but rush to take the temps. )

30-32psi hot has been below what is suggested by Hoosier, but has resulted in most all of the most recent track records for cars in the GT2, ITE, or NASA ST2, ST3 class. this means they are starting out in the 24psi range

in looking at many of the race tire specs for the leading manufacturers. Pirelli, michellin, Yok...... they all reference about a 8 psi pressure rise from cold to race temps. certainly this could be greater if you get to operating temps , starting from a very cold day....

Now, Paul is one of first people that has really seen such high pressure changes... Matt, also said he has seen them before too. (on others cars ) but, my take on what Matt said was that it worked for him and he has shown to have longer life with the higher pressures. However , Many (most) of the top drivers and cars in the west (and east) , are not seeing that and actually see faster times, and better grip at lower pressures (we are talking Vets,mustangs and my car, 928) . The real question and maybe the answer, is in your tire temps across the tire. what have you seen... if i see temps that are equal from center to the inside edge, i view that is being too high of pressure and will air down 2psi and go out again. what are you seeing for IR temps or tread depth gauge temps across the tire?

Im willing to try going higher temps this next race practice based on Matt's (aspen) experience, to give it a try and see what they feel like but also to see what the temps turn out to be across the tire. Ill let you know.

k722070

that's nice producing a 10 degree spread.
couldn't get my front tires above 160 degrees using hoosier's minimum starting psi of 27.5, no front grip with those temps
using 31 psi cold produced front inside temp of 170 but outside was 150 and middle 155. still way off for both camber and pressure but much better grip.
rears haven't been an issue, inside temps reached 190-200 easy but the spread was 20-30 degrees across tire and middle temps were always low until using 31 cold start.
hopefully the new camber settings will produce better temp spreads.
my guess is starting psi will end up 32 all four corners to reach the recommended 36-40+ range and hopefully 180 min temp in the fronts.

mark kibort

30 degree spread is too much in my opinion, but ill let the 911 guys comment on that.. that means you are not really using the full tire. (due to suspension or tire pressure) the fact that you had higher temps in the middle is a classic sign of over pressure. (you said you had 170 inside area, vs 155middle vs 150 outside) this could be a combination off too much pressure, too much camber and/or too soft of a suspension and maybe some toe out , bump steer and track configuration causes. so many factors to consider. i know for my car and those like it , like the Vet and mustangs, if you get a center pressure that is higher than the outside edge, it usually means too much pressure. its one of the reasons we try to get to near 30-32psi hot. again, ill test the higher pressure route next time out and let you know how that goes.

Gofishracing

subscribed. Jez

Matt Romanowski

30*F spread across the tire is not too much if you go by the published standards, what the engineers say, or a lot of successful teams. I think it was in this Speed Secrets Podcast (though it might have been a webinar) that Jeff Braun talks about spreads https://speedsecrets.com/speed-secre...best-the-best/

I use real time IR on a tire to see what it's doing in a corner, not in the pits. The two do not always, and often don't, match how you would think they do.

mark kibort

I guess a lot depends on the tire, the car , the track and the driver. the real IR temps are interesting, but what i have found , is the proportions dont change much from hot pits to paddock. sure the temps drop, but the spread and differentials dont change much... is that what you have seen? sure, what you are seeing is a specific performance measure in particular turns.. that is amazing stuff right there. And what im seeing and what most of us see is the average over an entire lap (or several laps). both are useful. i dont think they would match, but they are two different products of observation and conditions. for example, optimizing for turn 8 at willow springs, where we KNOW the inside edge of my inside front tire gets cooked ( and the rears of the 911 see this instead), could lure me to make changes that wold mess up the other 8 turns. great info for optimization and balancing though, I agree. For my car, 30F spread would be incredibly bad . if i saw 170 155 140F, would mean the tire was not being fully used.

Matt Romanowski

The bold is very wrong in my experience. The tire equalizes across the tread as it sits. It also changes pressures and temps as it sits. For some drivers and cars (they both have an influence), the pressures will go up, down, or down on one end and up on the other. This is often influenced by the driver, not the car or tire. Temps also change over time and come close to the average, but again, it's variable based on car, driver, tire, track conditions, etc.

k722070

I've read the 30 degree spread number but can't remember where, seems like it was paul haney's high performance tire book when he interviews the tire engineer towards the end.
but hoosier's email tech support suggestion was come in hot, get to tires quickly, target front tire temps would be 180 outside, 187 middle, 195 inside.
that 15 degrees spread would be max acceptable negative camber and correct psi because the middle should be the average of out and in.

my big mistake was making slow changes, I should have got data using -3.0 camber then dropped to -1.0 camber and tried to bookend the tire temp data so I know what the minimum setting was.

wanna911

I have this one a set of rear A7's that have one 3 lap heat cycle on them. I assumed it was rubbing even though it didn't look like rubbing and raised the rear ride height a bit.