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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...
IMHO I wouldn't over emphasize your pyrometer temperature spread technique. I run active IR temp sensors on all 4 wheels and the temp distribution at max grip has no resemblance to what you measure under static conditions in the hot pits.
To the OP, this looks like cold tears. I get them on Michelin Slicks all the time but you should still talk to somebody at Hoosier to make sure nothing is wrong.
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.
No question about the body of your comment. yes, the driver influences a lot, BUT , there are indications of set up, overall wear and issues that can be seen by tire tread outside, or penetrating temps, regardless of when you get them. sure, you can capture the actual data from the tire with active IR sensors, OR you can get hot pit temps, OR you can even get paddock readings. pressure do NOT change very fast , in fact you have about 10mins before you see any noticeable changes. (ive tested this with a timer vs pressure gauge to show this is true). yes, temps fall off quickly at first and then stabilize. the tire doesnt "equalize " across the tread as they sit.... try testing that at the track and you will see that the spread actually stays pretty close to intact, when comparing a hot pit temp (eg 200f, 190f 180f vs in the paddock that might be 170f, 160f 150f after traveling to your parking spot. the point here is the information is very useful , you just need to know what the tire is telling you and there is a lot of averaging in the hot pit that is near the same in the paddock and does not represent any particular part of the track where all the numbers can change.
Originally Posted by 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.
yep, thats what we look to see, and it would be interesting to see the difference for a large camber change.. many times the center temp proportions can be changed by pressure, not so much the overall proportions across the tire
Originally Posted by Frank 993 C4S
IMHO I wouldn't over emphasize your pyrometer temperature spread technique. I run active IR temp sensors on all 4 wheels and the temp distribution at max grip has no resemblance to what you measure under static conditions in the hot pits.
To the OP, this looks like cold tears. I get them on Michelin Slicks all the time but you should still talk to somebody at Hoosier to make sure nothing is wrong.
Actually, ive measured both for a long time and in the pits, as i was saying to Matt, the proportions still seem to stay in tact , but are not representative to any spread portions while at any particular part of the track.. Your active IR readings will allow you to make set up decisions for a good blend of both. For a real world example, you might come in with the 10 degree spread across the tire, but on a key turn, it is completely the opposite. correcting for the one actual turn ,might completely overheat other sections of the tire, to solve for performance on one turn. That's why both are very useful. the more info the better.
Here are a couple of pics of a Hankook Ventus Z214 275/35x18 that just came off of my Cayman with 15 HC's on them. The tire has plenty of tread left. The tires come with two grooves that run around the tire. The third "groove" you see in the photos is what I believe to be a "cold tear" as some of you have mentioned. Upon closer examination you can see the steel bands of the tire as you look into the tear. The tear does not go around the entire tire, only most of it. It was on the inside edge of the left rear tire. My starting pressures on these tires are around 26 - 27, not less. I bleed them down to 34 as they heat up. I definitely did not think I was pushing the car/tires hard on the first laps of my sessions on track. But here's evidence to suggest otherwise.
And to be clear, this tire was definitely not rubbing on anything that could have caused this damage.
I've gone through many sets of Hooser R7's and I've never had a tire failure like this. I've had several Hoosiers fail on me with blowouts in the sidewalls.
What's the lesson here? Take better care of the tires when they're cold? Start with higher pressures and wait for them to warm up before you hammer them? I guess so.
That's ugly and scary! HooHoo S03/S04 about 15 years ago I think used to say no 285x18's on 911's. Those tires could not handle the rear weight under load. I couple people hear say they have experienced this cold tear. I've been racing 15+ years never seen it in the flesh. It is also unheard of in front engine world where I am from. Have any of you guys done the math to see what loads are on the mid engine and rear engine cars especially if lower pressures are used and you go on banked tracks?
That is VERY ugly for sure! Ill tell you one thing, ill be more careful in heating up the tires to desired temps and pressures.
as far as loads, that is determined by weight transfer. just an FYI, there is Always more weight tansfer during braking , than there is in acceleration, so if it was a weight loading, you would think the higher weight of the front engine car, and the similar weight transfer (less about 15% in a front engine car) would provide a MUCH higher vertical load on the front tires, especially since they are generally smalller sized up front on both. In other words a car can only accelerate at something in the sub .5 to .2g range when on the track, however, braking can cause a constant 1.5g level of deceleration. certainly on banked tracks , those static weight proportions just go up............an example, there are plenty of corvettes with 1800lbs on 285 sized front tires and 1600lbs on the rear tires. im sure thats equal to many 911s that visit the track on the same size rear tire...........and under braking the Vet will subject the tire for much higher vertical loads. that's just at a glance . btw.
Originally Posted by fatbillybob
That's ugly and scary! HooHoo S03/S04 about 15 years ago I think used to say no 285x18's on 911's. Those tires could not handle the rear weight under load. I couple people hear say they have experienced this cold tear. I've been racing 15+ years never seen it in the flesh. It is also unheard of in front engine world where I am from. Have any of you guys done the math to see what loads are on the mid engine and rear engine cars especially if lower pressures are used and you go on banked tracks?
There may be something in the R7 compound these days? At Palmer I had a new set of R7s, and this time I started cold at 30 instead of 27, and bled down to 36.5 hot instead of 35 and it was better than the last 3 sets of tires, but I did get some minor grooving per the OP by the second day, just on the outside rear tire. Bystanders declared the tire to be rubbing, even though there was clearance. I also had painters tape on the fender lip just to check, and it was clean.
Unrelated, but here are the picks from the tires that cracked after 1 and 2 warmup session respectively. Those two tires are back at Hoosier, and I’m waiting on their verdict.
One heat cycle, not as bad as Johnathan’s! This is on the outer edge.
That looks REALLY bad............. Are the A's having these issues, as rare as they are, have we seen any of this cracking on other sizes or versions of hoosiers?
To be clear, the two pictures I posted are from the same build lot from late 2017, and I think there was either a defect in that build lot, or those particular tires were overexposed to cold before I got them. This is a different issue from the OP, but I thought I’d post it since Johnathan just saw a similar looking crack.
09-22-2018, 10:52 AM
