Car as below, camber settings are: fronts -3.5 degrees, LR -2.4 degrees, RR -1.3 degrees (not sure why these aren't closer--the shop that installed my Derlin RTAB's sent it out for alignment--this is what came back). Track is Portland International Raceway, classically harder on the left sided tires. Toyo starting pressures about 34 psi, ending about 38-40 psi, but 2-3 pounds higher on the left versus the right. The following pyrometer probe temps are after a cooldown lap and driving into the pits (listed outside-center-inside).

Left Front: 166/176/186
Right Front: 130/154/168
Left Rear: 182/197/205
Right Rear: 153/180/193

I welcome any input, but my core question is why are my rear tires hotter than my front??? Seems counterintuitive to me.

I'm guessing that the hotter inside readings indicating that I may be running a bit too much negative camber?

FWIW, the car seems relatively well balanced.

Thanks--Scott

rears are over-inflated?
do you put then even with the fronts? if so try 2-3psi less.


On the fronts hotter on the inside might be too much camber or toe?

The following pyrometer probe temps are after a cooldown lap and driving into the pits (listed outside-center-inside).

Left Front: 166/176/186
Right Front: 130/154/168
Left Rear: 182/197/205
Right Rear: 153/180/193
You really need to get the temps coming off of a hot lap with no cool down time. Pull in the pits and get them read right there. Otherwide the temps are almost wothless.

LF: too much camber
RF: too much camber
LR: too much camber
RR: too much camber
I guess it would be easier to say you're running too much camber all around :P .But like I said, since you ran a cool down lap the temps are almost worthless. The cool down lap would explain the high inside temps.
I'm guessing that the hotter inside readings indicating that I may be running a bit too much negative camber?
Correct.

What size tires are you running front and back?

Just to answer some questions. I may need to start with lower pressures in the rear--but the question still stands--do E36 M3's work the rears harder than the fronts?

See the note just before the temps--the first number listed is the outside temp, the middle number is the middle, the last number listed is the inside temp.

The left front is hotter (I think) because there are more right hand turns, thus loading/working the front left tire more.

Toyos are 235-17's all around.

And I know hot temps would be much better (next time).

Left Front: 166/176/186
Right Front: 130/154/168
Left Rear: 182/197/205
Right Rear: 153/180/193

OK, here goes my analysis:

First predicate: Temps are HOT right off the track. (they're not, so its an issue)
Principle one I follow: 15 to 20 degree spread is reasonable due to camber.
Principle two I follow: Middle number should be average of outer pair
Corrollary one: If middle number is higher than average, its over-inflated and if less, then under inflated.
Principle three: Don't assume left and right start pressures will be identical, this will be track specific

Assuming you had good grip, and were not over driving your front left tire:
Front left perfect: (20 degree spread, middle is spot on average)
Front Right: Take camber out first, the 38 difference is too much at this track. Probably too much pressure, but you'd have to narrow the gap first, and perhaps that would knock the middle number down closer to the average.
Left Rear: A bit too much camber, probably a bit to much air. (again, fix camber, then fine tune the air
Right Rear: Way too much camber, and perhaps too much air, but, again, I'd chase the camber first, then the air.

Keep in mind that what I've said is ABSOLUTELY not what I would do to this car as the readings were not hot. Driving a cool down lap can radically change the temperatures, and doesn't reflect what you want to adjust. You could probably use this as a starting point, but I'd prefer to get hot temps.

Given the softness or stifness of the suspension, you may not be able to get front right and left to operate at the same temperatures on a given track, but you can set the camber and pressure properly to maximize grip across the tire... and hope that the suspension lets both sides heat up into the RANGE that gives good grip. Adding pressure for example to the numbers shown in the front right side, just to get it to heat up to where the left is, would be a terrible idea if it resulted in a bulging out, and disproportionate middle temp as a result.

Not surprising the driven wheels are hotter. Note a consistancy on the right side of the car, that there is too much camber on the right side of the car for for this particular track.

It might be worth trying to contact the rep for the tire company to find out their opinion for temp range for maximum grip. Pressure consistancy (or alignment) from L to R or F to R is irrelevant if you use it along with suspension settings to balance the temps and you're in the "grippy" temp range when you check hot temps.

My 02 cents worth.

Alex "I love my pyrometer" Lipowich

Wouldn't too much air prevent the outside of the tire from making good contact with the road, Alex?

I think the answer to your question is "yes". Did I say something to conflict with answering yes to your question?

The proper amount of air will generate temperatures across the tire surface (when hot, and up to temperature) along the parameters that I described.

Too much air will cause the middle temperature to "rise" because the tire walls are rigid, so the tire "bulges" out in the middle, more or less rubbing harder, or having more contact with the road than it should. It will take weight off the edges because its over inflated.

Conversely, too little air will cause a "bow" in for the middle portion of the tire, with the tire walls taking the brunt of the contact, raising their temperatures, or, effectively lowering the middle temperature.

This is at least my understanding of the situation.

Alex.

I think the answer to your question is "yes". Did I say something to conflict with answering yes to your question?

The proper amount of air will generate temperatures across the tire surface (when hot, and up to temperature) along the parameters that I described.

Too much air will cause the middle temperature to "rise" because the tire walls are rigid, so the tire "bulges" out in the middle, more or less rubbing harder, or having more contact with the road than it should. It will take weight off the edges because its over inflated.

Conversely, too little air will cause a "bow" in for the middle portion of the tire, with the tire walls taking the brunt of the contact, raising their temperatures, or, effectively lowering the middle temperature.

This is at least my understanding of the situation.

Alex.
Well, mostly I was thinking of the left rear. 182 to 205 isn't that big a spread. Middle temp of 197 tells me too much air, camber is probably pretty much right. The spread would likely come down a hair with a pressure change.

Is there a good guide to using a probe pyrometer? I just got one, and I'm not sure exactly how to use it effectively. Basically, what I'm looking for:
- where on the tire do you measure? 1" from edge? 2"?
- How long do I hold it in for? Seems that the temp keeps climbing for a while
- How deep do i stick it in? (that's one of those "sounds dirty, but isn't" :) )

Alex--Thanks for all of the good info. I appreciate the feedback, even though I know it is all qualified b/c the temps are not "pure hot" temps.

ScotcH-- go to http://www.longacreracing.com/articles/art.asp?ARTID=16
This should answer most of your questions.

I know this is kind of a second question, but can one adjust the rear camber on the car without using an alignment rack (which I don't have)?

Scott wrote:
welcome any input, but my core question is why are my rear tires hotter than my front??? Seems counterintuitive to me.
1st of all... take the above advice about taking tire temps without a cool down lap. Best way is to have a buddy waiting with the pyrometer near the hot pits. Try to take them either on the pit lane (of course, well away from cars entering the pits) or as close to the paddock entrance from the pits as possible to get the most accurate readings... of course, end your session early as opposed to trying to run a fast cool down lap... not safe and really not cool.

First thing before your next event is to have the car aligned AND corner balanced by a race shop. Both can effect the temps adversely if they aren't set right.

First thing to do at your next event would be to take a series of temp readings... for example, use one day to get a baseline of temps. Take readings after the first 10 laps of each session, WITHOUT adjusting anything. This should tell you whether you are driving consitently. If not (i.e. the temps vary non-linearly after each reading) then adjusting anything mechanically probably won't make much of a difference. It might change the numbers, but the overall variance probably won't change. At this point, its driving consistently that should be your bigger concern (of course, poor contact patches could be contributing to this as well).

Without knowing if your line is consistent, AND the car is aligned and corner balanced properly, this is all hypothetical... but all things being equal, depending on the track, I'd say that yes, the rear tires could be worked harder than the fronts. I see E36 M3s carry the inside front wheel off the ground all the time, especially with ultra stiff suspensions. Also, if you're using a slow-in-fast-out driving style, then you're probably getting on the power early and accelerating through the apex to track out. With greater than necessary neg camber in the rear, this will cause more heat in the tires (contact patch not ideal, cause greater scrub, if not slip)... at the same time, with greater than necessary camber in the front, the outside and center of the tread will be out-of-contact with the asphalt for extended periods of time as well... all of these things contributing to the hot inside/cool outside temp readings. Now lets add the variable in that you might have some toe-out in front... this will add to the inside of the tire getting hotter quicker as well.

StackTrack--GREAT info! Thanks to you and others that have responded. I agree that I need hot temps, I have read the Longacre Racing article about properly using a tire temp probe, and I have figured out someone who can do the temps when I pull off of the track.

The suggestion to check after several sessions to check consistency is a GREAT idea.

For further background, the car was cornerweighted and aligned by a race shop earlier in the season, but it may be time to have it done again. I am using a datalogger, and my lap to lap and session to session times seem to be very consistent (allowing for variations in slow traffic, etc.). Still, I am sure I have driver's issues--so tire temps are a great idea to further evaluate consistency.

Scott

This is an awesome thread... thanks for some great info, guys. :buttrock

For further background, the car was cornerweighted and aligned by a race shop earlier in the season, but it may be time to have it done again. I am using a datalogger, and my lap to lap and session to session times seem to be very consistent (allowing for variations in slow traffic, etc.). Still, I am sure I have driver's issues--so tire temps are a great idea to further evaluate consistency.

Scott

Scott... since this is the case, once you verify your alignment and balancing, and once you verify you don't have any bent suspension pieces... then I'd start by reducing your camber at all fours. Not drastically... maybe .2 or .3 degrees. Generally you'll want to keep the suspension set up equal (same front L-R and same rear L-R) then fine-tune with air pressures and driving line on a given track.

What datalogger are you using? Does it have the ability to show your driving line? Such that you can overlay lap by lap to see where any variences are? Using a datalogger could let you elliminate the need to take tire temps to determine consistency... actually, its lightyears better cause you can compare turn-by-turn data with the DL.

Important thing here is, only change one thing at a time... don't change the camber AND the pressures, you won't know what did what.

Heck... maybe you're not pushing the car ENOUGH. Are you sliding through the turns as it is? Are the tires making any noise? If not, try pushing a little harder, see if the center temps don't start creeping up. If you're sliding around as it is, especially if you feel like you're not driving the car to its max, then its got to be too much camber causing poor contact patches.

IMHO opinion of course :D

Stacy--Using a Traqmate--I have the lap overlay feature. Except for the occasionally pooched corner my line is very consistent. I do think that I could push the car harder through some turns--it is a learning curve thing. But I run in the advanced group, and I'm usually passing more cars than visa versa, so I feel I am doing a reasonable job going around the track.

Any thoughts on an acceptable lap to lap time variance? Of course, given having to slow for slower cars until a passing zone, having to lift to let faster cars by, etc. comparsions are a bit difficult (though I may get a video cam mount--that would allow me to know which laps were "unimpeded" and which weren't). My lap to lap variance seems to be less than 1-2 seconds on 1 minute 35 second laps--is that too much?

Any thoughts on an acceptable lap to lap time variance? Of course, given having to slow for slower cars until a passing zone, having to lift to let faster cars by, etc. comparsions are a bit difficult (though I may get a video cam mount--that would allow me to know which laps were "unimpeded" and which weren't). My lap to lap variance seems to be less than 1-2 seconds on 1 minute 35 second laps--is that too much?

Over 35 minutes, with traffic, I would probably say no, its not too much. It's mostly pointless to compare lap-to-lap times in an HPDE setting (I assume thats what we're talking about) because of all the variables. If you can find a group that runs time trials... one where you can reasonably expect not to encounter much (if any) traffic... then you can start really comparing them. Plus, consistency has as much to do with the ECU behind the steering wheel as any mechanical issue.

BTW... I just watched a few vids of PIR... higher temps on the driver side are a given it looks like... lots of long right-hand sweepers and carousels (is that an Alan Wilson design?)

Car as below, camber settings are: fronts -3.5 degrees, LR -2.4 degrees, RR -1.3 degrees (not sure why these aren't closer--the shop that installed my Derlin RTAB's sent it out for alignment--this is what came back). Track is Portland International Raceway, classically harder on the left sided tires. Toyo starting pressures about 34 psi, ending about 38-40 psi, but 2-3 pounds higher on the left versus the right. The following pyrometer probe temps are after a cooldown lap and driving into the pits (listed outside-center-inside).

Left Front: 166/176/186
Right Front: 130/154/168
Left Rear: 182/197/205
Right Rear: 153/180/193

I welcome any input, but my core question is why are my rear tires hotter than my front??? Seems counterintuitive to me.

I'm guessing that the hotter inside readings indicating that I may be running a bit too much negative camber?

FWIW, the car seems relatively well balanced.

Thanks--Scott


Rear is over inflated and the last hard turn is a right hander?