Help me read my Tires

[mmasse]

I was at a DE event last Saturday at Limerock park. My car is a 911 1976 chasis with 3.6 (993) engine. 245/35.18 front and 295/30/18 rear Toyo R888 tires.

I am currently running 2° negative camber on the front and 2.5° on the rear

I took temp and pressure reading after my runs and I was getting pretty consitent results.


1) Hot pressure was 40° (maybe too high as per below?)
2) I took Temp measurements on the inside mid and outside of the tires
- On the driver's side I got pretty stablke measuments on both fron and rear tires, arond 107°

- On the passenger side the outside temp reading was consistenly 10° lower than the center and inner measurement. Suggesting that the outer part of the tire was not being used as much


Now her is what I got in term of specification from themanufacturer of my tires.


"Toyo Tires recommends the following general set up guidelines for the Proxes R888:

Operating Temperature: 160°F to 220°F
Hot Inflation Pressures: 32 to 38 (psi)
Camber: -2.5° to -5.0°
Caster: As much positive as possible"

Hence, my questions:

1) Why are the tires not reaching the ideal operating temp, even under higher than recommended pressure?

2) For the same track, should I reduce the camber on the passenger side? Or is the temperature reading a consequences of Limerock having mostly right handed turns. My thinking is that if i reduce the camber, the car will not be optimized for the couple of left hand turns.

This is the layout opf limerock

[Zeke]

10 degrees is not much. Yes, teams will adjust from track to track and analyze changes at any given track. Are you that ambitious for 10 degrees?

[TimT]

Lime Rock is all right turns with one throwaway left. So your outside tires will be hotter, and the tire pressure will come up more on the drivers side of the car.

The outside of the passenger side tire will be the least loaded part of the tire, hence lower temps..

Per Toyos specs you are outside of there recommendations on the front, and on the rear just meeting the spec. Not sure if you use the car much on the street, you should increase front camber if possible, on some cars it take bit of work to achieve.

Why are the tires not reaching the ideal operating temp, even under higher than recommended pressure?

Push the car more slide it around more and the temps will come up. I don't remember what the weather was like last saturday, if on the cool side, and the track temp was low because of cloud cover, you might not get temps..

Also start with 1# less tire pressure..

What sort of suspension mods do you have? if your car rolls a lot, your passenger side front wheel may barely be contacting the track.

We have set cars up to "turn right" better..

[boba]

Some things to consider,

how long after you came in did you take your Temps?

Did you run a cool down lap?

If either of these are the case your temps are not indicative of how you were working the tires.

You need to come to the pits off a hot lap and take temps in the hot pit or as soon as possible in the paddock.

As was stated Lime Rock is a right turn track so that will effect your temps.

You need to get good temps outside/middle/inside to see how each tire is working. You can then judge how the setup is for each corner.

Does Toyo give you recommended cold start pressures?
If not you will need to experiment with where to start to get to their recommended trgt pressures.

Depending in car setup you may not even get good temps in your RF.

[Quicksilver]

To really tell what tire pressures work with your tires, car setup, and driving style you can't beat time on a skid pad.
The basics of suspension/tire tuning is: Work on raising the grip on the end with the least grip and then kill some of the grip on the other end so they work together.

Here is a basic methodology:
- Lower the tire pressure some to get in the ballpark... (my guess for starting on the R888s would be cold 27psi front and 32psi rear)
- Get the tires warm so they are working. Couple track laps would be a good way to heat them. It will be more even left and right.
- Record your warm pressure before working the skidpad. (Get a helper so you don't have to stop too much.)
- Do a few laps around the skidpad and find out if the car is loose or pushing.
- Adjust the pressure on the end of the car with less grip. Adjust till you have the highest grip with that end. (you will probably have to drop the pressure.)
- Once you have what you think is the best from the first end adjust the other end upward until grip is somewhat equal.
- Alternate adjustment of either end to get the last bit of grip from the end of your car that has the least grip. and get the other end so it is pretty equal.
- Record pressures (or better record your pressures all through this process.)
- Remember to give the car a slight bias to push unless you know exactly what you are doing. Loose can be fast but it also can be way too "exciting". (and expensive)


You now have a baseline for your tire pressures. Now go get your inner/middle/outer temperatures from some track laps. Surface IR guns are easy but the surface of the tire cools too fast. Use a pyrometer with a needle probe.
After working the skid pad you shouldn't be adjusting pressures that much. That should be more to tell you how to adjust the suspension and alignment.

Last bit is when you get it all happy don't touch the pressures at the end of the day. Cover the car so the sun doesn't heat it next morning and get the dead cold pressures after it has set overnight.

You keep that notebook as it will teach you things that you would never learn otherwise.

[mmasse]

Originally Posted by Quicksilver

To really tell what tire pressures work with your tires, car setup, and driving style you can't beat time on a skid pad.
.

How do you get access to a skid pad? I know that skip barber has one at Limerock, but would they rent time on it?


Thanks for all the inputs