Porsche 944 Track Car – Tire Temperatures

In my article here, I discuss the recent track event that I attended at the North Carolina Center for Automotive Research.  NCCAR is just what it sounds like.  It is a purpose built facility for automotive testing.  Here is the track map:

As you can see, there are a lot of long, constant radius turns.  This turns out to have several advantages.  You are in the corners long enough that the transient effects of corner entry and exit die out and you experience the true mid-corner handling response of your car.  Kind of like a giant skid pad.  The track is laid out so there are a generous number of right and left hand turns in each lap.  The track can be run in either direction, which we did. Clockwise on Saturday. CCW on Sunday.  You are in the corners long enough to get good heat in the tires.

Looking at the “big loop” in particular, my data tells me I was able to generate just a tad over 1 g with Toyo Proxes RA-1 Rcomp tires and that I was in the turn about 6 seconds.  Following is a series of tire data that I took on Sunday, when we were running CCW.

First, here are the corner weights for the car with me (200#) and about 1/3 of a tank of fuel in the car:

LF  630#  RF 604#

LR  662#  RR 578#

Total 2470#

As you can see, the car weighs just a tad over 2200# totally empty, which I am quite proud of.  See that article here.

The day started out cool, with an ambient temp of 44 deg.  My sway bars were set to a neutral setting. My camber is set at about 2 deg front and rear.  I understand the RA-1s may like more than this but it allows me to throw on street tires when it’s cold or wet.  All temps are in degrees F and pressures (P) in psi.  I run regular room air in the tires.  No nitrogen.  Tire temps were measured with a Longacre tire temp gauge at the inside (I), middle (M), and outside (O) of the tread.  The only variable I chose to deal with was tire pressure, i.e. I didn’t mess with camber or sway bar settings.  Note that based on corner weights, you would expect the tire with more weight on it to run a little hotter.  You want and expect the inside of the tire to run a little hotter due to the camber effect.

Session  Amb Temp            LR                          LF                           RF                            RR                           Comment        
                                  I      M       O   P      I      M     O     P     I        M     O    P          I     M      O      P

1    44     109    105     100  36      93    93    91   36        107     104   104    37       92      92     88    34.5       Baseline, first run of the day

2   48     110      111     105  35      123  107   95  36        110    111   109     36      115    116  109      37      Good camber indication on RR

3   56     112    110   107   35         124   122   103  37     115     116  112     37       115    114   114     38

For the final run, you can see a few trends.  The car felt pretty neutral.  The LR has a modest but noticeable camber effect.The LR also had the lowest tire temp yet the highest corner weight!  But with the CCW course, the left side of the car is not working as hard so maybe that explains it. The LF had a pretty big camber temp effect so I may need to double check camber there.  The RF had almost no camber effect nor did the RR.  So the only main takeaway is that I might want to check the camber on the LF and see if there is any looseness in the suspension.

Guys, this is not an exact science.  I hear the NASCAR guys screaming over the radio every weekend about how the car is handling like shit and those guys spend a lot more time thinking about it than I do.  But it’s fun to check and keep track of.  For instance, by midday on Saturday with the street tires, the middles of the tires were running hotter than the edges. Taking out 2 psi in each tire fixed that.  I’ll take the small victories.

Here is some info I found at the TireRack.com website:

Toyo Tires recommends the following general set-up guidelines for the Proxes RA1:

• Operating Temperature: 160°F to 220°F
• Hot Inflation Pressures: High 30s to Low 40s (psi)
• Camber: -2.5° to -5.0°
• Caster: As much positive as possible

So you can see that on this cool day, I really wasn’t getting up to the recommended operating temperature. I’m sure my next event in the summer will take care of that!

BTW, the best book on tires that I have ever read is The Racing and High Performance Tire by Paul Haney.  My book review is here.  Well worth purchasing and absorbing.