Hi all,

I am confused by this page at Tire Rack. I was under the impression that tires should be deflated for high-speed driving, to compensate for the heat buildup, not inflated.

When they say, "Required Tire Pressure Increase," are they really instructing me to over-inflate my Z-rated tires before driving at speed?!

Any help is appreciated.

Dave

 

For anyone interested, the following answer came to me off-list:

Air Pressure/Load Adjustment for High Speed Driving

I suppose my confusion came from the fact that I typically lower tire pressures at the autocross. This might be high-performance driving, but not high-speed driving.

FWIW.

Dave

 

I'm not sure why you lower for auto-x. For track use we generally increase tire pressure. It decreases sidewall flex, and does a better job of maintaining the size and shape of the contact patch. At low tire pressures the tire will roll over onto the sidewalls in cornering situations.

 

At an autocross event, I will chalk my tires and note the contact wear after running the course. Inevitably, the first run of the day (with factory recommended pressures) will produce a chalk line which continues well into the tread. I'll drop a few pounds of pressure, rechalk and rerun the course. By the time I've dialed in a perfect contact patch, I've usually dropped several pounds of pressure.

But, knowing what I know now, I would never apply this technique outside of the autocross, where speeds are generally low.

Dave

 

Apparently you are in good company if you're confused about high speed settings for street tires. Thankfully, I rarely have to try to figure out where I should start street tires for track, for the most confusing and seemingly contradictory advice seems to come for street tire settings. I follow the manufacturer's inflation recommendations for my R-compound tires. They usually suggest to start with cold inflation pressures that get the tires to some range of pressures hot; maybe mid-30s or mid-to-high 30s. I know that my track tires get very skatey if they get over 40 psi on track. On a warm day they may gain 8-10 psi, so I usually set them at about 30 psi. For autox, I usually start them around 34 psi and they may get to about 38 psi warm. I rarely use chalk anymore because the sidewalls on R-compound tires are so stiff that it takes a lot of psi change to make any noticable difference.