Re: [ST] Tire Pressure

[Jim Crate <jim@xxxxxxxxxxxxxx>]

On Jun 23, 2006, at 4:43 PM, Jeremy Witt wrote:

> I was under the impression that under inflated tires heated up nice  
> and
> quick.  Which is why racers run lower pressures and why cages with
> really low tires tend to blow them up.  More tread on the road, higher
> rolling resistance, higher heat.  At least on cage tires.

Racers run whatever pressure gives them the best combination between  
grip and response, and sometimes tire wear is also factored in.  This  
varies according to the construction of the race tire, and for  
racecars tire contruction is different between manufacturers and  
types of tires.  Some tires like lower pressures, some like higher  
pressures.  I don't know anything about motorcycle race tires, though.

Someone mentioned the fact tire temps are taken across the tread on  
race cars, this is not so much about the tire pressure but more about  
the alignment and suspension settings.  You can tell if pressures are  
severely high or low, but if you are in a normal range tire temps  
will tell you more about whether alignment and suspension settings  
are correct.

To finally get around to answering the previous questions, a tire  
with lower cold pressure should see more increase in tire pressure  
than one with a higher cold pressure.  An underinflated tire will  
usually run higher temps.   For example, a tire with cold pressures  
of 32 psi may run 38 psi hot (6 psi increase), while a tire with 36  
psi may run 40 psi hot (only 4 psi increase).  On a race car you are  
looking for a target hot tire pressure, and cold pressures are set  
accordingly.

On the street, conditions change so much that you can't really look  
for a target hot tire pressure.  Obviously, a tire will run much  
cooler on a cool rainy day than when road temps are 140F+, and that  
will be reflected in the "hot" pressure.

Jim

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