[T3] Tire inflation pressures

[Jim Adney]

A few years ago, a tire shop I was at mentioned that they had added a 
few extra psi to my new tires. I didn't understand why until they 
mentioned that the pressure would drop once I took the car outside. 
It was winter and the temp outside was well below freezing.

I had never thought about the difference between tire pressure as 
measured on a warm car in the shop and the tire pressure as it exists 
outside. So this morning the topic came up again, after the local VW 
dealership overinflated my Jetta tires.

This time I did the numbers. On a cold winter day, a tire that's 
inflated to 35 psi (correct Jetta pressure) in the shop will drop 4.6 
psi when it is taken outside where it is zero F.

A tire taken from an airconditioned shop into a hot summer day will 
rise a much smaller amount, simply because there's no way to get an 
equal amount of temp rise outside. (That would be 140 F!)

Our Type 3 tires would see smaller pressure changes because they 
start with less pressure. Remember that for best results you should 
use ~20 psi front and ~30 psi rear. Squarebacks can use up to 36 in 
the rear if fully loaded.

Type 3s with wider than stock tires will use LESS pressure.

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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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