<VV> On tire pressure

[Padgett]

> > This is a general question regarding tire pressure

For autocrossing on street tires my rule of thumb was to divide the weight 
on each end of the car by the load rating of the tire and multiply by the 
max pressure. On my V-8 Sunbird this worked out to 50 psi front, 38 psi 
rear. It worked, first time I went out like that I was hitting inside pylons.

Now you would not want to do that on the street, I figured that way because 
in a max rate turn all the weight is on the outside tires. I suspect that 
using this technique and multiplying by 3/4 for a normal car (weight is 
usually on two tires at each end) might be a starting point for sporting 
driving. Anyone know what the weight distribution is for a 66 Monza convert ?

Numbers I see are 2760 lbs total and 40% front 60% rear. This would be 1104 
front and 1656 rear.

185x80x13s I just took off were rated at 1301 lbs at 35 psi. New 195x70x14s 
are, son of a gun, 1312 lb at 35psi. 215x65x15s on back are 1510 lb at 44 psi

.75*35 psi*1104lb/1312lb= 22 psi
.75*44psi*1656lb/1510lb = 36 psi

If I had the 185x80s all around the rear would be .75*35*1656/1301= 33 psi 
(22/33 is pretty close to what most people run. For a softer ride use 2/3 
instead of 3/4.

So if you feel a need to have a calculated pressure to use with a digital 
tire gauge, there you are. I just thought mine felt pretty good at 25/35 
and didn't bother to calculate.

Note: to be really scientific you would also have to toss in a fudge factor 
for section width vs rim width. but I didn't bother.

Padgett