I'm not so sure about the math on the rear...
Pr = ((Wr*Tf)/(Wf*Tr)
so,
Pr=((1650 X 225)/(1350 X 255))
That gives us 371,250 / 344,250
I'm getting 1.078..
Where am I going wrong??
I'm very interested in this formula, too.
FWIW, to get a quick F/R weight distribution, measure between the wheel centers and mark the center of the car on the door sill with a piece of tape. Take the car to a truck scale and park the car on the scale wit the tape directly lined up with the split in the scale plates. Should do the trick for around $10.
Quote:
Originally Posted by JayG
Thanks Tom,
That's exactly what I was looking for.
The formula I got to estimate correct tire pressure in relation to weight and tread width is:
Pf = (weight/100) + 2
Pr = ((Wr*Tf)/(Wf*Tr)
Pf - front pressure
Pr - rear pressure
Wr - weight rear
Wf - weight front
Tf - tread width front
Tr - tread width rear
Using
3000 lbs as total weight
1650 lbs as rear weight
1350 lbs as front weight
255 as rear width
225 as front width
we get
(3000 / 100) + 2 =32 front pressure
((1650 * 225) / (1350 * 255)) = 34.5 rear pressure
That should be a good starting point for tire pressure for best performance
Yes, it will vary due to lots of variables such as tire compound, ambient temp, track condition, turns and lots more, but at least it give you some idea where to start
Factory spec is 29 front / 36 rear and that builds in more understeer. Raising the front in relation to the rear will reduce the understeer, so going to 34.5 rear & 32 front makes sense that it would be more neutral.
Of course, this would all have to be adjusted once the tires heat up. You can also check the temp of the tire tread on the inside, center and outside. They should be relatively even across the tread. You can adjust pressure based on those measurements. if the center is higher, lower the pressure a little and if the outside is higher, raise it a little.
Whats really interesting is for stock 17" tires 205 / 255 combo the calc give you 32 front and 31.4 rear! On stock 18" 225 / 265 its 32 front and 33 rear!
Yes, the weights are approximate for my car, but it is close enough for government work
Just my 2 cents FWIW |