Calculating Tire Pressure

Oookay so, I have before me... a problem, the worst kind of problem... a math problem (with a bit of physics...)

Calculating my tire pressures.

I work in the tire industry and have experienced the side effects of over inflation and under inflation.
Overinflation can cause center tread wear, and underinflation can cause the outer tread wear (Though both actions
can cause a number of other effects pertaining to handling and mileage)

The Nitto Invos I bought for the previous season showed signs of center tread wear on the rear tires (not caused
by center rib runout - found on powerful cars with very wide tires). I figured the weight over my rear axles must
be low, and my factory tire pressures were too high for them.

Ok so.. math time (There is a VERY HIGH chance that my math may be wrong, feel free to correct me)

The forumula is not mine, I began to work on one... but became stupid .
Credit for the formula goes to "arumdevil" on UKLegacy.com

2008 Nissan Altima Coupe 3.5L 6MT

Curb Weight  : 3289lbs
Fuel                  :  100lbs
My fat ass       :  155lbs
Other Fluids:   40lbs
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                           3584lbs
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Tire information:

Micheling Pilot Super Sport - 245/40R19

1653 @ 50PSi

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Factory Weight Distribution:

Front: 62% = 2222lbs
Rear : 38% = 1362lbs

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Assuming there is 25% weight distribution over each wheel (LOL...)

1653 x 4 = 6612lbs (The tires theoretically, together would support this much weight at 50psi)

6612 (max load) ÷ 3584lbs (vehicle weight) = 1.84

50 (PSi) ÷ 1.84 = 27.2psi

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But, my car sucks in the weight distribution department... so

1653 x 2 = 3306

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Front:

3306 ÷ 2222 = 1.49

50PSi ÷ 1.49 = 33.5PSi

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Rear:

3306 ÷ 1362 = 2.43

50PSi ÷ 2.43 = 20.6PSi (seems low..)

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So according to the numbers, my front tires are to be set at 33.5PSi and my rear tires to 20.6PSi

Obviously, 20PSI seems way to low for any tire, and that is one of my worries. My next worry is vehicle weight
trasnfer under braking and cornering. My car is far from needing this much attention to detail, but... I'm curious.

Anyone here able to shed some light on vehicle dynamics and tire pressures?

I hope the formula can help you guys... somehow =/

(had to type this in notepad first before posting here because of the white background. Some of the format may be wrong

uh.....

What does it say on the side of your tires?

it was worth a shot =(

, side of the tires state 50psi, to support 1653lbs

I'd just use manufacturer recommended pressures... Usually like 32 psi? 20 psi seems crazy low and would kill fuel economy as well kill the tires quicker

mattcanada wrote:I'd just use manufacturer recommended pressures... Usually like 32 psi? 20 psi seems crazy low and would kill fuel economy as well kill the tires quicker

Nissan reccomends 33/33psi on my car.

according to the math 20psi would support the weight I currently have over my rear wheels.

My last tires, the Nitto Invos had 33PSi in them. The rear tires had center tread wear, a sign of over-inflation. Maybe 28psi and I'll see what happens.

The Honda crv... 1998s? i believe suggest 26psi in all four tires

Yeah, I just googled the tires and pressures seem to be all over the place, but mostly in the mid-high 30's... BMW's seemed to be going with 32/35 - 35/37 (front/rear) and Porsche's like slightly higher 35/37 - 37/39 (mostly depended on usage, track vs street) Guess you just gotta play around with it until you find a pressure you like good compromise between handling and tread wear... Always fun