Quote:
Originally Posted by CapriRacer
Do you mind sharing? As a tire engineer who has been told how the vehicle tire placard values are calculated, it would be interesting to know what other methods exist.
|
1. Obtain the following information(mostly on the tires, and stickers on vehicle door frame):
GAWR(gross axle weight) values for front and rear axles.
Max. cold pressure and USTA max load rating from OEM tire, if possible. *Some replacement tires, even with exact same size, speed-rating letter code, and maximum cold pressure as the OEMs, might have a different USTA max load stamped on them. Use it in those cases.
2. Divide both front and rear GAWR/2 - remember: you want final pressure per tire, not per axle!
3. Plug figures into following formula:
Front: [(GAWR/2) /USTA max load] * Max Cold Pressure from OEM tires.
Repeat for Rear axle.
My 2015 Hyundai example: The B-pillar sticker specifies 33psi cold, front & rear - nice n easy for average Schmoe consumer to remember and set their tires to!
B-pillar Front GAWR: 2,160lbs. Rear GAWR: 2006lbs.
OEM Tires: 44psi Max cold, USTA max load 1,356lbs.
So for front tires:
Half of front GAWR = 1,080. Half of Rear GAWR = 1003
(1080/1,356 )
= 0.7964601 * 44 = 35.04psi
For rear tires:
(1003/1356)
= 0.7396755 * 44 = 32.5psi(I rounded down to 32psi for convenience!)
35psi front, 32 rears.
Or alternatively(for summer): 34 front, 31 rear - as long as that difference is maintained.
Essentially it calculates GAWR/2 as a percentage of the USTA maximum load
(in my case, 1,356lbs) per tire. 1080lbs = 79% of max load for the front tires, and 1003lbs = 73% of max load for the rear tires.
It does not work for all vehicles! Like I said previously, the formulas above returned some ridiculous figures for my friend's 2005 Subaru Legacy.
Your mileage - and pressures - may vary