View Single Post
Old 06-26-2019, 03:30 PM   #13
RidingOnRailz
AF Regular
Thread starter
 
RidingOnRailz's Avatar
 
Join Date: Jun 2009
Location: Stamford, Connecticut
Posts: 304
Thanks: 7
Thanked 0 Times in 0 Posts
Cool Re: For Anyone Who Owns a Digital Tire Gauge

Quote:
Originally Posted by CapriRacer View Post
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

Last edited by RidingOnRailz; 06-27-2019 at 05:31 AM.
RidingOnRailz is offline   Reply With Quote