Calculating speed and MPG with 285's? (1 Viewer)

[perk]

Tired of searching. What calculations are used to determine actual speed and mpg when running 285/75/16's? I know I need the speedo correction gear from Slee, but in the mean time I'd like to know what my numbers are.

Thanks,
Perk

 

[alaskacruiser]

From Slee's website:

http://www.sleeoffroad.com/products/products_speedo.htm

"The most common size tire installed to gain extra clearance is 285/75R16. When the diameter of this tire is calculated, it comes to 32.8". The stock tire size is 275/70R16, which equated to a 31.2" diameter. So when installed the larger tires, your speedometer will read 57 mph when you are traveling 60 mph. Using the correction gear, your speedometer will read 58.9 mph."

 

[informationjunky]

Easiest is to buy or borrow a GPS.

 

[shocker]

(32.8 - 31.2)/31.2 = about .05

Your speedometer/odometer are about 5% off right now without the speedo correction gear.

Take your current speed or odometer readings you gather during this time and multiply them by 1.05

 

[NorCalDoug]

when I went to 285s, my speedo was off by about 5% per my GPS.

Now with 315s, it's off by about 10% (also per my GPS).

...the math is easier for me now