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'nother new guy

1K views 6 replies 5 participants last post by  RacerXXL 
#1 ·
My first Nissan, 2000 Xterra 4x4 SE Auto 152k.

Gonna be my daily driver, with a 70 mile one way commute. Some easy trail stuff on weekends.

Already has 31x10.50 15s but otherwise stone stock, clean slate.

Checked speedo against gps and seems spot on, last owner must have had it calibrated? Owners manual calls for P265/70R15 anyone know height difference between the two?
 
#2 · (Edited)
A General Grabber 265/70/15 for example (An OEM option) was ~ 29.6" in diameter.

Most 31x10.5/15 are ~ 31" or maybe 30.5 - 31" or so, etc. (Those same Grabbers are ~ 30.8" for example)

So, for all intents and purposes the 265/70/15 is ~ a 30" tire, as 29.6" would be ~ like a 30x9.5 in diameter.

265 mm is ~ the same as a 10.5 in section width....

So a 265/70/15 would be roughly equivalent to a 30x10.5/15 if they made one.


If you now have 31x10.5's on there....your section width is the same as stock, but an inch more in diameter.

30/31 = ~ 96.8 %, or, your speedo would be off by a theoretical 3.2% or so.

The PSI you run, the load range of the tire, etc, all change the speedo calibration specifics, but, that's your order of magnitude error between the two tire sizes mentioned.


If you notice the potential overlap in size ranges though, a smaller 31x10.5 might be only a little over 30", and a larger 265/70/15 might be close to 30" in diameter....so the differences could essentially be so small so as to be non-measurable by GPS.


Your X can fit 32x11.5/15 stock (no lifts) btw.

:D
 
#3 ·
Thank you for the explanation.

Messed with it a bit more on the way to work this evening. Between the gps lag and the roller coaster road (hard to maintain speed real steady) looks like it might be going a mile or two faster than spedo reads at 55. Certainly close enough not to worry with.

Good part is the .544 I can add to the 17 mpg I got on my first tank...LOL

Thanks again ...
 
#4 ·
Thank you for the explanation.

Messed with it a bit more on the way to work this evening. Between the gps lag and the roller coaster road (hard to maintain speed real steady) looks like it might be going a mile or two faster than spedo reads at 55. Certainly close enough not to worry with.

Good part is the .544 I can add to the 17 mpg I got on my first tank...LOL

Thanks again ...
LOL

Of course, if going faster than you thought, that reduces MPG too...as well as the missing miles on the odometer.

>:D
 
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