Stock Tire Size

Does anyone know what the stock tire size of a 1999 4x4 SR5 TRD Manual Extended Cab? I am trying to calculate my speedometer difference but I'm not sure what the OEM tire size was. Thanks!

 

31x10.5 R15

Edit: By the way - to calc your speedo difference, the OEM tire size doesn't matter (unless you're trying to calc it for the time when you had your original tires, and you no longer have them).

For your current set of tires, you want to use your speedo and a good GPS (like your phone), and figure out the difference in speed at some high rate of speed (say 70mph). Then, you can figure out the % difference, and that's how far off your speedo is.

Wrote up a fun article about all this which you're welcome to check out. Has the relevant math formulas you need in it too.

Speedometers, Odometers, and Gas Mileage - All Lies!

 

Very cool, thank you! I have a very similar chart I use:



I found it easier to put a multiplier for the actual miles in my sheet then calculating the difference while driving. I really don't mind if my speedo/mileage are off in the truck, so long as they are accurate in my sheet I'm happy. I multiplied my miles by 1.0645 to get an accurate result going from a 31" to 33" tire.

Nice write up! I see we are very like minded.

Edit: Fixed my multiplier

 

Nice, I use a multiplier in my spreadsheet as well, rather than calculating it on the fly while I'm driving.

I think my current calculation is something like .92, in that I only go 92 miles for every 100 miles on my odometer. I'm not sure how your multiplier works, but 1.6xxx seems very high to me, it means that your speedometer or odometer is off by between 38-62%. That seems like a pretty big discrepancy for moving from 31 inch to 33 inch tires.

But again, I'm not sure exactly how your spreadsheet works, so it may be totally spot-on.

 

Oh shoot my bad, I meant 1.0645. It multiplies my mileage shown by the truck by 1.0645 to get the actual mileage I drove then uses that number to do the rest of the calculating (such as cost per mile and mpg). So if my truck shows I drove 100 miles I actually drove 106.45 miles. So it's only a 6.45% difference with the bigger tires.