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Discussion Starter #1
I just bought a used 96' T100 Xtra-Cab 4x4 SR5, and the previous owner had a Pro Comp Mud Terrain 32x11.50R15LT tire set up.

I'm trying to calculate my MPG so I can charge my boss, but after some quick calculations it appears to be around 16-17mpg. I'm thinking that the larger tires are throwing these numbers off. I found a few websites that will approximate the difference between stock and new tires, but I'm having trouble finding the dimensions of my truck's stock tires.

The owners manual has two listings under the four-wheel drive Xtra-Cab models. P235/75R15 and 31x10.5r15lt. Anyone know which ones likely came with my truck?

Also, it mentions that the front tires should have a psi of 29, and the rears 35. Should I keep these ranges for the aftermarket tires?
 

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1998 T100 SR5 2WD
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Most of the T100s that I've come across were using P series tires fer stock. I know my 1993 SR5 were supposed to have as stock the 215/75-15 tires. I currently run the Yokohama Geolander A/T-S 235/75-15LT tires...really nice and smooth on the road. :D

I run my tires at 40lbs fer the front and 45lbs fer the rear...but I have LT tires. It all depends on how soft you want yer ride. I can't tell the difference with my road travels at all.

Plus Zero 225/75-15 255/70-15 265/70-15 30/950-15 31/1050-15 32/1150-15
Plus One 265/75-16 275/70-16 285/75-16
Plus Two 255/65-17


Here's one of the more popular tire size calculators on the web... ;)
 

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Discussion Starter #3
Thanks BZP, I already had that calculator but the links to those tires was exactly what I was after.

So all the 4WD base tires were 235/75r15 and the 4WD optionals were 31x10.5R15. I'm somewhat ignorant as to why the BASE model uses metric, and the OPT uses standard, but I used this calculator to convert the standards to metric, and came up with 267/76/15. My current tires are apparently 292/74/15 using metric measuremnts.

So would it be correct to assume that my speedometer is off anywhere between 12.3% 6.1% slow? If I were to travell 100 miles, my trip meter would actually read between 87.7miles to 93.9miles?

I know it;s a pretty insignificant difference, but i'm just curious if I did the simple math properly.
 
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