Tire Size Designations?

[dovehunter]

I have been looking to get some replacement tires for my truck. I have been running P265-75R15s which is the same size that came on it. However, this seems to be a bastard size and I am having a hard time finding suitable replacements in this size. Everything I have seen (with the exception of the Goodyear Wrangler RT/S that I am currently using) seems to have strictly street-type treads. I don’t want Monster Mudders, etc. but I would like something with a little more aggressive tread. I seem to recollect someone here saying once that they replaced this size with one of the truck sizes (I don’t recall the designation) that was like the 31” variety. Is there a web site where one might go that either compares the designations or gives comparable appropriate replacement in the truck designation sizes?

[klsm54]

A 31x10.50R15LT, or 31x11.50R15LT, would be the same diameter. With your current wheels I'm guessing the 10.50's would be a better bet.

Here is the chart I got that information from.... Tire Size Chart

[dovehunter]

klsm54:

Thanks, that chart is exactly the sort of thing I was looking for.

[jabba]

Or... figure it out yourself...

P265 75 R 15

265 = 265 millimeters wide.
75 = side wall height is 75% of the width.
R = Radial
15 = wheel diameter

so...

(265 x .75) x 2 = 397.5 mm

25.4 mm/inch

397.5 / 25.4 = 15.64

15.64 + 15 wheel diameter = 30.64" tire height.

Jabba

[dovehunter]

Jabba:

Taking your calculation one step further -

265 / 25.4 (mm per inch) = 10.43 inches is the width

That confirms klsm54's estimate that the tire size I need using the equivalent truck size designations is 31x10.5R15.

Thanks for the insight. I was never really sure before what the "P Metric" designations actually meant. Now it makes perfectly good sense.

[srwshooter]

dovehunter,they told me that 10.50 were the same as 265's ,i bought them and my speedo is 2 mph off now.

[dovehunter]

I guess it's due to the fact (if the caculations are correct) that the 265 is slightly smaller in diameter than the 31. Just for curiosity sake, how do you know your speed is off 2mph? When I had my old GMC S-15 4x4 pickup I got a ticket going through Cumberland County - worst damn place in the state in my opinion. The cop noticed the big tires on my truck - P255.70R15s - he said I should have my speedometer checked. The tires that originally came on the truck were P195.75R15s. I bought it used with the P255.70R15s. That's several sizes bigger than what the speedometer was originally calibrated for. However, when I had the speedometer checked, it showed I was only off by 8-9 mph at speeds from 55-65, which was enough to cause me to get a ticket when my speedometer was only showing about 58-60 in a 55 zone. I went to court - a kangaroo court where you are guilty until proven innocent - and the judge said he would do me a favor and reduce the charge to improper equipment, which wouldn't go down as a moving violation.

[jimiowa]

DoveHunter an easy way to check your speedometer is to take it out on the highway. One with the milemarkers,spacedone mile apart @60 mph it should take 60 seconds or one minute to run from one to the next.
Or you can take it over several miles and average it.

I remember getting away with a warning in my 70 Plymoth Duster, by claiming I had just changed tires and had not got my speedometer calibrated yet.
I passed a state Trooper going 85 mph? Glad he did not look too closely at those tires since they were Mc Creary Racing Slicks ;D

[srwshooter]

dovehunter,i checked mine before and after with a GPS.