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Old August 10th, 2006, 10:39 AM
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Cory Hula
1995 D90
Join Date: Apr 2004
Location: sacramento
Posts: 13
Educate me on Tires for my 90

Ok, somebody educate me on what the difference between tires that are rated by size vs. ratios (if that's even the right question). What's the difference between 33, 35, 31, vs. a 265/75/16 and why would I choose one over the other? Also, do these differences impact turning capabilities, would offsetting or lifting be necessary to accomodate a tire measured in inches vs. millimeters?


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Old August 10th, 2006, 11:01 AM
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Loic Fabro
95 D90 - 96 Disco -06 LR3
Join Date: Oct 2003
Location: Herndon, VA - USA
Posts: 1,600
Probably discussed on this site/forum already. I did a quick google search with those keywords: "+tire +size +faq +turning +radius +radial"
The first hit I got looks decent (did not read the details):

265 / 75 / 16:
- 265: width (in millimeter) of the tire
- 75: 75% of the width for the height (i.e. 265x75/100 = 198.75 millimeter)
- 16: size of the rim (in inches.... yeah I know....)
(theorical) Size of that tire: 16" + 2 x (198.75 millimeters) = 16" + (2 x 7.82") ~ 31.64"

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Old August 10th, 2006, 11:04 AM
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Mike Doligalski
'95 D90 ST
Join Date: Oct 2003
Location: Tampa, FL
Posts: 603
Loic, you beat me to the punch.....

33, 35, 31 etc. are the height of the tire in inches. 31x10.5 R15 says the tire is 31 inches tall, 10.5 inches wide with a 15 inch wheel. 265/75R16 is just the metric way of expressing tire size. There is no difference in the actual tire composition, tread, etc....265 means the tire is 265 mm wide and the 75 is called the aspect ratio and is a percentage of the first number (265 here). 75% of 265mm is about 199mm and that is how much tire is between the wheel and the top or bottom of the tire. Again, the last number means the wheel is 16 inches in diameter. If you want to find out how tall a metric tire is you must multiply the aspect ratio by the width (.75 x 265 = 199mm), multiply the answer by 2 to get the tire above and below the wheel (2 x 199 = ~398mm), convert to inches b/c i dont know the metric system (25.4 mm/inch x 1/398 1/inch = 15.6 inches), and finally add that answer to the wheel size (15.6 + 16 = 31.6 inches). Thus a 265/75R16 tire is 31.6 inches tall. Just be careful because every tire manufacturer is different and just because the tire says it's a 32 doesn't mean that it is exactly 32 inches.

Different width tires do influence turning ability as a wider tire will force a wider turning radius becuase the steering stops may need to be adjusted. Offset and lift are needed for certain size tires, but has nothing to do with metric versus standard measurements. If you want to know what tire size fits what lift I'm sure you there are several threads on the board which talk about it.

Hope this clarifies more than confuses...
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Old August 10th, 2006, 04:08 PM
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Neil Steinhagen
1986 Tithonus LHD
Join Date: Apr 2006
Location: Periscope Depth
Posts: 632
Also, check out the TIRES/WHEELS link on the top.. all the math is done for you. If you're an Excell geek, try the following:

Column A: 265
Column B: 75
Column C: 16
Column D (width in inches) : =A1/25.4
Column E (height in inches): =(A1*B1/100*2/25.4)+C1

Copy the rest of the cells down and you've just created your own tire calculator.

Remember what Mike said though, this is only the nominal height/width. Kinda like a 2x4 ain't really a 2x4. The manufacuturer can most likely provide you with the actual measurements and when all else fails, go to the tire store with tape in hand. I carry one in the cubby. My wife is embarrased to walk with me when I grab it because she knows that I'm gonna measure somebody's tires in the Wal-Mart parking lot.

Also, check out this thread:
It discusses a BFG M/T 255/85R16. You don't need a lift and requires no adjusting of your steering stops.
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Old August 10th, 2006, 08:24 PM
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Jack Walter
1966 109 SW Diesel
Join Date: Mar 2005
Location: Roswell, GA, USA
Posts: 783
I had to adjust the steering stops on my truck when going from a 235/85R16 to the BFG M/T 255/85/R16. I also didn't think it drove as well on the 255's. I went back to the 235/85R16 size ( new Cooper STT's) with my latest set of tires - 32" diameter and I think it drives and looks better. Ive also been able to crank the stops in and get back some of teh turning circle I lost with the 255's. NAS trucks come with the stops adjusted farther out than Euro models.
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Old August 15th, 2006, 10:08 PM
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Charles Galpin
'94 D90 ST, '63 SeriesIIA
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Posts: 11,538
Is there a reason you guys are not switching to 15" rims? It looks like the number of tires available in 16" is rather limited.

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Old August 15th, 2006, 11:05 PM
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Re-Fendered 90
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