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Old 08-21-2007, 04:50 PM   #1
bojangles
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Default Difference in R70 vs R75 tires?

Is there a noticable difference in the width of a R70 series vs a R75 series tire? I would like to replace my 6.70 x 15's with a 205 x R75 X 15. I seen on Coker's site they have only 205 xR70 x15's.
Any recommendations?
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Old 08-21-2007, 04:59 PM   #2
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The width of an R70 and an R75 should be the same -- in this case 205 millimeters -- about 8 inches. The difference will be in the height. The sidewall of a 70-series tire will be 70% of the width, a 75 series will be 75% of the width. If you want the same HEIGHT in a 70 series, then you need to go wider in the width -- about 219. Of course, they don't make 219...

a 215 will be a little wider and a little shorter, while a 225 will be even wider, and a little taller.

Frank

Last edited by decarmine; 08-21-2007 at 06:52 PM.
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Old 08-21-2007, 05:02 PM   #3
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205 is the mounted width (in mm) of the tire on a particular rim width (probably 6" for a 205)
R is for Radial
70 (or 75) is the ratio of the width to the sidewall height.
15 is the rim diameter

So a 75 will be a taller tire, and closer to the height of the 6.70x15.

If you go 70 then a 215 will get you closer to correct height

I see Frank (decarmine) answered at the same time I did!!

Last edited by 66since71; 08-21-2007 at 05:04 PM. Reason: decarmine
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Old 08-21-2007, 07:37 PM   #4
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thanks for the information.. Will 215's fit on a '63 Vette?
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Old 08-22-2007, 09:14 AM   #5
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205 70 15 = 8.1" wide 5.7" tall Side wall 26.3" height
205 75 15 = 8.1" wide 6.1" tall Side wall 27.1" height
215 70 15 = 8.5" wide 5.9" tall Side wall 26.9" height
225 70 15 = 8.9" wide 6.2" tall Side wall 27.4" height

These are generic calculations as all tire manufactures are different.
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Old 08-22-2007, 11:27 AM   #6
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Of further interest to you is the spare if you elect to carry one. If the size does not match what's on the ground if you get a flat on the rear you should rotate a front to the rear installing the spare (odd size) on the front. This is only important if you have posi.

I have 215/70's all around mounted on 15x6 knockoffs. The tire fits in my spare tire tub using the longer hanger bolts. This gives a slight exposure of the spare to the elements.
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Old 08-22-2007, 11:47 AM   #7
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The Diamond Back 205/75-15 Firestone Supreme Si tire has about a 1-1/4" wider tread than the Coker 205/75-15, and doesn't look "skinny" like the Coker and the original 7.75-15's do; no rubbing under any conditions, no problems, they balance, and they're round.

Click the image to open in full size.

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Old 08-23-2007, 09:39 AM   #8
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I also have 215/70's all around with no problems. I would caution you to check the archives for a lot of material on Coker tires. In short, most folks think that they are junk compared to the Diamondback. I have had both, and I would not take another set of Cokers if they were free. The Diamondbacks that I have now are great.

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Old 08-23-2007, 09:39 AM
 
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