Tire Size Modification 285/70/17  285/75/17  305/70/17


JK Enthusiast
I believe the 75's are taller, considered a 34 inch where 70' are a 33. I run the 285 70 17 with spacers

JK Super Freak
Originally Posted by
pabl0007
Hi all
Please explain to me the difference between these tires size
I have a headache already trying to decide on which tires to get for my stuck rubicon.
I do know I will be buying wheels spacers with my new tires I get, Please helpppp.
pictures will be awesome
the first number, which is the larger, is the width of the tread in mm. the second number is a ratio. The sidewall height is 70% of the width. IF the second number is 65, then it is 65% of the width.
the final number, is the rim size. The size of the hole in the tire for a simple explanation.
285/70R17 for the most part, measure about 32.8" tall and about 11" wide. (every manufacturer differs a bit, but this seems to be a good average and is based upon my direct experience with a BFG M/T km2)
285/75R17 is a 33.?" where the ? is a number I honestly don't know. It is often referred to as a true 34" tire. It is also about 11" wide.
The 305/70R17 will be about the same size as the 285/75R17.
A 305/65R17 is about the same size as a 285/70R17. It is about 2/10th" smaller. The wide increases to 12" though with a 305. This makes a HUGE!!! difference in the size of the tread blocks and the size of the voids. The larger tread blocks and larger voids make it MUCH better offroad.
I've run 235, 245, 255, 265, and now 305 section width tires and by far, the 305 width wins hands down for offroad performance.
As a general rule, the second number will always be a multiple of "5." For each increment of "5" you go up, you gain almost an inch. For each increment of "5" you go down, you lose almost an inch.
the same is true for the section width but based upon increments of 10. Assuming the aspect ratio stays the same, for each increase of 10mm in the width, you gain almost an 1" in height.
285/75R17 is essentially a 34" tire
285/70R17 is essentially a 33" tire
285/65R17 is essentially a 32" tire
305/65R17 is essentially a 33" tire
305/70R17 is essentially a 34" tire
305/75R17 is essentially a 35" tire
285/75R16 is essentially a 32" tire
295/75R16 is essentially a 33" tire
305/75R16 is essentially a 34" tire
so on and so forth. You can see the pattern and apply it accordingly. Real world numbers do vary slightly, so only use this as a general rule.
'09 Rubicon Unlimited
305/65R17 BFG M/T KM2 on 17x9 rugged ridge
AEV 3.5"
Shrockworks midwidth
XD9000i
'02 WJ 3" OME/spacer lift and lots of other stuff.(rip)
'94 ZJ 4" of lift F=>R and lots of other stuff too. (rip)

JK Freak
Google tire calculator and you will be able to see the difference between the tire sizes.
Hope this will help you out.

JK Super Freak
Originally Posted by
CerOf
A 305/65R17 is about the same size as a 285/70R17. It is about 2/10th" smaller. The wide increases to 12" though with a 305. This makes a HUGE!!! difference in the size of the tread blocks and the size of the voids. The larger tread blocks and larger voids make it MUCH better offroad.
I've run 235, 245, 255, 265, and now 305 section width tires and by far, the 305 width wins hands down for offroad performance.
As a general rule, the second number will always be a multiple of "5." For each increment of "5" you go up, you gain almost an inch. For each increment of "5" you go down, you lose almost an inch.
the same is true for the section width but based upon increments of 10. Assuming the aspect ratio stays the same, for each increase of 10mm in the width, you gain almost an 1" in height.
285/75R17 is essentially a 34" tire
285/70R17 is essentially a 33" tire
285/65R17 is essentially a 32" tire
305/65R17 is essentially a 33" tire
305/70R17 is essentially a 34" tire
305/75R17 is essentially a 35" tire
285/75R16 is essentially a 32" tire
295/75R16 is essentially a 33" tire
305/75R16 is essentially a 34" tire
so on and so forth. You can see the pattern and apply it accordingly. Real world numbers do vary slightly, so only use this as a general rule.
^^Great info here. Don't forget that actual mounted measurements are sometimes VERY different than the math. My 285/70/17 measures a little bit over 32". that was a bit of a disappointment, but live and learn.
Gone but not forgotten:
'99 XJ
'03 KJ
'07 KJ
'10 JKUS
Hospitality is making your guests feel at home even when you wish they were.

JK Super Freak
'09 Rubicon Unlimited
305/65R17 BFG M/T KM2 on 17x9 rugged ridge
AEV 3.5"
Shrockworks midwidth
XD9000i
'02 WJ 3" OME/spacer lift and lots of other stuff.(rip)
'94 ZJ 4" of lift F=>R and lots of other stuff too. (rip)

JK Newbie
How much does rim width factor into the overall size? For example, I'm looking at getting new 17x9 rims. Theoretically, my stock 30" SRAs will be less than 30" when I add 1.5" to the width of the rims, right? Is there a calculator for sidewall adjustments based on the rim width?

JK Freak
Originally Posted by
pabl0007
Hi all
Please explain to me the difference between these tires size
I have a headache already trying to decide on which tires to get for my stuck rubicon.
I do know I will be buying wheels spacers with my new tires I get, Please helpppp.
pictures will be awesome
Basically these sizes are essentially:
285/7017 = 33x11.50
285/7517 = 34x11.50
295/7017 = 34x12.00
305/7017 = 34x12.50

JK Super Freak
Originally Posted by
Wandell
Basically these sizes are essentially:
285/7017 = 33x11.50
285/7517 = 34x11.50
295/7017 = 34x12.00
305/7017 = 34x12.50
Close. 315 is the 12.5"
305 is the 12" wide
295 is 11.5
285 is about 11"
265 is 10.5"
I put the 285/7017 and 305/65R17 side by side and the 285 was .3" taller in the BFG MT km2. 32.5" and 32.8" respectively.
'09 Rubicon Unlimited
305/65R17 BFG M/T KM2 on 17x9 rugged ridge
AEV 3.5"
Shrockworks midwidth
XD9000i
'02 WJ 3" OME/spacer lift and lots of other stuff.(rip)
'94 ZJ 4" of lift F=>R and lots of other stuff too. (rip)

06182012 07:56 PM
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