Tire Experience

[Phil O]

I never measured a fresh pair of ko2 tires.

But if you do the math, even the stock ko2 is not truly 35.
In fact, no stock tire on the stock rim can be 35:

((315*70%) * 2)) + (17" converted into millimeters) = 34.4 or something.

So maybe the 315*79% is not calculated to the absolute roof of the tire?

But if you take a gander at my installation photos, you'll notice that the stt pro is significantly taller than a depleted ko2.

Actually, I could measure because my spare ko2 is unused.

But then it'd be a on rim vs free rolling comparison.

Yeah. It doesn’t look like cooper makes the stt pro in a 35x12.5r17?

 

[NASSTY]

I never measured a fresh pair of ko2 tires.

But if you do the math, even the stock ko2 is not truly 35.
In fact, no stock tire on the stock rim can be 35:

((315*70%) * 2)) + (17" converted into millimeters) = 34.4 or something.

So maybe the 315*79% is not calculated to the absolute roof of the tire?

But if you take a gander at my installation photos, you'll notice that the stt pro is significantly taller than a depleted ko2.

Actually, I could measure because my spare ko2 is unused.

But then it'd be a on rim vs free rolling comparison.

Stock 315/70/17 KO2s - 34.4"
35x12.5x17 KO2s - 34.5"
315/70/17 KM3s - 34.4"
35x12.5x17 KM3s - 34.5"
315/70/17 STT Pros - 34.6"

 

[ljn21]

Stock 315/70/17 KO2s - 34.4"
35x12.5x17 KO2s - 34.5"
315/70/17 KM3s - 34.4"
35x12.5x17 KM3s - 34.5"
315/70/17 STT Pros - 34.6"

Are those the numbers from the mfg spec pages? Using the width and aspect ratio calculation mwthod, all 315/70/17 tires would be identical, the formula is the same. I am fairly certain the BFGs in real world actually measure less than the BFG spec on their sote shows. I couldn't find it now but a couple days ago I came across a way to calculate diameter based off the revs per mile and it seemed closer to reality but my math-fu isnt strong enough to remember how to do the math that way and google didn't find me the same page that showed the way to calculate it.

 

[NASSTY]

Tire Rack says the STT Pros are 34.6", but Discount Tire Direct and the Cooper site says they are 34.57".

 

[Phil O]

Stock 315/70/17 KO2s - 34.4"
35x12.5x17 KO2s - 34.5"
315/70/17 KM3s - 34.4"
35x12.5x17 KM3s - 34.5"
315/70/17 STT Pros - 34.6"

I read on the forum recently of a guy who bought a set of 315/70r17 KM3’s from 4WheelParts and he said they were about an inch shorter than the KO2’s. Luckily because of this 4WheelParts let him exchange the tires for the 35 version.

 

[NASSTY]

I read on the forum recently of a guy who bought a set of 315/70r17 KM3’s from 4WheelParts and he said they were about an inch shorter than the KO2’s. Luckily because of this 4WheelParts let him exchange the tires for the 35 version.

I dunno According to the BFG website the KO2s and the KM3s are the same diameter in both sizes 315/70/17 (34.4")and 35x12.5x17(34.5").

 

[Phil O]

I dunno According to the BFG website the KO2s and the KM3s are the same diameter in both sizes 315/70/17 (34.4")and 35x12.5x17(34.5").

Here is the thread.

https://www.fordraptorforum.com/threads/bfg-km3.71987/

 

[NASSTY]

Here is the thread.

https://www.fordraptorforum.com/threads/bfg-km3.71987/

If so the advertised specs can't be accurate because .1" difference shouldn't be noticeable to the naked eye.

 

[ljn21]

I found the page online that showed the other way to calculate diameter, using the revolutions per mile...

For the BFG KM3 as an example from the specs on the bfg website:


315/70/17 are listed as 34.4" but also show 604 revs/mile. 604 revs/mile = 33.41"

35/12.5/17 are listed as 34.5" but also show 602 revs/mile. 602 revs/mile = 33.51"

37/12.5 are listed as 36.5" but also show 569 revs/mile. 569 revs/mile = 35.46"

I think the BFG diameters in their spec's are too generous, the diameters calculated off the revs/mile seem to match the real world experiences everyone is having that the BFGs run small to size.

If you want to calculate other tires for comparison, the formula is:

1 mile divided by circumference = revs per mile

Doing all the mathemagical switching, unit conversions, and substituting pi × dia for circumference gives you:

(5280 × 12 )/ (pi × revs per mile) = circumference in inches

 

[Flash1034]

Very true. Many Jeepers have known for years that BFG and some other manufacturers over estimate their tires diameters. BFGs run small. Toyos and Goodyears tend to be true to size.