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Actual vs. listed tire size

R

Rod Knee

NAXJA Forum User
Location
Grand Jct., CO
The stated conversion factor for converting metric tire size format to inches is .03937 (or its reciprical 25.4 if you like division). Using this number, a 235/75/15 translates to a tire height of 28.88 inches, call it 29 inches and be happy. However, when I measure my 235 BFG AT's I get 28 inches, and that's measuring horizontally. My tires are not brand new but I know they haven't lost anything close to an inch of tread.

Anyone know the actual height of a BFG AT 30 inch or 31 inch tire?
 
All tires to my knowledge are about 1.5" short. My 37's measured 35.5 my 42's measure 40.5".
 
Rod Knee said:
The stated conversion factor for converting metric tire size format to inches is .03937 (or its reciprical 25.4 if you like division). Using this number, a 235/75/15 translates to a tire height of 28.88 inches, call it 29 inches and be happy. However, when I measure my 235 BFG AT's I get 28 inches, and that's measuring horizontally. My tires are not brand new but I know they haven't lost anything close to an inch of tread.

Anyone know the actual height of a BFG AT 30 inch or 31 inch tire?
Click to expand...

I think the 31" comes out to something like 30.8". However, they're listed on the BFG site, so why not check there?

Also, you may be more interested in "rolling radius," which is the distance between the centreline of the axle shaft and the ground line, when loaded.

Why for are you trying to find all this out? Working on a recalibration, or just a maths freak?:gag:
 
5-90 said:
Why for are you trying to find all this out? Working on a recalibration, or just a maths freak?:gag:
Click to expand...

I put a two inch lift on my XJ last November. I've been reluctant to go to 31's due to trimming and power loss issues and reluctant to go to 30's because its been my assumption that they aren't substantially bigger than my 235's, which are in good shape. However, if 30's are actually 30's (or close) then I would gain a full inch clearance, which to my modest lift would be substantial.
 
BRIANHO13 said:
All tires to my knowledge are about 1.5" short. My 37's measured 35.5 my 42's measure 40.5".
Click to expand...

My 33's are 32.5
 
5-90 said:
I think the 31" comes out to something like 30.8". However, they're listed on the BFG site, so why not check there?
Click to expand...

According to the site 30's are only a inch higher than 235's, but it also says 235's are 29 inches. I don't believe my 235's were ever 29 inch. I can still cover most all of Lincoln's head on the penny test for tread wear.

http://www.bfgoodrichtires.com/specs/all-terrain-t-a-ko/44.html
 
Rod Knee said:
The stated conversion factor for converting metric tire size format to inches is .03937 (or its reciprical 25.4 if you like division). Using this number, a 235/75/15 translates to a tire height of 28.88 inches, call it 29 inches and be happy. However, when I measure my 235 BFG AT's I get 28 inches, and that's measuring horizontally. My tires are not brand new but I know they haven't lost anything close to an inch of tread.

Anyone know the actual height of a BFG AT 30 inch or 31 inch tire?
Click to expand...

Are you measuring the tires "Mounted on the vehicle"?
If you want a good size measurment take one wheel/tire off ( or jack the vehicle up lifting one tire off the ground) & check it, I'll bet you gain an inch!
 
garr said:
Are you measuring the tires "Mounted on the vehicle"?
If you want a good size measurment take one wheel/tire off ( or jack the vehicle up lifting one tire off the ground) & check it, I'll bet you gain an inch!
Click to expand...

That sounds like a good suggestion, but like I say I did measure horizontally, and I did so to avoid measuring the part of the tire that was on the ground being compressed by the weight of the vehicle.
 
correction SSR 33's = 33.4", 34 LTB's = 33.6. not much of a difference. i think interco tires are one of the only companies that tend to run taller on most of their tires.
 
91 Jeep Project said:
Intercos are the one brand that actually measure out to what is advertised. Almost all other brands measure less than what it is supposed to be, but there does not seem to be any rhyme or reason to those shortfalls.
Click to expand...

I guess the tire mfg.s are just followed suit with what other industries do.
example: a 2X4 piece of lumber is 1-5/8 X 3-5/8 (If you are lucky).
 
redneck23ms said:
in a 235/75/15 the 235 is the wisth of the tire. the 75 is the sidewall hieght. meaning the tire is 235 mm wide and the sidewall is 75% of 235
Click to expand...

In a perfect world yes.....in actual application by the tire companies no
 
I run a tire shop, and 1 31"BFG is never the same as a 31"Goodyear or a 31"whatever... The majority measure smaller.... 1"is average, but some measure bigger too,

Just like the UTQG ratings, its useless for comparison purposes.
 
It's all about marketing and economics. A 31 inch tire or whatever looks much better on paper than 30.7 or 30.8. There is an actual term for it that I learned in economics, but that was a while back:lecture:
 
You could take a mounted tire (off the truck) and measure it with 20psi then with 30psi and it would probably be an inch difference right there :)
 
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