post your true tire diameters
 

trying to decide what tires to buy? so how about every body running a 285 70-75 , a 305 70-75 or a 315 70 -75 measure your tires from the ground and record it here, list your tire brand and make and true size thanks to all and happy thanksgiving !

36.7in Falkens Rocky Mountains

I believe tire rack has the true diameter size listed for each tire

The "true" size depends on more factors than Tire Rack can factor.


To the OP- true tire size will depend on weight of the vehicle, air pressure, and rim width- so expect the numbers to be off between everyone.

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Goodyear Duratracs 285-70-17 on 17x8.5 wheels.
Measures 32.5" @ 32-34 psi and 32" @ 28-30psi on Stock JKU
http://img.tapatalk.com/d/13/11/28/rusepy5e.jpg

Those are unmounted specs.

By the time you mount them on wheels and put them under the full weight of the vehicle, the actual height can be as much as 1" shorter than spec.

It depends on the width of the wheel, the weight of the vehicle, the actual psi in the tires, and the stiffness of the sidewalls.

Most tires run 0.5" to 1" shorter than spec.

37" Gooodyear MTR Kevlars with 28psi and normal load of Jeep is just shy of 36.75":yup:

I see this come up often. Yes, overall height will be less than specified when weighted. However, for the purpose of fitment, the radius is what matters. Take a 37" that actually measures 37" off a wheel. Throw the weight of a jeep on it and from the center of the hub to the ground, it is less than half of 37". From the hub center to any other point, it will be half 37". The bottom flattens, not the rest of the tire.

315 /70 r17 Duratrac mounted on 17x 8.5 wheels with 30 psi stock bumpers. Measures 33.5 inches.

285/70-17 toyo open country at2 E rated tire on stock 2014 rubicon rim with 32psi on 2014 jkur is just under 32" same tire and rim not on jeep measured is just over 32.5"
These are brand new no wear. Same tire e rated 285/75-16 on a 16x8 rim was slightly taller.

I have had others tell me their tires were taller but when measuring them on their vehicles using a carpenters level and tape measure on a smooth cement surface they are always smaller then people think.
http://i743.photobucket.com/albums/x...ps08633722.jpg

yes X100.....

33.25 @ 32 psi with 285/75/17 KM2s

... on factory 7.5s

35x12.50r17 KM2 on 17x8.5 on JKUR with 30psi. 33.5" is what I measured and used with me Procal.

Previous JKUR with 315/70r17 Duratrac on 17x9 with 32psi. 33.5".


BFGoodrich website says that size is 34.8.
Goodyear website says that size is 34.4.

35 12.50 17 bfg km2 on 17x9 measured at 33.75. Found that when measuring for my flashcal.

315-75/R-16. Two door JK. 37psi. Nitto Terra Grapplers.

Procal has 33.75" loaded, and me speedo is still off a small bit (likely smaller). On 16x8 wheels.

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It doesn't work that way for speedometer programming. Diameter will give you a correct speed, not radius.

If the wheel width exactly matched the tire bead width and the tire psi were exactly right, then radius if an unmounted tire might be the same to the top. However, tires flex and bulge. So, the radius to the top when the tire is bulged on a narrower wheel can exceed the unmounted radius.

Measuring to the bottom while parked may be different when park than when in motion though correct? Wouldn't centrifugal force cause the center of the tire to expand thus creating a different radius/diameter? May be thinking of this wrong and or maybe change is so minor that it doesn't matter

It doesn't make that much difference.

If you measure to the top of the tire while parked and use that measurement in your ProCal/Superchips/Diablosport, you should be close to exact with your speedometer when verified with a GPS.

Ok and that makes sense. For some reason I thought someone said to measure from center to bottom and I was thinking that it would be under compression but measuring to top makes sense

285/70 R17 Maxxis Buckshot Mudders measure 32"

255/80/17 cooper discovery st maxx 35 psi on stock rims measure 32 1/4

I have 255 Rubicon BFG MT. I measure the rolling circumference and divided by PI. This gave me the diameter of 30.75. I programmed my Procal with that number, and the speedometer is right on the money. I checked it with 2 different GPS's.

toyo open country at2 285/75-17 28psi on 14 jkur just a hair over 33". stamped on the side is 34"od

Yes, it will. And so will temperature as the tires heat and cool. May not be much but it is quantifiable.

This would likely be the most accurate way to calibrate a speedometer but ... for the reasons mentioned by Planman, not an accurate way to measure resting tire height.

315/70/r17 Pro Comp MT/2 Xtremes. 33 1/4 is the actual diameter when mounted and under a normal load.

315/70/17 Hankook Dynapro MT - 34PSI. 58 degrees measure 34.05

Toyo Open Country MT 285/75/17 @ 28psi = 33.5"

35” (315/70/17) Mickey Thompson MTZ
With 30psi for DD - actual diameter 34”.

Sorry to breath New life to an old post.

255/75r-17 Goodyear Wrangler MTR on OEM 17x7.5 31.75" in diameter ( Flat board laid on on tread and measured to level ground)
255/75r-17 Goodyear Wrangler MTR on 17x9 ARE ATX 194 Ravine Part # AX19479050612N 31.50 in diameter.

35x12.50x17 Pitbull Rockers - actual 35"
37x12.50x17 Pitbull Rockers - actual 37.115"

For calibrating you speed.
Measure from hub center to ground double it and use this number to program
Confirm with GPS.

I have done it this way for years and it is alway right on or as close as possible. Some programmers adjust tire size in 1/4" increments.

Mastercraft Courser MTX

37X12.50 on 17" Wheel 8.5" wide and 4.5" backspace

36.1" Measured and calibrated with GPS

Toyo's and Nitto's as well as Pitbulls run more true to size than other brands.

*Edit* Forgot to add I Run 21 PSI thats where I get the best wear

well, my interest was more about the values on an unmounted tire, in order to have data as clear as possible,
especially for people interested in upgrading to big and heavy sizes, anyway
here data sorted

hope it helps


BF Goodrich
All-Terrain KO2

• 315/70 r17

Mud-Terrain KM2s

• 255/75 r17

• 285/75 r17

• 35x12.50r17

• 35x12.50r17

Cooper
Discoverer S/T Maxx

• 255/80 r17

Falken
Rocky Mountains

• 37x?????r??

Goodride
SL366

• 37x12.50r17 31.9kg/70.3lb -> 36.77" JUST TIRE (by syr)

Goodyear
Duratracs

• 255/80 r17

• 285/70 r17

• 285/70 r17

• 315/70 r17

• 315/70 r17

Wrangler MT/R kevlar

• 37x?????r??

Wrangler MT/R

• 255/75 r17

• 255/75 r17

Hankook
Dynapro MT

• 315/70 r17

Mastercraft
Courser MXT

• 37x12.50r17

Maxxis
Buckshot Mudders

• 285/70 r17

Mickey Thompson
MTZ

• 315/70 r17

Nankang
FT-9

• 35x12.50 r17 29kg/63.9lb JUST TIRE

Nitto
Terra Grapplers

• 315/75 r16

Ridge Grappler

• 285/75 r17

Pitbull
Rockers

• 35x12.50r17

• 37x12.50r17

Pro Comp
Xtremes MT/2

• 315/70 r17

Toyo
Open Country A/T II

• 285/70 r17

• 285/75 r16

• 285/75 r17

Open Country M/T

• 285/75 r17

Nitto Ridge Grappler

• LT285 / 75 r 17 E

@ 40psi on 17'' x 8.5'' 33.86 (34'') (by OscarMlke)

:thumbsup:

BFG KO2 315/70R17 C load range
 

I’ve measured these up at 33.5 at 28 psi.
At 32-35 psi they’re about 33.75
When using the Superchips flashcal and a Garmin GPS to verify I had to set it to 33.25 to make the speedo match the GPS. Can’t speak to weight as I never weighed them, but as far as getting weight specs Tire Rack has every weight listed, even for the KO2s which aren’t listed on BFG’s website.

You should also be concerned with the section width of the tire which will widely vary. It has just as much to do with weight and fitment as height.

Added thanks
you are right, but gets tricky to objectively measure it, anyway, if we define a way, I can update the post :)