BF Goodrich K02 All Terrain Actual Tire Size Specs

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All,
Just found this table of BF Goodrich tire size specs.

This table includes actual measured diameters for various tire sizes.

Thought this might be useful for anyone adjusting their tire sizes with the Tazer JL or other programmers.

https://www.bfgoodrichtires.com/upload/bfgoodrich/specifications/specs-all-terrain-t-a-ko2.pdf
that's still not actual size under load, tire flattened out at the point of contact, so will still be slightly off with your Speedo.
 
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that's still not actual size under load, tire flattened out at the point of contact, so will still be slightly off with your Speedo.
I agree but hopefully its good enough as a general starting point for most people. I doubt there will be enough change to warrant a significant deviation from these values even under load.
 

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that's still not actual size under load, tire flattened out at the point of contact, so will still be slightly off with your Speedo.
True. It's not even close.

For example, that chart (which is straight from their website) shows 33.9" for the 285/75-17, but when I got my set they were 33.5" tall unmounted. Once mounted and installed on the Jeep they were 33.0" measured with a level and a tape measure. That's nearly a full inch difference from the listing, which is several percent to the speedometer.
 

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True. It's not even close.

For example, that chart (which is straight from their website) shows 33.9" for the 285/75-17, but when I got my set they were 33.5" tall unmounted. Once mounted and installed on the Jeep they were 33.0" measured with a level and a tape measure. That's nearly a full inch difference from the listing, which is several percent to the speedometer.

But that 33" is not a rolling diameter, the tire should flex from centrifugal forces.

The real number that should be needed is the overall circumference, which would be the exact distance the vehicle will travel in one revolution of the tire, regardless of tire pressure fluctuation. But out jeeps seem to want tire diameter, so I would use the unmounted diamteer.
 

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But that 33" is not a rolling diameter, the tire should flex from centrifugal forces.

The real number that should be needed is the overall circumference, which would be the exact distance the vehicle will travel in one revolution of the tire, regardless of tire pressure fluctuation. But out jeeps seem to want tire diameter, so I would use the unmounted diamteer.
I don't think you'll see a tire carcass flex from centrifugal force unless you go to a drag strip.

I used the exact measurement of the tires while mounted and installed on the Jeep (33.0") in my Tazer programmer and it put my speedometer dead-nuts on verified by handheld GPS.
 

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If'n you're taking the time to adjust tire size the only way to fly is to measure static loaded diameter (radius actually) at the street pressure you wanna run.

But certainly a chart - if accurate and not just posting the mathematical conversions of nominal size - could help one know if a tire tends to run big or small
 

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I don't think you'll see a tire carcass flex from centrifugal force unless you go to a drag strip.

I used the exact measurement of the tires while mounted and installed on the Jeep (33.0") in my Tazer programmer and it put my speedometer dead-nuts on verified by handheld GPS.
I have 315/70/17 ko2's which are claimed by bfg to be 34.4" tall unmounted. I calibrated the speedometer with a gps on the hwy and the speedometer matched the gps with the tire size on the tazer set at 34.4".
 
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I have 315/70/17 ko2's which are claimed by bfg to be 34.4" tall unmounted. I calibrated the speedometer with a gps on the hwy and the speedometer matched the gps with the tire size on the tazer set at 34.4".
Same here. i have the 35x12.5R20 and set them closest to 34.5 with the Tazer (which is what the chart I attached shows). Tires are inflated to 35PSI and GPS shows the MPH dead on with the speedo. So the chart seems to be correct.
 

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True. It's not even close.

For example, that chart (which is straight from their website) shows 33.9" for the 285/75-17, but when I got my set they were 33.5" tall unmounted. Once mounted and installed on the Jeep they were 33.0" measured with a level and a tape measure. That's nearly a full inch difference from the listing, which is several percent to the speedometer.
Tire ride height when the tire has weight on it won’t effect your speedometer. The actual radius without distortion will give you the true real estate of the circumference of the tire. The bigger the circumference the more you travel with each revolution. So absolutely not, weight deflection has no effect on the soeedometer
 

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Tire ride height when the tire has weight on it won’t effect your speedometer. The actual radius without distortion will give you the true real estate of the circumference of the tire. The bigger the circumference the more you travel with each revolution. So absolutely not, weight deflection has no effect on the soeedometer
The tazer only takes 96% of the input tire size to account for the rolling diameter for you.
 

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It is not really a "claim" by the manufacturer but rather a calculation based on the tire size. Let's look at a 315/70/17 tire size. First we need to convert mm and % to inches;

Tire width = 315mm (12.40")
Tire aspect ratio = 70% of tire width (12.4"X 70% = 8.68")
Rim size = 17"

Using the above one can do the following simple calculation;

Wheel Height = Rim size + (Aspect Ratio X 2)
Rim size = 17"
Tire aspect ratio of 70% (8.68 X 2) = 17.36"
Wheel Height = 17" + 17.36"
Wheel Height = 34.36" (Rounded = 34.4")

The actual question should be; is the manufacturer's claimed tire width really 315mm as it forms the base of the calculation.
 

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The tazer only takes 96% of the input tire size to account for the rolling diameter for you.
I think there is potentially one additional variable. What calculations and adjustments is the Jeep computer doing once the tire size setting is adjusted? For example, if you use the Tazer to tell the Jeep the tire height is 34.4 (per specs), perhaps the computer makes the necessary adjustments to account for the rolling diameter? It is purely speculation on my part, but I would the jeep computer to do something like that - after all even the stock tires experience those same distortions.
 
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