JScan tire size is... Right?

[OHJeeper]

Not sure if this is even the right section, but here goes.

I ditched my stock 245 75R17 tires for 285 70R17 KO2s. Love 'em. Hooked up JScan and followed the directions about tire measurements. Measuring from the ground to top through the center my tires are 32.25". Load up JScan, connect and it's already set to 32.25.

Huh?

I know the sizes aren't that far apart diameter wise, but I didn't expect to see 32.25. I even measured the old tires and they are under 32". I also understand different manufacturers are slightly different sizes. Should I just leave it? Even if it's off, I think at 60 mph it's only like a 2 mph difference. Am I just being too anal?

I know this is controversial, but I have never had luck with the "measure the height" method. For instance, when I upgrade to 37's (also KO2's) I measured the height at 35.25" under load. Using that measurement, my speedo was WAY off. I slowly incremented by 0.25" (which I think is the minimum increment for JScan) and worked my way up to.... 36.25 and my speedo/GPS/mileage is darn near perfect.

The BFG specs say the 37" KO2 is actually 36.5 (maybe at 55 psi!) so my actual measurement in JScan was only 0.25" less.

For your tire, the BFG site says 32.8". I would start with 32.75 in JScan and go from there (probably down to 32.5).

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[OHJeeper]

I'll also add that the stock Falken AT/3's (33") measured 32" under load when I got the JT from the dealer. The size in the PCM (when I reprogrammed it for my new tires) was 32.7" from the factory.

 

[JTNARJ]

Mine said 32.25 as well. Did you wind up leaving it or is there a sweet spot you found

I messed with it for awhile and just decided to leave it where it was 32.25. if/when I bump up tire size again I'll revisit.

 

[Vtur]

Based off my observations when setting mine is that, it'll read a little higher at 75mph vs 40mph as the tires expands some at higher speed. I set mine at around 65-70 mph.

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