Anyone know a good starting point when I readjust my speedo after the new tires go on? I already have an X-cal 2 to change it, I just need to know what a good number is to start with.

The old tires are 275/55/20 and I plan on going with 35x12.50x20 trail grapps, the nitto website says those tires are 35.04" in diameter.

 

I'd start with 35 inches and go from there. I think I wound up using 34.5 or something to calibrate for my 35's.

 

I wish it were that easy, I thought I read at one time you have to enter the rolling circumference in millimeters. I suppose i could just convert it on paper and enter it in then use my gps to see how close I am and adjust as needed.

35 / 2 = 17.5 x 17.5 = 306.25 x pi = 962.11 x 25.4 = 24437

that number seems way too high, maybe it's just diameter in mm's

35 x 25.4 = 889

now that one seems too low

I guess I'll have to dig out my x-cal 2 manual and see what is required to change the speedo

 

you can mark your tire mark the ground then roll ahead then mark the ground again when the mark is in the same spot you started. then just measure mark to mark and you should be close.this is how i did the aftermarket speedo for my bike and it pretty dame close.

 

The Edge and Gryphon use mm where as I think the SCT uses revolutions.

 

Wrong calculation. What you did is the area of a circle.

Circumference is diameter x pi, or (35 x 25.4) x 3.14 = 2791.46.

 

On my tuner, you enter the revolutions per mile (which can be found on the Nitto website for your tire size). I haven't checked it against my gps since I changed it last week to see if I need to tweak it a little.

 

Oops, I guess I did I always get those two mixed up.


What kind of tuner do you have, I have an x-cal 2.
I just looked at the nitto site and the tires I want have a revs per mile of 592

 

I have a Diablosport Predator.

 

SCT Xcal2 = Revs / mile...

==> http://www.gordon-glasgow.org/tirecalc.html

Don't fergit ta factor in 'squish' - typically ~3%.

And confirm with a GPS if possible.


MGD