I know this has been asked a million times but this Regearing thread is a little different.
So, I want to regear the JK, I have looked at the gearing chart that has been floating around, and on 35s it looking like 4.88 are the go, BUT!, I have used a ProCal to set up the recalibration of the speedo, taco, shift patterns and so forth. OK.
Stay with me please. So I measure my tyres the way the ProCal says to do it, measuring from the ground to the top of the tyre at normal driving pressures, I used on small level on the top of the tyre and a level with a tape measure to to get the height for the tyres so I can set the ProCal correctly.
I measure my 315x70x17 BFGoodrich ATs and they measure 33.25 inches, not 35.00 inches, 33.25inches.
So I get a friend to help me do it again, 33.25 inches is what we get.
And so we measure his 305x75x16 Bighorneys, 31.50 inches.
And finally here is what Im getting at when looking at the gearing chart, should I be looking at the chart for 33s or 35s?? Because I allways thaught 315s were 35s!!!!!

Thanks for your patients,

Yeahright

 

Use the actual tire height, not what is printed on the sidewall

 

I would say go with 33" since you're closer to it than 35".

 

Agreed with the above comment. Go with 33, its the closest you will get for an accurate speedo.

 

This is how I measured my tire height. It's the most accurate way I can come up with.

Stick a piece of chalk in the tread.
Move ahead until the chalk has made two marks on the pavement.
Measure the distance between the two marks, and divide by 3.1416.
This will remove any variables encountered with measuring from the ground to the top of the tire.