Best I can figure out that a 295/70R17 equals around a 33.50. Can anyone tell me is this correct. Trying to get my tire size right for download.

 

I think they want true tire size. Take a straight edge out from the top of the tire and measure down to the ground. that should get you close. then you can tweak it a bit.

 

Yup Just measure it to the 1/4 inch (full diameter).

 

Hi, You will have to measure. 295s range in size. With my Nitto, Trail Grapplers I went with33.25" (Nitto lists them as being 33.54") speedo checked out perfect.

 

measure. set your flashpaq. go for a drive with a gps in your Jeep with you. make sure the new calibration on the speedo is accurate. after I installed my flashpaq and set the tire size to what I measured, I had to go back and set it 1/4" lower to make the speedo accurate.

 

Stop and think about it. The rolling diameter that the speed sensors see is 2 times the distance from the road up to the center of the wheel hub. It doesn't matter what the distance is from the ground up to the top of the tire, unless your tire doesn't flex when the top gets to the bottom. The size to put into the Superchip is the actual rolling diameter, which is 2X(the distance from the ground up to the hub). My 305/70R17 MTRs are supposed to be 34.1". At 28psi, the road to hub distance is 16"s. I put 32" into the Superchip and my speedo is exactly correct with the GPS and a timed distance between mile markers. My guess is that a 35" tire is close to a 32.4" rolling diameter.

If you enter a number larger than the rolling diameter, your speedo will read faster than your actual speed and your mpg will indicate higher than actual.

 

lol, is there a single JK out there with an accurate mpg indicator? mine read 1-2 mpg high when it was stock. still does after tires and flaspaq.

 

Mine read high when it was new also. I flashed a lower tire size (twice the distance from road to hub) and it was right on with the GPS and of course the mpg went down 5%. Try it and yours will be correct also. The computer can only calculate the rotations times the circumference based on the diameter you tell it to use. Give it a number 5% too high and the speedo will be 5% high along with the indicated mpg.

 

And don't forget to measure it with the same amount of air you plan on running.....

 

Just put in what you come up with when you measure and put it in. Then keep lowering the diameter size until your speedo matches a gps. When you get it correct, I'll wager that number is TWICE THE DISTANCE FROM THE ROAD TO THE CENTER OF THE HUB. That is the ONLY number that will give correct info from your Jeeps computer.

With the 295/70R17 size @30psi, the calculated inflated diameter is with no load on it is 33.25". When you put a load on it that 16.6" radius will drop to 15.7". 2X15.7=31.4. 31.4" will be very close to your rolling diameter that will get your speedo accurate.