Tire Size

[twintips_17]

Originally Posted by JackandJanet

Mine is set with "squish". You DO need to include this correction if you want the speed and odometer readings to be correct, and, it will have a small effect on your shift points which can effect the benefits of your tunes. I've subtracted about 3% from my tire's "unloaded" circumference and find that to be about the right amount. My tires are 275/65R18s and they are inflated to 40 PSI.

Whatever value you try, it's a "starting point". The way I first calibrated mine was on a trip to California on the interstate. Over a distance of 100 miles (using highway markers - which are quite accurate) I found I had less than 0.1 miles error on the odometer. Later, using a hiking GPS with WAAS, I found the Gryphon's and GPS' speed matched (while the dashboard speedo read 2MPH faster - it always will read fast).

My guess is, you MAY have to increase your "squish" factor more for the tires and pressure you use. Let's say you tried the "distance" test like I did and found your odometer read 101 miles after 100 actual miles. That would be a 1% error, so, you could subtract an additional 1% from your tire's circumference.

Hope this makes at least a little bit of sense!

- Jack

This is the first I have heard of this. Maybe I’m a little slacked on it. Haven’t been on the forums in about 8 months. Maybe I just missed it before I left. What is a ball park formula for the "squish" factor?

Maybe this is something you and Bluejay Thought about!!!!

Also how much does tire size play in shift points.

I run my stock tires all the time I can, but I have a second set of tires for off roading and hunting.... Such other things. I used to switch them out for a weekend here and there.... But with money being tight lately I have been running them as they are the only set that has a any good tread for winter driving in Montana.

Anyways my stock tires are 265/70-17's and I’m running 285/75-16's. There about 2 inches bigger on diameter.

Would it make a big difference.

I told bill to write my tunes for 265/70-17's.

Can I still mess with the tires size on my custom tunes when I get them for the times I will be running my Mudder's???

Thanks Jack!