tire size

guidosrt8 · Post by **guidosrt8** » Wed Oct 17, 2007 9:00 pm

what does this change shift points??? or speedometer???

Post by **mikel** » Thu Oct 18, 2007 11:51 am

It corrects the speedo when using taller tires.

Thanks

T91WHEELER · Post by **T91WHEELER** » Tue Nov 13, 2007 1:29 pm

The speed is based on the size of the rear tire? Just want to be sure as front is 28" and rear is 29"...

Thanks

Post by **mikel** » Tue Nov 13, 2007 1:42 pm

Yes, based on the rear tire size.

Mike_Levy · Post by **Mike_Levy** » Tue Nov 13, 2007 5:36 pm

Its the rear tire, so if I go from a 255/45-20 to a 275/40 I'll need to change that? The fronts are 245/45, which is the same height as the 275/40, but slightly shorter then the stock 255/45 rears.

muellge · Post by **muellge** » Fri Mar 14, 2008 11:19 am

Does this apply to the Jeep Cherokee SRT8s as well. Changed tire sizes and want to know if I need to change my tire size went to a 315/35 rear sized tire. Front is 275/40, so at r20, the magic figure is 28.6 for both, but I still would like to change the tire size to get my instruments reading correctly. Thanks in advance for any advice. Seems like the answer is to enter in my 315/35/20 information in the tire size menu and I am good to go. Can someone confirm?

Post by **mikel** » Fri Mar 14, 2008 11:24 am

muellge wrote:Does this apply to the Jeep Cherokee SRT8s as well. Changed tire sizes and want to know if I need to change my tire size went to a 315/35 rear sized tire. Front is 275/40, so at r20, the magic figure is 28.6 for both, but I still would like to change the tire size to get my instruments reading correctly. Thanks in advance for any advice. Seems like the answer is to enter in my 315/35/20 information in the tire size menu and I am good to go. Can someone confirm?

If the new tires and the stock tires are the same height, then no change is required.
If you have changed the overall height by at least .5", you want to change the tire size info in the tune.

Thanks

muellge · Post by **muellge** » Fri Mar 14, 2008 11:50 am

Thanks for the response. The rear tire size, correct?

Post by **mikel** » Fri Mar 14, 2008 11:55 am

muellge · Post by **muellge** » Fri Mar 14, 2008 12:09 pm

Following up, the stock 285/40 r 20 has a diameter of 29 inches even. My Vred rear 315/35 r20 has diameter of 28.7 inches. My special math tells me that that is only .3 inches smaller, which provides for a 1% faster reading with my new tires, at least that's what the miata.net tire size calculator shoots out. Looks like no real entry is necessary. Thanks again.

Post by **mikel** » Fri Mar 14, 2008 3:56 pm

muellge wrote:Following up, the stock 285/40 r 20 has a diameter of 29 inches even. My Vred rear 315/35 r20 has diameter of 28.7 inches. My special math tells me that that is only .3 inches smaller, which provides for a 1% faster reading with my new tires, at least that's what the miata.net tire size calculator shoots out. Looks like no real entry is necessary. Thanks again.

Yeah, you should be fine.
Here is a handy tool for you guys to use:

hemiboy29 · Post by **hemiboy29** » Sun Mar 23, 2008 6:46 pm

Great thanks for the calc.... does it work for dodge vehicles as well??? dont see why not...

Thanks,
Chris

tire size

tire size

RE: tire size