I just ordered new wheels and tires. I have a question...my stock tire size is 235/55-17. I bought front tires that are 255/45-18 and rears are 275/40-18. What should I set my revs per mile on my tuner? According to the tire calculator I was thinking at 775 revs per mile but I really have no idea what to set it to. Any input would be appreciated. Below are my tire calculator results.

Stock Tire - 235/55R17
Revs per Mile:765.5
Actual Speed:60 mph100 km/h

Tire 1 - 255/45R18
Revs per Mile:769.5
Speedometer1:60.3 mph100. km/h
Speedometer Difference: 0.522% too fast
Diameter Difference: 0.52%

Tire 2 - 275/40R18
Revs per Mile:780.1
Speedometer1:61.1 mph101. km/h
Speedometer Difference: 1.907% too fast
Diameter Difference: 1.88%

 

Well the speedometer goes off the rear tires, so I would think that you would want to go with 780.1.

 

Thanks for the info. That solved my issue. Now I just gotta wait for my wheels to get here.

 

I think that the 275/40 is going to be a little smaller sidewall than the 255/45. Most people have gone with the 285/40 in the rear.

 

I've seen this ? come up a lot. Check out this link. You can put in your stock size, and then your modified size/sizes and it'll calculate what percenage differance as well as actual speed verses spedometer readout, revs per mile etc, etc!

It's a Great TOOL!!!!

http://www.1010tires.com/TireSizeCalculator.asp

 

This is a good site also.

http://www.bigcustomwheels.com/info_specs.jsp

 

I am glad you mentioned it 05-1947. I went back and reread the various posts about tire size and I realized that most people were doing 285/40 in the rear not 275/40. For some reason I was thinking many people had 275/40 and 255/45 combination tire setup. I was able to change my order on the tire size. I am going with the 275/40-18 on all four instead.