I have the sct programmer, can I do it with that? Or do I need to go back to Doug at Bamma and have him edit my three programs?
(I'm putting 295 45 18's on the back and they are 1.5" taller)



Bill

 

All you have to do is change tire size in your user-adjustable parameters on your SCT tuner...they also have an option for gear ratio.

 

The parameters on my SCT for tire size list RPM instead of tire size. Do you know what the approx RPM is for 18in tires? Thanks

 

899 revs per mile. I think the tuner only goes by fives? so 900 would be the setting.

 

You need the revolutions per mile for your size tire. Check the manufacturer's web site and see if they have the info. For my Nitto 555's, they had the revs/mile listed for each tire size.

 

Just figure the circumference of the tire. C = pi*diameter

Figure diameter by converting tire size into milimeters, then adding the sidewall size which is a certain percentage of the tire width (i.e. 35, 40, 45). Add those and you have tire diameter in MM.

So now you can figure circumference (c=pi*tire diameter in MM).

So now you know the distance the tire covers in one revolution. Convert to feet for easier measurement, then divide by 5280.

Simple, right?

 

It'd prolly be easier to search for the number, and thats coming from an engineer.

 

Cmon, I already gave him the # already.

 

I would definitely go with the mfg specs. Even the same (fitment)size tires have variances due to tread style/depth.

 

http://www.miata.net/garage/tirecalc.html


easiest way to figure the revs.

 

Thanks everyone. The calculator showed 746 RP/mile
Old tire size was 235/55/17 New tire size is 255/45/18

 

the # I gave was for blplemmons size.

745 sandyman, it only goes by fives on the tuner.

 

Thanks Stoenr.

 

NP. What tires did you go with?