Do I need a tune when installing aftermarket wheels??

[Siggy33]

My car is ordered with the regular 17"s and I want to upgrade to the 18" FR500 replicas (10" outback and 9" upfront). Do I need to retune my ECU after putting these on? Or should I just get a sidewall height (aspect ratio, for you technical lads) that would make my wheels/tires package comperable to the stock 17"s height?

Also, on a somewhat related note: how much performance do you guys think I might loose by going with the bigger wheels and tires (due to the increasaed rotational intertia)? Are the FR500s that much heavier than stock?

 

[AznStanger3v]

If you can keep the overall diameter of the new tires the same as the stock, you wont need to mess with the computer. As far as performance loss, that is all dependent upon weight along with size. Rotational mass is quite a principle.

 

[celticstanger]

My car is ordered with the regular 17"s and I want to upgrade to the 18" FR500 replicas (10" outback and 9" upfront). Do I need to retune my ECU after putting these on? Or should I just get a sidewall height (aspect ratio, for you technical lads) that would make my wheels/tires package comperable to the stock 17"s height?

Also, on a somewhat related note: how much performance do you guys think I might loose by going with the bigger wheels and tires (due to the increasaed rotational intertia)? Are the FR500s that much heavier than stock?

If you match the stock diameter, your speedo won't be off. If you differ, I'd tune the new revs per mile in.

 

[LarryS]

ABS light might come on if you vary more than about an inch. Cant' say for sure but that's what happened with my Camaro.

 

[Siggy33]

Does anyone know what sidewall height would match the 18" wheel to the stock 17" wheel with an aspect ratio of 55? I'm thinkin maybe 40 or 35?

 

[GT in Detroit]

Give this site a try, its helped me a couple of times..

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

jim

 

[I8URVTEC]

You can use your tuner to put in the revolutions per mile and once the computer knows that your speedo will be fine. As far as performance goes I wouldn't worry too much. There is not a lot of additional unsprung weight there. I wouldn't go above 18" though. When you start running 20" wheels is where you start hurting your performance IMO.

 

[Siggy33]

A guy on another forum showed me this site...its pretty cool
http://www.1010tires.com/TireSizeCalculator.asp

According to it, it looks like the best match would be 255/45/18 on the fronts and 285/40/18 out back and that would match almost perfectly - only a .52%and .74% difference from stock.
However they I cannot match any one tiremaker and/or afford any of the tires matching both those measurements. Luckily Falken (GRB FK-451) makes a 255/45/18 and a 275/40/18 for a VERY good price. The rear tire is only a 1.88% difference from stock (and its on sale!)...that is not a big deal right?

Does anyone know anything about those tires? They guy at Big-O really liked them...

 

[nycstang37]

not to hijack the thread here but when you retune for the bigger wheels and tires, do you use the rear or front tire measurement, i know its kinda dumb but i was never sure.

 

[Siggy33]

not to hijack the thread here but when you retune for the bigger wheels and tires, do you use the rear or front tire measurement, i know its kinda dumb but i was never sure.

Good question, add that one to my never-ending list...

If it is the front wheels, I'm gonna throw some different wheels outback.