Tires + Fuel Economy?

[walter]

Ok so we all heard that you gotta keep the tires aired up for optimal fuel economy. But what about changing wheel/tires?

I was thinking about going with a nice staggered 18 inch setup with some fat tires on there but will that hit me fuel economy wise considering I have stock 18's now?

 

[kooldawg6]

I stayed with 18s, but went staggered. The front tire size stayed nearly the same going from a 235/50 to 255/45 while the back grew 1.2"(235/50 to 295/45). I've actually gained 1-1.5 MPG since my RPMs dropped by around 200-300. I can also cruise 85 MPH @ 3000 RPM which is nice considering the 4.10s in my automatic.

 

[Art161]

How do you compute the difference in mpg when you switch tire sizes? The change in tire size is going to change what the speedometer (and the odometer) shows. So if you don't make some kind of correction, it seems to me that you are not going to get an accurate indication of change in mpg.

 

[kooldawg6]

I changed the revs per mile with my SCT tuner.

 

[walter]

I can't seem to find how to do that on my SCT tuner how do you change parameters and such?

Oh I'm thinking about going with Black Chrome FR500's on my car (255 and 275 staggered). And later getting some polished/black GT500's (255 all around) as a backup set.

Now if I could only just get rid of this set of wheel/tires that I have in my garage I can start ordering away

 

[kooldawg6]

Go into the custom tune program and scroll thorugh and you will see the various things you can change. I can't remember what the first step is after hooking up the tuner It's something I just do and can't repeat it while not actualy doing it at the same time... Once in the tire revs per mile, you select the closest to your tire(incriments of 5).