Rim size & RPM's at highway speeds

[Greg]

I just have plain ol' 13's on my car, and my engine rev's at about 3000 when I'm going 70-75MPH on the highway.

What RPM's are you guys with 15's, 16's, or 17's getting for the same speeds?

I have an 87LX (carbed).

I'll probably be doing more highway and less city driving in the future, and I've been thinking about getting bigger rims just to give myself better highway cruising.

Right now I'm getting like 37mpg going through a full tank when driving from NY to Chicago on I80.,

Do you think I'd get even a little better if I had bigger rims since my rpm's would be lower?

[AZmike]

If you get the right size tire for plus-sized wheels there should be <5% difference in rolling diameter up through 17" wheels.

[crwa]

I have 18"s on my car, and I run at the same rpm's as you do with your 13"s. So don't worry about rims effecting mileage or rpm's, but with less rubber you will feel the highway more and have a different sound from the tires.

You only mess with rpm's and mileage when you start to add aftermarket parts to your motor...

[Jims 86LXI HB]

Originally posted by crwa
I have 18"s on my car, and I run at the same rpm's as you do with your 13"s. So don't worry about rims effecting mileage or rpm's, but with less rubber you will feel the highway more and have a different sound from the tires.

You only mess with rpm's and mileage when you start to add aftermarket parts to your motor...

215/35-18's = 3.1% larger over stock, or 3.1% speedo error
so when your speedo say's your doing 80mph, your actually doing 82.48mph

We don't have a choice in tire size in 18", but proper plus sizing, doesn't go beyond 1%+or- in tire size differances.

These are proper plus size's for the 3g

14"
195/60-14

15"
195/55-15
205/50-15

16"
205/45-16
215/40-16 (still not quite right at -1.8%)
215/45-18 (still not quite right at +1.8%)

17"
205/40-17

18"
215/35-18 (our only choice so you'll have to live with +3.1%)