Rim/tire width
 

I have a 2001 civic EX. Right now it has stock 15 inch rim that are 6 inches wide. I have 185/65-15 size tires on it. I'm looking to upgrade to a new set of rims but they are 6.5 inches wide and recommend 195/65-15 size tires. I'm wondering if I continue to use the old 185/65-15 tires on the new rims if I will continue to get the same mpg on the new rims as I am on the old?

You might want to check the specs on your tires. They will usually have a rim width range (i.e., the rim widths that they can safely be installed on). Typically, though, you won't have much trouble upsizing or downsizing .5". If you go too far in either direction, you risk compromising the performance of the tire, but that usually only happens in extreme cases where you stretch or bulge the tire to the point that it loses its bead on the rim. As far as the mpg difference... you'll have to wait and see, I guess.

I went the other way on my wife's car. Your tire size will fit fine on the new rims, but it was noticed that the fuel economy savings was not that great, and her lead foot made a difference too. The car should handle better with a wider tire on though.

"stretching" the tire will reduce sidewall flex. Running the 185 on a 6.5" wheel would have a positive (although inconsequential) impact on economy if the wheels were of equal weight and aerodynamic drag.

There is a point where you have too much stretch, but a 185/65 on a 6.5" wheel will have no issues at all.

Okay, but what about the rim still being .5 in wider. I was hoping that by keeping the same size tire that the .5 wouldn't matter. What are your opinions on that?

The rim being .5" wider won't make a difference in terms of needing new tires. If the wheel was 1" wider or more, you'd likely need a wider tire. Right now I have 155 wide tires on 5" wide rims, up from the stock 4.5" wide.

Sorry I didn't clarify... I meant would the .5 matter for mpg.

What is going to affect your MPG the most is the spokes of the wheel, if your new wheels are more disk like then your old ones then you should see an improvement in mileage, if your new wheels are more like paddle boat paddles then they will hurt your mileage.

There's also the weight difference to consider, as adding weight will increase fuel consumption in city driving.

What about going the other way. I have 225's and would love to go narrower. Any idea on how much narrower I could go. Even a ballpark figure is OK. I would like to keep my current rims only because they are alloys and fairly light, not because they are "aero" in any way. I'd love to fab some "moons" for them though.