What does the common practice of going to a smaller tire size do to the overall gas mileage? I'm considering going to the original stock size tires for comfort (I don't race and may possibly increase my commute from 30 miles to over 100 mileas a day, round trip) and was wondering if I'll get noticeably better or worse mileage. If worse, I certainly won't bother.

Larger diameter tire = better mpg.

Think about it....if your tire is say 12inch circum. now and your new tire is 24 inch circum., you will double the distance that you go for every rotation of the drive axle/tranny/engine...

This would apply for highway driving more than city driving...

now in a hilly city SF for instance, there could be an arguement for smaller tires....if you need less torque/reving to get the car from a stopped position to moving and going up hill (smaller tire) than you might gain mpg....

So for highway i would say bigger tires...

Rich

Oh yes, moving back to stock will make you some nice economy.

If you use those Pep Boys metric tires, you can burn out in second!


M

[QUOTE=redshift,Feb 28 2005, 07:30 PM]Oh yes, moving back to stock will make you some nice economy.

If you use those Pep Boys metric tires, you can burn out in second!


M[/QUOTE]
[/QUOTE]

I don't feel like I know you well enough to make accusations, but are you being sarcastic? Somehow I just feel like I'm being made fun of

Wait. Now if you're driving on the surface streets, every time you accelerate you're going to use that much more power to get it going. And I=MR^2, so the bigger the smaller the radius, the smaller the moment of Inertia gets. So bigger wheels will be better on the highway, but worse on the streets... unless of course you accelerate slower on the surface streets with smaller tires.

No I am not being sarcastic!

(rare, dun't get used to it...)



M

I am doing the same with my car. I have found that 195/65 x 15 is the best choice in a modern size. Many brands make that size and it is very close to the diameter of the original 165x15, which is made by very few manufacturers now. You get 30mm more width, a lower profile and 195's don't require any adjustments to the rear fender arches. 195/65's have an overall diameter of about 25", stock 165 is about 25.5. The 195/50's that are commonly used are 22.7" or so. Makes the car lower geared, higher rpm for a given highway speed, and therefore fewer mpg.

My current commute is about 10 miles "city" 20 miles "highway" (70mph). If I get the new job, the commute will look more like 10 miles "city" 90 miles "highway" (80mph). Would a minor increase in size be worth it from an economy and ride comfort perspective? I'm currently running 195/60 15s. Opinions?

If you have some room between the tire and the fender now I would go to 205/65's. That will give you the exact diameter (and therefore gear ratio) as stock 165's. The 195/65's are not different enough from what you have to justify new tires, unless what you have need replacing anyway. You will get best ride and mileage with the 205's but they might rub on one side or the other unless you roll the lip.

Tires I have now are nearly new. Probably not worth replacing. Maybe I'll review this post when I need new tires. Thanks for the help!

what kind of mileage are you getting now? hopefully 25-30mpg highway?