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brucepick · 09-13-2008, 03:38 PM

About overall final tire diameter -
Remember that if you change the overall diameter you will need to change your speedometer/odometer for them to be accurate. Or ignore them and use a GPS.

That really doesn't seem practical to me for daily use over the long run.

But there's usually a variety of tire sizes you could use for any given car. They will have different widths and/or wheel rim sizes and profiles (aspect ratio). But there will be several different sizes with the same diameter/circumference that you can use on the car.

Out of those available options, I think the narrowest tire would give the best fuel economy, all other things being equal.

Last summer I went from 197/75-14's to 205/65-15's (all wheels were/are steelies). Same outer diameter. If you look at my fuel log, this summer I haven't been able to match the FE numbers I got last summer. My commute route is different but the overall distance is similar. I suspect my bigger, heavier tires and wheels.

09-13-2008, 03:38 PM	#6 (permalink)
brucepick OCD Master EcoModder Join Date: Dec 2007 Location: Eastern CT, USA Posts: 1,936 Outasight - '00 Honda Insight Team Honda Gen-1 Insights 90 day: 54.18 mpg (US) Thanks: 431 Thanked 396 Times in 264 Posts	About overall final tire diameter - Remember that if you change the overall diameter you will need to change your speedometer/odometer for them to be accurate. Or ignore them and use a GPS. That really doesn't seem practical to me for daily use over the long run. But there's usually a variety of tire sizes you could use for any given car. They will have different widths and/or wheel rim sizes and profiles (aspect ratio). But there will be several different sizes with the same diameter/circumference that you can use on the car. Out of those available options, I think the narrowest tire would give the best fuel economy, all other things being equal. Last summer I went from 197/75-14's to 205/65-15's (all wheels were/are steelies). Same outer diameter. If you look at my fuel log, this summer I haven't been able to match the FE numbers I got last summer. My commute route is different but the overall distance is similar. I suspect my bigger, heavier tires and wheels. __________________ Coast long and prosper. Driving '00 Honda Insight, acquired Feb 2016.