TeamSwift

I have a 1987 Sprint Plus that I bought with 13" metro wheels on it. It has always gotten around 38 mpg with about 80% highway driving. The tire/wheel combo diameter is about 1" taller than the original making speedometer off by about 3 mph at 55 mph. My mpg figure was adjusted up slightly to account for that.

I never thought much about it until I came across this review...

"I bought my first in 1986. Got about 47mpg around town and over 50 on the highway. I replaced the wheels with 13" ones at one point, with low profile tires the same diameter as the 12" originals. This change alone reduced the gas miliage to 37 in town. I sold it to a friend in 1994 and have since owned 3 additional Geo Metros. The Metros never got as good mileage as the 86, only 37 to 40 around town. I attribute that to the Metro's 13" wheels (the fuel injection should have helped)."

Is there any truth to this? Has anyone else experienced this? It doesn't really make sense to me why that would happen.

I find it highly unlikely that +1" diameter rims with the same overall diameter tires could reduce mileage by 10 MPG all by itself...

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1991 Geo Metro 2dr HB 1.0 Auto

When I upgraded to 13's the height was 7% taller and I expected little to no mileage effect what I saw for two years was an increase of of 2.5 MPG. I'd suspect something else.

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1990 Metro G10 5-speed
Econo cam +8 degrees, Miata 14s
54 MPG

Ok thanks. I would have expected a slightly increase due to the higher effective gearing. Interesting.

did you correct for the tire size difference? IE your odometer would no longer be correct.

when I went from 12's to 13's my odo changed by a factor of 1.05 ie I "lost .1 miles every 2 miles.

so when my odometer says I have gone 100 miles I have actually gone 105 miles. IE your FE might actually be UP but because your odo is no longer correct you might "measure" lower.

the difference for me is quite a lot. if we assume 50 mpg for 500 miles 10 gallons

but if the odo is "off" by 1.05 then the the actual distance traveled is 525 miles or 52.5mpg

the lower your FE the "bigger" this difference will be.

You have to look at the weight difference too. A heavier wheel/tire combo take more power to move and stop.

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1987 Chevrolet Sprint Turbo under construction

Maybe someone should actually weigh a 12" wheel with the standard tire size and a 13" tire/wheel combo to have a measurable standard.

I gained about 1 MPG after the 13" swap. I still have the 12's too so maybe I'll weigh them next time I have the wheels off the car, which should be pretty soon.

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1991 Geo Metro 2dr HB 1.0 Auto

I did a different swap.. I got rid of my 12's (which weighed 21.5 lbs each on my scale- in OLD condition) and put on some 155/60/15's (which weighed around 29 lbs each on the same scale). There's a 6% increase in diameter going to the 15's, and I accounted for that in my mileage calculations. I haven't noticed a big change in mileage one way or the other. The 15's do a bit better on the highway, and the 12's probably did better around town, but I didn't notice a difference as my driving is almost always a mix. Just for handling and safety issues I would NEVER go back to the 12's though. Too flabby in a car that's so narrow. And does anyone make a GOOD 155R12 anymore? Having had a blowout in a Sprint, I just don't trust the 12s anymore. (This is one of my pet topics! Can you tell?)
Hope that's helpful!

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85 Chevy Sprint Plus
87 Chevy Sprint Plus
It may only have 3 cylinders and be less than 1 liter.....
BUT IT'S GOT A HEMI!!
XD

When I first bought my MK1 it had 13" wheels on it...needless to say I took them off and put the factory 12" wheels on it.
I should have weighed them but the weight difference was HUGE.