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Effect of 13" wheels on MPG for a MK1 http://www.teamswift.net/viewtopic.php?f=34&t=44299 
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Author:  Tweedle_Dee [ Sat Jul 11, 2009 1:28 pm ] 
Post subject:  Effect of 13" wheels on MPG for a MK1 
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. 
Author:  robertwb70 [ Sat Jul 11, 2009 9:48 pm ] 
Post subject:  Re: Effect of 13" wheels on MPG for a MK1 
I find it highly unlikely that +1" diameter rims with the same overall diameter tires could reduce mileage by 10 MPG all by itself... 
Author:  90LSI [ Mon Jul 13, 2009 2:06 pm ] 
Post subject:  Re: Effect of 13" wheels on MPG for a MK1 
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. 
Author:  Tweedle_Dee [ Mon Jul 13, 2009 2:25 pm ] 
Post subject:  Re: Effect of 13" wheels on MPG for a MK1 
Ok thanks. I would have expected a slightly increase due to the higher effective gearing. Interesting. 
Author:  nerys [ Fri Apr 02, 2010 10:35 pm ] 
Post subject:  Re: Effect of 13" wheels on MPG for a MK1 
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. 
Author:  1987TurboSprint [ Sat Apr 03, 2010 12:38 am ] 
Post subject:  Re: Effect of 13" wheels on MPG for a MK1 
You have to look at the weight difference too. A heavier wheel/tire combo take more power to move and stop. 
Author:  tecnopolis [ Sun Apr 11, 2010 2:16 pm ] 
Post subject:  Re: Effect of 13" wheels on MPG for a MK1 
Maybe someone should actually weigh a 12" wheel with the standard tire size and a 13" tire/wheel combo to have a measurable standard. 
Author:  robertwb70 [ Sun Apr 11, 2010 4:01 pm ] 
Post subject:  Re: Effect of 13" wheels on MPG for a MK1 
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. 
Author:  sbdeadelf [ Sat Apr 24, 2010 6:52 pm ] 
Post subject:  Re: Effect of 13" wheels on MPG for a MK1 
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! 
Author:  Jetskiracer113 [ Sun Aug 18, 2013 1:48 pm ] 
Post subject:  Re: Effect of 13" wheels on MPG for a MK1 
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. 
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