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Old 06-30-2004, 06:53 PM   #1
pgrace
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Member#: 65367
Join Date: Jun 2004
Chapter/Region: BAIC
Vehicle:
2005 Baja Turbo
Regatta Red

Default New wheels/tires

I have replaced my original Baja wheels/tires with 18" x 8.5" SSR comps, 51mm offset, with 235/50/18 rubber (BF Goodrich g-force T/As) inflated to 33psi. The tires started off a bit rough, but with 500 miles on them they have smoothed out considerably, and they seem great. HOWEVER. My mileage (in typical use) has dropped by about 20%, from 25mpg to about 20mpg. Any ideas? I have checked, and there is no interference, although the tires are about 3% larger than stock, and 10mm wider. (Guess that's one way to correct the speedo) The difference seems insignificant to me, although the shift points should be different by 3% (I'm not sure which is right, since the speedo used to be +5%, and the odo was +2%. Now I am speedo +2%, odo -1%)

Has anyone experienced similar problems with slightly larger tires? My tire dealer has no ideas, and thinks I'm wrong. But swapping back to stock gets me my mpg back.
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Old 06-30-2004, 10:23 PM   #2
2003Baja
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Chapter/Region: Tri-State
Location: Pennsylvania
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larger tires change your gear ratio. They make your engine work harder and that results in more gas consumption. Do your 18's rub? I am thinking of getting some 17 inch Kazera rims
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Old 07-01-2004, 10:53 PM   #3
pgrace
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Join Date: Jun 2004
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2005 Baja Turbo
Regatta Red

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I realize the ratio is different, but only 3% taller, so I wouldn't think it would have such a dramatic effect on MPG. (the 235/50-18 is as close as you can get on an 18 inch wheel to stock)

I have no rub, but I would not go to any larger tire. The outside edge at the back of the front tire gets very close to the fender liner during hard turns (about 3/4 of the way to lock). I have about 3/8 inch clearance worst case.

My wheels are 8.5 wide, and I'm sure a 9" would fit for depth. A 9.5 might touch the rear spring when fully extended.

At least for my Baja.
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Old 07-02-2004, 10:02 AM   #4
theoldman
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Seems to me that with larger tires you would travel further with each revolution of the axle and therefore get better mileage. This increase would be offset by more rotational mass -- but not by much if the tires weren't much heavier. Also when computing your mileage you would have to add the percent error back the odometer reading, i.e., you went further than the reading says.

But what do I know?
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