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Discussion Starter #1
Hi all,
I have been riding with my new winter tires for about a week now. The size is 235/65/18 on the infiniti mags.
I have noticed a great improvement on fuel economy. I am talking like 4 mpg more. Same driving conditions. Can this be due to the 235 width compared to the 265 with of the tire?
thanx
 

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Maybe you are not going as far as the speedo indicates

Since your "new" tires are of a smaller outside diameter your speedometer is indicated that you have traveled farther than you really have. Doing the math you should be traveling 4% than indicated by your speedometer.

Jack
 

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Then why is his mpg up about 30%?
 

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Re: Maybe you are not going as far as the speedo indicates

millsjq said:
Since your "new" tires are of a smaller outside diameter your speedometer is indicated that you have traveled farther than you really have. Doing the math you should be traveling 4% than indicated by your speedometer.

Jack
Actually his new tires + rim 235/65/18 is of a larger outside diameter (thus circumference) than stock(235 width don't matter in diameter measurement - just aspect and rim size - C= pi x diameter or (2 x radius) x pi). Stock for 18s is 265/55/18. The "65" number increases your diameter (thus circumference) and thus your speedo and odo is affected since they are calibrated for stock circumference.

The reason that switching from 18"s to 20"s while keeping the stock tires is ok without recalibration is that the 265/55/18 measurement of the 18"s is very close to 265/45/20 measurement of the 20's w/r/t diameter and circumference.
 

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Discussion Starter #6
it is almost the same radius.
and the speedometer reads the same

265/60/18=100 km
235/65/18=100.6km
I ahve a nav system that tells me the true speed of the vehicle
 

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The reason that switching from 18"s to 20"s while keeping the stock tires is ok without recalibration is that the 265/55/18 measurement of the 18"s is very close to 265/45/20 measurement of the 20's w/r/t diameter and circumference.
Oops. Stock is 265/60/18 for the 18"s and 265/50/20 for the 20"s. So yeah, you're new ones are only a little bigger.
 

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GeoFX said:
The reason that switching from 18"s to 20"s while keeping the stock tires is ok without recalibration is that the 265/55/18 measurement of the 18"s is very close to 265/45/20 measurement of the 20's w/r/t diameter and circumference.
Oops. Stock is 265/60/18 for the 18"s and 265/50/20 for the 20"s. So yeah, you're new ones are only a little bigger.
dude, why you are doing this to me? I never want to be a smart ass man!!!
 

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phamgiaj said:
dude, why you are doing this to me? I never want to be a smart ass man!!!
You must've wrote that at the same time I was correcting my first post. :p
 
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