Gas Mileage Differance With Upsized Tires

[chappy]

I'm planning on upsizing the tires on my '02 (stock suspension) I'm thinking about 245 70 16's. How much of an effect on gas mileage did you guys notice when upsizing? I'm going AT not too nobby.

Edited April 19, 2007 by chappy

[94extreme]

i went from 29' ATs to 31MTs and i may have lost a mile or two. may..

[XPLORx4]

First thing you should do is take into account any speedometer accuracy errors introduced by changing your tire size. A 245/70R16 tire is 29.5" in diameter. What size are the tires currently? Let's say they're 245/65R16, which are 28.54" in diameter. The new tires are about 3% larger (29.5/28.54=1.03). So, your speedometer would read 3% too slow, your odometer would read 3% too low, so your MPG would seem to be 3% lower.

 

Basically, for every 100 miles you drive, your odometer would only read 97.

 

Run the actual numbers for your current tire size.

[94extreme]

^^^ yeah, it's actualy exponencial.. B (precise) posted a "chart" of speeds/tires a while back somewhere here last year.

[XPLORx4]

^^^ yeah, it's actualy exponencial.. B (precise) posted a "chart" of speeds/tires a while back somewhere here last year.

 

Actually, "exponential" is not the correct term. The % difference in tire size is constant, not exponential. You may be confused by the difference between reported speed and ACTUAL speed, which does increase the faster you go:

 

Speedometer @ 25mph + 3% tire size error = 25.75mph ACTUAL

 

Speedometer @ 60mph + 3% tire size error = 61.8mph ACTUAL

 

Speedometer @ 80mph + 3% tire size error = 82.4mph ACTUAL

[Trancebear]

I have 245/75/16 on my 2003 and it seems my gas mileage is the same crappy MPG it always is. According to my Garmin GPS NAV my speedo reads the correct MPH even with the taller tires.

[90seven]

I went from 29s to 31s as well. Same with mzxtreme, I lost the same amount of miles to the gallon, but it was expected. My speedo actually became more accuate. With the 29s at 65+ MPH, the speedo would read ~ 3-5MPH more than the actual. Ex. Speed 60MPH, Speedo 64MPH. As I go faster, the difference becomes a little more greater. Haha, I used to like it. Gave me the feeling that my rig can haul a__.

[Damn Yankee]

Can anyone tell me if the 2WD and 4WD can run the same size tires on stock suspension? I have a 2wd R50 and will be getting tires soon, and wanted to bump up a size.