cooper tires and crappy gas milage

[di_LR3_co]

so.. i decided to "step it up" and go from the 265 GoodYear SA to 285 coopers.. it may just be a coincidence, but now my gas milage has dropped from avg of 15 in city to 11.xx

i've got 43K miles.. anyone else experience a drop like this is mpg with bigger tires?

 

[CMGRover]

When was the last time you had a "tune up"?

 

[di_LR3_co]

what do you mean by "tune up"?

 

[blackforestham]

Are the aspect ratio's the same (265/60 vs 285/60)? What psi?

 

[di_LR3_co]

265/60 v 285/65

 

[ryan-in-oregon]

Of course your milage would go down. You get hit twice. 1st - Takes more to get her moving now. 2nd - your speedo is now off the wrong direction indicating even worse milage. Calculate consumption based on miles driven via GPS to check actual usage.
32" tire versus stock 30"!!!!

 

[di_LR3_co]

yeah.. i've been calculating it "old school" and the trip mpg is only off by 1-2 tenths.. (negligible in my mind) ..

 

[umbertob]

Part of the difference is the new aspect ratio of the new tires (about 6-7% larger than the 265s) fooling the computer, which would explain about half of your mpg "loss". The rest is probably a combo of slightly higher consumption due to the wider and more grabby patch of rubber rolling on the road and perhaps a couple of red lights too many... Even in the best of days I only averaged about 15-16 mpg in mixed city / busy L.A. highway driving with stockers on (RRS with 4.4 V8), now that I run on Cooper Zeon LTZ 285/60s I have settled to about 14 mixed, according to the on-board computer... That's about right. If I was city driving only, I'd probably be down to around 11-12 myself.

 

[ryan-in-oregon]

When you fuel up take your (trip milage x1.085)/Gal. The 1.085 is the 8.5% difference in speed due to the diameter difference. This should also give you an accurate consumption reading.

 

[tommithy]

My mileage went down as well when I swapped over to the Coopers. As everyone else is pointing out, you've changed a few things.

The Coopers weigh more then the stock Goodyears. Takes extra power to get them rolling thus you press the pedal down more to get the same accelleration you were used to with the Goodyears.

The Coopers are 1.5 inches taller then the Goodyears. This is throwing your speedometer off and your in-car mileage calculations.

When we first swapped over our city mileage went from about 14.5 down to the 11-12 range. We realized we were trying to drive like we did with the smaller, lighter tires which was increasing our fuel consumption. Now we just drive a little slower/don't accelerate as fast and we are back up to about 13.5 mpg in our city driving.