The affect of wider tires on mileage

[Greg Webdale]

I am considering a wheel upgrade to my new smart car, & would like to find out from others who have made the upgrade, what affect did wider tires have on fuel economy.

My car has 2000 kilometres on it & has been getting 6.9 litres to 100 km. That will improve as the engine breaks in, I expect (as the advertised mileage is 5.9 l/100km.)

[forestacademy]

Edit - Got to get glasses, I thought you said Winter tires

[rfernatt]

No noticeable MPG difference for me with 195/50 all the way around. Check my Fuelly entries for a tank by tank play by play for nearly a year. I swapped to the different wheels/tires this past January.

[sato7]

I saw a huge difference in handling and comfort.. but in mpg I saw a 1 mpg diff.. by the way yesterday I averaged the whole day at over 50 mpg so having wides all around does not noticeably change your mpgs

[Old smart]

I once overheard the owner of of a G&K 450 gasser that he'd wheeled-up and "BRABUS-ized" say that the fat rubber cost him a 13%-15% reduction in mileage. It was pretty fat rubber.

[SmartChip]

Greg, I have Genius 17" wheels and Yokohama S-drive tires,front 195/40's and rear 225/35's. I had to adjust air pressure to 34 lbs front and 42 lbs rear. This change got me back to the same mpg's as the stock wheels and tires. The big changes are more comfort while driving, much more stability,and way better handling. Cheerz, SmartChip

[RussBarnes]

I wasn't the very first (but close) to put four, equal wider tires on (186/60-15's), but I made the change in about March a year ago. Since then I have put about 6,500 miles on mine. I was still going through break-in when I installed them so that wasn't a fair comparison. I also found after changing that my speedo now reads the correct mph, but my odometer reads low. I did a series of calibration runs on the interestate of at least 20 miles to determine that my odometer is now low. So after taking the readings I now multiply the odometer reading by 1.056 to get the actual miles driven. Using that and recording EVERY SINGLE fill up I am one of the higher average mpg users on Fuelly. I avg about 42.3 and have seen the random high 40's once in a while, but those randoms are why I don't look at them, rather the average. Everything else is so superior with the change I made to these Michelin's that I wouldn't care if my mpg fell by 5. I do wish the government would get their noses out of free trade when some of the things they do are shown as being bad and do things like get rid of the ethanol so we could do better.

[pmolink]

Originally Posted by SmartChip

Greg, I have Genius 17" wheels and Yokohama S-drive tires,front 195/40's and rear 225/35's. I had to adjust air pressure to 34 lbs front and 42 lbs rear. This change got me back to the same mpg's as the stock wheels and tires. The big changes are more comfort while driving, much more stability,and way better handling. Cheerz, SmartChip

SmartChip -

I have the same setup as you.

I checked the Yokohama website and it recommends that you go with the car manufacturers recommended inflation values. I just called the place that I bought my wheels and tires from (a certified dealer for both Genius and Yokohama) and they recommended the same: use smart's recommended pressures.

Do you run the higher pressures only for gas mileage considerations?

Aside from rolling resistance, another consideration for larger rubber is aerodynamic drag.

[SmartChip]

Pmolink, I first tried standard pressure for several weeks. MPG's were down by 3-4 MPG"s. I started upping pressure 3 lbs.at a time until the car "felt " the same as the stock set-up. Rolling resistance, braking,cornering,etc. Final proof was achived at the Dragon run. Both dry and wet roads, I was not able to make the car slip or slide on the hairpin turns. I pushed the speed until the E.S.P. system kicked in to assist, which it did. I now have total confidence in the car and tire set-up. I am now happy with all that has been done to my Smart.

[Old smart]

Originally Posted by SmartChip

Greg, I have Genius 17" wheels and Yokohama S-drive tires,front 195/40's and rear 225/35's. I had to adjust air pressure to 34 lbs front and 42 lbs rear. This change got me back to the same mpg's as the stock wheels and tires. The big changes are more comfort while driving, much more stability,and way better handling. Cheerz, SmartChip

Notwithstanding the (re-)presentation of brands of rims and tires for the appreciation of the audience, I just can't fathom the sort of knowledge it takes to raise pressures to those levels for an 1800 lb curb-weight car, just to regain lost mileage. I have a Subaru Outback at more than twice the weight that stands on four 225s with a factory optimum pressure (for both safety and economy) of 30/29 psi front/rear.