What diameter tires are you using at the moment?

[Big Dave]

LT 235-85Ex16 OD=31.7"

OEM-sized rubber.

[BikerModder]

Low rolling resistance is anything not "knobby". Because of the laws affecting styles of bumpers and tinted windows and everything on up... Bumper law in at least 9" for certain jurisdictions. Tires we go by the manual. A light enough tire-would help in town and a larger diameter would help lower the revolutions (RPM) for touring. I keep hoping a high mileage compound would come out with the 100,000 mile range would be introduced with hopefully the aerospace technology and industrial process. Maybe gray.

[drv2die]

i went from stock 215-45-17 24.5 " to 225-40-18 25.1" didnt notice alot of difference my car is not ideal for fe though

[Vekke]

Originally Posted by cfg83

Vekke -

195/65 15, one size up from stock, about 2+% larger diameter and 1 lb heavier than stock. I don't know of a specific law in the USA that prohibits tire size change. It's more a physical thing of fitting in the wheelwell. I could have fit two-sizes up from stock for a 4% larger diameter, but the tire jumped to 3+ lbs heavier.

CarloSW2

At lest on my lupo I can barely fit even 12% taller with only minimal rubbing on normal driving. I have plans to suggest totally new tire design to them, what I have in my mind. It will have 3 things which will make it ultimate eco tire . But I need to discuss with their techichians if those changes are possible to manufacture like they work on my tiny head... They will also be lighter but thats not one the three things...

[oil pan 4]

Originally Posted by echoRS

Dumb question everyone,
has anyone noted a significant gain in MPG's due to lower cruising RPM's with bigger wheels, in spite of possible losses in aerodynamics and gains in weight?

Very true. On my truck I went from a 235/75/R15 that weighed about 25lb that held 35psi of air to my 31/10.5/R15 that weigh about 40lb and held a max of 50psi of air (I keep about 40 in them) and saw no loss in MPGs. If any thing they went up slightly.
I believe it was due to the better drive ratio and lower rolling resistance from being able to put +5psi in them. (when the truck is loaded I N2 them up to 50psi)
I tested them in combinded city + highway and highway only driving.
The result was unexpected to say the least.

[some_other_dave]

I went about 4% larger than stock. I went from 22.7" diameter (what was listed for one particular 185/60-14) to 23.7" (what is listed for my specific 175/70-14s). Note that tires can deviate from the "calculated" size, which is why getting a specific rolling diameter or revs/mile figure from the manufacturer is more accurate than calculating the diameter from the section width, aspect ratio, and rim diameter.

-soD

[Arragonis]

Skinny 155/65x14s.

[PaleMelanesian]

175/70-13.

They're getting harder to find. Only the base model 1996 had this size, and the 97 went up to 14's on all trim levels.

[Kodak]

Stock size. P225/75R15 (I chose 235 on the poll for closest size).

Different configurations of Canyons were sized differently (I think 205 on the work trucks and 235 for some others).

[oil pan 4]

13s are a dead rim size. They use to be very popular and made in the USA.
Best bet might be to move up to 14s.