When you change your rims(size, width...), does it affect your m.p.h or how many miles you get to a tank?

 

I don't know about losing MPH or MPG but your speedo can become off because of how many revolutions the bigger or smaller the tire is doing, is going to be different than your stock tire.

 

Thats what i thought too, but my friend told me it affect the mpg.

 

It can because if the outer tire diameter is larger or smaller than stock, it changes the gear ratios....so certain speeds may be higher or lower RPM's than you used to have and that can affect the MPG's. It'd have to be a big difference in diameter to truly cause any major MPG changes though.

 

Changing wheels and tires won't affect your *true* fuel economy, unless your new setup is significantly heavier or lighter than your old one, but it will affect the *reported* fuel economy from the car's computer.

The width of the rim doesn't matter at all, and the diameter of the rim itself doesn't really matter either. What matters is the diameter of the new tire compared to the old one:

If you go with tires that are taller (larger diameter) than the old ones, your speedometer will read lower than it used to for any particular road speed, your odometer won't rack up miles as quickly, and your computer-reported MPG will be lower.

Everything's opposite with tires that are shorter than your old ones - speedometer/odometer/fuel economy readout will read all read higher than before.

There are lots of applets on the web that will tell you the percentage speedometer change when switching from one tire size to another. The percentage changes for the odometer and fuel economy will be the same. Google "tire calculator" to find the applets.

 

With the exception of dramatic wheel diamter changes, like 15-19 where the position from the center of the spinning mass changes - this is true! (properties of centrifical force robbing power)

Alex

 

Here's what I've experienced, I drive an 05' MC non S.

I use gps for speed as my speedo is 3 mph off.

running 225/50 17" MPG was reduced on adverage by 3-4 mpg and top speed was reduced by as much as 10 mph from stock size.

Running 205/50 15" MPG was increased by 2-3 mpg and top speed was reduced by 3-4 mph from stock size.

Go either way (shorter or taller) and you move away from optimum gearing. BMW (IMHO) did a pretty good job with the gearing on the Mini.

 

A comparison of the above-
225/50-17 fits rims 6-8" wide, 25.9" tire diameter, 807 rev per mile

205/50-17 fits rims 5.5-7.5" wide, 23.1" tire diameter, 899 rev per mile

vs stock
205/45-17 fits rims 6.5-7.5" wide, 24.3" tire diameter, 858 rev per mile

A wider rim itself is not affecting mpg directly unless it's weight is drastically different than a similar less wide rim. Very light rims are easier to change speeds during acceleration and braking.

A taller diameter rim (17 vs 15") by itself will not affect mpg unless it is mounted on a tire of other than stock tire diameter (and has the same weight considerations).

Wider tires mounted on any rim wide or not will increase rolling resistance and decrease mpg and the weight of the tire itself can vary.

Your true mpg is whatever it is given the car and wheel setup but the speedometer and odometer can be tricked into displaying numbers that are a little higher or lower than actual. A smaller diameter tire will make more revolutions per mile and display a speed that is slightly higher. It may wear out a little faster as well and increase wheel gap when using a stock suspension.

A smaller diameter tire can be mounted on various size diameter rims. Tire size should match wheel size so the two are interrelated and limited by the size of the MINI wheel well opening and suspension clearance.

So the OP asked-
When you change your rims(size, width...), does it affect your m.p.h or how many miles you get to a tank?

Changing rims alone diameter or width does not need to change mph if the tire size is kept close enough to stock size by width or tire diameter. But if you do change tire size then it can be affected. Changing width of the rims alone will increase rolling resistance to some degree but most of the time the difference is small unless you look at extremes.

My stock 15x5.5" rims and stock 175/65-15 tires can get about 3 mpg more than stock 17x7 rims and 205/45-17 non runflat tires on the same MCS driving the same roads on the same gas. The biggest difference is rolling resistance and weight is reduced by the narrow 15" tires/rims.