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Wheels And Mpg

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I know the general concensus is that a larger diameter wheel equates to less mileage...or is it? I want to go to a 17 inch wheel and new tires, since we all know the OE tires suck. As long as the overall diameter of the tire is +/- 3% of the original 195/55R15 then wouldn't the mileage remain about the same? The +/- 3% of the original tire diameter is considered replacement by most tire shops...it keeps your speedo consistent, or so they say. Does anyone have some experience with this sort of thing?

It is more that the diameter/circumference of the tire that you have to worry about. The concensus is correct - larger wheels generally equal less fuel mileage.

Generally as you increase the diameter of the wheel - you will tend to increase the width of the wheel as well. This will allow for keeping the load capacity the same as you decrease sidewall height. The additional weight of the larger tire/wheel combination along with the increased width generally will pull down acceleration performance and fuel economy. The plus side is generally much better choices in summer type tires, much increased corning grip and improved braking performance.

What about the weight of the upgrades wheel/tire combo? How and to what degree does this effect performance?

As you increase the amount of unsprung weight (amount of weight not directly supported by the suspension) - you increase the amount of work done by the suspension. They have to work harder to keep the wheels and tires in contact with the road.

There is also the performance hit in acceleration with heavier/wider wheels. Not a problem if the car has ample power (Dodge Viper, Covette Z06, etc.) But in something with a little less power - the increase in the moment of inertia from the larger, heavier wheel will pull down acceleration numbers. This also goes toward lightwieght alloys - even though they may be very similar to weight of the OEM setup - the distribution of the mass of the wheel will still generate greater moments of inertia.

Granted - there are always exceptions - but pick at random, wheel/tire combinations that are +2 or larger and place them on most cars - their overall acceleration will suffer while gaining better braking and cornering. For some - that lose in acceleration is a small price to pay for better braking/cornering.

How much will it affect the performance - it varies according to the width and weight of the wheels. Usually it is on the order of every increase in static weight by 100lbs, will drop 1/4 times ETs a tenth. For every 10lbs in extra unsprung weight, ETs will drop a 10th.

What this means for most people - probably not much. To lose a half second in the 1/4 or 3-5 MPG is not a deal breaker.

I have identical mileage with the wider 195/60/14 tires that I had with the thinner stock 185/65/14 tires. 30-33mpg automatic.

Thanks for all the info. I think I'll be switching to a 16 inch wheel, and who knows...the overall weight may be the same as that of the stock 15 inch. Maybe it wouldn't hurt to pull a wheel off now and weigh it. I know tirerack.com will tell you the weight of the wheel and finding out the weight of the tire should be just as easy.

P.S.

This site is awesome and I love my Corolla.

yah tirerack shows the tire weights also.

Anybody know what a stock 15" Alloy wheel weighs? I guess I could just go pull one off and toss the whole thing on the bathroom scale...although I'm not sure how accurate that would be.

Larger diameter wheels also cause speedometer error. It will appear as though you are dirivng slower and have traveled a shorter distance than you actually have.

As mentioned before, I agree, tire width has th greatest negative impact. After that lower profile tire give a rougher ride which wastes energy as well.

16" wheels might be a better compromise and for keep a smoother ride, it might be worth spending an extra $200 on lighter weght wheels if your going to upgrade.

I think I found the right combination. 16" wheel with a weight of 16.3 lbs per wrapped in Kumho ECSTA ASX 205/55 tires. The tires weigh 21 lbs and are a tenth of an inch shorter than stock. All total this combo would weigh 0.2 lbs less than what is on the car and be almost the exact same diameter. Mileage and the speedo should all stay the same or if there are changes they would be so minute you couldn't tell...with the exception of much better handling.

Any thoughts?

if you have good roads then the khumo's will be fine but if you dont then get something else because the khumo sidewalls are too soft and you'll risk bent wheels. Ive had to replace two bent wheels and 3 khumo tires, and they bubble easy too btw.

Try the Falken Azenis ST115s. They have a very rigid sidewall, stick like glue in wet and dry, and are designed to be silent. I can't say much bad about them. Not all weather. 360 treadwear rating may be a bit overdone.