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Wheel size-gas milage

The difference between circumferences of a 17" wheel and a 18" wheel is about 3" per revolution. Therefore its takes 64 more wheel revolutions of a 17" wheel to travel a mile than a 18" wheel. So will the same car with 18" wheels get better gas milage than with 17" wheels traveling at the same speed?

Wheel size is irrelavant. The tire circumference is the issue. Usually an 18 rim has a shorter profile tire on it than the 17 and many times the final circumference is the same. If the tire is actually bigger then the revolutions per mile theory is true. You can keep your 17s and buy bigger tires but watch out for the fit under the vehicle ; suspension travel and turning radius rub. Your low speed tourque will be affected but you decide which you need most.

First it is the tyre circumference. Second, it will depend on the car and the rout and the driver. Different engine, different gearing, more or less aggressive driver and the kind of driver (rout) that is driven. Expect little difference.

Wind resistance is the biggest factor in gas consumption. That said, the true answer to your question would depend on the vehicle. A modern vehicle will unlikely be affected by a small change in wheel diameter. However, an antique car without an overdrive gear for the highway might benefit slightly from taller tires on the highway.

As a general rule:

If you keep the diameter of the tire the same, increasing the diameter of the rim results in a slightly wider tire. Directionally, this means more mass in the tire and therefore more rolling resistance. However, the difference is small enough that the variation in rolling resistance between tires of different brand / type / styles / etc. have more effect.

Some things to remember:

Worn tires give better fuel economy than new tires - everything else being equal.

OE tires give better fuel economy than tires designed specifically for the replacement market.

Original equipment tires DO NOT as a rule give better mileage. That’s so broad a statement it’s incredible. That’s like saying cars painted silver as a rule rust faster than cars painted blue. Original equipment tires are chosen by manufacturers based on cost and need. Most high-volume affordable cars do not come with top of the line tires.

in fact, I believe most cars come with some of the lowest end tires on the market. Just look at Subaru with those RE-92 bridgestones, I’d rather run summer tires in the winter than those RE-92s

Is super low rolling resistance really a design priority with premium high end tires? I always figured they were designed for “performance”.

Why are people confusing quality and performance?? They are two separate things. You pay for quality, and you can also choose to opt for a quality “performance” tire as well.

Oh, we know the difference, it’s just that a lot of things are only available as package deals. Like trying to buy refinement and luxury in a car without getting a lot of weight and a thirsty engine along with it.

If I recall correctly from a long ago thread, I believe CapriRacer worked as a tire manufacturer or engineer. I suspect there was some valid rationale behind his comment of: “OE tires give better fuel economy than tires designed specifically for the replacement market.”

Still employed by a tire manufacturer - still an engineer.

Comments: I also find it funny that many folks equate quality and performance. The fact is that OE tire are generally the highest quality tires - if you use the measure “consisitency”. However, the tire’s performance characteristics - which is what seems to get the most negative ratings - is something else entirely.

Vehicle manufacturers have to meet a Corporate Average Fuel Economy requirement. One of the ways they do that is by specifying tires with lower rolling resistance. To get low RR, the tire manufacturers have to sacrifice wear and / or grip. If you’ll notice, those 2 items are the ones that lead people to believe OE tires are “cheap”. They are, in fact, not “better” or “worse”, just designed with a different goal in mind.

Most of the time, OE tires are just “OK” for the performance characteristics that people equate to “quality” - usually traction or wear. But sometimes, the vehicle manufacturer specifies very low rolling resistance and one of those characteristics suffers. The Bridgestone RE92 mentioned above is a really good example of how this actually works.

As a side note: Because the requirements for one vehicle may be completely different that another vehicles, the tires will be different as well. You can see ths in the mixed reviews ceratin tire lines get - it all depends on what the specs were for the particular vehicle they came on.

Bottomline: Not enough negative feedback has been given to the vehicle manufacturers regarding the tires they specify. If wear and grip are important, then every time a new vehicle fails to please in this department, the vehicle manufacturer needs to get a letter. (BTW, it doesn’t do any good to send a letter to the tire manufacturer. They already know the problems with the product and the vehicle manufacturer is the customer, not the consumer.)

I think the question was “do 18 inch tires get more gas mileage than 17 inch tires?” Of course it depends upon many things, but with todays cars running an overdrive that they can barely handle, it is doubtful that would increase gas mileage.