Unsprung wheel weight

[whizbyu]

I have steel 15 inch wheels, that weight about 15-16 lbs, and also have a set of 16 inch alloy wheels that are about 16-17 lbs each. I used the bathroom scale.
I assume the tires from the 15 inch tire have more rubber than the 16 inch wheel.
Question is: how does this impact my fuel economy? Is 1-2 pounds more per corner that much of a big deal?

 

[simple_gifts]

Quote:

I assume the tires from the 15 inch tire have more rubber than the 16 inch wheel.


?

Proper tire inflation and type of tire is going to be the mpg factor here.

 

[The_Jeff]

What size tire are on both rims and what does the car call for?

If your overall wheel plus tire diameter is too small, the car will be peppy but buzzy on the highway, but you won't know, because the speedometer will read fast, and you'll look like you're getting good MPG.

But to answer your question, the weight on the outside of the wheel plus tire, effectively the weight of the steel belts behind the tread, matter more for accelerating the mass. But you won't notice this compared to the effect of diameter change.

 

[whizbyu]

Stock is 195/65R15 @ 19 lbs each. Upgraded model wheel fits 205/55R16 @ 23 lbs each.

 

[The_Jeff]

Don't forget the 55 series tire is going to need more structure to hold similar weight. Belts, sidewall stuff.

The 195/65/15s would come out way ahead, IMO, except for looks which are subjective of course.

Cheaper replacement tires, lighter rubber, lighter rims, better ride, longer life, better acceleration (rotation angle of inertia or whatever they call it). Assuming these are fitted to a Cavalier type car the cornering of 16 inchers won't really be noticeable.

 

[Kira]

Hello, The original post mentioned unsprung weight. I believe lighter wheel weight lets a wheel react to bumps quicker-the car is more easily controlled.
I thought handling was the game not mileage.
I'd assume mileage wouldn't be effected by the difference in the mentioned tires sizes. Kira

 

[whizbyu]

Originally Posted By: eljefino
Don't forget the 55 series tire is going to need more structure to hold similar weight. Belts, sidewall stuff.

The 195/65/15s would come out way ahead, IMO, except for looks which are subjective of course.

Cheaper replacement tires, lighter rubber, lighter rims, better ride, longer life, better acceleration (rotation angle of inertia or whatever they call it). Assuming these are fitted to a Cavalier type car the cornering of 16 inchers won't really be noticeable.


VW Passat Wagon TDi, 2005 with 246,000 miles. This is my daily driver. I have a "toy" car for going fast.

 

[antiqueshell]

Originally Posted By: Kira
Hello, The original post mentioned unsprung weight. I believe lighter wheel weight lets a wheel react to bumps quicker-the car is more easily controlled.
I thought handling was the game not mileage.
I'd assume mileage wouldn't be effected by the difference in the mentioned tires sizes. Kira


Yes, better handling, even if you keep your stock suspension and significantly reduce the unsprung weight with lighter wheels and tires your handling will noticeably improve. It is almost a forgotten
aspect of improving handling for street driven cars.

 

[d00df00d]

Unsprung mass affects handling. Rotating mass affects acceleration, braking, and MPG.

Wheel mass is both unsprung AND rotating.

Don't forget that a larger rim has more of its mass farther from the center, so the difference it makes will be more than the weight difference alone would suggest.

In most cases, tires will be the main factor for MPG. Next will be inflation pressure.

That said, for a road car, you should always go for the smallest, lightest rim that will fit over your brakes. It's just better all around. The only possible exception is if you just can't find a good tire for it.

 

[antiqueshell]

Originally Posted By: d00df00d


That said, for a road car, you should always go for the smallest, lightest rim that will fit over your brakes. It's just better all around. The only possible exception is if you just can't find a good tire for it.


Yet the OEM manufacturers insist on selling their cars with huge unneeded "dubs" today, and even if they are aluminum they are huge 18" is common today and the tires are pretty heavy as well.
All because they feel it makes the car look better with the arches filled in...

 

[1 FMF]

f = ma
theoretically it would affect fuel economy but realistically very little if not nil it depends on your type of driving. for strictly highway once at a constant speed you are not accelerating so no impact on fuel economy then, but if you do a lot of stop and go then that is acceleration and might result in decrease in fuel economy... how much and if its significant i dont know probably not since new cars offer similar wheel options and you dont see a different number for city/highway fuel economy on the window sticker.
i would think tire tread type, pressure, and rolling resistance would be more significant Rthan the little bit of weight difference

 

[d00df00d]

Originally Posted By: antiqueshell
Originally Posted By: d00df00d


That said, for a road car, you should always go for the smallest, lightest rim that will fit over your brakes. It's just better all around. The only possible exception is if you just can't find a good tire for it.


Yet the OEM manufacturers insist on selling their cars with huge unneeded "dubs" today, and even if they are aluminum they are huge 18" is common today and the tires are pretty heavy as well.
All because they feel it makes the car look better with the arches filled in...

Well... it honestly does.

But yes, I agree with you. Just another reason why the push for taller vehicles is wrecking things for everyone.

 

[SteveSRT8]

Originally Posted By: d00df00d
Unsprung mass affects handling. Rotating mass affects acceleration, braking, and MPG.

Wheel mass is both unsprung AND rotating.


That said, for a road car, you should always go for the smallest, lightest rim that will fit over your brakes.


Fantastic points all.

Modern cars that were designed with large rims in mind are different, they may perform quite well on OEM 20+ inch wheels. Add the same rims to a car not designed for them and expect a huge mash up of problems from worn suspension parts to dangerous handling, etc...

 

[antiqueshell]

Originally Posted By: SteveSRT8


Modern cars that were designed with large rims in mind are different, they may perform quite well on OEM 20+ inch wheels. Add the same rims to a car not designed for them and expect a huge mash up of problems from worn suspension parts to dangerous handling, etc...


They "may" perform well on cars that were designed for them, but they could perform "better" if they didn't have those heavy wheels and tires. Physics is always a factor.