18" wheels heavier than stock?

[72bluNblu]

Not necessarily.

I've heard from a few people that going to larger rims, 17's, 18's etc, hurts performance because the wheels weigh more. Although it's hard to argue that the additional traction from running a wider, modern compound tire isn't worth it, I really didn't buy it. But, I also didn't have any proof other than adding up manufacturer's specs. Until now.

So, what I had to compare was your basic 15x7 police wheel. Nothing fancy, pretty similar to a lot of the stock steel rims. On it I had a 225/60/15 Falken Ziex 512. Maybe not the lightest tire out there, but pretty average at about 25lbs. To compare to that, I had a 275/35/18 BFG KDW 2 on an 18x9" Enkei RPF1. One of the lighter rims out there for sure, but not the lightest. Also, a 295/35/18 on an 18x10 Enkei RPF1. The 18x9 weighs in at 17.1 lbs, the 18x10 at 18.45 lbs. The rims are light for sure, but those are MUCH wider tires.

I found the police wheel and tire to weigh 50 lbs. Definitely not all the light. And then things got interesting. The 275/35/18 on 18x9 weighed in at 45.8 lbs. That's 4.2 lbs lighter per wheel, not a small margin, especially talking about rotating mass. The 295? It weighed in at 49.4 lbs. Half a pound lighter than the little 225/60/15 on a 15x7" rim.

Obviously, not the "end all be all". The RPF1's are very light for their size, so there are no doubt 18's out there that would be heavier. And the Falken's may not be the lightest 225/60/15 you can get. But, considering the difference in tire size, there are more than a few 18" combo's out there that would be lighter than the stock steelies, even running relatively small 225/60/15's.

Just how much bigger is a 295/35/18 than a 225/60/15? A LOT bigger.

 

[1970Duster]

So you lose a little weight but get a much wider footprint and more traction. Sounds good to me!

 

[MuuMuu101]

I've heard from a few people that going to larger rims, 17's, 18's etc, hurts performance because the wheels weigh more.

This is not the case... However, just because the wheel and tire is lighter doesn't mean you're automatically going to have less losses and an increase in performance due to weight alone (not taking into consideration grip, contact patch, compound, sidewall flex, etc). What really matters when it comes to wheels is the mass moment of inertia. Essentially, it's how much energy it takes to revolve an object around an axis. Basically, the farther away the mass is away from the center of an axis, the harder it is going to be to rotate that object. Although your 18" wheel may weigh the same or less as a steel wheel, your tire for the 18" wheel may weigh more than the one for the 15" wheel causing more mass to be farther away from the center. Thus, an 18" wheel vs. a 15" in wheel with the same overall tire size may have a larger mass moment of inertia than the 15" wheel.

That being said, I'd rather have a 17"+ wheel over a 15" wheel any day. There are so many more benefits than the loss produced by rotational mass.

 

[72bluNblu]

This is not the case... However, just because the wheel and tire is lighter doesn't mean you're automatically going to have less losses and an increase in performance due to weight alone (not taking into consideration grip, contact patch, compound, sidewall flex, etc). What really matters when it comes to wheels is the mass moment of inertia. Essentially, it's how much energy it takes to revolve an object around an axis. Basically, the farther away the mass is away from the center of an axis, the harder it is going to be to rotate that object. Although your 18" wheel may weigh the same or less as a steel wheel, your tire for the 18" wheel may weigh more than the one for the 15" wheel causing more mass to be farther away from the center. Thus, an 18" wheel vs. a 15" in wheel with the same overall tire size may have a larger mass moment of inertia than the 15" wheel.

That being said, I'd rather have a 17"+ wheel over a 15" wheel any day. There are so many more benefits than the loss produced by rotational mass.

This is true, but consider that I was not comparing apples to apples with a 225/60/15 vs 275's and 295's.

For example, a 295/50/15 BFG T/A tire weighs in at 32 lbs. Even if you assumed the 15x9 or 10 that you'd need to mount it weighed the same 25 lbs as the 15x7, that would make for a 57 lb wheel. That's almost 8 lbs heavier than the 295/35/18, and I would guess that the moment of inertia would be higher as well.

Sidewalls are not a constant thickness, they taper and carry a lot more weight as they move away from the rim. To truly figure out the moment of inertia you'd need the weight distribution of the tire.

Of course, not all tires are as heavy as the BFG T/A's either. Still, I don't think that the moment of inertia discussion is as clear cut as it might seem on the surface.

 

[1968FormulaS340]

You could take 40, 18" wheels and they will all have a different weight. What you posted shows nothing more than a wheel tire combo that happens to weigh less.

Wheel weight is very often overlooked in wheel selection. What I see there is still heavy, but at least they are marginally lighter...

More thought put into selection could give real gains.

 

[MuuMuu101]

This is true, but consider that I was not comparing apples to apples with a 225/60/15 vs 275's and 295's.

For example, a 295/50/15 BFG T/A tire weighs in at 32 lbs. Even if you assumed the 15x9 or 10 that you'd need to mount it weighed the same 25 lbs as the 15x7, that would make for a 57 lb wheel. That's almost 8 lbs heavier than the 295/35/18, and I would guess that the moment of inertia would be higher as well.

Sidewalls are not a constant thickness, they taper and carry a lot more weight as they move away from the rim. To truly figure out the moment of inertia you'd need the weight distribution of the tire.

Of course, not all tires are as heavy as the BFG T/A's either. Still, I don't think that the moment of inertia discussion is as clear cut as it might seem on the surface.

O, I wasn't trumping your test. I was disproving the the fact that weight is the reason why there's a loss of performance (in an equal weight scenario). All of your points are valid and not everyone swaps for the same wheel and tire width when upgrading wheel size.

 

[briankaplan]

When the UPS guy CARRIED in my set of Weld Pro Stars. He couldn't believe it when I told him that was a set of 4 rims. He said it was the lightest set he ever see/ carried.

 

[mvh]

It should be pointed out that the 15 x 7 cop wheel is considerably heavier than any A-body stock wheel (14 x 4.5 or 14 x 5.5). So your comparison isn't really against "stock", it's big aluminum wheel against big steel wheel.

The other point I would make is that as the wheel diameter increases, the profile of the tire decreases (in order to maintain approximately the same overall diameter) -- the effect of this is essentially replacing air and rubber with aluminum. Which is heavier? Moreover, you are adding the weight out near the circumference of the combo, where it has a much greater effect due to rotational inertia. Forged wheels are much stronger and have the potential to be much lighter, so they can compensate for this issue. But they are also much more expensive.

Lots of factors to consider.