Effect of weight on alloy wheels?

Siggyboy · 08-02-05, 04:09

I just bought a set of 17" BBS factory Saab two-piece alloy rims for my Saab 95 Aero. I'm surprised at their weight....about 28 pounds each. I was expecting them to be well under 25. Now I'm wondering whether to keep them or look for something lighter for better handling and steering performance. What do you guys think? Is 28 pounds too heavy for a sports sedan? Should I get some lighter aftermarket wheels?

JDookie · 08-02-05, 05:32

How much do your stock wheels weigh?

SidiousXXX · 08-02-05, 05:36

For that car it doesnt matter. People read too much into that.

Rule of thumb is every 100 pounds you eliminate you can decrease 1/4 mile by 1/10th of a second.

Siggyboy · 08-02-05, 07:23

I don't know what my stock wheels weigh. They are also 17" BBS rims, but have less metal and more spokes, so I'm assuming they are lighter. I wish I could find a website with all the stats on these different wheels!

I'm not so concerned about loss of speed, but more with loss of agility in steering and handling due to the increase in unsprung weight. I'm planning on moding this car to get some real decent horsepower and performance. Although these are quality rims and spec'ed directly from Saab, I'm worried that their weight will detract from the car's performance potential. For instance, I could get SSR GT1 rims that only weigh about 17 pounds, a difference of about 40 pounds total. So am I worrying over nothing? Thanks.

JDookie · 08-02-05, 07:54

40 lbs. is pretty big difference when it comes to rotating mass. I know you weren't talking about drag racing, so that's not where I'm headed.

Actually, in regards to the drag racing, every 100lbs does equate to 1/10th of a second, but that's not rotating mass or "un-sprung" weight, that's curb/static weight which is a different deal all together.

Anyway, in some cases, when going to a performance wheel/tire package, you are increasing the weight without realizing, which is why I as asking how much your stockers weighed. You might start off with a lighter wheel, but most people increase the diameter and width of their wheel/tire, which means you are increasing the size and weight of the tire. In those cases, a lighter wheel is a must to compensate for the much heavier tire in order to bring you back to "zero".

In general, a lighter wheel/tire combo will give you better peformance, hence why race cars use the lightest combo possible. That being said, a lighter wheel/tire will make your car ride rougher for everyday use, and will also be easier to damage. There's a balance here that you have to find.

I asked what your stock wheels weigh because I think, if it were my car, I'd try to stay close to what the stock wheels are, hopefully losing a pound or two. I just wouldn't go *over* what the stock wheels are, which can happen very easily when increasing the size like I mentioned.

Heavier wheels are definitely more stable and more comfortable, which is why lighter wheels are for racing.

Accumulator · 08-02-05, 08:29

Quote:

Originally Posted by Siggyboy

.. So am I worrying over nothing?...

Yeah, IMO you are. I've never noticed any differences from the weight of wheels, at least not on a street-driven vehicle. And on the track there are a zillion variables that'll be more significant anyhow; I've never noticed it there either. On a FWD car you're not gonna notice any difference in steering feel from the difference in what the wheels weigh, just too many other things going on that *do* have a huge effect on that.

Siggyboy · 08-02-05, 09:08

Thanks for the input. JDookie is spot on. There is a trade off, as with most things in life. I wish I knew what my stock wheels weigh, but haven't found out yet. I'm figuring that since the new rims were made for Saab, they have to be ok performance wise, but they do seem heavy. What can I say, I'm anal about my car! At least fellow autopians can sympathize with that!

Lowejackson · 08-02-05, 10:08

The weight of the wheels is often accounted for in setting up the suspension parameters ie rebound rates. Significantly heavier wheels will alter the suspension interactions but is it perceptible - hard to say. If the dampeners are worn, it probably will be noticeable.

In practical terms of day to day driving, you may not notice any real difference

JustinTRW · 08-02-05, 12:04

I would agree that it is relative to the car and it's intended usage. Small changes in a Caterham will be noticeable, but maybe not so on a 4000+ .lbs plus luxury sedan. Reducing unsprung weight is more effective pound for pound in a performance context, but it depends what you are going for and how attuned you are to small changes.

JDookie · 08-02-05, 12:59

Quote:

Originally Posted by Lowejackson

The weight of the wheels is often accounted for in setting up the suspension parameters ie rebound rates. Significantly heavier wheels will alter the suspension interactions but is it perceptible - hard to say. If the dampeners are worn, it probably will be noticeable.

In practical terms of day to day driving, you may not notice any real difference

This is a very good point. Going with too light of a wheel/tire can cause them to "hang" when hitting bumps and pot holes. As far as being on the track, this can equate to loss of control around a tight corner. On the other hand, the same can be said for a heavier wheel/tire that rebounds too fast.

I say screw it, and get the lightest combo you can buy and then go buy a set of adjustable Koni coil overs and be done!

Seriously though, I'm sure your BBS wheels are just fine. There was a period of time where I remember Infiniti offering BBS wheels as an option on the Q45, and I seriously doubt Infiniti would allow a wheel to go on their car that wouldn't work correctly.

G35stilez · 08-02-05, 01:08

I'm a big believer on unsprung weight.

Coming from a 4-cyl owner with low amounts of torque, wheel weights are huge. I went with forged 17's and they have proved to be the lightest I've owned @ 16.5lbs each. I've noticed a big difference changing between wheels that weigh 10 lbs more on each corner. Saab is a VERY hard vehicle to get fitments for. I would just stick with the BBSs.

Siggyboy · 08-02-05, 02:05

Sean, I'm not sure I follow your post. What was the big difference that you felt in changing your wheels? You noticed a big difference? How heavy were your previous wheels? Does your car handle better with the 16.5 pounders? (those are light!!). The Saab is a 4 cylinder too, but has a high output turbo that gives it over 230 hp.