Shaving wheel weight

[C4Bird]

How much performance gain, acceleration and stopping, would one gain by shaving 2, 3 or even 5 pounds off of each wheel/tire set?

-Nate

[andrewb70]

Nate,

I am not sure that there is a definite answer to this, because each vehicle is different. However, I have heard a rough rule of thumb, that removing one pound of unsprung weight is like removing five pounds of sprung weight.

Andrew

[C4Bird]

Thanks Andrew. Trying to decide if $800 a piece forged wheels are going to be that much of an advantage. So if I can shave 20 pounds of unsprung weight (5 from each wheel), it would be a gain of a tenth in the quarter as well as a more nimble feeling to the car. Hmm....

-Nate

[baz67]

Better responce to changes in motion of the wheel i.e. suspension movement, cornering, acceleration and braking. Think of it this way, take a weight of some sort and hold it at arms length. Then move it up and down quickly while ignoring the ridicule that you friends give you when they see this. Now do the same thing with a lighter weight. You should feel the differance in the force needed to change directions.

You will also reduce rotational inertia. Energy increases exponentialy to mass and velocity. That means less mass going round and round requires less braking and less HP to change. That leaves relatively more brake to slow and HP to accelerate your car.

Weight, like power, have diminishing returns. The more(power) or less(weight) you want the more you will need to pay to get there.

[KWIKND]

If what Andrew said is true, 5:1, then I would think rotating unsprung weight (wheels, tires, axles) would be that much more important.
Does anyone have a rule of thumb formula for that?

Dan

[sinned]

Now lets throw this into the mix....take (2) 20 lbs wheels, one is a 17" and one is a 19". The 19" wheel although has the same unsprung weight as the 17" wheel has more rotational inertia and therefore reacts the same as a heavier wheel. Add that to the list why of "bling" wheels are bad.

[dipren443]

Dennis68 mentioned a great point as well. Diameter has a huge factor in the rotational inertia of an object, and it's not linear, its exponential. Another great rule of thumb to follow is to use the smallest diameter wheel available that will clear your brakes.

[C4Bird]

So as we increase our brakes and wheel sizes, we are creating more rotational inertia, but in the hopes of better performance. Obviously larger brakes help out when set up correctly, but I had only thought going too big on the wheel would only hurt your drivability and track ability. It all is starting to make sense now. I always wondered why GT-1, formula one and others ran the wheel sizes they do. A harmony of handling and physics. So if I could lose 10 pounds off the rear axle and 20 off each side of the front, not to mention 5 off each wheel, the car is going to be a completely different animal. I need to get back in the garage.
-Nate

[andrewb70]

Please don't assume that my formula is right. Its just a rule of thumb. I am sure there is something more accurate out there. The other big thing to consider is tire weight. Go on tirerack.com and compare the weights on the tires. You will quickly see that going big and wide add weight very quickly. Most 18 inchs wheels will swallow the most aggressive brake setups that are available. Going larger than an 18 inch wheels is rarely worth it. Going with the lightest wheels you can afford is also worth it. My Kinesis 18x10.5 rears are about 22 pounds.

Andrew

[DarkBuddha]

I was just doing some research on the wheels I'm planning to buy, and I was kinda shocked at how heavy they are... 26lbs. each. Ouch, right? Well then I was looking at tire weights on top of it... OUCH!!! The "little" 245/45/17s I'm planning on are 24lbs each. But I know some guys are running mammouth 315/40/19... guess how much they weigh... approx. 33lbs each depending on manufacturer. I guess that's not bad when you add it to a light weight 18 or 19lbs. wheel, but add it to the typical reasonably priced wheel (26-30lbs.), and that is damn heavy. There's gotta be a breaking point in the performance to weight to price equation...

[C4Bird]

Buddha, That is exactly what I was looking at when I started my wheel planning. Using reasonably priced wheels and tires (reasonable being around $300 a wheel, $200 a tire), I was ending up with about 48 pounds per wheel/tire. Going with a 2 or 3 piece forged wheel is going to save me 3-5+ pounds, but at nearly double the price. Is the performance gain really worth it? I could take that $1200-$1500 extra and put it in nicers seats, engine upgrades, you name it. I guess it comes down to , if you are not racing the car every week, will you really feel the difference from a set of lighter wheels? We all know there are definate gains, but are they noticable? Does springing for the nicer/lighter wheels really make sense to the hobby racer?
-Nate

[DarkBuddha]

Using reasonably priced wheels and tires (reasonable being around $300 a wheel, $200 a tire), I was ending up with about 48 pounds per wheel/tire.
My definition of "reasonable" is a bit cheaper than those numbers... Heck, I just bought the wheel/tire combo I wanted and they were $250 for the set of 4. Yep, you read right... 4 17" wheels with 245/zr45 Goodyears for $250. Their used, but totally mint and the tires only have 8000 miles on 'em. Should be good for another 10K-12K before they're done.

Anyway, I was thinking sub $200 per wheel, sub $150 per tire, is "reasonable". That way I figure you could actually shoe your car for $1000-$1400 as opposed to your $1600-$2000. I figure 50lbs. is reasonable for a 17"-19" wheel/tire combo. If you can do better, all the better. Otherwise, I say spend your coin elsewhere... especially if the difference is $1200-$1500. That's a set of heads or a heck of rear end rehab!

[C4Bird]

I hear you on the rear end rehab, just shelled out $1000 just for the carrier and axle sticks, not to mention the 40 hours of modification to get a 5 link in the back of an f body. Can you get me a pair of 17x11 for that price? :)

[DarkBuddha]

I hear you on the rear end rehab, just shelled out $1000 just for the carrier and axle sticks, not to mention the 40 hours of modification to get a 5 link in the back of an f body. Can you get me a pair of 17x11 for that price? :)
Yeah... no. 17x11s are gonna be a bit spendy. And it sounds like you've spent more on your rearend than I did on my entire car at this point. :jawdrop:

[C4Bird]

So did I, only paid $600 for the car. Ha ha! Maybe I will just save up the money for the better/lighter wheels. I see your point on saving the cash and sinking it into the engine or other stuff. But I haven't spared expense on the other parts so far, best to keep with the plan, especially since it's what I want to do in the end anyway.

Andrew, you happy with Kinesis? I was thining along the lines of Fikse, but have very little personal experience with Kinesis. Is there any cost/quality difference between the 2?
-Nate