996toomey

I have a 997S with the Carrera Sport wheels. I was looking at these wheels

http://www.wheelenhancement.com/getp..._137_White.jpg

http://www.wheelenhancement.com/getp...137_Orange.jpg

which are close to 10lbs. lighter for the rears not sure on fronts but lighter.

This seems like a huge amount of weight. Would a novice or fairly new driver be able to tell the difference and what would the advantages be with the lighter wheel?

Thanks.

PsyD4Me

The rule of thumb is that a 1lb reduction in unsprung weight has a comparable effect on performance as an 8lb reduction in sprung weight. How true that feels in actual practice I cannot say. I would imagine though that the change in gyroscopic force due to the lighter wheels should be noticeable. My .02

Jon70

It also depends on the distribution of the weight. For example, with wheels, weight at the periphery requires more force to get moving than weight at the center. So, a dymag wheel with similar weight to an aluminum wheel should perform better than the aluminum wheel. The weight distribution of the dymag is more favorable, given the barrels being CF.

340Elise

Are you sure about that? I thought it was closer to 4 times, but not 8?

Also, there is a difference between unsprung mass and unsprung rotational mass. The brake discs and calipers vs. the wheels would have a different affect. I realize you did mentione the gyroscopic effect, but either way, 8 lbs seems kind of high to me. If I saved 50 lbs on wheels and brakes (this is possible since I have the stock GT3 brakes and wheels), then this is supposed to be the equivlent of 400 lbs of sprung mass???

If that is true, then I am definetly getting new wheels.

lawjdc

David Donahue explained it as 3lbs at PDE

sheep911

this might help...http://en.wikipedia.org/wiki/Unsprung_weight

SpeedGeek

Low unsprung weight is good because it helps the suspension react more quickly to bumps, etc. So the car rides with more compliance and the wheels stay planted to the ground better.

Low rotational mass, whether sprung (flywheel) or unsprung (wheels, brakes), helps the car accelerate better because less engine power goes to spinning those parts. And as Jon70 said, spinning parts are worse still if their weight is concentrated far from their spin axis.

///Mous3

it takes a net force to change momentum.
Sice momentum is a vector quantity, a change can either be in terms of direction or magnitude.
Momentum is the mass multiply by the velocity.
To reduce the amount of force require to change the momentum, you reduce the mass.

C.J. Ichiban

short answer is yes you will be able to feel it.


where and how?

when you hit little bumps in the road, you will feel less impact. if you drive hard on the street or even occasionally on the track- you'll probably feel this the most in mid corner bumps, but your freeway driving will be much more pleasant.

pros can certainly feel the difference when rapidly changing direction, accelerating and decelerating. I really notice the weight change of the PCCBs to the Steel rotors which I imagine would be comparable to losing wheel weight.

If you can feel the difference in steering between having a 1/4 tank and 1/2 tank of gas- you're noticing that the car is at least 50lbs different of sprung weight in the front of the car (gas is about 8.5lbs /gallon iirc). If you can feel that- you'll definitely feel wheels or brakes that are 20-30lbs lighter.

340Elise

A passenger in my Elise or Exige was like night and day; those are the only cars that I owned that had that effect. But 50 lbs less of fuel I really could not feel in those cars, and certainly not in a 3000 + lb GT3.

I believe that the pros can tell the difference, but I also believe that some "think" they can feel the difference, but it is more in their mind than anything. Still, reducing weight is a good thing, and if you can get rid of enough to add up to 100 or 200 lbs, then you are really talkin'!

C.J. Ichiban

340- I've had fat (250lb+), medium (210lb) and skinny passengers (~175), and I can feel the difference...the car just reacts that slight touch slower on turn in, and needs more room to brake...must just be the hand-eye coordination and feel I have, but if I can tell the weight difference in my glove if it's a bit humid and soaking up water, or in a lighter baseball...maybe that's why I can tell the weight difference.

but hey driving 3700 miles in less than a month in a car has a way of melding man and machine a bit faster...


but anyway the point of the thread- you will be able to tell if you get lighter wheels.

SpeedGeek

I can definitely feel the difference with and without a passenger. And I can also definitely feel the difference with a full and empty tank. (I'm talking about street driving.) But I live at 6000 feet where power and torque are in short supply.

I am very sensitive to how my car feels. I can tell you with some accuracy how a barometer reads on any given day based on how my engine feels.

340Elise

I believe you, and as I wrote, 100 or 200 lbs is significant. I was talking about 50 lbs difference in a GT3 (or a 1/4 to 1/2 tank difference in fuel). As a pro athlete I can believe that you can tell, as can many others on a passenger. I probably could too if I do a back to back and really pay attention, but for the most part it takes at least a 7 to 8% in weight difference before I really begin to notice the difference. And btw, I am not that observant; with many things in life!