reducing unsprung weight

If you're interested in what the effects might be on your car check out:

www.356registry.org/Tech/wheels.html

Just for s$%ts and grins I'm gonna weigh one of my wheels tonight. Just for comparison.

Jerome

Does anyone have experience with the quality of the chrome on the wheels that Tweeks sells?
ed

Tweeks and everyone else sells chrome plated steel Mangel VW and Porsche replica wheels from Brazil. Chrome quality will be hit or miss depending on the manufacturing lot.

Weighed one of my wheels last night: 48.5#!

17X8 aluminum alloys w/ Goodyear 245/35s

Jerome

Could someone please enlighten me on "unsprung"? First, what exactly are we concerned about here - vertical motion or rotational inertia? I had always thought that the primary concern was that getting the wheels to rotate from a standing stop uses horsepower. Reducing wheel weight reduces the horsepower required to get 'em spinning, thus that horsepower goes to moving the entire vehicle forward.

Second, what comprises unsprung weight? Is it just the wheels and tires, or also the brake rotors, or could we say it's "all rotating parts associated with the wheels"?

Thanks.

Bruce, you are correct; lighter wheels will accellerate more quickly and also impose lower loads on the brake system when braking.

For the sake of arguement, unsprung weight is "everything from the spring down", that is, those assemblies in jounce/rebound which impart loads to the chassis via the springs.

So, wheel/tire, spindle, brake rotor and caliper unit, etc. are all unsprung weight.

Bruce, the primary concern here with regards to unsprung weight is the effect that it has on the suspension. As unspring weight increases, it becomes more difficult for the suspension to respond to changes. We want the tire to follow the contour of the road as closely as possible, i.e., the tire in contact with the road rather than bouncing from bump to bump.

Unsprung weight (from my 1966 class in Vehicle Dynamics from General Motors Institute) includes all the above you mentioned, plus half the shock absorber weight, and half the coil spring weight, the other half being attached to the chassis and considered "sprung". I guess that would include half the weight of each torsion bar. As my wife observes, once an engineer, anal retentive for life!

David, you're right about the "halves", but I thought if I mentioned that it would just confuse people...:o)

Actually, it would be only the portion of the shock that moves with the suspension. Now if you have a coil-over spring, that's another matter. I'm not sure how you figure in the weight of the spring, maybe one-half is right.

The issue of "Unsprung Weight" is very important is you are racing the vehicle and "Lap after Lap" is compared to compensate for Ambient Change, Track Temperature and Driving linflunce / Tire Varience.

Most people drive "Fast/Quick" for short periods of time and it may
be in a "Straight Line or Twist Bit".

Neutral is "Best" for Weekend Drivers.

If you want to get serious, consider Tires, Suspension and to make them work a set of Chassis Scales.

Speedsters are Over-Steering Vehicles just like 911 or any other rear engine cars.

Get the Rear Tires to "Grip" and make sure the Front Doesn't Under Steer (Push) and if you can "Drive the Car into the Corner" you've got a quick car.

Unsprund weight is anything "Outside the Suspension".

Check out the Book "How to Make Your Car Handle" or "Race Care Fabrication and Preparation" by Steve Smith. Steve Smith has alot of Booke regarding "Handling".

Good Luck,

Jack Blake

There is a line in the recent movie, "A Perfect Storm" something like, "the captain of a sword boat heading for the open sea. Is there anything finer than that?"

To which I humbly offer, "hitting the perfect apex and reaching for the gas pedal while the poor bloke behind you is still struggling with his braking. Then watching the separation of your car from his as the side G loads grow. Is there anything finer than that?"

Really great sex comes to mind...

Yes, but we're talking about thrills we can get, and also handle ;-)

I remember when "sex was safe and fast cars were dangerous". Eddie

Bruce, try moter trend mag june 2003, There is a great 'insert' that WILL inlighten you to todays 'stuff'on 'rollers' and 'stoppers, GET IT

Thanks Dave K. Engineers are COOL so long as thay can think out of the box. That is what is so nice about these cars. There simple enouhg to be a challenge. :)

I want to thank George for all of his time and GREAT input.