Rotating Wheel Mass Question?

[Robbie-87plz]

Mahalo Bruce.

Thanks a million for your input Bruce. I'm in the same boat as "gtiblklv", trying to learn about these cars some more. Unfortunately, I already purchased the Bilsteins f&r. So I'm going to have to go with some springs. Any thoughts on the Eibachs? This will all be mated to a ST rear swaybar.

 

[bruce]

Re: Mahalo Bruce.

Originally posted by Robbie-87plz
Any thoughts on the Eibachs? This will all be mated to a ST rear swaybar.

I've never run them, so I really can't say anything about the Eibach's.

After running about every rear bar other then the Adam's, the HRParts N Stuff, IMO, is the unchallenged winner. For a full-on drag race car, the Wolfe might have an advantage.

 

[Robbie-87plz]

Rear LCA's?

What one's are you running/heard opinions on? I seem to be batting 0 for 2 so far. The ST sway bar came with the Bils. I'm thinking that the larger diameter rear swaybar will help point the car towards a more nuetral handling with the stock front bar.

 

[DeltaT]

The typical road racing (RR) rule is that every 1 pound of unsprung weight (pretty much your wheels and tires and portions of all the suspension things that droop down when you jack the car up) is equal to 7 pounds of sprung weight. RR wheels need to be stronger than drag race wheels due to frequent side loadings.

Jim

 

[gtiblklv]

WELL SAID....

 

[Robbie-87plz]

I prefer function over form. Any suggestions, in regards to wheels? I'm thinking KDW next time around w/ rims.

 

[DeltaT]

Wheel Vintiques (www.wheelwintiques.com) has some nice stuff for reasonable prices.

I chose the Billet 90's in 17x8 and 17x9.5. They fit very nicely.
Since it's Northern Cal and it is my second car, I picked the BFG KD tires. You can get caught in the rain and be OK, but they're biased towards dry conditions.

Jim

 

[Robbie-87plz]

Jim, now you know I'm gonna ask to see a pic

 

[UNGN]

I swapped to front runners/3.5" welds from my normal 20+ lbs heavier per wheel radials/T-wheels and picked up about .5 mph in the 1/4 (117.7 to 118.3). I would think a 10 or 15 lbs difference in wheel weight, especially rear wheel weight, would give you less of a difference.

.5 mph is about .05 in ET.

 

[Robbie-87plz]

UNGN, loved what you've done to your car. I'm scared of 3.5" fronts. I'm looking at this from a windy road view, after all, Hawaii has alot of those. Thanks for the input guys.

 

[UNGN]

Originally posted by Robbie-87plz
UNGN, loved what you've done to your car. I'm scared of 3.5" fronts. I'm looking at this from a windy road view, after all, Hawaii has alot of those. Thanks for the input guys.

For a windy road, its hard to beat GTA's. They are only 17 lbs for 16X8's and they are cheap.

I only used the front runner example to show shaving 40 lbs of rotating mass off the front of the car only made .5 mph faster in the 1/4. It would be hard to feel .5 mph, so don't get too carried away trying to save 5 - 10 lbs on wheels. The car will handle better with lighter wheels, but it'd be hard to measure.

I wouldn't go too wide of tire/wheel in back, either. It looks cool, but it hard to get a front tire that's large enough to balance the handling and the car will under steer more than a car on 215/65's.

 

[NJVetteGuy]

Generally, 100 lbs. sprung weight = .1 in the 1/4, and 10 lbs unsprung weight = .1 in the 1/4. I don't remember the exact math, just what the track tells me when I race.

 

[UNGN]

Originally posted by NJVetteGuy
... and 10 lbs unsprung weight = .1 in the 1/4. I don't remember the exact math, just what the track tells me when I race.

Maybe on a really slow, light car

As I stated, I took 40lbs of unsprung weight off the front of the car (where it would matter more) and I picked up .5 mph and about .05 seconds.

This was back to back and not different days/different tracks.

 

[Robbie-87plz]

I'm slowly going about this, as a motorcyclist would...a lil here, a lil there...first starting with a weight loss program for moi.
List I'm thinking of includes:
-lighter starter
-hollow front bar
-1/2 - none capacity windshield washer fluid
things like that...
How does that sound UNGN?

 

[NJVetteGuy]

Originally posted by UNGN
Maybe on a really slow, light car

The car was 3220 w/driver, I picked up .2 from swapping to skinnies(borrowed while at the track) from my heavy stock wheels (saved around 30 lbs.). I need to go back through my logs from 2 years ago and see exactly what the unsprung weight vs. ET was to get an accurate formula, I know for a fact unsprung weight is worth more but have to narrow down the exact #.

 

[BoostKillsStres]

According to HotRod mag:
Many chassis engineers say that if high-speed maneuvering or road racing is in the cards, removing one pound of unsprung weight is equal to three pounds of sprung weight. Though our straight-line Duster won't go autocrossing anytime soon, we'll take the 30 pounds.
http://www.hotrod.com/howto/113_0310_loseii/index1.html

You can find more threads about it if you google for 'sprung weight hotrod'
HTH

 

[Robbie-87plz]

Thanks for that tip Boostkills. Great article btw.

 

[Ormand]

.Discussion of rotating mass
Check the above. Somehow this thread got changed from ROTATING mass to UNSPRUNG mass, and they are completely different. As far as acceleration is concerned, there is NO difference between sprung and unsprung weight, unless that weight is also rotating. For example, the rear axle housing, the front spindles, are unsprung, and non-rotating. Making them lighter will help handling, and maybe ride, but will not affect acceleration. Lighter wheels, tires, and brakes, on the other hand, will improve both acceleration, and handling/ride. The multiplier, as described at the link above, is only about 2, however. Rotating mass at the engine is a little different, since it takes torque out before it ever gets through the drive train, and the gears- but that wasn't part of the question

 

[Robbie-87plz]

Well ORmand, they say ignorance is bliss. I was waiting for you to contribute to this thread (one that I jacked btw) Thanks for chiming in.

 

[Robbie-87plz]

Bruce, can you comment on this?

I got tired of isking having a sort rear spring fall out so went to Coil-Overs in the rear. The QA-1s are nice. I still have my Bilsteins up front, FWIW.

New here, is that a common occurence? Thanks for your time.