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914World.com _ The Paddock _ Unsprung Weight
Posted by: McMark Apr 11 2013, 02:38 PM
I'm getting my alternate-alternate 914 running while my primary car is stripped and on the rotisserie. I'm thinking about focusing on reducing weight in a somewhat reasonable manner. I won't be doing any permanent alterations but what about unsprung weight? This is the area where I want to explore and see what a stock 914 can feel like with minimized unsprung weight. Here's the list of components in my mind to address:
- Wheels
- Brakes
- Torsion bars
What else is out there that I'm not thinking about?
Posted by: Racer Chris Apr 11 2013, 02:47 PM
I'm getting my alternate-alternate 914 running while my primary car is stripped and on the rotisserie. I'm thinking about focusing on reducing weight in a somewhat reasonable manner. I won't be doing any permanent alterations but what about unsprung weight? This is the area where I want to explore and see what a stock 914 can feel like with minimized unsprung weight. Here's the list of components in my mind to address:
- Wheels
- Brakes
- Torsion bars
Struts, rotors & hubs.
Torsion bars are not unsprung wt.
Trailing arms are roughly half unsprung.
Posted by: jhadler Apr 11 2013, 05:13 PM
For unsprung weight, wheels and tires are the easiest to achieve big results with. I'm assuming that this is for a competition car. If so, a set of really light weight race wheels and light weight race tires will make big differences in the behavior of the the car. If this is for the street... Why?
Rotors would make a big difference too, as would calipers.
-Josh
Posted by: Borderline Apr 11 2013, 06:31 PM
I removed about 80 lbs from the car when I switched to 13" wheels and bias ply tires. Wilwood calipers weigh about 2lb each where the stock calipers weigh close to 8 lbs. I machined down the rotors to clear the wheels. I know you're not interested in going this route, but it was a lot of fun.
I'd love to figure out a way to lighten the struts. I'm running shortened struts with the Koni race inserts. I wonder if Bilsteins are lighter than Konis?
I just switched over to Penske rear shocks. They are lighter and mount upside down so the shaft is the unsprung wt as opposed to the shock body.
FWIW
Bill
Posted by: McMark Apr 11 2013, 07:27 PM
Bill, I may end up going that route with this car. As long as I can swap 'road wheels' back on, which IIRC you can.
So why do they have hollow torsion bars? Just for those last few ounces? It does make sense that torsion bars wouldn't be unsprung. 
Posted by: Racer Chris Apr 11 2013, 07:43 PM
So why do they have hollow torsion bars?
The material at the center of the bar does very little work, so it's wasted weight from a performance standpoint.
Also, heat treatment is more uniform resulting in better mechanical properties.
Posted by: ThePaintedMan Apr 11 2013, 09:39 PM
The material at the center of the bar does very little work, so it's wasted weight from a performance standpoint.
Also, heat treatment is more uniform resulting in better mechanical properties.
Chris, your mechanical nerdiness never ceases to amaze me!
Posted by: ChrisNPDrider Apr 13 2013, 11:12 AM
Wilwood calipers 
If you get the parts and machine work sorted for the front Wilwood adapters, calipers, and rotors (drilled are lighter, but beware of safety debate) that is an awesome route to drop pounds. Others in NorCal (me!) would find the $$ to go this route with your parts. Bill C's streetable AX 914 is awesome 
I noticed a HUGE difference with needle bearing suspension bushings vs. old rubber. Lots of the benefits of low unsprung weight are realized w low friction on these pivots.
Dream parts: carbon fiber rotors, titanium studs and lug nuts!
Posted by: Borderline Apr 14 2013, 12:28 PM
Wilwood calipers
If you get the parts and machine work sorted for the front Wilwood adapters, calipers, and rotors (drilled are lighter, but beware of safety debate) that is an awesome route to drop pounds. Others in NorCal (me!) would find the $$ to go this route with your parts. Bill C's streetable AX 914 is awesome
I noticed a HUGE difference with needle bearing suspension bushings vs. old rubber. Lots of the benefits of low unsprung weight are realized w low friction on these pivots.
Dream parts: carbon fiber rotors, titanium studs and lug nuts!
I guess in full disclosure it should be noted that my car is pretty much a dedicated AX car. I basically drive it to and from the AX with very little other driving. The light wt brakes and smaller rotors may not be advisable for high speed driving that requires repeated high levels of braking.
Trekkor was able to put some 13" steel wheels on his car without cutting the rotors down, but they need spacers and very small backspace numbers and flairs.
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