Unsprung weight question
02-17-2006, 06:19 PM
#1
Instructor
Thread Starter
Unsprung weight question
Hi all, been a while since i've been on rennlist, moved on from my 993 to a lhd '99 GT3 a year ago.
I'm thinking of changing the alloys on my GT3 Mk1.
I want to minimise unsprung weight.
I've read in the past (although can't remember where) that 1kg of unsprung weight saved is like saving 4 kg of sprung weight.
Lighter wheels (as long as they are strong enough for use, like the BBS LMs, Kinesis etc) are therefore a good thing.
When i think how much weight Porsche take off a std car and then call it an RS, seems a no brainer to save unsprung weight.
Anyone got any views of the 4:1 above?
I do know from experience that i ruined the feel of my old 993 by going from light porsche wheels to heavy aftermarket 18s.
Cheers
Ajit.
I'm thinking of changing the alloys on my GT3 Mk1.
I want to minimise unsprung weight.
I've read in the past (although can't remember where) that 1kg of unsprung weight saved is like saving 4 kg of sprung weight.
Lighter wheels (as long as they are strong enough for use, like the BBS LMs, Kinesis etc) are therefore a good thing.
When i think how much weight Porsche take off a std car and then call it an RS, seems a no brainer to save unsprung weight.
Anyone got any views of the 4:1 above?
I do know from experience that i ruined the feel of my old 993 by going from light porsche wheels to heavy aftermarket 18s.
Cheers
Ajit.
02-17-2006, 06:47 PM
#3
Instructor
Thread Starter
Mine's a mk1, not sure ceramics are avaialbe - plus they'd be too expensive for track use.
Most of the guys in the UK with Ceramics on their GT3/RSs take the ceramics off and put steel ones on. The warranty in the UK doesnt cover the ceramics
Ajit.
Most of the guys in the UK with Ceramics on their GT3/RSs take the ceramics off and put steel ones on. The warranty in the UK doesnt cover the ceramics
Ajit.
02-17-2006, 07:59 PM
#4
Burning Brakes
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Not sure the 4:1 comparison is really relevant. Yes, there is some small flywheel affect from reducing rotating upsprung weight, but the real advantage is in handling as the lower the unsprung weight, the closer the wheel can follow the undulations in the road. That's the real advantage.
Lighter wheels, lighter tyres (there are variations in weight), titanium lug nuts, lighter dampers, lighter brake rotors, lighter callipers and then things start to get really expensive with custom parts such as half shafts, hubs, etc.
Stephen
Lighter wheels, lighter tyres (there are variations in weight), titanium lug nuts, lighter dampers, lighter brake rotors, lighter callipers and then things start to get really expensive with custom parts such as half shafts, hubs, etc.
Stephen
02-17-2006, 08:04 PM
#5
Rennlist Member
I do not believe there is a general mathematical formula to relate savings in unsprung weight to sprung weight. I expect race car designers and high level teams have an estimation process but those would be model specific. Knowing that it is beneficial to reduce the unsprung weight shall have to suffice.
The disadvantages of a lighter wheel are that it is typically less reliable as it is fragile and the materials are much more expensive. Fragility is a trade off with mass reduction. 1. material fatigue due to minimum material 2. designed to handle lower peak forces (loadings) such as when one hits a curb with the tire/wheel
Brake components. Many modifications involve more massive brakes to increase stopping power but the least expensive mods of this type usually add unsprung weight. So... if one has the funds an iron disk with light weight hat, PCCB, or carbon ($$$$) are options.
The disadvantages of a lighter wheel are that it is typically less reliable as it is fragile and the materials are much more expensive. Fragility is a trade off with mass reduction. 1. material fatigue due to minimum material 2. designed to handle lower peak forces (loadings) such as when one hits a curb with the tire/wheel
Brake components. Many modifications involve more massive brakes to increase stopping power but the least expensive mods of this type usually add unsprung weight. So... if one has the funds an iron disk with light weight hat, PCCB, or carbon ($$$$) are options.
