Unsprung weight
Discussion
I'm thinking of changing the alloys on my GT3.
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 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.
singh911 said:My non-technical understanding is that saving 1kg of rotating unsprung wieght is like saving 5 kg of sprund weight. It would matter whether the weight was at the centre of the wheel or at the rim.
I'm thinking of changing the alloys on my GT3.
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?
They're dear, but have you considered the Mnnthey magnesium wheels? They are the lightest TUV-approved wheels around, and specifically meant for 996s.
A couple of websites... suggest different ratios from between 2:1 to 10:1...
www.audiworld.com/tech/wheel13.shtml
http://victorylibrary.com/mopar/sprun
And these suggest that the ratio varies:
www.answers.com/topic/unsprung-weight
www.rqriley.com/suspensn.htm
Logically, I suspect that the answer is that it does, indeed, vary. Afterall, the sprung weight of the GT3 to the unsprung weight of the GT3 would be very different to the equivalent of a Mustang. The ratio would be different for every car variety out there... But one thing seems evident: that for the same car, the higher the ratio of sprung to unsprung weight, the better.
www.audiworld.com/tech/wheel13.shtml
http://victorylibrary.com/mopar/sprun
And these suggest that the ratio varies:
www.answers.com/topic/unsprung-weight
www.rqriley.com/suspensn.htm
Logically, I suspect that the answer is that it does, indeed, vary. Afterall, the sprung weight of the GT3 to the unsprung weight of the GT3 would be very different to the equivalent of a Mustang. The ratio would be different for every car variety out there... But one thing seems evident: that for the same car, the higher the ratio of sprung to unsprung weight, the better.
The unsprung mass affects the grip and handling because it determines how well the wheel follows the road. It's very hard to quantify the effect though. Rotating unsprung mass also affects the straight line performance because it picks up rotational energy as well as translational energy. This is easier to quantify, and up to 5:1 might be realistic, but if you are only talking about saving a few Kg on a heavy car the overall effects will still be small.
Stretch your arm out and wave it quickly from side to side. Then hold a bag of sugar, (or lentils for the more health conscious amongst you) and do the same. Can you feel how the hand wanted to carry on travelling in it`s original direction and you had to use more force to change direction back the other way ?
well that`s what the suspenion has to do with heavier wheels. The lighter the wheel the more in control the suspension is. As the bumps throw the wheel upwards into the car the suspension can push it back onto the road.
So endeth the ladybird guide to heavy wheels book 1
Porsche actually fit quite light wheels as standard. 964 owners for instance have a real easy way of saving unsprung weight. Fit a set of design 90`s...... !
Henry
well that`s what the suspenion has to do with heavier wheels. The lighter the wheel the more in control the suspension is. As the bumps throw the wheel upwards into the car the suspension can push it back onto the road.
So endeth the ladybird guide to heavy wheels book 1
Porsche actually fit quite light wheels as standard. 964 owners for instance have a real easy way of saving unsprung weight. Fit a set of design 90`s...... !
Henry
So there you go, fit design 90s to your GT3 and the some nice light weight thin tyres, get rid of those big heavy discs and calipers, IIRC 924 brakes can be made to fit, et voila low unsprung weight so obviously superior performance.
MMC spend £2.5k+ 0n lightweight mag BBS wheels and then put cheap tyres on to save a few quid
MMC spend £2.5k+ 0n lightweight mag BBS wheels and then put cheap tyres on to save a few quid
Thank you Gents, thats great info.
The GT3 mk1 std alloys weigh 11.5F/13.1R.
By way of contrast, the BBS LMs are 10.6F/11 R.
Using a 4:1 ratio, I would save 24Kgs.
Given that Porsche went to great lengths to shave 100kgs off a Carrera 2 in the past to make an RS, it seems a good thing to do.
The Mathey BBS Mags are too expensive and i wouldn't want to have to maintain them.
However, the BBS LMs are around £2k.
For similar money, the lightest wheel seems to be the Kinesis K-28 or the Fikse FMs. These save another 12kgs off against the BBS LMs.
Does anyone have any thoughts or opinions on these? There were some issues with cracks in the US (on hte Rennlist forums) a couple of yrs ago with these. What concerns me about these is i'd have to source them from the US which may make it difficult to service/repair/maintain them over here.
Cheers
Ajit.
The GT3 mk1 std alloys weigh 11.5F/13.1R.
By way of contrast, the BBS LMs are 10.6F/11 R.
Using a 4:1 ratio, I would save 24Kgs.
Given that Porsche went to great lengths to shave 100kgs off a Carrera 2 in the past to make an RS, it seems a good thing to do.
The Mathey BBS Mags are too expensive and i wouldn't want to have to maintain them.
However, the BBS LMs are around £2k.
For similar money, the lightest wheel seems to be the Kinesis K-28 or the Fikse FMs. These save another 12kgs off against the BBS LMs.
Does anyone have any thoughts or opinions on these? There were some issues with cracks in the US (on hte Rennlist forums) a couple of yrs ago with these. What concerns me about these is i'd have to source them from the US which may make it difficult to service/repair/maintain them over here.
Cheers
Ajit.
Have a look at the Cargraphic 18" Racing,for similar money - 2.3K.
www.cargraphic.de
Look directly on their site, and then speak to Mark King (really helpful) at Stuttgart Connection (UK Agent)www.stuttgart.co.uk.
Not sure about the weight, but I wanted to change my Mk1 wheels because they kept on delaminating around the rim (polished area) and looked awful against the rest of the car.
Having gone for these all I can say is they look awsome, and change the look of the car completely, and the quality is excellent.
As for driving(road use)I cannot detect any major differences.
www.cargraphic.de
Look directly on their site, and then speak to Mark King (really helpful) at Stuttgart Connection (UK Agent)www.stuttgart.co.uk.
Not sure about the weight, but I wanted to change my Mk1 wheels because they kept on delaminating around the rim (polished area) and looked awful against the rest of the car.
Having gone for these all I can say is they look awsome, and change the look of the car completely, and the quality is excellent.
As for driving(road use)I cannot detect any major differences.
If you are working on a ratio of 4-1;the Alcon floating disc's on the front save about 2 kilos a side due to the aluminuim bells = 16kgs of rotating mass,, and the latest ones don't rattle!! JZM also do the rears now so that could be 32kgs of rotating mass.
The BBS LM wheels look an expensive option to me with marginal weight saving I would rather budget for more frequent tyre changes,,new Cups are not far off Slicks grip levels!!!
The BBS LM wheels look an expensive option to me with marginal weight saving I would rather budget for more frequent tyre changes,,new Cups are not far off Slicks grip levels!!!
Somebody's going to have to explain this to me. I am one of those people who trust the excellence of Porsche engineers, so whenever I read about claimed horsepower gains of 20bp by fitting an aftermarket exhaust to a GT3, I am hugely sceptical.
I tend to apply a similar logic to wheel technology. I cannot believe there can be huge (if any) savings in unsprung weight without compromising on durability. Why don't Porsche fit BBS LMs as standard?
Genuine question, by the way, I'm not trying to put you off, Ajit, in fact I think the BBS wheels look the DB's!
I tend to apply a similar logic to wheel technology. I cannot believe there can be huge (if any) savings in unsprung weight without compromising on durability. Why don't Porsche fit BBS LMs as standard?
Genuine question, by the way, I'm not trying to put you off, Ajit, in fact I think the BBS wheels look the DB's!
Are you lot getting the BBS 'LM's' mixed up with the BBS Motorsport 'Trans-Am' wheels????
Whilst the LM is a lightweight wheel it is designed with road use in mind and is made of aluminium.
The Trans-Am is ultra light and is designed for Motorsport use and used to have a magnesium alloy centre and now, because of cracking issues, is now available aluminium centres.
The TA's can be used on the road, some people have used them for years without damage but you are more likely to suffer a buckled rim on our poor roads. And on track heavy use of kerbs can also do damage.
What are the relative weights??? Depends on size obviously but can't find the info anywhere.
I MUST get some scales!
Whilst the LM is a lightweight wheel it is designed with road use in mind and is made of aluminium.
The Trans-Am is ultra light and is designed for Motorsport use and used to have a magnesium alloy centre and now, because of cracking issues, is now available aluminium centres.
The TA's can be used on the road, some people have used them for years without damage but you are more likely to suffer a buckled rim on our poor roads. And on track heavy use of kerbs can also do damage.
What are the relative weights??? Depends on size obviously but can't find the info anywhere.
I MUST get some scales!
polarexpress said:
Ajit, forget the Fiske/Kinesis... go for the BBS LMs. Beautiful proven wheels which you will have absolutely no problem getting rid of when (IF!) it comes to sell.
Just my £0.01
Now... ally or mag?
Cheers,
Adrien
BBS LMs are all alumium. You get to choose between aluminium or magnesium alloy when you buy BBS race wheels. These are better looking than LMs in my view, and much cooler as well! I shall get some soon. Gold centres for me.
Carnewal.com lists BBS LMs and then BBS Racing wheels - available in both alu and mag centres as Johnny said - gold and black centres available.
I think the Racing wheels look better too - when they say gold centre, do they mean the whole wheel apart from the outer rim is gold? Very cool - but would gold or black look better on my silver car?
Cheers
Ajit
I think the Racing wheels look better too - when they say gold centre, do they mean the whole wheel apart from the outer rim is gold? Very cool - but would gold or black look better on my silver car?
Cheers
Ajit
Seen the light now - the pix gfreeman posted above, the gold one is the BBS Racing wheel with gold centres, and look the Dogs!
Carnewal.com quote them at Euros3635 for 8.5 and 10 J 18"s including shipping.
I love the look of the gold, but can't decide between gold or black for my silver car!
Ajit.
Carnewal.com quote them at Euros3635 for 8.5 and 10 J 18"s including shipping.
I love the look of the gold, but can't decide between gold or black for my silver car!
Ajit.
singh911 said:
Seen the light now - the pix gfreeman posted above, the gold one is the BBS Racing wheel with gold centres, and look the Dogs!
Carnewal.com quote them at Euros3635 for 8.5 and 10 J 18"s including shipping.
I love the look of the gold, but can't decide between gold or black for my silver car!
Ajit.
I agree, the racing wheel looks better than the LM.
I would go for gold spokes (they all come with the silver coloured polished rim). The gold ones remind me of racing Porsches. Even the LMP2 race car they have just started campaigning has the gold centres. Gold wheels would look fine on a silver GT3 (as it is a track biased car).
Don't mean to piss on any bonfires here, but we are talking about a road car here ( albeit a great one ).
Surely you are trying to convince yourself that the pretty new wheels you want can be bought with a clear conscious due to weight savings !!
It has already been pointed out that new floating discs will make more of a difference. Maybe new back boxes for the exhaust system are needed to save an extra few kg's ??
Where does it end, a new gym membership to get rid of the 3 kg's put on over christmas ?
The car has air con, a stereo, electric windows, carpets, etc, etc.
If you really want to go full on in the weight stakes get a caterham, radical, atom, gt3 cup car etc. These have less un sprung mass issues to worry about and will probably go around corners faster than you with bbs lm's or no bbs lm's fitted.
As i said don't mean to be harsh but unless you are one hell of a driver i fail to see how you could notice what wheels were on a gt3 half way around any track. Sitting in the paddock talking about what went on half way around the track is a different matter !!
Surely you are trying to convince yourself that the pretty new wheels you want can be bought with a clear conscious due to weight savings !!
It has already been pointed out that new floating discs will make more of a difference. Maybe new back boxes for the exhaust system are needed to save an extra few kg's ??
Where does it end, a new gym membership to get rid of the 3 kg's put on over christmas ?
The car has air con, a stereo, electric windows, carpets, etc, etc.
If you really want to go full on in the weight stakes get a caterham, radical, atom, gt3 cup car etc. These have less un sprung mass issues to worry about and will probably go around corners faster than you with bbs lm's or no bbs lm's fitted.
As i said don't mean to be harsh but unless you are one hell of a driver i fail to see how you could notice what wheels were on a gt3 half way around any track. Sitting in the paddock talking about what went on half way around the track is a different matter !!
lsb - to be fair i want the wheels for the look. But i am interested in the weight of them because i don't want to do what i did on my old 993 when i went from 17s to a heavy set of 18s and ruined the handling of the car.
I ended up selling those heavy 18s a few years later and reverting to my 17s.
Ajit.
I ended up selling those heavy 18s a few years later and reverting to my 17s.
Ajit.
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