Lighter wheel benefits
09-08-2011, 05:07 PM
#31
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IMO, the ratios should be used as follows. Also, I think part of the reason that Rad's 996 killed the 997 was due to the much better gearing 4.00 r&p.
Car 1:
2300# sprung weight 400# unsprung weight. Effective total dynamic weight 4700#
Car 2:
2350# sprung wieght 350# unsprung weight. Effective total dynamic weight 4450#
Same static weight, but car 2 should be quicker.
Car 1:
2300# sprung weight 400# unsprung weight. Effective total dynamic weight 4700#
Car 2:
2350# sprung wieght 350# unsprung weight. Effective total dynamic weight 4450#
Same static weight, but car 2 should be quicker.
That's so wrong from Mr. Manthey, and even worse from Porsche.
Case in point, my 997 GT3 RS at 3,075 lbs with 3 gallons of fuel. Carbon GT2 seats, LW battery, Sharkwerks center muffler bypass pipes, no rollbar, everything else standard. Assume same tire brand, model, width.
Car1: 3,075 lbs 2007 GT3 RS
Now I replace the rotors with 996 GT3 PCCB and the wheels with BBS 9"/11"x18 Magesium wheels, for a total unsprung weight saving of 90 lbs.
Car2: 2,985 lbs 2007 GT3 RS (PCCB+BBS Mg)
So, this German company and this other German guy claim that Car2 has the equivalent to a weight loss of 540 lbs or 630 lbs? Car2 has the equivalent to a weight loss of 630 lbs to get down to 2,445 lbs. 2,445 lbs? really?
Car2 should be massively faster than Car1, Car2 would actually beat a GT3 Cup.
Biggest BS I have read in a long time. I stick to my 1:1 ratio.
Car3: 2,675 lbs 2007 GT3 RS (400 lbs lighter than Car1) but still carrying the heavy brakes and wheels as stock.
Manthey and Porsche say Car2 would be faster (I mean lap times, not drag racing), I say Car3 beats them all by a mile.
Case in point, my 997 GT3 RS at 3,075 lbs with 3 gallons of fuel. Carbon GT2 seats, LW battery, Sharkwerks center muffler bypass pipes, no rollbar, everything else standard. Assume same tire brand, model, width.
Car1: 3,075 lbs 2007 GT3 RS
Now I replace the rotors with 996 GT3 PCCB and the wheels with BBS 9"/11"x18 Magesium wheels, for a total unsprung weight saving of 90 lbs.
Car2: 2,985 lbs 2007 GT3 RS (PCCB+BBS Mg)
So, this German company and this other German guy claim that Car2 has the equivalent to a weight loss of 540 lbs or 630 lbs? Car2 has the equivalent to a weight loss of 630 lbs to get down to 2,445 lbs. 2,445 lbs? really?
Car2 should be massively faster than Car1, Car2 would actually beat a GT3 Cup.
Biggest BS I have read in a long time. I stick to my 1:1 ratio.
Car3: 2,675 lbs 2007 GT3 RS (400 lbs lighter than Car1) but still carrying the heavy brakes and wheels as stock.
Manthey and Porsche say Car2 would be faster (I mean lap times, not drag racing), I say Car3 beats them all by a mile.
09-08-2011, 05:43 PM
#32
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OK guys here it goes. I did the complete maths on this a while back based on the rotational inertias of various common parts of unsprung weight, while I was contemplating changing to Dymag Carbon wheels on my GT2 and these were my conclusions:
1. The impact of unsprung weight on suspension reaction as a benefit is unquantifiable and probably small on a smooth track anyway. It also requires suspension re-calibration to maximise the benefit. You may actually lose time on the road/track if you just reduce unsprung weight, since an optimised suspension may then become unoptimised.
2. The multiplier impact on Dymag Carbon rims from GT2 stock rims was around 4:1 in terms of rotational inertia and it's effect on acceleration and braking. However this multiplier only works in terms of these two characteristics, there is no such multiplier when it comes to the benefit on cornering, since the static weight reduction is only 1x. So for part of a lap you have 4x benefit, for part of it 1x, therefore no clear certainty as to the overall benefit over a lap, perhaps 2x?
Note Dymags have a bigger multiplier than most wheels since the greatest weight reduction is from the barrel, not the spokes, where it has the biggest effect. You model the rim/spokes separately for ease of maths. A normal 18" rim with single element construction has a lower multiplier, nearer 3x. 19" rims will see slightly higher multipliers.
3. The benefit for PCCBs is far far less, as they have a far smaller diameter. Something like 2x from memory, but over a lap perhaps nearer 1.5X for reasons above. Tyres have the biggest benefit since they have the greatest average diameter, so perhaps 5x on longitudal inertia ie brakes/acceleration..
So, there are range of multipliers for a range of parts and their impact on different elements of a lap. A drag-racer will feel all the benefit of a multiplier, since only longitudal acceleration counts. A track-racer less so. I would say overall that based on the car discussed by NJ-GT, with PCCBs and wheels, I would expect it have something like a 3x effect on acceleration/braking and nearer 1.5-1.75x effect on overall lap-time, so for a 92lb reduction, it would feel like a 150lb lighter car not a 500lb lighter car.
1. The impact of unsprung weight on suspension reaction as a benefit is unquantifiable and probably small on a smooth track anyway. It also requires suspension re-calibration to maximise the benefit. You may actually lose time on the road/track if you just reduce unsprung weight, since an optimised suspension may then become unoptimised.
2. The multiplier impact on Dymag Carbon rims from GT2 stock rims was around 4:1 in terms of rotational inertia and it's effect on acceleration and braking. However this multiplier only works in terms of these two characteristics, there is no such multiplier when it comes to the benefit on cornering, since the static weight reduction is only 1x. So for part of a lap you have 4x benefit, for part of it 1x, therefore no clear certainty as to the overall benefit over a lap, perhaps 2x?
Note Dymags have a bigger multiplier than most wheels since the greatest weight reduction is from the barrel, not the spokes, where it has the biggest effect. You model the rim/spokes separately for ease of maths. A normal 18" rim with single element construction has a lower multiplier, nearer 3x. 19" rims will see slightly higher multipliers.
3. The benefit for PCCBs is far far less, as they have a far smaller diameter. Something like 2x from memory, but over a lap perhaps nearer 1.5X for reasons above. Tyres have the biggest benefit since they have the greatest average diameter, so perhaps 5x on longitudal inertia ie brakes/acceleration..
So, there are range of multipliers for a range of parts and their impact on different elements of a lap. A drag-racer will feel all the benefit of a multiplier, since only longitudal acceleration counts. A track-racer less so. I would say overall that based on the car discussed by NJ-GT, with PCCBs and wheels, I would expect it have something like a 3x effect on acceleration/braking and nearer 1.5-1.75x effect on overall lap-time, so for a 92lb reduction, it would feel like a 150lb lighter car not a 500lb lighter car.
09-08-2011, 07:03 PM
#33
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OK guys here it goes. I did the complete maths on this a while back based on the rotational inertias of various common parts of unsprung weight, while I was contemplating changing to Dymag Carbon wheels on my GT2 and these were my conclusions:
1. The impact of unsprung weight on suspension reaction as a benefit is unquantifiable and probably small on a smooth track anyway. It also requires suspension re-calibration to maximise the benefit. You may actually lose time on the road/track if you just reduce unsprung weight, since an optimised suspension may then become unoptimised.
2. The multiplier impact on Dymag Carbon rims from GT2 stock rims was around 4:1 in terms of rotational inertia and it's effect on acceleration and braking. However this multiplier only works in terms of these two characteristics, there is no such multiplier when it comes to the benefit on cornering, since the static weight reduction is only 1x. So for part of a lap you have 4x benefit, for part of it 1x, therefore no clear certainty as to the overall benefit over a lap, perhaps 2x?
Note Dymags have a bigger multiplier than most wheels since the greatest weight reduction is from the barrel, not the spokes, where it has the biggest effect. You model the rim/spokes separately for ease of maths. A normal 18" rim with single element construction has a lower multiplier, nearer 3x. 19" rims will see slightly higher multipliers.
3. The benefit for PCCBs is far far less, as they have a far smaller diameter. Something like 2x from memory, but over a lap perhaps nearer 1.5X for reasons above. Tyres have the biggest benefit since they have the greatest average diameter, so perhaps 5x on longitudal inertia ie brakes/acceleration..
So, there are range of multipliers for a range of parts and their impact on different elements of a lap. A drag-racer will feel all the benefit of a multiplier, since only longitudal acceleration counts. A track-racer less so. I would say overall that based on the car discussed by NJ-GT, with PCCBs and wheels, I would expect it have something like a 3x effect on acceleration/braking and nearer 1.5-1.75x effect on overall lap-time, so for a 92lb reduction, it would feel like a 150lb lighter car not a 500lb lighter car.
1. The impact of unsprung weight on suspension reaction as a benefit is unquantifiable and probably small on a smooth track anyway. It also requires suspension re-calibration to maximise the benefit. You may actually lose time on the road/track if you just reduce unsprung weight, since an optimised suspension may then become unoptimised.
2. The multiplier impact on Dymag Carbon rims from GT2 stock rims was around 4:1 in terms of rotational inertia and it's effect on acceleration and braking. However this multiplier only works in terms of these two characteristics, there is no such multiplier when it comes to the benefit on cornering, since the static weight reduction is only 1x. So for part of a lap you have 4x benefit, for part of it 1x, therefore no clear certainty as to the overall benefit over a lap, perhaps 2x?
Note Dymags have a bigger multiplier than most wheels since the greatest weight reduction is from the barrel, not the spokes, where it has the biggest effect. You model the rim/spokes separately for ease of maths. A normal 18" rim with single element construction has a lower multiplier, nearer 3x. 19" rims will see slightly higher multipliers.
3. The benefit for PCCBs is far far less, as they have a far smaller diameter. Something like 2x from memory, but over a lap perhaps nearer 1.5X for reasons above. Tyres have the biggest benefit since they have the greatest average diameter, so perhaps 5x on longitudal inertia ie brakes/acceleration..
So, there are range of multipliers for a range of parts and their impact on different elements of a lap. A drag-racer will feel all the benefit of a multiplier, since only longitudal acceleration counts. A track-racer less so. I would say overall that based on the car discussed by NJ-GT, with PCCBs and wheels, I would expect it have something like a 3x effect on acceleration/braking and nearer 1.5-1.75x effect on overall lap-time, so for a 92lb reduction, it would feel like a 150lb lighter car not a 500lb lighter car.
However, Porsche and Olaf Manthey think my car got 630 lbs lighter.
Feeling 150 lbs lighter after 90 lbs of unsprung weight reduction, feasible. 500 lbs lighter or 630 lbs lighter, not even in dreams.
09-09-2011, 02:20 AM
#34
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[quote]
Interesting to know - I would assume stock road suspension is far too un-optimized to be affected from commercially available wheel reductions.
Makes sense that whatever benefit you would find would manifest in acceleration and braking ONLY, since the "improvement" would be from the wheel itself requiring less effort to spin up and down.
Note Dymags have a bigger multiplier than most wheels since the greatest weight reduction is from the barrel, not the spokes, where it has the biggest effect. You model the rim/spokes separately for ease of maths. A normal 18" rim with single element construction has a lower multiplier, nearer 3x. 19" rims will see slightly higher multipliers.
So, overall then, over a lap, it would feel like taking a medium sized passenger out. I would imagine that for cars with less power, the "effect" may feel more pronounced because dropping weight gives acceleration benefit across the rev range. For our cars maybe harder to notice.
I had not done the maths this way but it looks right, since we are talking about dynamic weights. At the moment of acceleration, the car has to accelerate its static body, as well as rotate AND accelerate wheels etc. So its all about the dynamic weight. Dropping unsprung mass from the car reducing the DYNAMIC weight of the car by a factor of 6:1 is believable.
1. The impact of unsprung weight on suspension reaction as a benefit is unquantifiable and probably small on a smooth track anyway. It also requires suspension re-calibration to maximise the benefit. You may actually lose time on the road/track if you just reduce unsprung weight, since an optimised suspension may then become unoptimised.
2. The multiplier impact on Dymag Carbon rims from GT2 stock rims was around 4:1 in terms of rotational inertia and it's effect on acceleration and braking. However this multiplier only works in terms of these two characteristics, there is no such multiplier when it comes to the benefit on cornering, since the static weight reduction is only 1x. So for part of a lap you have 4x benefit, for part of it 1x, therefore no clear certainty as to the overall benefit over a lap, perhaps 2x?
Note Dymags have a bigger multiplier than most wheels since the greatest weight reduction is from the barrel, not the spokes, where it has the biggest effect. You model the rim/spokes separately for ease of maths. A normal 18" rim with single element construction has a lower multiplier, nearer 3x. 19" rims will see slightly higher multipliers.
3. The benefit for PCCBs is far far less, as they have a far smaller diameter. Something like 2x from memory, but over a lap perhaps nearer 1.5X for reasons above. Tyres have the biggest benefit since they have the greatest average diameter, so perhaps 5x on longitudal inertia ie brakes/acceleration..
So, there are range of multipliers for a range of parts and their impact on different elements of a lap. A drag-racer will feel all the benefit of a multiplier, since only longitudal acceleration counts. A track-racer less so. I would say overall that based on the car discussed by NJ-GT, with PCCBs and wheels, I would expect it have something like a 3x effect on acceleration/braking and nearer 1.5-1.75x effect on overall lap-time, so for a 92lb reduction, it would feel like a 150lb lighter car not a 500lb lighter car.
IMO, the ratios should be used as follows. Also, I think part of the reason that Rad's 996 killed the 997 was due to the much better gearing 4.00 r&p.
Car 1:
2300# sprung weight 400# unsprung weight. Effective total dynamic weight 4700#
Car 2:
2350# sprung wieght 350# unsprung weight. Effective total dynamic weight 4450#
Same static weight, but car 2 should be quicker.
Car 1:
2300# sprung weight 400# unsprung weight. Effective total dynamic weight 4700#
Car 2:
2350# sprung wieght 350# unsprung weight. Effective total dynamic weight 4450#
Same static weight, but car 2 should be quicker.
09-09-2011, 08:22 AM
#35
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It would be interesting if we could find some real time testing/results where a car is well driven around a track, and lap times compared between weight changes via the wheels (unsprung) versus changing ballast in the car (sprung).
09-09-2011, 08:57 AM
#36
Race Car
Grassroots Motorsports has done this test a couple of times and did show gains but not nearly what was expected.
my CCW's sure are a heck of a lot easier to mount than my OEM wheels though...makes my back happy for sure :-)
my CCW's sure are a heck of a lot easier to mount than my OEM wheels though...makes my back happy for sure :-)
09-09-2011, 11:12 AM
#37
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I ran Dymags on my 7GT2 for quite a while. I got rid of them and changed to BBS Fi.
The weights of the Dymags and BBS Fi are virtually identical at 7.4kg front and 8.9kg rear.
The difference in steering feel is quite unbelievable, no numbers to put to it but the Dymags with their carbon rim (presumably giving less gyroscopic effect) made the steering feel 40% sharper and more nimble to steering input.....
Shame they break
The weights of the Dymags and BBS Fi are virtually identical at 7.4kg front and 8.9kg rear.
The difference in steering feel is quite unbelievable, no numbers to put to it but the Dymags with their carbon rim (presumably giving less gyroscopic effect) made the steering feel 40% sharper and more nimble to steering input.....
Shame they break
09-09-2011, 11:21 AM
#38
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is dymag still alive? heard they went belly up a while ago. no real loss.
for me, I never just look at the weight of wheel itself as that's an easy thing to measure. it's mass + strength. i was reading an article in this japanese tuning magazine doing some testing on how much X brand wheel deforms under load, braking etc. def made an impact on the way the car grips.
given there's no way for us to measure strength other than anecdotal testimony (ie no issues over x track days), we have to essentially place trust (our $) in the brand's rep thus the reason why i will never buy anything but BBS/OZ and some of the smaller boutiques like Formula43, champion, fikse, hre et al.
for me, I never just look at the weight of wheel itself as that's an easy thing to measure. it's mass + strength. i was reading an article in this japanese tuning magazine doing some testing on how much X brand wheel deforms under load, braking etc. def made an impact on the way the car grips.
given there's no way for us to measure strength other than anecdotal testimony (ie no issues over x track days), we have to essentially place trust (our $) in the brand's rep thus the reason why i will never buy anything but BBS/OZ and some of the smaller boutiques like Formula43, champion, fikse, hre et al.
09-11-2011, 03:25 PM
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Or the Manthey engineers that built two Manthey GT3 engines I know of that blew up?
No-one is infallible.
Any simple assumption such as a ridiculous 6:1 is easily disproved. Imagine that you owned a 911 that weighed 1200kg (a dream in recent years), but of which the wheels/tyres/brakes weighed 200kg in total. Now imagine that these were replaced with ones made of some amazing theoretical material that was weightless. The car would weigh 1000kg, but have saved 200kg of unsprung weight. So according to the 6:1 rule the car should perform as if it had zero weight (1200kg -200kg X 6). Zero to warp speed 10 in a milli-second.
09-11-2011, 03:43 PM
#42
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If you were to ask the same question to any real automotive engineer (6+ years spent in university), they would agree with Porsche/Manthey.
to keep it simple an example i can give you....relates more to suspension operation....
sprung weight = 15lbs bowling ball
Unsprung = ping pong ball
Throw the ping pong ball at the bowling ball...Bowling ball doesn't move = the chassis is controlling the wheels
Unsprung = 8lbs bowling ball, throw the 8lbs bowling ball at the 15lbs'er....it moves a lot = the wheels are controlling the chassis.
Why do you think they would not tell the truth? They don't gain anything.
As for Manthey with only 2 engines blowing up, they build approx 30+ motors per year, why don't you ask PMNA how many of theirs blow up? I've seen theirs last less than 2 hours.
to keep it simple an example i can give you....relates more to suspension operation....
sprung weight = 15lbs bowling ball
Unsprung = ping pong ball
Throw the ping pong ball at the bowling ball...Bowling ball doesn't move = the chassis is controlling the wheels
Unsprung = 8lbs bowling ball, throw the 8lbs bowling ball at the 15lbs'er....it moves a lot = the wheels are controlling the chassis.
Why do you think they would not tell the truth? They don't gain anything.
As for Manthey with only 2 engines blowing up, they build approx 30+ motors per year, why don't you ask PMNA how many of theirs blow up? I've seen theirs last less than 2 hours.
09-11-2011, 07:49 PM
#43
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If you were to ask the same question to any real automotive engineer (6+ years spent in university), they would agree with Porsche/Manthey.
to keep it simple an example i can give you....relates more to suspension operation....
sprung weight = 15lbs bowling ball
Unsprung = ping pong ball
Throw the ping pong ball at the bowling ball...Bowling ball doesn't move = the chassis is controlling the wheels
Unsprung = 8lbs bowling ball, throw the 8lbs bowling ball at the 15lbs'er....it moves a lot = the wheels are controlling the chassis.
Why do you think they would not tell the truth? They don't gain anything.
As for Manthey with only 2 engines blowing up, they build approx 30+ motors per year, why don't you ask PMNA how many of theirs blow up? I've seen theirs last less than 2 hours.
to keep it simple an example i can give you....relates more to suspension operation....
sprung weight = 15lbs bowling ball
Unsprung = ping pong ball
Throw the ping pong ball at the bowling ball...Bowling ball doesn't move = the chassis is controlling the wheels
Unsprung = 8lbs bowling ball, throw the 8lbs bowling ball at the 15lbs'er....it moves a lot = the wheels are controlling the chassis.
Why do you think they would not tell the truth? They don't gain anything.
As for Manthey with only 2 engines blowing up, they build approx 30+ motors per year, why don't you ask PMNA how many of theirs blow up? I've seen theirs last less than 2 hours.
Assuming same cars, same power, same size wheels,tires and same compound. Car A is lighter on unsprung weight, Car B is lighter on sprung weight.
- Car A: 3,000 lbs, 2900 lbs on chassis and 100 lbs on unsprung weight (super light wheels, tires, brakes, carriers).
- Car B: 2,000 lbs, 1,600 lbs on chassis and 400 lbs on unsprung weight (heavy wheels, tires, brakes, hubs).
300 lbs lighter unsprung weight on Car A, and factor of 7:1 means the equivalent to 2,100 lbs removed from car A, making it feel like a 900 lbs car (according to Porsche and Manthey, and a few others in here).
Good luck with that. I will take Car B, in my book it is faster on acceleration, brake better and handle more Gs on the turns than Car A.
09-11-2011, 10:57 PM
#45
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well NJ-GT, if it came to a car build off between you and Olaf Manthey.... my money is on Olaf!
the green and yellow car in my avatar pic is one he built, this is the fastest 996 in the USA, i only know of 3 997's faster, and they are in Germany
the green and yellow car in my avatar pic is one he built, this is the fastest 996 in the USA, i only know of 3 997's faster, and they are in Germany