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    Un-sprung Weight. What do you think?

     

     

    Can reducing un-sprung weight by 54.5 lbs (After-market wheels + PCCB's) really be equivalent to losing 381.5 lbs from the body of the car??

     

    Found this in June 2009's excellence:

     

    Olaf Manthey in excellence : “Removing 33 pounds of unsprung weight at the wheels is equivalent to losing 198 pounds from the body of the car, as a 1:6 factor has to be applied when the car is moving and that weight becomes mass. In fact, we are conservative with the 1:6 ratio, as Porsche considers it to be 1:7.” http://www.excellence-mag.com/art1/art1p1.html

     

    Porsche Factory 997 Turbo
    8.5x19" 23 lbs. 14 oz.
    11x19" 28 lbs. 13 oz.
    -
    HRE M40 Monoblok
    8.5x19" 21 lbs. 8 oz.
    11x19" 24 lbs. 14 oz.
    -
    Champion RS171:
    8.5x19" 20 lbs. 1 oz.
    11.5x19" 24 lbs. 3 oz.

     

    Approx. Champion RS171 weight savings (wheels) vs. stock = 17.5 lbs.

     

    PCCB un-sprung weight savings = 37 lbs.
     

    Total (wheels + PCCB) un-sprung weight savings = 54.5 lbs

     

    54.5 lbs x a factor of 7 (according to the above) = removing 381.5 lbs from the body of the car

     

    Smiley


    --


     
    "typical superficial American" & "unapologetic racist"    

    08 PORSCHE Turbo Cabriolet, 06 Ferrari F430,  04 Durango HEMI,  04 Harley Davidson Screamin Eagle,  93 Harley Davidson Nostalgia

     


    Re: Un-sprung Weight. What do you think?

    I have read on many sites it's a 1:8 ratio!
    --


    Click for bigger picture!


    Re: Un-sprung Weight. What do you think?

     Dymag wheels can save you another 20lbs...


    Re: Un-sprung Weight. What do you think?

    So the RS 171s are equivalent to me losing 120 pounds without dieting! ....Sweet, top that Oprah!!


    --

    Doug

    Houston, Texas USA 

    997TT ...RUF550


    Re: Un-sprung Weight. What do you think?

    losing weight is very important but it is more beneficial the further the weight loss is from the axis of rotation. Tire weight > wheel weight > brake weight as far as impact and performance. Brake weight loss is nowhere near as important as tire weight in other words. That's why I obsess over tire weights, and wheel weights.


    --

    track vid

    0-300kph

    chasing a 997GT2

     

     


    Re: Un-sprung Weight. What do you think?

    In short the difference is quite noticeable. I shaved 23-25 kgs with dymags and titanium bolts and the difference was really amazing. Even pulling out of the garage you suddenly feel the car a lot lighter, like -100kgs. Is the case of the turbo I found them to have also a substancial improvement in turn and understeer. The suspensions is working noticeably quicker (and stiffer) and overall the car has a lot better control. Dymags will inherently be better than any of the other wheels in that respect since the outer part of the wheel weighs almost nth (carbon). Hence comparing to other wheels the weight saving is more like 50%-55% vs stock and not 35%. No affiliation but if I keep buying powerful sports cars, this mod will be among the first I will explore since it transformed the turbo in many respects.

    Re: Un-sprung Weight. What do you think?

    TT Gasman:

    So the RS 171s are equivalent to me losing 120 pounds without dieting! ....Sweet, top that Oprah!!

     

    Smiley Smiley


    --


     
    "typical superficial American" & "unapologetic racist"    

    08 PORSCHE Turbo Cabriolet, 06 Ferrari F430,  04 Durango HEMI,  04 Harley Davidson Screamin Eagle,  93 Harley Davidson Nostalgia

     


    Re: Un-sprung Weight. What do you think?

    GT:
    In short the difference is quite noticeable. I shaved 23-25 kgs with dymags and titanium bolts and the difference was really amazing. Even pulling out of the garage you suddenly feel the car a lot lighter, like -100kgs. Is the case of the turbo I found them to have also a substancial improvement in turn and understeer. The suspensions is working noticeably quicker (and stiffer) and overall the car has a lot better control. Dymags will inherently be better than any of the other wheels in that respect since the outer part of the wheel weighs almost nth (carbon). Hence comparing to other wheels the weight saving is more like 50%-55% vs stock and not 35%. No affiliation but if I keep buying powerful sports cars, this mod will be among the first I will explore since it transformed the turbo in many respects.

     

    GT - Smiley

    eclou, Alex, SciFrog - Thanks, interesting.

    What was the other thing I heard one day about weight & 1/4 mile times? I probably dont have this right & I guess it really depends on the %'s but something about for every 100 lbs of weight reduction = .1 quicker 1/4 mile times ? 

     


    --


     
    "typical superficial American" & "unapologetic racist"    

    08 PORSCHE Turbo Cabriolet, 06 Ferrari F430,  04 Durango HEMI,  04 Harley Davidson Screamin Eagle,  93 Harley Davidson Nostalgia

     


    Re: Un-sprung Weight. What do you think?

    also posted here:    http://www.rennteam.com/forum/index.html?vs=5 

    not sure if it all adds up:  would there be a lot more noise about 0-100 tim reductions (and those differences being significant)


    Re: Un-sprung Weight. What do you think?

     

    I posted this before, but here it is again since it seems relevant to this thread:

     
     
    Moment of inertia facts
     
     


    Determination of moment of inertia for a wheel is very difficult because the “normal” calculations are for a thin wall cylinder or solid rod, the calculation being a function of the mass multiplied by the square of the radius. With the Dymag carbon / magnesium wheel being of different materials and different masses as you radiate out from the hub, then the calculation needs to take on some assumptions.

    Therefore if we take the whole wheel, then the basic formula is:
    MOI = ½ mr²

    If the carbon barrel alone is measured versus a metal rim it would be:

    MOI = mr²
    So because of the radius being squared in each calculation, the greater the diameter of any wheel then the greater the effect of reducing the MOI.

    As you can see if we use the generally accepted first formula then we are very conservative in our result, especially if we compare the Dymag wheel with an aluminium centred wheel where we could be as much as 50% greater on MOI than in reality! Hence the importance of measuring MOI of 2 wheels accurately on the same machine to make any comparison.
    Porsche 997 rear wheel comparison

    Comparing a 19x11.5” Porsche 997 Carrera S wheel with a Dymag carbon/magnesium 19x12” wheel.
    Porsche: 30lb x19” M=30lb, R=9.5”
    Therefore: ½ x 30 x 9.5² = 1,353.75 lb/in² MOI

    Dymag: 19lb x 19” M=19lb, R=9.5”

    Therefore: ½ x 19 x 9.5² = 857.375 lb/in² MOI which is 63% of the MOI of the Porsche wheel.


    Why is this important?
    Consider 2 factors of the wheel in use, rotating and steering.
    To rotate the wheel, the work energy required is calculated as force of net angular position change = ½ MOI x angular velocity², strictly speaking it is Force net θ = Δ( ½ MOI ω²)

    Which in English means that the energy consumption goes up as a function of the moment of inertia x the square of the speed, or as you go quicker it takes much more energy! This equation also shows that both acceleration and braking are both effected significantly by a reduction in MOI

    Steering changes are even easier to understand. The change in direction is governed by the momentum of the wheel which is calculated as the MOI x angular velocity, so in the above example, the Porsche on the Dymag wheel will use 47% less energy input to steer the car, either driver or power steering input, this is why the car feels “lighter” to drive and more responsive to steering input.

    Rule of thumb calculations

    This is a minefield of assumptions!! 2 of the old tuning rules of thumb were that 6lb weight saved on a car was equal to 1 bhp and that 1lb of rotating weight was worth 10lb of static weight, so in the Porsche example above, we are saving 11lb per wheel, x 10 = 110lb x 4 = 440lb ÷6 = 73.33 bhp we think this is probably excessive as the 10 factor does not take into account the diameter of the rotating part. A carbon propshaft would not have the same effect for example.
    We have been stating that the rotating/static weight factor is about 6:1, this would give a result as above of 44bhp, which is roughly the gain effect that Parr Porsche said about the original tests of the carbon car wheels on the 996 GT3 RS!!

    Power to weight calculation

    Now if we take the Porsche wheels, the 997 Carrera S weighs 3131lbs and has 355 bhp, which gives it a power to weight ratio of 8.82:1 or, if you lose 8.82 lbs it is equivalent to 1bhp equivalent gained.

    So if we take the Dymag 6x factor for the carbon wheels then saving11lb per wheel x 6, x 4 wheels ÷ 8.82 lb/bhp = 29.93 bhp an important 8.43% power gain simply by bolting on different wheels.
    But if we take the sometimes accepted10x rotating to static weight factor this figure comes to 49.88 bhp

    Obviously using this type of formula, the more power to weight ratio, the bigger the wheel effect on performance – not too surprising really!

    Fuel saving and emissions reduction

    The best estimates available for fuel and emissions savings by using carbon wheels are between 3.0% and 8.0% fuel savings. The increased % would be with stop – start driving for the obvious reasons of overcoming inertia and momentum. Also air drag factors mask the wheels performance at higher & more consistent speeds.

    Emissions are much more difficult to calculate, especially when taking into account warm up and urban type cycles of car use. However as gasoline produces an average of 2.35kg per litre of fuel at the tailpipe, then it is safe to assume an initial saving of emissions to match fuel consumption. Again urban cycles will show a greater effect from the carbon wheel. So if the average car produces 165g of CO2 per km (at 7litres per 100km) the carbon wheels may reduce this to nearly 151g, a 9% improvement.

    The fuel and emissions savings/reductions caused by carbon wheels need much more work. It is not possible to calculate these effects due to the other rotating components of the car which contribute to the overall moment of inertia, plus there are effects on non-rotating parts such as suspension where lighter wheels would give softer settings which require less energy to use the car in normal road conditions due to the reduction in energy losses with tyre deflections. 

    Conclusion

    Carbon rims have a noticeable effect on a car’s performance and handling, the variations in moment of inertia of the complete system are not well enough researched to give absolute figures of the improvements that the wheels give. That the improvement is significant is beyond doubt, the independent testing and standards agencies now need to make these evaluations, equally condemning many of the very heavy aftermarket products.


    --


    2009 997 GT2 RS Tuning 542PS/736NM


    Re: Un-sprung Weight. What do you think?

     

    In addition to reduced polar inertia, the generally lower inertia of unsprung mass allows the suspension to "follow" road irregularities more quickly. So traction is not as easily lost when going over a small bump.

    Regarding carbon wheels, I have had some experience using them in kart races. They turned out to be much more prone to cracking upon light impact (in the heat of a race) where the regular magnesium or aluminium wheels would have deformed only slightly (remaining usable). But this was just for karting, it is very possible that expensive carbon wheels for cars like a Porsche are made much more durable. Still, I would keep the issue in mind before instaling them on a regular road car.

     

     


    --
    Costas

    Re: Un-sprung Weight. What do you think?

    Jay:

    also posted here:    http://www.rennteam.com/forum/index.html?vs=5 

    not sure if it all adds up:  would there be a lot more noise about 0-100 tim reductions (and those differences being significant)

     

    It didnt work for me, brought me to a listing of threads.


    --

    08 PORSCHE Turbo Cabriolet, 06 Ferrari F430,  04 Durango HEMI,  04 Harley Davidson Screamin Eagle,  93 Harley Davidson Nostalgia

     


    Re: Un-sprung Weight. What do you think?

    TB993tt:

     

    I posted this before, but here it is again since it seems relevant to this thread:

     
     
    Moment of inertia facts
     
     


    Determination of moment of inertia for a wheel is very difficult because the “normal” calculations are for a thin wall cylinder or solid rod, the calculation being a function of the mass multiplied by the square of the radius. With the Dymag carbon / magnesium wheel being of different materials and different masses as you radiate out from the hub, then the calculation needs to take on some assumptions.

    Therefore if we take the whole wheel, then the basic formula is:
    MOI = ½ mr²

    If the carbon barrel alone is measured versus a metal rim it would be:

    MOI = mr²
    So because of the radius being squared in each calculation, the greater the diameter of any wheel then the greater the effect of reducing the MOI.

    As you can see if we use the generally accepted first formula then we are very conservative in our result, especially if we compare the Dymag wheel with an aluminium centred wheel where we could be as much as 50% greater on MOI than in reality! Hence the importance of measuring MOI of 2 wheels accurately on the same machine to make any comparison.
    Porsche 997 rear wheel comparison

    Comparing a 19x11.5” Porsche 997 Carrera S wheel with a Dymag carbon/magnesium 19x12” wheel.
    Porsche: 30lb x19” M=30lb, R=9.5”
    Therefore: ½ x 30 x 9.5² = 1,353.75 lb/in² MOI

    Dymag: 19lb x 19” M=19lb, R=9.5”

    Therefore: ½ x 19 x 9.5² = 857.375 lb/in² MOI which is 63% of the MOI of the Porsche wheel.


    Why is this important?
    Consider 2 factors of the wheel in use, rotating and steering.
    To rotate the wheel, the work energy required is calculated as force of net angular position change = ½ MOI x angular velocity², strictly speaking it is Force net θ = Δ( ½ MOI ω²)

    Which in English means that the energy consumption goes up as a function of the moment of inertia x the square of the speed, or as you go quicker it takes much more energy! This equation also shows that both acceleration and braking are both effected significantly by a reduction in MOI

    Steering changes are even easier to understand. The change in direction is governed by the momentum of the wheel which is calculated as the MOI x angular velocity, so in the above example, the Porsche on the Dymag wheel will use 47% less energy input to steer the car, either driver or power steering input, this is why the car feels “lighter” to drive and more responsive to steering input.

    Rule of thumb calculations

    This is a minefield of assumptions!! 2 of the old tuning rules of thumb were that 6lb weight saved on a car was equal to 1 bhp and that 1lb of rotating weight was worth 10lb of static weight, so in the Porsche example above, we are saving 11lb per wheel, x 10 = 110lb x 4 = 440lb ÷6 = 73.33 bhp we think this is probably excessive as the 10 factor does not take into account the diameter of the rotating part. A carbon propshaft would not have the same effect for example.
    We have been stating that the rotating/static weight factor is about 6:1, this would give a result as above of 44bhp, which is roughly the gain effect that Parr Porsche said about the original tests of the carbon car wheels on the 996 GT3 RS!!

    Power to weight calculation

    Now if we take the Porsche wheels, the 997 Carrera S weighs 3131lbs and has 355 bhp, which gives it a power to weight ratio of 8.82:1 or, if you lose 8.82 lbs it is equivalent to 1bhp equivalent gained.

    So if we take the Dymag 6x factor for the carbon wheels then saving11lb per wheel x 6, x 4 wheels ÷ 8.82 lb/bhp = 29.93 bhp an important 8.43% power gain simply by bolting on different wheels.
    But if we take the sometimes accepted10x rotating to static weight factor this figure comes to 49.88 bhp

    Obviously using this type of formula, the more power to weight ratio, the bigger the wheel effect on performance – not too surprising really!

    Fuel saving and emissions reduction

    The best estimates available for fuel and emissions savings by using carbon wheels are between 3.0% and 8.0% fuel savings. The increased % would be with stop – start driving for the obvious reasons of overcoming inertia and momentum. Also air drag factors mask the wheels performance at higher & more consistent speeds.

    Emissions are much more difficult to calculate, especially when taking into account warm up and urban type cycles of car use. However as gasoline produces an average of 2.35kg per litre of fuel at the tailpipe, then it is safe to assume an initial saving of emissions to match fuel consumption. Again urban cycles will show a greater effect from the carbon wheel. So if the average car produces 165g of CO2 per km (at 7litres per 100km) the carbon wheels may reduce this to nearly 151g, a 9% improvement.

    The fuel and emissions savings/reductions caused by carbon wheels need much more work. It is not possible to calculate these effects due to the other rotating components of the car which contribute to the overall moment of inertia, plus there are effects on non-rotating parts such as suspension where lighter wheels would give softer settings which require less energy to use the car in normal road conditions due to the reduction in energy losses with tyre deflections. 

    Conclusion

    Carbon rims have a noticeable effect on a car’s performance and handling, the variations in moment of inertia of the complete system are not well enough researched to give absolute figures of the improvements that the wheels give. That the improvement is significant is beyond doubt, the independent testing and standards agencies now need to make these evaluations, equally condemning many of the very heavy aftermarket products.

     

    Smiley



    --

    08 PORSCHE Turbo Cabriolet, 06 Ferrari F430,  04 Durango HEMI,  04 Harley Davidson Screamin Eagle,  93 Harley Davidson Nostalgia

     


     
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