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    Re: Incoming GT2

    fritz:
    TB993tt:

    Just the Maha dyno test to see what the Cargraphic/RS stuff actually did. Frankly the sales guy Jan was IMO completely clueless but that is probably because he is not used to selling to anoraks like me - my BS detector was off the scale !

    FWIW, I don't think that your use of the noun "anoraks" in this context will be understood as you intended it to be anywhere outside of the UK.  Smiley

    There is always wikipedia:

    Do a search under Anorak(slang)

    en.wikipedia.org/wiki/Anorak_(slang)



    --
    It's not where you're going, it's how you get there that counts


    Re: Incoming GT2

     TB, could you please post some more pics of the wheels. thanx.


    Re: Incoming GT2

    I have saved some pics in my pc, could be from TB not sure.

    DYMAG09 new.jpg

     

    DYMAG006.jpg

     

    DYMAG005.jpg


    Re: Incoming GT2

    Here is some tech info someone (I forget who so no credit I'm afraid) shared with me about the benefits of these wheels:


    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.

    Some bad pics I had on my computer - note the spokes are on Platinum Silver, the ones posted earlier are the darker smoked version I think.

    dymag4 002.jpgdymagnew.jpg


    --


    2009 997 GT2 RS Tuning 542PS/736NM


    Re: Incoming GT2

    beautiful wheels and great write-up.   It'll make me think of PCCB's again too!


    Re: Incoming GT2

    TB993tt:

    Just the Maha dyno test to see what the Cargraphic/RS stuff actually did. Frankly the sales guy Jan was IMO completely clueless but that is probably because he is not used to selling to anoraks like me - my BS detector was off the scale !

    thanks for the info and the tech-links about your wheels!I appreciated a lot!


    --
    Dedi La vita è troppo corta per non guidare italiano.....


    Re: Incoming GT2

    An 'obvious' question maybe regarding the implied HP increase using these wheels - or PCCB's for that matter.   Assuming the above math is ~correct, then you should be able to need a 'noticeable' 0-100 time difference etc.  

    I'm guessing that something like 0.3, on par with a FL model's power upgrade etc.  

     

    If the above is the case, then Porsche seem to have been quiet marketing it for their PCCB's


    Re: Incoming GT2

    If the above is the case, then Porsche seem to have been quiet marketing it for their PCCB's


    i have a question about the carbon rotors on the GT2. i have been told they are not a true full carbon rotor, but a steel rotor with a carbon coating?


    Re: Incoming GT2

     I love the idea of removing rotating, unsprung mass - and mailed Dymag for a quote - they never even replied 


    --

    2007 987S, KW v3 1964 Type 1


    Re: Incoming GT2

    DaveGordon:

     I love the idea of removing rotating, unsprung mass - and mailed Dymag for a quote - they never even replied 

    They have gone bankrupt as far as I know...

     

    http://thekneeslider.com/archives/2009/11/30/dymag-racing-uk-ltd-in-bankruptcy-machinery-available-in-online-auction/


    Re: Incoming GT2

    Porker:
    DaveGordon:

     I love the idea of removing rotating, unsprung mass - and mailed Dymag for a quote - they never even replied 

    They have gone bankrupt as far as I know...

     

    http://thekneeslider.com/archives/2009/11/30/dymag-racing-uk-ltd-in-bankruptcy-machinery-available-in-online-auction/


    Wow, what a shame Smiley


    --

    Slow In, Fast Out


    Re: Incoming GT2

    Porker:
    DaveGordon:

     I love the idea of removing rotating, unsprung mass - and mailed Dymag for a quote - they never even replied 

    They have gone bankrupt as far as I know...

     Hmmm, I thought that selling carbon-rimmed wheels for road use would have to end in tears.  Smiley


    --

    fritz


    Re: Incoming GT2

     They will be back trading in the next few months. Spoke to someone in the management team. They will focus on certain applications, car wheels will be one of those. So dont despair, you might still be able to get some. This was probably the best mod i did to this car todate..


    Re: Incoming GT2

    HRE is now selling a line of wheels using the Dymag carbon rims.

    http://www.hrewheels.com/wheels/series.php?q=/CARBON/CF43/

     


    Re: Incoming GT2

    Source: autogespot

     

     


    Re: Incoming GT2

    Fixed  Smiley

    1.jpg12630687232273.jpg12630687323835.jpg12630688345522.jpg 

     

     

     


    Re: Incoming GT2

     nice pics


    Re: Incoming GT2

    Obrigado c4c.

    Thanks.

     


    Re: Incoming GT2

    Smiley 


     
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