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Thread: what is an ideal weight distribution ? 50/50 ? 40/60 ? 30/70 ?

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    Senior Member bellwilliam's Avatar
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    Default what is an ideal weight distribution ? 50/50 ? 40/60 ? 30/70 ?

    what is an ideal weight distribution for a car ?

    Miata, Corvette and BMW brag about their 50/50.
    Porsche and Ferrari brag about their ~40/60.

    so one of them must be wrong ? or it depends ?

    can we agree that front heavy is ALWAYS bad ?

    say say I have a 50/50 car, I can move some weight to the back, should I ?
    Last edited by bellwilliam; 05-02-2012 at 11:56 AM.
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    If you have a choice about where to put ballast, put it over the rear wheels. I don't know much more than that. I think it was Emilio who said that racing 911s are fast inspite of their rear engine design, not because of it. You can't deny that a Ferrari 458 Italia is a spectacular car.
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    If you have a choice to put ballast, wouldn't you want to put it as low as possible and as close to the yaw axis as possible?

    I think a moderate rear-biased weight distribution is ideal, something like 40/60. The rearward weight bias would help utilize all four wheels under braking, and help traction out of corners. Front weight bias would be the opposite, so I think it would always be bad, just like FWD is always worse than RWD. The reason I think only moderate rear-biased is you wouldn't want the center of gravity to be too far from the yaw axis, which would hurt steady state cornering. I think that's why Emilio says rear-engined Porsches are fast despite their setup.
    Last edited by NammyBoy; 05-02-2012 at 03:27 PM.

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    40/60 is a design compromise. It can be worked around, as Porsche has shown, but if they could choose they would go for 50/50. In fact they are moving in that direction: 997 C2 was 38/62, in the 991 they have moved the engine forward 7 cms and the ratio is now 42/58.

    If you have a 50/50 car and could move a few things around -> Focus on mass centralization and lowering polar moment of inertia more than F/R ratio.
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    Track Newbie NammyBoy's Avatar
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    F1 cars have 45/55. So maybe that is the magic number?

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    50/50 dynamic load distribution (whether it be front/rear, left/right, whatever) is ideal for a given acceleration amount & direction (assuming non-staggered tires and a perfect AWD system). The problem is that cars accelerate in an infinite number of directions....

    So the answer is, everything is a compromise and there is no such thing as perfect. But, for a RWD car, something like ~45/55-40/60 should be the best compromise. This results in ~50/50 under braking and more load on the rears when you're on throttle.

    And as Drew will remind us, you can't forget about aero....

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    obviously, anything hanging after rear axle or in front of front axle is never a good thing.

    for the sake of simplifying argument, just say weight can be moved within axles.
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    Quote Originally Posted by bellwilliam View Post
    obviously, anything hanging after rear axle or in front of front axle is never a good thing.

    for the sake of simplifying argument, just say weight can be moved within axles.
    Then why have 911s had the engine hanging off the rear axle for nearly 50 years and are still so successful in racing and popular with the sports car buying public?
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    Quote Originally Posted by J. Tyler View Post
    50/50 dynamic load distribution (whether it be front/rear, left/right, whatever) is ideal for a given acceleration amount & direction (assuming non-staggered tires and a perfect AWD system). The problem is that cars accelerate in an infinite number of directions....

    So the answer is, everything is a compromise and there is no such thing as perfect. But, for a RWD car, something like ~45/55-40/60 should be the best compromise. This results in ~50/50 under braking and more load on the rears when you're on throttle.

    And as Drew will remind us, you can't forget about aero....
    +1 in street cars your always trying to fix handling quirks. Weight can be is an engineers worst nightmare and best friend.

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    I have my ST2 vette to 50/50 not only front to back but also side to side. I bet more weight to the rear would be a benefit, however I agree that aero forces probably become a dominating factor at speed. Especially for F1 type race cars.
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    Quote Originally Posted by Richard EVO View Post
    Then why have 911s had the engine hanging off the rear axle for nearly 50 years and are still so successful in racing and popular with the sports car buying public?
    Usually if it is competing, the class rules help the 911 be competitive. It is a 'heritage' thing... rear-engined is just what a 911 is. Without that, it wouldn't be unique and it wouldn't be a 911. Which is why Porsche keeps building them; people pay for that heritage and uniqueness. That having been said, Porsche has been developing the 911 platform for, like you said, 50 years. It is a great car in spite of its layout, not because of it. "Sports car buying public" = doctors/lawyers/etc who don't know any better.

    With similar power & components, the Cayman would be a faster and better car.

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    Quote Originally Posted by J. Tyler View Post
    50/50 dynamic load distribution (whether it be front/rear, left/right, whatever) is ideal for a given acceleration amount & direction (assuming non-staggered tires and a perfect AWD system). The problem is that cars accelerate in an infinite number of directions....

    So the answer is, everything is a compromise and there is no such thing as perfect. But, for a RWD car, something like ~45/55-40/60 should be the best compromise. This results in ~50/50 under braking and more load on the rears when you're on throttle.

    And as Drew will remind us, you can't forget about aero....
    +1
    This is the answer. To find what is ideal, you need look no further than the fastest cars in the world.
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    Senior Member robburgoon's Avatar
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    Quote Originally Posted by J. Tyler View Post
    Usually if it is competing, the class rules help the 911 be competitive. It is a 'heritage' thing... rear-engined is just what a 911 is. Without that, it wouldn't be unique and it wouldn't be a 911. Which is why Porsche keeps building them; people pay for that heritage and uniqueness. That having been said, Porsche has been developing the 911 platform for, like you said, 50 years. It is a decent car in spite of its layout, not because of it. "Sports car buying public" = doctors/lawyers/etc who don't know any better.

    With similar power & components, the Cayman would be a faster and better car.
    That's gotta be the most frustrating thing about sports car racing. Companies with s***box FWD cars get to compete with double wishbone mazdas that get nerfed for being a superior car.

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    Quote Originally Posted by J. Tyler View Post
    With similar power & components, the Cayman would be a faster and better car.
    But Porsche will never drop a 991S or GT3 engine in the Cayman, precisely because it would be faster than a 911, handle better, and cost less. That would cut into 911 sales quite a bit.
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    There is no IDEAL weight distribution because it depends on so many factors, ie aero balance, suspension type, number of wheels driven, power output, design goal of the vehicle, tire grip levels, etc. In this video Tada-san explains why the FRS has a 53/47 weight distribution; very interesting.
    2013 Scion FR-S Chief Engineer Tetsuya Tada Interview - YouTube
    (skip to 5:05 mark for those impatient people)
    Last edited by madant15; 05-02-2012 at 06:35 PM.

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    Quote Originally Posted by madant15 View Post
    There is no IDEAL weight distribution because it depends on so many factors, ie aero balance, suspension type, number of wheels driven, power output, design goal of the vehicle, tire grip levels, etc. In this video Tada-san explains why the FRS has a 53/47 weight distribution; very interesting.
    2013 Scion FR-S Chief Engineer Tetsuya Tada Interview - YouTube
    (skip to 5:05 mark for those impatient people)
    I believe that interview is just marketing talk, because they can't make it 50/50 or a rearward bias. I don't believe front heavy is better in FRS for any reason.
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    Senior Member bellwilliam's Avatar
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    Quote Originally Posted by J. Tyler View Post
    Usually if it is competing, the class rules help the 911 be competitive.

    +1, applies to all racing regulation. it is just how the rules are written. in LeMan, diesel are favored so much that it is ridiculous...
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    Quote Originally Posted by bellwilliam View Post
    I believe that interview is just marketing talk, because they can't make it 50/50 or a rearward bias. I don't believe front heavy is better in FRS for any reason.
    Good god he was laying the bull on thick in that video.
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    Quote Originally Posted by robburgoon View Post
    That's gotta be the most frustrating thing about sports car racing. Companies with s***box FWD cars get to compete with double wishbone mazdas that get nerfed for being a superior car.

    Nerfed?

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    I think that was Jackie Chan

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