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Thread: CMC 17" Wheel Weight & Welded Spacers

  1. #11
    This horse was beat to death in the CMC forum a few years ago when the Bulletin came out allowing a welded spacer to be included in the weight of the wheel, and the subsequent "End of the season rule debate" about it.
    Good read. Get your popcorn.

    But, here's what I come away with.
    The Enkei wheels with spacer welded come in just over 18lbs.
    The only way a 17 x 9.5 GM wheel can get close to 18lbs is a set of custom wheels, which cost thousands of dollars.
    So, nearly all GM's buy Z06 wheels that weight 19.5 - 20 lbs and still have to install a spacer for another 3/4 - 1 lb, and that's about 20 - 21 lbs.

    A few pounds doesn't sound like that much, but it is rotating mass, so it is a big deal. Plus there is another benefit of the Enkei with spacer. In order to make the minimum , it has more of its weight in the hub. And, that one is important also.

    From what I have read, rotating mass weight is a factor of 10 when compared to sprung mass. So, 8-10 total lbs of rotating mass is equivalent to 80-100lbs of sprung mass. That's a big number. Some of that would show up on the dyno and get negated , but only a portion of it. Im not an engineer, so fire away. But everything I have read, indicates that rotating weight is a very big deal. As I'm sure some already know. Or we would all be using 26 lbs wheels.

  2. #12
    Quote Originally Posted by mach1 View Post
    Any mod to the wheel compromises safety IMO, I don’t understand the point of it being permanently attached, potential safety issue with no upside that I can see. If someone was protested you would audit the same way in impound, pull the wheel, dismount tire, weigh with with spacer as it came off the track.
    So in this scenario, a Ford can run a 16lb wheel with a 2lb spacer and get to the 18lb minimum. Great
    However, there are no off the shelf, other than custom $$ GM 17 x 9.5 wheels that weigh any where close to 16 lbs or 18lbs with the proper spacer, Or 18lb that have the proper offset. They don't exist. Closest a GM car gets its about 21lbs with a needed spacer.

  3. #13
    Senior Member Carroll Shelby Supercharged111's Avatar
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    Rotating mass isn't a linear factor. It's exponential, and the farther out the weight is the much bigger of an impact it will have. I could google the equation, but it's out there and it's pretty simple.
    RM CMC Director

  4. #14
    Senior Member Carroll Shelby
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    Quote Originally Posted by DAlgozine View Post
    So in this scenario, a Ford can run a 16lb wheel with a 2lb spacer and get to the 18lb minimum. Great
    However, there are no off the shelf, other than custom $$ GM 17 x 9.5 wheels that weigh any where close to 16 lbs or 18lbs with the proper spacer, Or 18lb that have the proper offset. They don't exist. Closest a GM car gets its about 21lbs with a needed spacer.
    Right, same as today, ford can run a 16lb with a 2lb spacer and perhaps sacrifice the integrity of the wheel. I would hate to see a wheel fail and take out 5 cars going into T1 just because you have to compromise safety to make it legal.
    Tyler Gardner
    CMC #13 2015-2017
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  5. #15
    Senior Member Carroll Shelby
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    I'm going to drill holes in my z06 wheels to make it an 18lb wheel.

    Since the cheater mustangs are getting center of mass close to the hub, I'm going to drill into the wheel barrels.

  6. #16
    Senior Member Carroll Shelby
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    Quote Originally Posted by Pranav View Post
    I'm going to drill holes in my z06 wheels to make it an 18lb wheel.

    Since the cheater mustangs are getting center of mass close to the hub, I'm going to drill into the wheel barrels.
    Drill em and dab some rtv in the holes, Chevy P1!
    Tyler Gardner
    CMC #13 2015-2017
    SM #013 2018
    www.dfwmustangs.net

  7. #17
    Quote Originally Posted by mach1 View Post
    Right, same as today, ford can run a 16lb with a 2lb spacer and perhaps sacrifice the integrity of the wheel. I would hate to see a wheel fail and take out 5 cars going into T1 just because you have to compromise safety to make it legal.
    Or stick to the original intent of the 18lb wheel rule and don't allow 16lb wheels. All off the shelf wheels require spacers. Including the spacer with the wheel is a goofy loop hole. And I always thought goofy loop holes don't have a place in CMC.
    I supposed by welding the spacer it is a custom wheel, which by rule is not illegal.

  8. #18
    Senior Member Carroll Shelby
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    Quote Originally Posted by mach1 View Post
    Drill em and dab some rtv in the holes, Chevy P1!
    I once RTVed a valve stem on my Honda and did a few 1/4 mile passes on it then drove home.

    It actually failed but because it was an Azeni RT-615, I never noticed. Sidewalls of steel...

  9. #19
    Senior Member Carroll Shelby
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    Quote Originally Posted by DAlgozine View Post
    Or stick to the original intent of the 18lb wheel rule and don't allow 16lb wheels. All off the shelf wheels require spacers. Including the spacer with the wheel is a goofy loop hole. And I always thought goofy loop holes don't have a place in CMC.
    I supposed by welding the spacer it is a custom wheel, which by rule is not illegal.
    So the fords have no 18lb options?
    Tyler Gardner
    CMC #13 2015-2017
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    www.dfwmustangs.net

  10. #20
    Senior Member Carroll Shelby marshall_mosty's Avatar
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    Quote Originally Posted by DAlgozine View Post
    I supposed by welding the spacer it is a custom wheel, which by rule is not illegal.
    Doug,
    The original intent of the steel spacer, attached to the wheel with plug welded screws was to create a pseudo custom wheel that met the letter of the rule.
    Marshall Mosty
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