CMC 17" Wheel Weight & Welded Spacers

[marshall_mosty]

The real genesis of the rule change was due to an Enkei RPF1 with a steel spacer that was attached to the wheel with screws (drilled the wheel and counterbore in the spacer) then plug welded so the attachment screws can’t back out or the wheel separated from the spacer, making a pseudo custom wheel).

That led to folks saying the heavier spacer “mass” was in the middle of the wheel, hence lowering the rotational inertia which created an advantage. That prompted the rule to be written around an aluminum wheel and aluminum spacer.

I’d still lobby for a permanently attached (screws plus plug weld which is easier with standard billet 6061 spacers).

Since the original steel spacer and alumunimum wheel combo was my idea and Jeremy was clever enough to try it (and McSpadden copied the idea with my CAD file for the spacer and took it to Nationals), blame all this on me... LOL

[Sook]

The real genesis of the rule change was due to an Enkei RPF1 with a steel spacer that was attached to the wheel with screws (drilled the wheel and counterbore in the spacer) then plug welded so the attachment screws can’t back out or the wheel separated from the spacer, making a pseudo custom wheel).

Adding holes to the center bore of the wheel scares me... and then plug welding them will locally destroy the wheel's temper.

That led to folks saying the heavier spacer “mass” was in the middle of the wheel, hence lowering the rotational inertia which created an advantage. That prompted the rule to be written around an aluminum wheel and aluminum spacer.

How does going to aluminum solve remove the inertial advantage? I'd rather go with a steel non-attached spacer. I can make your wheels (thanks for the deal btw) work with steel spacers.

So here's the question, if I show up to COTA with aluminum spacers not welded to my wheels will I be DQ'd? I wouldn't take the risk of showing up with a car that directly goes against the rule book, if we can get clarification ahead of time against welding wheels it'd be awesome.

- Josh

[Suck fumes]

yah sook make sure you get clarification on anything wheel related. I saved all Marshals approval messages on my phone when i took my setup to Utah at miller mot park just to cover my butt cause it created a firestorm online once people realized what i did to the wheels (marshals idea) to make weight. BUT it’s the budget way around spending thousands in fikse or ccw wheels.

[marshall_mosty]

Just to clarify the plug weld would ONLY be on the spacer, not the wheel. The only permanent modification are the tapped holes that the screws which hold the spacer on screw into.

Regarding steel vs aluminum spacers, for a given weight and thickness, the outer diameter of the spacer would be smaller on the steel spacer (advantage)...

[mach1]

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.

[Suck fumes]

exactly!

[DAlgozine]

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.

[DAlgozine]

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.

[Supercharged111]

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.

[mach1]

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.