Is this the source of my balance problem?

[2cheap]

I recently picked up a set of 11" Zimmermann rotors [Corrado, I think] for my 99 on CR.


I have also picked up a set of 16x8 wheels.

I presently have the car torn down, but I got some driving time in before I tore everything apart. During that, I had a horrible balance problem., immediately after installing the large rotors.

Between the rotors and the calipers and the wheels, I have probably more than doubled my unsprung mass, so I am not really all that surprised....

I can't test it now, but my recall was that I drove with the new wheels without much drama, and that all of the balance problem started after putting on the new rotors. I could be mistaken - can't remember.

It is important to note that the larger rotors only have one flat head screw countersink, not two.

Also, the hub diameter for the rotor is larger than the miata hub.

I assume that all of this makes the rotor hub-centric, and that I need to tighten down the lugs with the wheels up, so that the wheels center the rotor....

HOWEVER, I cannot help but think that I am getting some fierce radial runout...I could probably use a dial indicator to measure this. I am betting that it would be significant.

What are my options for confirming / correcting the source of the balance problem?

Have second pilot hole drilled in the rotor?

Dynamic balance the wheels on the car?

Shock tower bar?

I am not really in the mood to switch back to the old rotors just to confirm that the bigger rotors are the source of the trouble. That would be a lot of work just to confirm something I would still need to fix.

I am attaching a picture for reference - note the one pilot screw and the oversize hub dia.


Please help!
Thanks!

[Reverend Greg]

Those rotors WILLNOT work the hub bore is too large,you could get a ring machined for the difference,But come on this is your brakes,if you cant stop You will die.you need to get rotors that have the same size or smaller hub bore.Smaller is easy to fix,it is always easier to take metal off than to put it back on.Just My Opinion Your results may vary...
(G)

[2cheap]

Based on the lug nuts holding the rotor very tight against the wheel, I think that the worst that I can expect is radial misalignment and whatever runout was already in the disc.

I measured the runout on the face of the rotor - within .002 so I do not think that is the issue.

I have braked from speed with this setup - no problem there.

My real concern is the radial misalignment that will result in the brake rotor tracing out an oval as it rotates - and maybe inducing a balance problem as a result.

[RotorNutFD3S]

As mentioned already, it is because the rotors you have are not hubcentric. M-Tuned (aka etdracing) included a hub centering ring with their Corrado based kits for exactly this reason. You might want to contact them and see if you can purchase the rings alone, or get a ring machined as Rev. G suggested so that the rotors are centered.