Birkin front hubs

[Birkin42]

I made a set of rotor hats to mount 2 pc rotors on the front hubs of my Birkin. When I went to trial fit them, I noticed the hat would not pull up tight to the rotor mounting flange on the hubs. On a Birkin, the front rotors mount off the back side of the hub flange and are not trapped between the outboard side of the flange and the wheel. I first suspected that it was an interferance with the corner radius on the hub but after measuring it up, this was not the problem. I checked the flange for flatness and indeed they had run out (slightly conical) by about 0.006". I checked both hubs and both where the same. Any idea if this is may be intentional? If so why? I'm assuming this is a manufacturing error.

In checking the front hubs, I also noticed that one has radial indicated run out of 0.010" TIR for the pilot for the front wheel, but the remaining cylindrical features like the pilot for the brake rotor run true. Only one of the 2 hubs has this issue, so I know this is an error. How much run out is acceptable for a wheel? 0.010" may not be that much but it is bugging me.

 

Jack

[Ian7]

I'd be surprised if you could feel as little as .010" radial runout on the wheel mount pilot diameter. These are pretty 'harsh' cars with a million sensory inputs per second. Tires alone typically have more than that error on their moulded tread...

 

Curious why you made your own rotor hats? that's a pretty serious piece, with nasty a failure mode. No commercial item available?

 

Regards

[Birkin42]

None are available with the right pilot hole diameter and more importantly, the right offset that I have been able to find. Since on a Birkin the rotors are mounted off the inboard side of the flange, they have very little offset. They are more like a plate than a deep hat. The rears are more traditional.

I checked the anticipated stresses with FEA and tried to match wall thicknesses with commercially available hats so I don't have a lot of concerns about failure, but there is always a risk. With all the custom parts I'm making including the entire rear suspension, I'd never be able to drive the car when eventually done if didn't have confidence in what I am doing. I'm guessing there are going to be some teething problems, just hopefully noting too catastrophic!

[RDROCKT]

Have you tried Wilwood? They have offsets from .21" to 2.12". Try this http://www.wilwood.com/Products/003-Hats/003-GTSF/index.asp . Various center hole diameters and lug bolt patterns.

[Birkin42]

My rotors and calipers are from Wilwood so that was the first place I looked. They just didn't have what I needed.