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# 2-piece Floating rotor set-up design

## 2-piece Floating rotor set-up design

(OP)
Hi everybody,

I am working on designing a 2-piece floating set-up for a road car (that will also see some track time).

I understand the fundamentals of the floating rotor design.
I have the rotor material (G3000 Grey C.I)
I have the Hat material (6061 Alu)

I have seen rotor temperatures on a very similar set-up approach the 1100F mark on track, so I am using 1200F as my upper limit for operation temperature.

There are two dimensions for float: Radial and Axial

Given the thermal expansion coefficients, you can easily calculate the amount of radial float that must at least be present.

My question is: How to control the axial float?
I understand most race car set ups are not concerned with the noise that is generated with a floating set-up, however I need to have spring preload and still allow for axial thermal expansion.
I have experience using a set-up that uses belleville washers in between the bolt head and rotor flange. This allows me to torque the hat to the rotor without having relative movement.

How should I determine the amount of float needed in the axial direction? We are accounting for both thermal expansion and movement in the suspension/braking components bolted to the uprights.

This seems a little open ended, but I am looking for advice. If there is anything missing from this post that may be needed to pose an answer, please let me know.

I appreciate it, thank you.

### RE: 2-piece Floating rotor set-up design

(OP)
Do you design for a preload that does not exceed a value that would prohibit radial expansion? - Thinking out loud here...

### RE: 2-piece Floating rotor set-up design

(OP)
You know what - You are right, this was a little lengthy, I apologize about that.
I was able to figure this out. Calculate the force generated to move a given amount due to thermal expansion at your operating temperature. From there you can select your spring rates.

### RE: 2-piece Floating rotor set-up design

The floaters that I have seen used on the street used a shoulder bolt to seat the nut against and then a belleville washer between the nut and the floater to allow for the expansion and movement. The length of the shoulder was developed to give a certain amount of precompression of the belleville between the nut and rotor when the nut was seated against the end of the shoulder.

### RE: 2-piece Floating rotor set-up design

highboost-

With disc brakes you can use axial float of the rotor or axial float of the caliper. Racing disc brake systems usually allow radial and axial float at the rotor-to-hat attachment and use rigid caliper attachments. Most automotive disc brakes use a rigid radial/axial rotor attachment, and an axial float of all/part of the caliper.

Racing disc brake rotors are attached to the hat using "hat bushings" like this: http://www.apracing.com/drawings/CP2872_1000CD.pdf

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