Floating Rotors

[B]

Guys... I'm trying to decide wether or not to make our rotors (disc brakes) float or not....?

From what I can see the advantages and disadvantages are as follows;

Ad – 1) No unwanted stresses are put on the rotor
2) The face of the rotor will always be flat on the pads giving maximum area for the heat flux to dissipate over minimizing thermal stress and stress concentrations

Dis – 1) Makes a lot of noise!
2) Possibly more weight and cost and complexity

Is it worth it? I've noticed that a lot of the leading teams do float their rotors... Can ppls in the know please elaborate on my Advantages and Disadvantages.

Regards

Brett Walker
CMT 05

[Agent4573]

during design in may we were pretty much told by judges to float our rotors for next year.

[Jarrod]

Floating rotors has a number of advantages, the reduction of thermal stresses, and so reducing rotor distorion, being one, if the rotor is allowed to float it will reduce the effect of the pistons being pushed back into the caliper (there is a term for this but it escapes me at the moment?) due to misalignment, warping etc, which will improve pedal feel substantially, the rotors will not drag on the pads, so reducing rolling friction. There may be others, but these are the key ones i am aware of. The noise is really a non issue as far as i am concerned, i have never noticed any noise, even if there is, who cares, you have a motor spinning at up to 15000 rpm directly behind your head. NVH is for going to the shops. All motorbikes have floating rotors, maybe go to a bike shop and ask around, have a look at how they do it? The weight and complexity are fairly minimal, they are quite simple, and the cost will be less than $100.

[Nick McNaughton]

The term you're looking for is pad knockback. Floating rotors don't knock the pistons back into the caliper, so the driver's next brake application doesn't use up pedal travel for nothing. It's one of many sources of dead travel in a brake system.

[Denny Trimble]

Originally posted by Jarrod:
All motorbikes have floating rotors...

Completely off topic here, but if you find a Harley V-rod, have a look at the front rotor. From about 30 feet away it looks like a floating rotor, but it's just for looks...

Shame, shame.

[B]

So just to specify the term floating....

When I mean float I mean that you can actually move the rotor a couple of mm in the axial dirrection with your hands (so long as the pedal isn't compressed).

I want to specify this because you can't do that motorbike rotors. They generaly use large hollow rivers to mound the rotor to and Aluminum hat...

Jarrod and Agent4573... what r your coments?

Brett
CMT 05

[Psychosis]

2mm of axial float!!! isnt that a lot? i thought axial and radial float should be typically 0.4mm. most motorbike brakes are not true floaters because people worry when they hear a rattle, though ducati make some. we're moving to floaters next year. quite like these ones :
ducati floater (http://www.ducaticanada.com/articlesimg/images/closeup-of-the-wave-rotors.jpg)
the other factor no ones mentioned is the transfer of forces to the hub. the forces are in plane with a floater rather than using bolt shear.

[Big Bird]

B, I find it odd that you say can't get floating motorcycle discs - i.e. floating in an axial direction. They are very common on pukka road racing bikes. Take a look at Brembo genuine racing discs, they rattle around so much they sound like they are about to fall off.

You might not see such things if you only search at your local m/c dealer - Joe Public gets panicky if things don't seem to be well done up on his streetbike.

I don't know where CMT is - but if you are in Australia try Planet Tooling in Bayswater, Melbourne.

All above information true and correct as at June 1999. I won't be held responsible for any changes in motorcycling fashion since then http://fsae.com/groupee_common/emoticons/icon_smile.gif

Cheers

[B]

Also.. what is an acceptable amount of float?
2,3,4,5mm

Brett
CMT 05

[Big Bird]

From memory I think the Brembos were about 2mm (?). Also, just saw the tag saying you are from Curtin, so yep, I guess you are in Australia. Glad to see you guys lining up for another go!

Cheers

[Jarrod]

Thanks Nick, thats the one. knockoff was the term that came into my head, it didn't quite feel right.

yes, I did mean both radial and axial movement allowed, street bikes probably are a bit tighter for the above mentioned reasons, I have seen some that can move visibly, on our 03 car we had wave washers to retain some tension so the buttons weren't falling all over the place, but the disc could move about 3mm axially, about 0.25mm radially. Then we saw the 03 chalmers brakes (ISR?), superbike parts or something, and they just flopped all over the place.

[B]

ok... let me get this right.

2-3mm axial float.
0.25 – 0.4mm radial float - that seems a bit low to me I guess the rotors aren't going to expand any more than that... Currently I have it designed at 3-4mm radial float.
0.25mm circumferential float.... I currently have 0.4mm float.

What do ya think?

[B]

Jarod, just a thought.... you said that enabling the rotor to float prevents the piston from being pushed back thus preventing an increase in pedal travel... but if the rotor is loose and rattling around then doesn't that mean that it has pushed the pads back, thus it is loose...

[Buckingham]

If the rotor can float axially, then it "shouldn't" be able to sustain the reaction force needed to push the pad back. Meaning that when the rotor rubs against the pad, the rotor moves back (not the piston).

A properly floating rotor will not appear to be "loose and rattling around". If it is "loose and rattling" you probably have some degree of angular float (rotor not parallel to hat), this should be avoided.

[Brian Evans]

Ap Racing has a good info section on their web site: http://www.apracing.com/car/brakedisc/float.htm

Float from .15mm to about .5mm seems the range, and they have two ways to accomplish it, plus the bits and bobs to actually do it.

All you need to know, really...

Brian

[Jarrod]

The numbers i put up were just the numbers off the top of my head, they are by no means optimal or neccesarily the correct way of doing it, but thats what we had and it worked pretty well. The buttons didn't allow the disc to move directly back and forth by 3mm, but holding on to the disc you can move it freely around that distance, maybe more. There was probably 0.8-1mm of direct float in the buttons. The rotors don't really rattle when the calipers are on, because the pads are just resting against it at all times. I would go with APs recomendations, i'm pretty sure they know a bit more about it than I do.

[Cement Legs]

OK after reading through this post I feel that I have enough information to work through the rotor mounts but I am left with another question (or statement). It would now seem obvious to me that a floating rear sprocket, especially if the diff carrier mounts to the frame instead of the engine, would provide similar benefits (relieving stress if there is torsional distortion in the frame between these two components). We were starting to think about having the diff carrier mount to the frame when looking at ways to adjust the tension in the chain. Are there any obvious issues here that I am missing?

[Agent4573]

Floating the sprocket would probably be a good idea, but you would have to make sure to get your chainline exact. I would think that if your front and rear sprockets are out of alinement by anymore than the 2-4 mm of float you have on your buttons, that things would get ugly pretty fast.

[milky]

Originally posted by Jarrod:
Floating rotors has a number of advantages... the rotors will not drag on the pads, so reducing rolling friction.

I disagree muchly with that statement, especially if you also consider the reduction in pad knockback. Compliance in the upright will change the alignment of the caliper/pads to the rotor slightly and hence non floating rotors will have more drag through corners, but I imagine the frictional effect of this is minimal.
The other points I agree with - improved pedal feel, reduction in vibration, less knockback, reduction in stresses due to rotor temps, less heat transfer to bearings and so on.

[Homemade WRX]

I've been researching floating rotors and was wondering of the teams running them, are you running 10" or 13" wheels?
also did you design your float in the bell/hat or in the rotor?
pictures are always appreciated
Thanks, Micah