Floating Disc rotors

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  • Floating Disc rotors
  • skidartist
    Member

    they are filled with helium so that you can pull rad airs, and never come down.

    mojo5pro
    Member

    The outer steel braking surface is mounted (riveted) onto an aluminium inner spyder. This makes the the rotor lighter than a solid steel one and supposedly dissapates heat better.
    They are like for like size wise with the equivelent solid rotors.

    Premier Icon mboy
    Subscriber

    They are also technically, NOT "floating"…

    True floating rotors, like those fitted on the front end of my Ducati, actually "float"… As in they have some side to side wobble. This is so that they don't rub the brake pads at high speed, as they can self centre to a certain extent.

    Click here and read this thread for a reasonable explanation

    Don't know why, but it REALLY grates that Hope, Magura et al call their rotors floating. Cos they're not! They are stainless steel pad tracks mounted on aluminium bells using buttons, but they're not floating in the case of any MTB rotors I've ever seen.

    gee
    Member

    They float "out" – the buttons allow a degree of expansion when the rotor gets really hot, preventing warping. It's why they "tick" at the bottom of very long downhills (assuming you were braking…).

    GB

    hope and magura took the decision because

    "stainless steel pad tracks mounted on aluminium bells using buttons"

    didn't really sell it all that well.

    Premier Icon mboy
    Subscriber

    hope and magura took the decision because

    Yeah, but I still find this mis-selling very annoying. They're JUST brake discs if you buy new discs for your motorbike (most motorbikes don't have floating rotors, only very few do), so why does the MTB market have to try and be better?

    They float "out" – the buttons allow a degree of expansion when the rotor gets really hot, preventing warping. It's why they "tick" at the bottom of very long downhills (assuming you were braking…).

    Have you got any scientific evidence to back this up? Or at least proof of the theory perhaps. I find this hard to believe personally, the material does not get hot enough to expand by a LONG stretch… Steel doesn't melt til 1700 degrees C, and I would bet that your MTB brakes never exceed 250 degrees C, even on the most Alpine of Descents.

    The main reason they sell these (not floating) rotors for MTBs is that they look tarty… Which they do! In the motorbike world, it's cheaper to just get new pad tracks fitted onto the original ally bell/spider when you need new rotors, which I suspect it wouldn't be for the Hope MTB rotors. They will be marginally lighter than a full steel rotor though I suppose, but will you notice it?

    sailor74
    Member

    whets the definition of these and can they be used as direct replacements for standard rotors?

    theflatboy
    Member

    True floating rotors, like those fitted on the front end of my Ducati, actually "float"… As in they have some side to side wobble. This is so that they don't rub the brake pads at high speed, as they can self centre to a certain extent.

    i must be "floating" then, as people always tell me i'm self centred.

    Kramer
    Member

    Steel doesn't melt til 1700 degrees C, and I would bet that your MTB brakes never exceed 250 degrees C, even on the most Alpine of Descents.

    But it expands long before it gets close to melting.

    mojo5pro
    Member

    mboy – steel expands with heat, regardless of it's high melting point. Try spinning your back wheel after sustained braking on a long descent…

    tails
    Member

    Don't know why, but it REALLY grates that Hope, Magura et al call their rotors floating. Cos they're not!

    You need to get out more lad. 😉

    What I like about floating rotors are they don't distort bend as easily so no more rotors catching pads, thus no more sitting there with washers trying to centre a rotor.

    Premier Icon mboy
    Subscriber

    mboy – steel expands with heat, regardless of it's high melting point. Try spinning your back wheel after sustained braking on a long descent…

    It does, but at 250 degrees its expansion will be marginal, if anything. Try spinning my back wheel after a long descent? Errrr… Dunno how badly setup your bike is, but mine will always spin regardless. Unless I'm dragging the brake of course! Open brake systems were brought into the MTB market to combat this very problem, which of course was an issue when the only disc brakes you could get for an MTB were Hope C2's.

    You need to get out more lad.

    Yeah maybe, I do try though, restraining orders permitting 😉

    What I like about floating rotors are they don't distort bend as easily so no more rotors catching pads, thus no more sitting there with washers trying to centre a rotor.

    Fair point… I suppose they're stiffer too, so less susceptible to being bent. Still doesn't make them "floating" though!

    DaveGr
    Member

    I've found they don't last as long as standard rotors and if they get bent slightly (ie when transporting bike) then they're harder to bend back.

    TandemJeremy
    Member

    Brakes get to many hundreds of degrees. How hot to blue a stainless steel rotor? I have some nicely blued ones from heat damage

    The hope "floating" discs prevent warping by allowing the braking track to expand away from the spider. if the braking track and the spider are one piece the temp gradient can lead to warping in extermis. However for UK XC use this should not be an issue – it can be in alpine and tandem use

    Dibbs
    Member

    I've managed to turn my discs blue in the past (braking from 60+ mph), and according to my Chapman Workshop Technology book that needs 300 degrees C, the "floating" rotors where definitely ticking after that, so I presume they had expanded a bit.

    Hadge
    Member

    Floating rotors are "directional" – unlike hi-fi cables which only claim to be 😀 Hadge don't start them off again…………
    It's just soime marketing bull that's all – just like many other bike manufacturers saying their bikes the best. They look good and sound good at the bottom of a hill. End of.

    andyfb78
    Member

    As someone who worked for Ferodo R&D many moons ago here's my tuppence worth.

    Floating rotors were used originally on racing motorbikes because steel was (is) rubbish compared to cast iron for friction purposes. To save unpsrung mass and overall weight AND to reduce cracking caused by thermal expansion and warping on large diameter disks. they were mounted on pins so that they could move slightly. you can actually waggle the disk. The disk does 'auto align' under braking and it reduces the drag on the pads off brake, but this is secondary.

    Cast iron starts to glow red at about 600degC, and bright toward 850degC. Racing brakes achieve this temp quite easily under repeated stops, but settle at about 450degC otherwise fade is experienced with most pad materials. A floating brake does not cool better (the cooling area is reduced) but it does isolate the hub from the extreme heat allowing different materials to be used where appropriate.

    Racing brakes rarely use steel as it warps and is rubbish at friction compared to iron. F1 brakes are a totally different game, and racing bikes now often use carbon reinforced carbon disks and pads fro the same weight reasons as F1.

    I don't know much about MTB brakes, but the thermal split in the disk to spider, will allow the disk to get hot and keep the hub cooler, there were several cases of failed bearing in racing mbikes due to excess heat build up. it might help with alignment, but i have seen waggly ones and very tight ones so I'd be surprised if that was the design intention!
    Cynically it might actually be just a 'looks cool' but I'll bet the DH boys can see some serious disk surface temperatures and so this will help.
    Running a large diameter steel or iron disk is a lot of heavy material you don't need, so just keeping th efriction surface as a good material and using lighter spider improves stiffness and reduces unsprung mass, more important that overall weight I'd guess in a DH bike.

    ramble over.

    For my riding (XC) I use small disk, and so littel advantage for a 'floating rotor'..
    (still got one though, coz it was the same price 🙂

    Premier Icon mboy
    Subscriber

    BIG thumbs up and thanks for the explanation andyfb78

    coolfurcats
    Member

    [Don't know why, but it REALLY grates that Hope, Magura et al call their rotors floating. Cos they're not! They are stainless steel pad tracks mounted on aluminium bells using buttons, but they're not floating in the case of any MTB rotors I've ever seen. ]
    Magura don't have and I don't think ever have had floating rotors. Hope and Formula are the only two main producers who have ever used this system. What Magura have is plain steel rotors and "Venti Discs" that have a steel outer rotor with an aluminium spider that is riveted into the rotor. 🙄

    coffeeking
    Member

    Along with andyfb78s comments, I wonder if the disconnection of the braking surface from the spider actually helps by allowing the contact area to maintain a higher temp. Certainly brakes work better (to a point) when hotter. With it being a different material with a physical join there will be a relatively high thermal resistance between surface and spider and so the surface would remain warm longer. You'd just have to hope it cools sufficiently under duress.

    Hopes vented rotors are the ideal of this, seperated from the spider AND vented for cooling at the top end.

    keppoch
    Member

    Would I be right in thinking that a couple of mm movement between the aluminium spider and the steel track is a bad thing?

    Is this a return to manufacturer issue or a buy a new one issue?

    keppoch

    Premier Icon BadlyWiredDog
    Subscriber

    The main reason they sell these (not floating) rotors for MTBs is that they look tarty…

    Actually, it's because they're lighter. You save a big chunk of rotor weight using Hope's race level floating – or whatever they are – rotors, the ones they spec on the Mono Mini Pro. Arguably irrelevant for trail riding, but on a race bike, it all counts.

    But yes, they do look neat as well.

    coffeeking
    Member

    Would I be right in thinking that a couple of mm movement between the aluminium spider and the steel track is a bad thing?

    In what direction? Radial – yes. Circumferential – yes. Axial – not necessarily but possibly.

    Premier Icon BadlyWiredDog
    Subscriber

    I've found they don't last as long as standard rotors and if they get bent slightly (ie when transporting bike) then they're harder to bend back.

    I had one where the aluminium spider bent enough to rub against the caliper mount. A real pig to get straight again. Not had any issues with longevity though, the braking surface is the same as 'solid' rotors, so why would they wear quicker?

    Premier Icon glenh
    Subscriber

    On the bending thing, I find that this is actually the main benefit of 'floating' rotors.

    All steel ones always seem to get a little bent or warped in my experience and you can never get them perfectly straight again, so minor pad rub is inevitable.
    'Floating' ones are much stiffer (due to the alu spider), so don't get bent easily (although I imagine they are a pain to straighten if the do get bent!). Thus they stay nice and straight in my experince.

    andyfb78
    Member

    Temperature depends entirely on the pad material, soem like heat others do not. Most car and m-bike pads are what MTB world refers to as sintered,ie they are iron powder based, or metallic. what we call organic pads (ie carbon or aramid {we know as kevlar} flake based) are very rare in the car world due to excessive pad wear.

    I have never doen any scientific testing of MTB brakes so this is only extrapolation of the work I did on m-bike and racing car brakes:
    a really cold disk tends to squeal and you get some 'creep-groan' at very low speed. the mu (coefficiebnt of friction) is also reduced slightly. thsi improves from 50deg- approx 450 deg, when fade starts to set in. pad material is a balance of four things: noise (squeal as we know it), fade performance and pad/disk wear Vs maximising (or rather keeping constant through a stop) the coeff of friction. You can't have all four at once, usually wear versus friction and noise versus fade, but they are all interrelated.

    So my point is that you want a warm but not hot disk 50-450degC (linked directly to pad temp), so the float helps acheive both, faster warm up and isoplation from heat.

    Waggle on a floating disk is as expected, but too much movement rotationally around the common axis signifies wear. a proper floating disk willhave some axial and radial play. But it is the weight and thermal benefits that they are designed for.

    Hope that answers the questions above and I haven't sent anyone to sleep.

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