[Closed] Dangerous?

I'd say yes but likewise I don't think it makes a real difference

No, they are on the wrong way around but it won't do any harm.

I read the infamous rotor fail post and it specifically said you need to be very careful about rotor direction. How do you kow they're currently on the wrong way? I'm clueless.

Defiantly the wrong way.

No, not dangerous. Ideally the disc's spokes should be pointing the other way, so that they are being compressed under braking instead of stretched. The discs on my Hope C2s from the mid 90s (the ones with the separate aluminium spider and countersunk holes in the rotors) were like that and I used them for years with no problems and they are still being used on a friend's bike with no problems so don't worry too much about it. Easy enough to turn yours around if you want them the right way around though.

You could look at the little directional arrows... or think about how the braking forces are going to impact the rotor and how they'd have designed it structurally to counteract them...

I'd say it was less dangerous than your Red/Blue colour clash with the hubs and QRs.

The splines should point in the direction of travel.

normally hope rotors have an arrow on them near the centre, if it is there it would be hub side and hidden on yours as they are the wrong way around.

What difference does compression vs tension on the spider arms make? I'd have thought tension would be better.

Unlikely to matter bar lightweight/shoddily designed rotors Shirley?

I'll pop one off and have a look. Not much I can do about the colour clash. As it was when I bought it! I might even post a pic of the levers and reserves. I think the previous owner was colour blind... I might post a pic if everyone needs cheering up.. Rides like a Ferrari tho, so who cares?

I'd have thought that tension would be better too, what with it being steel.

?

No, not dangerous. Ideally the disc's spokes should be pointing the other way, so that they are being compressed under braking instead of stretched

I don't agree. Your disc should be under tensile load when braking, the other way could cause buckling.

I've always had mine rotating from the inside to out with the trailing edge at the rim.

Mind you, just show that it probably doesn't matter if people have them both ways with no ill effects.

Anyway, you have them on the right way imho, tensile load is good for a thin disc, not compressive load.

The disc (braking surface) should be in tension, the spokes should be in compression.

They should be the other way round.

Looked into it a while ago and from memory stainless steel is better under compression (spines facing foreward) than tension (spines facing to the rear) where in theory ss stretches more.
Newer Hope rotors have a rotation direction arrow etched on to them.

Probably only realy an issue riding DH or the Alps where rotors may get a bit warmer.
But I would swop them to be safe, especially the front. 😉

I've wondered if it is more to do with clearing debris/grime from the pads. If you look at newer rotors like the Monos then this effect is more evident. the top of spoke sweeps across a bit of the pad. when fitted correctly the spoke leading edge would (maybe) sweep grime out and down (possibly maintaining better braking and reducing pad wear?)
rotors fitted the other way would possibly 'collect' grime at the spoke/braking surface join

It's my belief that they may be less likely to squeel that way around, with the spokes acting in tension - less risk of 'chatter'.

I don't agree.

From a thread on [url= http://www.bikeforums.net/archive/index.php/t-597858.html ]Bikeforums:[/url]

Tech reply from Hayes this morning:

The reason for the spoke design is that there are two sources of stresses in the rotor. The first is mechanical stresses due to torque and the second is thermal stresses within the rotor. As the braking surface heats up, it expands. The inner portion of the rotor near the hub is comparatively much cooler. With the outer braking surface expanding with higher temperature and the temperature of the center remaining largely unchanged a thermal stress is imparted on the spokes. The spoke design is specified such that the mechanical stresses and the thermal stresses occur in opposite orientations, attempting to cancel each other out and lowering the total stress in spokes as opposed to adding together. The result is the “sweeping forward” spoke pattern.

Also, look at the direction arrows on all these discs:

Formula:
[img] [/img]

Avid:
[img] [/img]

Hayes:
[img] [/img]

Hope:
[img] [/img]

Magura:
[img] [/img]

Well any-one who says they are the wrong way round is wrong... As weeird as it sounds, they are mini rotors and they are the correct way round. These rotors should be fitted on the opposite way as you would put an avid/hayes/formula rotor. But just the mini rotors, not the mono mini, not the sports or pro.

HTH

Probably best to think of triangles rather than tension/compression and imagine if those arms were a lot thinner what would happen.

Well any-one who says they are the wrong way round is wrong... As weeird as it sounds, they are mini rotors and they are the correct way round. These rotors should be fitted on the opposite way as you would put an avid/hayes/formula rotor. But just the mini rotors, not the mono mini, not the sports or pro.

HTH

Why's that then?

Honestly no idea, but that is how I have seen them fitted since I can remember. LBS told me it was the correct way round. Best would be to call hope.

The inner portion of the rotor near the hub is comparatively much cooler. With the outer braking surface expanding with higher temperature and the temperature of the center remaining largely unchanged a thermal stress is imparted on the spokes

no conduction of heat then?

Would be nice to hear a proper explanation.

For what it's worth, mine never cause me any trouble. And I use them possibly more and in more demanding condition than most of people on here.

Have a look at this [url= http://singletrackmag.com/forum/topic/ashima-rotor-fail ]thread.[/url]

I seem to remember, yonks ago, a post where it was said that the makers specified one way, compression, to avoid an existing patent.

Someone fire up ANSYS...

Honestly no idea, but that is how I have seen them fitted since I can remember. LBS told me it was the correct way round. Best would be to call hope.

Look at section 2.2 of the [url= http://www.hopetech.com/webtop/modules/_repository/documents/userguide_printed_2002.pdf ]Hope C2, Mini and M4 instructions[/url].

no conduction of heat then?
Would be nice to hear a proper explanation.

Of course there is conduction of heat. The spokes, centre of the disc and the hub will heat up but the outer part of the disc, where the pads are contacting will always be hotter than the other parts when braking.
All the other parts will draw heat away from the braking surface but are cooled by the air flowing over them as the wheel is rotating.

Have a look at [url= http://uk.extreme.com/mountainbike/1012004/magura-brakes-and-suspension-storm-sl-rotor-test ]this video[/url]. The baking surface can be seen glowing yet the spokes and central part of the disc are not.

They are the wrong way round.

I don't care what someones LBS says.

Yeah but IIRC (not sure at all about this one), it was due to the fact that down here rotors were under too much strength/heat and this way provided better cooling but as I said I might be wrong.

I don't care what someones LBS says.

oh and as for the thermal conduction v torque forces...

I am guessing they mean this:

During braking the braking surface will obviously get very hot and it will conduct towards the hub. The braking surface will expand and put compressive loading onto the spokes which will make them want to buckle.

But when you have the rotors the right way round the torque effect from braking puts them under tension (on the inner surface at least) and is trying to open them outwards - thus counteracting the thermal expansion which is trying to twist the spokes inwards.

But yes, would be good to see it on Ansys.

cheers andyl, I get that!

...but the pics above show spider arms in compression?

Juan is right. They are fitted correctly. Hope just decided to be different for these ones. Might have been to reduce squeal problems maybe?
Looking at the size of the arms, I really wouldn't be worried about them failing.. Ashima Air rotors they are not.

no conduction of heat then?

Steel is a relatively poor conductor of heat. You could always touch the centre of the rotor after a big descent to check...

still going through it in my head...the spokes expanding as they heat will probably be the reason as the outer ring will mainly probably mainly expand outwards.

Al - the pics above show the spokes being pulled straight by the braking torque.

Imagine a weight on the right side of each disc pulling that side down while the hub part is fixed. The weight will try and pull the braking surface clockwise thus un-spiralling the spokes.

They are saying the thermal expansion forces act in the opposite direction and try and cause the spokes to spiral up more. More I think about it my correction must be what they mean and as everyone knows the more cooling you have in your rotor the less chance of it distorting due to thermal expansion.

Wrong way around! In practice, will probably be OK, but why take the chance.

Just have a look at the way the 'spokes' angle into the 'rim'. Imagine it's made of stiff card - which way would you have to pull the rim harder for it to collapse - then you've got your answer.

Nobody's posted this yet? The famous Ashima misprinted arrow on their rotors:

[img] [/img]

[img] [/img]

but the pics above show the rotor as rotating counterclockwise?

I've got hope minis, had a set for 10 years. and I can tell you, those rotors are on the wrong way round

cynical-al : from memory- they printed the arrow the wrong way. Once those photos appearer the arrow changed to the other way.

I was meaning the pics of 6 or so discs in one post.

OP - Given how often the hope skewer came loose on my wife's Five. Wouldn't be bothered about the rotor, more the skewer 😀

I've had this before and had people tell me my Hope rotors were wrong but they were installed as per the Hope guide. Still reckon mine were wrong based on other manufacturers info

Well the user manual show you the rotor for the close caliper system. Not the mini. There is no chance the mini rotor end up like the one above. Twice the width and probably three time the weight. And I too have a pair of these for 8 year fitted as the OP.

Oops....I take it back. Mine are actually on the way which would put the rotor into compression during braking.

If your bike's on a conveyor belt do the rotors go on the other way round?

cynic-al - Member

but the pics above show the rotor as rotating counterclockwise?

I was meaning the pics of 6 or so discs in one post.

Disc goes on the left side of the wheel, wheel rotates in a forward direction = counterclockwise from the outside/left side. No?

Forget the brakes that bike is way too big for you, look at the normal sized bike behind it

Not wanting to bring a dose of the real world into it, but I suspect the grip on the tyre will give way a long way before any tension / compression factors come into it... And if it didn't you'd pivot over the bars and hurt yourself that way...

wibble - yes

Wowzer. I nip out for a bit and I've started a pub brawl.
Reading through, for the fifth time, I'm still not sure what the consensus is.
I think the answer is to pop one off and check for markings which they don't currently have on the visible side.
Anyone know if these are hope rotors? I could contact them.
Am I right in saying my brakes are Hope Minis?

(the bike in the back is my daughter's Islabike - wish I'd had a bike like that when I was 4)

Thanks for the input and debate..

The wrong way around, definitely. The arms should alway be pointing forwards.

Take a pole, put it on the ground at an angle towards you, and lean onto it. It'll take your weight. Put the pole leaning away from you at the same angle, and try leaning on it.

That's effectively what you're doing - you're relying on the rigidity of the braking surface to transmit the load to all the arms evenly enough to not deform. Whereas with the rotor the right way around, the force is transmitted directly to the hub.

Horray! Still going...

No, they're not right as per the usual way round that rotors are made. They're so overbuilt that nobody is going to die, least of all a kid on an islabike.
Yes, they are fitted correctly, as the way that Hope instruct you to fit them. There's no markings on the disc however, and you could fit them the other way.
I reckon that it's down to the squeal you always get from old hope brakes.. some bright spark at the factory tried fitting the rotors backwards to see if it reduced it, and it did so that's what they instructed.. maybe?

@Al: "but the pics above show the rotor as rotating counterclockwise?"

yup. Disc is rotating CCW so the braking force acts clockwise.

Take a pole, put it on the ground at an angle towards you, and lean onto it. It'll take your weight. Put the pole leaning away from you at the same angle, and try leaning on it.

That's effectively what you're doing - you're relying on the rigidity of the braking surface to transmit the load to all the arms evenly enough to not deform. Whereas with the rotor the right way around, the force is transmitted directly to the hub.

But you're assuming that the force will increase as you lean on the arm no? In a bike the force would increase to a point and then stop as the wheel would loose traction. I'd imagine this point is much below the buckling strength (if that's the failure mode).

Yes, but hoping that one thing fails before another does isn't the best thing to do 🙂

I don't see the advantage in risking it.

cool i was right they are the good way round :d, if you're scared and want to listen to some bullshit on here turn them the other way round, you won't die anyway!!!

so i contacted Hope yesterday and they were helpfully quick to reply...

Hello Rick, when we manufactured this model we did indeed run them the
way you have shown us in the photo.

Many thanks
Nick

Service & Warranty
Hope Technology (IPCO) LTD

I tink i'll leave em. i'll sort a new dentist just in case

Well looks like some people on here should learn to respect professional opinion then.
So much for the "I don't care what somebody's LBS said"... Seems to me apologies are in order.

The Ashima issue was a problem with the rotor not just which way you fitted it.

Well looks like some people on here should learn to respect professional opinion then. So much for the "I don't care what somebody's LBS said"... Seems to me apologies are in order.

I think the operative word in the message from the chap at Hope is [b]did[/b].

Like I said in my original post, it won't matter which way around it is, but the better way [b]is[/b] the other way!

If we are all to have more respect for your LBS owner maybe you should also have some more respect for people on here that probably have more engineering experience and qualification than you might realise?

This wasn't towards you willej. Plus as you can read I have since the beginning said your brakes where the correct way forward, quoting a professional. As for the "more engineering experience" I have very much doubt most of the very vocal people on this thread are that qualified, as they would have told you the same than I and other did, to call hope directly.

Btw when I sold my hope mini originals (i.e. same vintage) had worn the braking surfaces pretty thin when I sold them a couple of years ago. Id check the rotor thickness of the braking surface vs the arms. Might want to have new rotors anyway...

Actually i thought will was the OP, so yes it was directed at you...

Dangerous?

Fox QR fork + Hope QR + disc brake = Yes (IME)

quoting a professional

I'm actually a 'professional'... you shoulda quoted me instead.

andyl - Member
@Al: "but the pics above show the rotor as rotating counterclockwise?"

yup. Disc is rotating CCW so the braking force acts clockwise.

But you said

andyl - Member
But when you have the rotors the right way round the torque effect from braking puts them under tension

clockwise force = compression! Or am I missing something?

TroutWrestler - Member
Dangerous?

Fox QR fork + Hope QR + disc brake = Yes (IME)

Why?

juan - Member
Actually i thought will was the OP, so yes it was directed at you...

You can call me Will if you like but it's not my name

titusrider - Member
Btw when I sold my hope mini originals (i.e. same vintage) had worn the braking surfaces pretty thin when I sold them a couple of years ago. Id check the rotor thickness of the braking surface vs the arms. Might want to have new rotors anyway...

Thanks will have a check

Yikes. I have the discs for my Hope Minis t'other way from the OP.

Hopefully death will be quick 😆

Me too - have done for 10 years 🙂

My feeling is the way round in the OP has the spokes in tension not compression which would be better?

Edit - all my bikes have the spokes of the disc in compression not tension. seems odd

If they were truly in tension, possibly - if, for example, there was a braking force at every point of the rotor (imagine lots of calipers on one rotor).

However it's not like that, there's an offset braking force at just one point on the rotor. If you imagine the hub held solid, and a tangental force at one point of the rotor, you'll see that the spoke is not in tension, it's experiencing a bending moment. Just like my analogy of trying to lean on a stick that's angled away from you.

Hope Mini User Guide has oposite way to OP.

Interesting Hope stated anything different.

I've a feeling the thermal expansion forces vs braking forces thing is wrong. Here's my reasoning.

braking causes heating of the rotor braking surface which expands, so the outer ring grows in circumference. the spokes stay cool and hence don't grow. the result is the spokes are in tension (a pure radial force actually), they are stretched slightly to 'reach' the expanded braking surface.

putting the rotor on with the spokes sweeping forward in the direction of rotation means gut feel is the spoke is in compression, but really it isn't. As bencooper points out, they feel bending moment and shear force, a pure tangential force, totally perpendicular to the expansion force.

I have the same brakes, with the same hub.
The set up was done by Merlin cycles, who I trust when it comes to mechanical stuff.
I mine are the otherway round to the OP's:

[IMG] [/IMG]

Sorry about the lack of colour clash.