[Closed] Brake disc "wrong" way round

The sticker is correct.

Question - why is the correct rotation that way? The construction looks like it would have less rotational "give" the other way round

Who do I trust?

Clearly not you

*centrelock discs prevents me needing to decide about such things

Opposite way to to Galfer, and hence Magura, to avoid a patent, IIRC (I may have misremembered though). Shimano are the same as Galfer as well… licensed I think.

I may have dreamt that… can’t find anything on the internet to back it up. Ignore me.

Puts the rotor spokes in tension. Which is a good thing as the other way bring potential buckling.

I'm going with my gut and putting it the normal way, not as the label. Interestingly (or not) it's a second hand disc and the witness marks show the previous owner did the same. I don't think it came from a deceased estate. Will find out tomorrow if I die.

Makes sense to follow the label as this puts the spokes under tension during braking.

Why would you ignore the instructions on how to fit something like brakes.

It'll likely be fine but it pretty bloody obvious

A. Thats what they want you to do.
B. It makes more sense that way.

It makes more sense that way.

So why is almost every disc fitted the other way?

Because they have designed it to resist buckling?

Anyone else remember when Ashima made all those rotors with the arrows the wrong way? Claimed it was for performance for a little while, internet debate raged, then they changed them when nobody was looking.

So, here's a more recent Hope rotor, with the same spoke design and the arrow pointing in the other direction (and the same as pretty much everyone else's)

I assume they had their reasons at the time, and tbh the rotor'll almost certainly work fine either way, but I'd ignore the arrow on your disc and go with the more recent advice

I had the ashima airs, went a bit wobbly after a while so destroyed them to death before they got me.

Don't know why you'd buy or sell secondhand rotors tbh, bit like tyres. OP pony up for some nice new ones, you tight arse! 😜

Don’t know why you’d buy or sell secondhand rotors tbh, bit like tyres. OP pony up for some nice new ones, you tight arse!

Trying to cut down on my consumerism. Plenty of decent second hand bits so I don't feel the need to constantly be buying shiny new bits and put old bits in the bin. Hardly ever buy anything new for the bikes. It's been a bit tricky recently, though. Prices are way up and there aren't any jumbles. We run 3 bikes each (road, xc, enduro) and there are barely any new parts on them.

I'm going to say that it's not a genuine Hope rotor and I would put it on the other way round .

Putting the discs on with the rotation reversed is going to be a Darwin award. These have failed spectacularly before now & there was a picture circulating for a while. Disc completely mangled & jammed into the caliper. Definite OTB moment if this happens on the front.

I’m going with my gut and putting it the normal way, not as the label. Interestingly (or not) it’s a second hand disc and the witness marks show the previous owner did the same. I don’t think it came from a deceased estate. Will find out tomorrow if I die.

Crack on.

It’s definitely a genuine old Hope disc. I was looking at an identical one today, looking for a disc for my Son’s bike.

Which ever way around you put them the pads will rub slightly & squeak because Hope brakes

These have failed spectacularly before now & there was a picture circulating for a while. Disc completely mangled

This one?

This one?

Possibly, definitely looks similar. Excuse the brevity of my previous post..tea was ready :o)

Which ever way around you put them the pads will rub slightly & squeak because Hope brakes

None of my hopes rub at all. I do however centre them properly which is a big help

Here’s a pro with his rotors fitted. Looks weird

I know I’ve had a couple of beers and I know that I’m not very clever.
But unless it says which side is the outer/inner, couldn’t you fit it either way round and be correct??

Go with the sticker, under tension. I put one on to my sons old cable front brake the wrong way round and it snapped. My mistake. No OTB fortunately. I’ll never make that mistake again.

Just “a couple” ?

I know I’ve had a couple of beers and I know that I’m not very clever.
But unless it says which side is the outer/inner, couldn’t you fit it either way round and be correct??

Just “a couple” ?

This will be fun in the morning.

@davesport pretty sure thats not a Hope rotor. People ran them the wrong way round for years before they put an inscription on them, nobody died or had catastrophic failure to my knowledge. Worst you had to worry about were your lightnings cracking.

Funnily enough I've always *wanted* to mount my discs that (old?) Hope way around, but they all have the opposite rotation direction indicated. Somehow feels better to me having the "spokes" under tension in braking, I feel as though the disc is less likely to collapse. Haven't died with them in compression though. Those Ashima rotors not a great example imo as they're so pared down they could fail either way.

I always thought spokes in compression was better. The outer disc will resist being stretched and enlarged much more effectively than the spokes in tension and folding/pringling the disc in on itself (as the failed one has)

My memory has just clicked… it was Galfer’s “Wave” patent that Hope tried to work around.

it's certainly the opposite to the current Hope design, so either it's a weird early model, or a fake, or they stamped the wrong side...

I'd buy a new rotor!

Every single Hope rotor ive ever seen, places the 'arms' facing forward

The rotor is I think mono6 and from that manual if shows the 'arms' on the rotor facing forward.
The rotor shown looks smaller but the arm pattern is the same, and its the same pic and instruction they've had in the C2,mini, then mono mini manuals. All show the arms facing forward. It's a generic pic, but if the arms were to face backwards, it would say so but in the manual it doesnt.

I'd say the stamp is wrong.
But you could just send hope an email

Maybe it's a rear wheel rotor?

There's something not right about that photo of the failed rotor to my eyes, unless the 'bluing' of the metal is a trick of the light?

If the rotor got hot enough to 'blue' the metal, then it would have done it all the way round, so all spokes would have been affected surely?

Anyone else remember when Ashima made all those rotors with the arrows the wrong way? Claimed it was for performance for a little while, internet debate raged, then they changed them when nobody was looking.

I might have remembered this wrong, but I remember them saying "we've decided to recommend you fit them this way, because it makes much more sense to have the spokes in tension, because metal"

Then a mea culpa after a load of failures saying "turns out the normal way is better, sorry!"

Did I make that up? Swear I didn't...

But unless it says which side is the outer/inner, couldn’t you fit it either way round and be correct??

I'm not saying you're an idiot, but only an idiot would think the writing is meant to be on the side you can't see.

I tend to follow the stamped instructions, but I've never thought much of them. I can't imagine that the steel is much different in compression vs tension and I don't believe that many manufacturers do any CFEA or whatever (especially not those selling cheap aftermarket items).

IANAE, but that failed rotor was made too light, with insufficient metal for heat transfer. Nothing to do with the spoke direction!

Did I make that up? Swear I didn’t…

Ned ,it was Ashima.
I remember someone starting a thread about it after they had a very bad crash when an Ashima rotor buckled.
I went straight out to the shed and checked the set I had just fitted.
The arrows were the 'wrong' way ,but I had ignored it and fitted them facing.

Edit> found it Tacoed < Edit

I've always gone with the other way, like a spiral trying to open out rather than close up.

Email hope and see if they had a dodgy batch.

First full row of holes from the right side of he picture, is that a crack to the edge on the outermost hole or just a mark? (or another sticker? 😉 )

Ramsey Neil - eh errr!

COMPUTER SAYS NO!

Spokes in tension looked the 'obvious' way round for me, until I checked my and Mrs' bikes, and they're all 'spokes in compression', as are most pics on the web. Thinking further, spokes in tension means the spokes are pulling the disc rim into the hub, which puts the rim into circumferential compression, in addition to the compression on the 'incoming' side of the caliper. Looking at the photo nickjb posted, it's the rim that's buckled, not the spokes, suggesting it's the rim that's the critical bit, at least for that design of disc.

If the spokes are in compression, they push the rim out and it's in circumferential tension. Adding tension to the rim and compression in the spokes might be best, since as it wears the rim could lose half its thickness - and buckling resistance depends on stiffness, which is proportional to thickness to the power four.

That's only a very simplistic analysis, the actually stress in the disc will be really complex and I'd be amazed if manufacturers didn't do FEA on the design, including thermal stress as well as mechanical, and lab test the prototype. It's probably feasible to make a disc with a wider rim and narrower spokes that would be intended to run with the spokes in tension, but that disc in the OP doesn't look like that. I wouldn't fit it anyway, as the pads have worn down the end of the spokes as well as the rim.

BlobOnAStick
Subscriber

There’s something not right about that photo of the failed rotor to my eyes, unless the ‘bluing’ of the metal is a trick of the light?

It looks weird I agree but bigdug is a good dude, it'll have happened as he said. (the pic looks almost like it's been blowtorched!)

Superficial
Member

IANAE, but that failed rotor was made too light, with insufficient metal for heat transfer. Nothing to do with the spoke direction!

Nah- I used the same rotors for a long long time, you'd not put them on an enduro bike, or I wouldn't, but they're absolutely fine, except for the spoke direction which was just plain wrong.

There was an excellent phase when some sizes had sold enough stock so that they had the corrected arrow direction but others didn't, and people still insisted that the arrow must be followed and that there'd be a sound engineering reason for 160 going one way and 180 the other.

This is a Hope Mono Mini 180mm rotor

It looks weird I agree but bigdug is a good dude, it’ll have happened as he said. (the pic looks almost like it’s been blowtorched!)

Yeah, that’s kinda what I thought, but if it comes from a trusted source then that’s kinda worrying!

I’ve run rotors any which way for years. I spent a week going round Mont Blanc with 180mm rotors (mounted incorrectly according to this thread). The heat generated expanded the rotor to the point it distorted like a Pringle - but they ‘popped’ from one side to the other as the wheel rotated and continued to feed through the calliper with very little resistance. They also turned blue during this time. But I never saw anything like that!

Yamaha wheels used to be the wrong way round as well.

Yamaha wheels used to be the wrong way round as well.

I disagree. They're the going in the flow of direction. If they were on the other way, that wouldn't look right.