[Closed] Has anyone ever actually had a disc brake wheel come out of a QR fork?

It's never come out on my disc CX bike but it has worked itself loose several times. Have to make sure it's done up super tight.

I'd rather have a closed drop out like Cotic do for piece of mind but it's not worth changing the bike as I love everything else about it.

Never, not in 10 years of MTBing and 4 years of CX discing.

No and my cx has a reasonably hard life and never had any problems. I have had a qr come loose on the rear end of a mtb at BPW. Fortunately it was the wife's so I was ok, swapped to Shimano qr and greased the qr rod / axle never had an issue since

Not had any come out, but had a few shift on Konas equipped with steel forks and cheap qr's, a change to Shimano sorted them out. Also had my own shift on a steel fork with a Hope qr under extremely heavy braking on tarmac, so just for the hell of it, tapped the hubs, and modded some Hope qr end caps in the lathe, and went bolt-in. A decent quality qr will, in all honesty, probably be perfectly sufficient for most eventualities, but we all want to believe we need bigger/better/faster/more 🙂

Was there not a huge court case over a serious injury cause by a front wheel coming out? Iirc it resulted in the addition of lawyer tabs.

I'm pretty sure lawyer tabs were pre disk brakes and were to be a feature on account of Joe public not being trusted to use a qr correctly, ie do it up tightly.

I've never had one come loose unintentionally

Use Halo Hex Key Skewers, instant bolt through!

I followed the case in court and wrote it up here.

http://spoomplim.blogspot.co.uk/

Some stuff I wrote ages ago about it:

http://www.kinetics-online.co.uk/technical-info/disc-brake-safety-issues/

I haven't had a QR come loose since I first fitted discs, I have seen other people's come loose though.

Always tighten it up as tight as ****. Use Shimano QR skewers, particularly at the front (where the position of the brake will lift the wheel out if you're braking hard).

Lawyer tabs will stop the wheel rattling out if your QR comes loose, but braking forces will tear through them without too much fuss.

Interesting link Stoner and a good read..

Summary, QR's are Ok especially when fitted with a nyloc style nut and checked before each ride... IANAL...

Wonder of the QR nuts with the small serrations that bite into the form remedy any problems.

Use Halo Hex Key Skewers, instant bolt through!

I've always thought that you'd be able to get more clamping force with a decent QR than those. They're obviously nothing like a bolt through, they're the equivalent of having a QR where you never do the cam up, just wind them up!

I had problems with a Kona too, steel forked Dew.
Fixed it with some better skewers and tightening them more than should be required.

I tried halo hex key skewers and one sheared after around 6 months of use. Seemed to be a not uncommon issue at the time.

Im having the exact same problem on my mountain bike with a rigid fork. My skewer does not loosen but moves when braking. From all the various topics i have read suggest the following.

Shimano skewers. They are all enclosed cam. The clamping is very good.

Another tip i read was mix very fine sand or glass with nail varnish and paint the drop outs. This should give extra clamping ability on the rough surface.

I have ordered shimano skewers and will see how it goes.

Tge enclosed cam skewers are much better then the later open cam types which are cheaper to produce

Nope, never. Always used Shimano skewers, after reading that their internal cam design was less susceptible to the problem than the external cams of trendier makes.

Never even had one go slack.
Use proper QR's not silly external cam ones.
Tullio got that one right.

There is at least the one case of Russ Pinder where there the front wheel has come out and very serious debilitating injuries occured. Russ is a highly competent person and if it happened to him it could happen to anybody else.

So I personally would look for a fork with 12mm thru axle. Not only does effectively eliminate any worries of wheel ejection but it appears to be the general standard that CX/disk road bikes are headed so you will be future proofed.

early on with disk cx stylee had a warning tinkling noise from front disk a couple of times and found wheel had shifted in fork very slightly - went to doing up QR much tighter than ever done with rim brakes and checking before each ride - now have swiss(?) ratchet qr's - will go thru axle on next bike

I was going to mention Russ. You have to have been here since it was all fields to remember though.

I use steel DT RWS skewers which are frankly as good as bolt through. The end of a qr axle has more surface area in contact with the dropout that a thru axle. With the right skewer holding it all together it is a perfectly adequate system.

Having said that, if enclosed thru axles already existed and somebody invented the open ended qr, would it catch on? Probably not. Starting afresh, thru axles are definitely stiffer and more secure, but a decent well adjusted qr is absolutely fine.

I had the rear skewer rattle loose on my CX bike. Wheel came out and jammed up/forward into the rear triangle. Normal, basic, black Shimano skewer

I've never even had one come loose, even external cam ones.
But then all mine have nyloc features and never get particularly old before they get replaced (i get bored). And almost all are shimano. Think i only have three or four sets that aren't.

Someone the other day mentioned closing the skewer over the caliper, and altering the closure angle by adjusting the locknut.

Both of which tell me that even on here people don't understand how QRs work.

Not surprised some have them coming loose.

There is at least the one case of Russ Pinder where there the front wheel has come out and very serious debilitating injuries occured. Russ is a highly competent person and if it happened to him it could happen to anybody else.

the court case I attended and wrote up (link above) was Russ's case. It wasn't concluded at the case what the complete causal path of the wheel ejection was though.

Everyone blames the QR but IME it isn't the QR but the area on the fork it clamps onto, if that is smooth then the QR can come loose under very heavy breaking, but if the area it clamps onto is correct i.e. rough enough, then you'll be fine.

I've ridden loads of bikes with QRs and disc wheels and it's only been an issue on one, which is now resolved.

Afraid IMO Russ's accident is most likley due to human error.

IME it isn't the QR but the area on the fork it clamps onto, if that is smooth then the QR can come loose under very heavy breaking, but if the area it clamps onto is correct i.e. rough enough, then you'll be fine.

Read my link - it's the serrations on the hub biting into the dropout that secure the hub, and it's the serrations on the QR biting into the dropout that secure the QR. Basically, good steel serrations on both are important. The dropout's function is to be softer to allow the serrations to bite.

I've had one come slightly loose and move in the dropout.

It was in some old 700c Kona P2 disc forks (before they adjusted the dropout angle).

Afraid IMO Russ's accident is most likley due to human error.

Well he said his QR was done up and that is proof enough for me. Ok, I'm not 100% objective on this know him a bit, although only on a geeky internet chat basis and I haven't kept in touch.

What is clear is that it is a relatively complicated retention interface which is subjected to huge forces from disk brakes. To be properly secured not only does the skewer need to be sufficiently tight but the serrations on the hub need to bite into the dropout, so the dropout needs to be softer than the material of the hub, but not so soft that the serrations could drag through the material. It is also conceivable that the QR can work loose over the course of a ride due to the huge forces involved. If there is a fault or human error somewhere then the system is susceptible to failing dangerous.

With all this the risk may well be manageable if user is careful, checks his hub serrations have not worn flat etc, but when buying a new bike I say why not go with the new system and just eliminate the risk entirely. It is far, far, better to eliminate a risk rather than manage it.

Even if you assume that the accident occurred due to human error then who is to say that you, I or anybody else can't make a similar human error. No human is completely infallible, and as I previously mentioned Russ is a highly competent person.

Thanks all for the replies - it reflects my own experiences on my rigid MTB. I'm pretty sure I'll go with the QR fork since it's part of a frameset I've had my eye on for a while (it's all about the paintjob!). I think I'll go with the DT Swiss RWS skewer as I've found them to be very secure. Had a terrible experience with a halo skewer - the bolt head snapped off despite me tightening the skewer to the recommended torque.

Had a terrible experience with a halo skewer - the bolt head snapped off despite me tightening the skewer to the recommended torque.

similar though not sure if an actual halo brand or just a similar design - popped when tightening with torque wrench - like a bullet from a gun

bencooper I completely agree with what you say.

when buying a new bike I say why not go with the new system and just eliminate the risk entirely.

Because it comes at a price, in that in the CX world there is currently no standard and it reduces your option of new bikes and wheels.

Back in the day (1999 iirc), I had a set of Pace RC36 EVO 2 forks, with a Hope Ti QR and some of the first Hope C2 disks on my bike.

Despite the fork having flat drop outs with no lawyer tab, and the springy QRs, I never had a problem when rattling down trails or heavy braking on road.

Having said that, I'd probably not ridethe same combination again. Daft I know, but with the introduction of technically superior fastenings there is no point.

in 36 years of all kinds of cycling, i have never had a wheel come out of a fork.

Afraid IMO Russ's accident is most likley due to human error.

I don't think so.

I had a set of the same QRs Russ was using. Had rear wheel fall out of a SC Superlight and front wheel come completely undone on a Pace rigid fork (luckily on road). Mechanically a QR and open dropout are a bad combination with disc brakes. Good design and materials remove most of the risk but a thru axle of some kind actually eliminates it (my rockshox rev bolt thru came loose on Saturday but was fine)

With the gazillions of QR forks around since disks came along it's a genuine wonder we can still cycle round our favourite trails without navigating through all the broken bikes and people.

OP - if you reckon you'll enjoy a stiffer fork/axle then by all means specify a through axle. Otherwise just ride with a QR and learn not too worry.

Ever since that Russ Pinder accident I've been uneasy with discs and QR - I still have a couple of QR forks but I'd never buy one now. My be overkill but that's fine by me; if I'm going to get battered while biking I'd like it to be my fault

If someone made some sort of cap that sat round the wider part of a QR dropout and clipped together to hold it on, I'd have a couple of sets tomorrow

TBH, no matter how tight Pinder did the syncros skewers up, that type are pretty crap anyway. Pretty much the worst type of externals cams you could get.

6 months use and they were (usually) fit for the bin.

If they were of the plastic bush generation, they were even worse.

yes, more than once has my front wheel tried to escape the QR (on the mtb not CX)

Pilot error though, I have a gimp hand and can't tighten QRs properly. Now I give them a good kick at the start of the first descent, seems to have solved the problem. Have never managed to sort a QR seatpost to stay shut however.

Having said that, if enclosed thru axles already existed and somebody invented the open ended qr, would it catch on? Probably not. Starting afresh, thru axles are definitely stiffer and more secure, but a decent well adjusted qr is absolutely fine.

Yes.
Around the time Russ had his accident, we had similar.

A friend of mine had RS Psylo for/Hope QR/Shimano hub. He was 18+stone, 203 rotor on Hope 4-pot brakes, travelling at spinning out speed - so 30mph(+/-) - on a hill track.

The front wheel came out the dropouts at high speed, braking hard moment.

The wheel came out so fast that the fork legs hit floor, and his (new) gloves had damage to the knuckles, where he was still holding the bars. The dropouts/bottom of forks was ground away by impact(s) and so we could not conclusively see what had happened fully - one dropout partially remained, and the 'tab' that held the wheel in was missing - and was 'sheared' not 'ground', but again, no reliable conclusions could be gained.

Cue serious injury, halfway up Helvellyn, miracles and co-incidences and an amazing rescue and hospital. I was told on the hillside he would not live.

He woke up a fortnight later. 6 months in rehab unit for brain injury. 10 months until back in his home alone. 16 months from accident ran London Marathon for the Glenridding MRT. He still bears the physical scars and memory issues, but its 95% back to how he was.

I have had no issues with shimano QRs in ~25 years of using them, other brands may differ in weight and operation but shimano are about the best for staying closed IME...

I can still see some further "standardisation" on the horizon for disc braked CX/Gravel/Road bikes/forks, 15mm vs QR (vs something else?) and Flat vs Post mount... They're going to piss us a about a bit more yet, it's almost certain.

Having jumped on the bandwagon with a QR/PM frameset, I can't help thinking I might have adopted a tad too early...
But it works and I am not yet dead from QR-disc brake related wheel ejection.

Hmmm, that is a grim tale.
I reckon I'll run 140mm rotors with a DT Swiss skewer and won't be tipping the scales beyond 13 stones, still your story is so sickening that it's making me think...

It has made me super careful about QR's being done up tight, and being checked mid ride.

I only use Shimano QR up front. It also made me only buy bolt through since then for myself, being a big lad.

Note also that the older Psylo's - like so many older forks - had minimal retention tabs compared to newer forks. We do also have to wonder that as such a big lad, had he damaged the forks before? Was it done up that day or come loose (we were a long way down the descent)?

On the brightside, we all made BBC's '999' programme and raised a metric sh*t load of cash for MRT.

Someone the other day mentioned closing the skewer over the caliper, and altering the closure angle by adjusting the locknut.
Both of which tell me that even on here people don't understand how QRs work.

That was me, your statement puts you in the camp your lumping me into.

Russ Pinder isn't the only out of court settlement that I know of. The problem was worse back in the days of boutique hubs and skewers with little or no knurling, forks with no retention lips, and dropout angles parallel to fork blade. The gross design error still persists but catastrophic failure is far less common due to a number of minor tweaks. Interesting to hear that despite these, people are still having occasional problems. Bolt-through is such a clearly superior design (when disks are involved) that I'm surprised it hasn't caught on more widely, even for road bikes.

Wasn't the problem actually vertical dropouts? Any axle can be loose (whether or not it works loose or was simply insufficiently tightened in the first place). As I understand it, a loose axle will try and trace a circular path around the calliper when the brake is applied; with a calliper behind the hub the axle could move through the open part of the dropout.

I thought that forward facing dropouts were meant to solve the problem as the same axle tracing the same path in a forward facing dropout would simply be driven hard against a solid part of the dropout (I could be wrong though!).

[quote="nixie"]That was me, your statement puts you in the camp your lumping me into.Hardly, i can work a QR, not only that, i understand how they work.

Over the caliper indicates that the lever is sticking out, [i]over the caliper[/i], i.e. hasn't gone over cam, so it's not closed properly.
Unless you mean over the caliper in the sense of above and in plane.

Altering the closure angle by tightening or loosening the nut puts the skewer in the same position, the lever not going over cam. even though it's the same load going through the lever. (Given that it's set up properly in the first place.) The closure angle is a given. At least 90 degrees.

The orientation of the skewer, to clear bits of frame/fork/caliper doesn't need the nut adjusting.

matt_outandabout - Member
Yes.
Around the time Russ had his accident, we had similar.

A friend of mine had RS Psylo for/Hope QR/Shimano hub. He was 18+stone, 203 rotor on Hope 4-pot brakes, travelling at spinning out speed - so 30mph(+/-) - on a hill track.

The front wheel came out the dropouts at high speed, braking hard moment.

The wheel came out so fast that the fork legs hit floor, and his (new) gloves had damage to the knuckles, where he was still holding the bars. The dropouts/bottom of forks was ground away by impact(s) and so we could not conclusively see what had happened fully - one dropout partially remained, and the 'tab' that held the wheel in was missing - and was 'sheared' not 'ground', but again, no reliable conclusions could be gained.

Cue serious injury, halfway up Helvellyn, miracles and co-incidences and an amazing rescue and hospital. I was told on the hillside he would not live.

He woke up a fortnight later. 6 months in rehab unit for brain injury. 10 months until back in his home alone. 16 months from accident ran London Marathon for the Glenridding MRT. He still bears the physical scars and memory issues, but its 95% back to how he was.

😯 crikey, that sounds hellish.

I'm pretty sure it was either Rock Shox or Manitou who said not to use larger than 160mm, or maybe a 180mm rotor with their QR forks. Don't think this was right away though, probably after an event like the above.

I've personally never had a problem, but I've never used anything other than internal cam skewers. I remember a mates rear Hope QR once came undone; not really an issue on the rear though.

Altering the closure angle by tightening or loosening the nut puts the skewer in the same position, the lever not going over cam. even though it's the same load going through the lever. (Given that it's set up properly in the first place.) The closure angle is a given. At least 90 degrees.

But you don't need to adjust the nut for that. you just rotate the entire QR around it's axis.

OP: Yes. But nowadays QR dropouts are designed slightly better, for example with the "lawyer tab"(?) - basically you have to loosen the QR significantly further to actually get the wheel out of the dropout

I'm pretty sure it was either Rock Shox or Manitou who said not to use larger than 160mm, or maybe a 180mm rotor with their QR forks. Don't think this was right away though, probably after an event like the above.

That's not the reason for the max limit on rotor size - larger rotors are actually better because it's the [i]ratio[/i] of wheel size to rotor size that's the issue. Braking at the same speed, a 29er with 140mm rotors puts quite a bit more force through the axle etc than a 26" with 205mm rotors.

The size limit is, as far as I can work out, more about the type of customer who would fit big rotors.

The fundamental problem is that both dropouts and quick releases were invented decades before the disc brake, and when discs came along no-one properly considered that the QR was now not just to stop the wheel falling out, it was taking 4x as much force from the brake.

The only time I've had problems with qr loosening was on a rim braked bike - the problem was the crappy qrs (Kore) . Changed the qrs - never had problem since even on disc braked bikes as long as you do them up tight enough.

I've had a rear road disc wheel partially pop out of the dropout on the brake side. May have been my fault for not tightening the QR enough. Or maybe I did - I don't know. Not had a problem on the front but I have seen my steel fork twist under high speed braking and cornering (40mph+ descents over 20km) and that was alarming. Given the choice today I'd always go for a thru-bolt now.

There was a big debate about this some years ago (just looked it up, 2003!) largely driven by James Annan, who had an accident and published a website arguing it was caused by using discs with QRs and conventional dropouts.
This argument rumbled on for quite a few years. Given that the use of discs and QRs must have become much more common since then, I'm not aware that we've seen any evidence that it is a genuine problem.

My anecdotal evidence is that I've been using discs and QRs for 16+ years on and off road, including 13 years of commuting 5 days a week, and I've never seen a QR work loose. I've always used old style enclosed cam Shimano or Mavic QRs, and I suspect a lot of the lightweight alternative QR designs are a bit suspect. I remember someone on here explaining how he had solved the problem of his loose QRs by clamping them shut and then rotating the closed lever 90 degrees to lock them tight....!

My work was prompted by Annan - since then, through axles have become much more common, so that's why the number of incidents is low I think.

Well, I've just gone and done it. I've been staring at this frameset for months and the recent serious illness of a couple of near and dear ones has convinced me that life's too short not to.

I paid 100 Euros extra to upgrade to a thru axle fork. Didn't want to have it going through my mind on some of my more extreme cross outings.
[img] ?t=1471281696[/img]

I suspect a lot of the lightweight alternative QR designs are [s]a bit suspect[/s] not fit for purpose.

FIFY

Since the original Campag design was enclosed, fair play to the guy for getting it right from the off.

since then, through axles have become much more common, so that's why the number of incidents is low I think.

I'm not so sure about this, plenty of XC, CX, Road and lower end mtbs still come with discs and QR's. I think if there was a major issue it would have been noted by now. Key thing to note is most bike brands use 'proper' QR's designs from Shimano, Mavic, Sram etc. not the lightweight after market items that I suspect are the main culprits.

The fundamental problem is that both dropouts and quick releases were invented decades before the disc brake, and when discs came along no-one properly considered that the QR was now not just to stop the wheel falling out, it was taking 4x as much force from the brake

Well yes, except that on a horizontal dropout they may be taking pretty significant loads from the chain. My first changeout of external cam for Shimano was due to an SS with horizontal dropouts creaking due to pedalling loads (it worked). Wasn't the QR invented due to the need to swap between fixed and freewheel quickly during a race with cold/tired hands?

Edit - of course the consequences of popping the front wheel out are more severe than pulling the rear out of place.

If QR is so bad its amazing the wheels stay on the pro roadies bikes when there doing 70mph down mountain passes, putting several hundred watts or more power through the wheels in the sprints and especially when the mechanics chuck the wheels in within seconds after a puncture,
Really there should be wheels flying off right, left and centre.

unvolo - do those same roadies use discs? 😉

I had many customers at freeborn Esher buying lightweight qr skewers and putting their steel shimano back on pronto. Dirt jump, DH, FR all best on through axle or steel skewers.

If you ride hard or are heavy you can put a huge load into the axle interface with disc brakes? Old articles mentioned 400nm+ peak load.

For QR, Shimano, Campag, or DT Swiss RTS work well but make sure to clean/oil the cam and skewer shaft from time to time.

I had a hydro disc brake road bike last year. The bike had 45 degree forward/down fork dropout to help counter twisting force.

I rode that bike very hard 60mph+ DH runs, , front wheel secure but rotor tinkling on climbs or sprints, and rear wheel tendency to unseat ever slightly under repeated hard braking. Creaking under power, had to stop, open the QR, wiggle wheel to reseat and retightented. Often...tried shimano, DT Swiss RTS no difference.

Bike got sold off, got 7kg caliper race bike with Shimano dura ace skewers. Lovely....

2017 model of my disc brake bike has 12mm through axle DT Swiss front and rear. Fantastic!!

This happened to a friend of a friend, wheel came out on a non technical fast descent. I don't know the full technical details but the case was settled with the fork manufacturers just before the case was due in court. The rider had serious back injuries and I think he was lucky to walk again.

The fundamental problem is that both dropouts and quick releases were invented decades before the disc brake, and when discs came along no-one properly considered that the QR was now not just to stop the wheel falling out, it was taking 4x as much force from the brake

I think there were two slip ups when disk brakes were introduced:

]Mounting disk brakes on the back of the forks creates a large force pushing the wheel out of the dropout. Why not mount it on the front of the forks so the force is pushing the wheel into the dropout?

To run disks people needed to switch their hubs and frame/fork to be disk compatible anyway so the opportunity should have been taken at that time to switch to a stiffer and more secure wheel clamping system - esp. as it was obvious that putting the caliper on the back of the fork creates a force pushing the wheel out of the dropout

The road/CX bikes with QR and disks on the rear of the fork do concern me a bit as it is possible to generate huge braking forces when running sticky slicks on a grippy road.

Note that in terms of the amount of force created pushing the axle downwards and out of the dropout. This piston position:
[img] ?1[/img]

is not as bad as this piston position:
[img] ?1[/img]

[u]

That's not the reason for the max limit on rotor size - larger rotors are actually better because it's the ratio of wheel size to rotor size that's the issue. Braking at the same speed, a 29er with 140mm rotors puts quite a bit more force through the axle etc than a 26" with 205mm rotors.

I do not agree. If same braking force (at the tyre) is done then force on the axle will pretty much the same no matter what the rotor size is, although the position of the force may vary if the different rotor size also means moving the pistons angular position on the disk as per above illustration.

If one does the kind of worst case assumption that these max sizes are based on e.g. at high speed the piston clamps the rotor with a certain maximum force then the larger rotor will create a larger force at the axle than the smaller rotor for two reasons 1)larger distance between piston and axle creates a larger lever 2)at the same angular velocity a larger rotor has greater displacement past the piston, meaning more braking force generated when clamped with the same force.

Edit:Sorry the formatting of this appears to be a bit broken tried a few things but I cannot fix it - looks fine in the preview.

Why not mount it on the front of the forks so the force is pushing the wheel into the dropout?

I've done that a few times on tandems. People have commented that the caliper bolts might snap, but that shows a misunderstanding of the IS mount at least (post mount, they might have had a point).

If same braking force (at the tyre) is done then force on the axle will pretty much the same no matter what the rotor size is

Not the case, there are two components to the force on the axle. There's the reaction force to the braking momentum, which acts directly backwards and is indeed independent of the braking system. But we're not concerned about that force, we're concerned about the ejection force acting downwards(ish) caused by the caliper. That force is proportional to the ratio between the wheel size and the rotor size - a larger rotor means a lower force. The ultimate example of this, of course, is a rim brake where the ratio is near 1:1 and there's no significant ejection force.

[u]

Not the case, there are two components to the force on the axle. There's the reaction force to the braking momentum, which acts directly backwards and is indeed independent of the braking system. But we're not concerned about that force, we're concerned about the ejection force acting downwards(ish) caused by the caliper. That force is proportional to the ratio between the wheel size and the rotor size - a larger rotor means a lower force. The ultimate example of this, of course, is a rim brake where the ratio is near 1:1 and there's no significant ejection force.

I don't see it this way, I see the ejection force as being the force acting on the rim/rotor fulcrumming through the structure of the wheel and acting on the axle.
Larger rotor means a lower piston force to achieve a certain amount of braking effort (this is not the worst case situation I described), but is then magnified by a longer fulcrum so results in an equal force on the axle.
The vector of the force on the axle is 180.deg or pi.rad of the vector of the force on the rotor/rim for rim brakes the force is pretty much horizontal hence little downward ejection force.

Yes.

Although it did take one hell of a sideways landing and crash to get there.

This was a few days after that video of Cedric Gracia rupturing his femoral artery, so when I picked myself up and found the wet sticky patch growing from my crotch/hip I panicked! Thankfully it was just a burst gel in my pocket!

"

but is then magnified by a longer fulcrum so results in an equal force on the axle

You've got that backwards. The longer fulcrum means less force.

Imagine a pole, with one end on the ground - that end is the caliper.
Imagine lifting the end of the pole with a certain force - that end is the tyre on the ground, and the lifting force is the braking reaction force.
Now imagine using this pole to lift something heavy, like a workbench. The farther the lifting point is from the ground, the less force you have.

The fulcrum is a fixed point. The braking reaction force is the same (you're slowing down at the same speed). What changes is the distance from the pivot to the load, and the greater that distance the less the force.

It's also true that the angles are different for rim brakes, but that doesn't alter the basic fact that the smaller rotor means a larger ejection force.

PS, stop underlining everything, you've borked the quotes system 😉

I had one of those Syncros QRs fall apart - the head was threaded on with a tiny spot weld(?) keeping it from coming unscrewed.

No braking involved, just a low speed heave and twist on the bars and it shot off into the bushes...

I've used Shimano QRs ever since.

I read a bit of this thread a few days back and have to admit I largely put it down to user error. Came down Ditchling Beacon on my Defy on the way home from work today, car in front held me up so was on the brakes the whole way down. Brake pads were tinging on the rotor at the bottom and found both QRs were coming loose....About to buy some Shimanos to replace the OEM Giants. Next bike will have thru axles.

Has anyone had any experience of the DT Swiss RWS skewers? I've not had a problem with my current skewers except that I end up doing them up so tight that they're a pain to undo so wonder if they're worth a try.

You've got that backwards. The longer fulcrum means less force.
...
The braking reaction force is the same (you're slowing down at the same speed). What changes is the distance from the pivot to the load, and the greater that distance the less the force.

It's also true that the angles are different for rim brakes, but that doesn't alter the basic fact that the smaller rotor means a larger ejection force.

Gotcha, I stand corrected and see now that smaller rotor means more ejection force, also a larger distance between tyre contact patch and the piston means more ejection force - and that often decreasing rotor size increases tyre contact patch to piston distance so creates a double whammy effect.

However, a larger disk also means less piston clamping force for a given braking force, and what I can't get my head around is if this makes the piston more or less of a pivot point that creates axle ejection forces. I mean, it isn't an actual pivot (unless the front wheel is skidding, sort of) because the rotor is always moving through the piston, but a kinematic one created by the friction between the pad and rotor.

[u]

PS, stop underlining everything, you've borked the quotes system 😉

test quote

Twisty, you have to squeeze the brakes harder for a smaller rotor to get the same braking effect (for a given calliper/lever design).

However, a larger disk also means less piston clamping force for a given braking force, and what I can't get my head around is if this makes the piston more or less of a pivot point that creates axle ejection forces.

Less. Don't worry about the rotor actually moving through the caliper, what matters is the resulting force on the caliper, and the equal and opposite force on the axle.

The piston clamping force doesn't have a direct relationship here, it depends on whether it's a 2- or 4-piston caliper, the pad size and material, etc. All that matters is that it applies a certain braking force to the rotor, and that force is proportional to the ratio between rotor diameter and wheel diameter, for a given rate of deceleration.

Don't worry about the rotor actually moving through the caliper

<sigh>Sometimes I almost wonder if I should have studied mechanical rather than electrical engineering 🙂

No need to respond, I think I've learnt enough about this for now.
The important thing is that large diameter disks are good which is comforting because: I like big disks and I can not lie.

[i]Has anyone had any experience of the DT Swiss RWS skewers[/i]

Scary bloody things they are. Work themselves loose if you don't check them every ride (this is my experience of them anyway) - Shimano are best, no doubt.

In answer to OP - no, never.

Conversely, I once did a day's riding at Gwydrr Forest on my old hardtail equipped with Marz forks with their QR20 system, which had a 20mm bolt thru QR with 'tabs' that screwed in on the bottom to enclose the axle. This wasn't the newer version, but the original where the tabs had to be fixed on with a 4mm bolt. Bike had a Hope 4-pot with 6" rotor.

Did the whole day without having fitted the tabs so effectively only having half the clamping force. That was scary when I came to take the front wheel off afterwards! 😯

Few years back my wheel came out of a Kona Project 2 rigid fork, the QR was a Shimano one IIRC and had been done up tight.

Luckily for me it fell out as I stopped to take a breather at the top of a climb rather than during the descent I was just about to start... 😯