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Disc brake front wheel shifting in dropouts under hard braking...

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Disc brake front wheel shifting in dropouts under hard braking...

Old 05-12-14, 10:42 AM
  #1  
alexxander.fost
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Disc brake front wheel shifting in dropouts under hard braking...

Hello!

I've got a problem with my disc equipped bike and wanted to get some input from you guys on a possible solution.

So I own a 2014 Specialized Sirrus Comp Disc. I absolutely love it and am smitten over the performance of disc brakes as compared to rim brakes! But I've noticed that under hard braking the front wheel will shift in the dropouts. It moves from the apex of the dropout slot towards the opening. Under extreme braking, the torque from the brakes seems to be powerful enough to move the whole wheel down just slightly. I don't think this is a serious safety issue since the wheel will only move as far as the "lawyer lips", then it stops. But that distance is enough to cause rubbing between the rotor and pads as well as bend my rotor.

I've been looking through all different types of cycling forums and I'm getting the impression my problem isn't unique. But the solutions I'm finding all say "tighten the skewer more", or "just live with it". I've already torqued my skewer beyond its recommended limits and I'm still getting movement. My Specialized dealer installed some safety washers to help with the problem but the wheel is still moving. Not only is the skewer still moving towards the "lawyer lips" (the safety washer isn't very precise), but its also taking up the void space between the skewer rod and the inner walls of the axle. I've been following the axle and QR skewer movement with a paint pen and its between 1/8" and 1/4" of movement even with the safety washer installed.

Right now I'm thinking about changing out the front and rear hollow axles for solid axles. I live in a city and have no need for QR skewers. My theory is the larger diameter thread will allow greater clamping torque. And its already a pretty heavy bike so I'm not too concerned about the weight penalty.

Does anyone have any other possible solutions or advice for this problem? Am I way off the mark with this idea of switching to solid axles?

Thanks in advance!
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Old 05-12-14, 11:00 AM
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Since it is a 2014 bike, have it replaced or refunded under warranty.
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Old 05-12-14, 11:01 AM
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First of all the problem is caused by a poor design decision that goes back to the very beginning of bicycle disc brakes. That was to place the brake behind the fork rather than in front. Probably they went this route because discs were installed on mtn bikes first, and they might have thought that this would reduces the chance of a brake being damaged by rocks or whatever.

Unfortunately, with the brake behind the fork, the reaction torque from braking drives the axle down which is the way dropouts are open. (if mounted in front, the reaction torque would drive the axle up, eliminating the problem).

In your case, the best bet would be to buy a new skewer with a serrated steel face which can bite into the dropout providing better grip. This is the same solution that provides enough holding power for rear wheels not to slip with horizontal dropouts. Quality skewers provide the same or greater gripping power than axle nuts, so there's no need to go to solid axles.

If you want more assurance, you can mix some grit, (fine sand, ground glass, or abrasive grit) into nail polish an paint the faces of the locknuts. This will give you grip on the inside of the dropouts more than tripling the holding power of any mounting system.

BTW- since the fork has a stop before the wheel can drop (lawyers' lips), you might consider installing the wheel butted up against the lips, vs. at the top of the slot. That will address the migration problem, by having the wheel start where it wants to go anyway. Alternatively, you can use JB Weld to build the lip up until it touches the QR or locknut with the wheel at the top of the dropout, so there, no possibility of movement in either direction.

In you shoes, I'd start with the better skewer and/or the grit paint on the axle, and let Specialized foot the bill, since the OEM arrangement doesn't work, then modify the dropout only if necessary.
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Old 05-12-14, 11:11 AM
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Nutted solid axles are no more secure than a properly tightened quick release so that won't solve your problem. BTW, what type of quick release do you have? If it's an external cam type, it will not provide the clamping force a good internal cam (Shimano or Campy type). If you don't have an internal cam skewer, get one.

"Through Axles" (closed dropouts with an completely enclosed axle) are the most secure design and are becoming more prevalent but require a compatible hub and fork. Another solution is to design the front dropouts to face forward so the torque reaction tends to seat the axle, not eject it. A moderate help is to make the layer's lips almost completely surround the dropouts to better contain the skewer ends.

At this point, other than a fork and hub change, all you can do is use a proper type of qr, keep it tight and hope the lawyer's lips don't wear off.
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Old 05-12-14, 11:18 AM
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MHO, I would look for some thing other than building with JB Weld. Epoxy has tremendous holding power, but sheer strength is next to nothing..... you can knock it off with a screwdriver.........
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Old 05-12-14, 11:38 AM
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Stainless Steel skewers and crank em down hard. (forget the torque wrench)
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Old 05-12-14, 11:40 AM
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Originally Posted by Wanderer View Post
MHO, I would look for some thing other than building with JB Weld. Epoxy has tremendous holding power, but sheer strength is next to nothing..... you can knock it off with a screwdriver.........
I offered this as a last resort, and I don't believe it'll come to that. However the build up will be supported by the existing lip, so if the dropout is prepared properly, the fill should hold fine. While I mentioned JB Weld, just about anything, from any of the "plastic aluminum" products, to auto body filler will do the trick.

Either pair of Shimano skewers (front and rear) and/or grit paint will solve it, but since Specialized provided a lousy design combined with a lousy skewer, they should foot the bill.
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Old 05-12-14, 11:54 AM
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Agreed. And the fork is chromoly (sp) so I'll likely just hire a welder and add material or swap it out before I'd epoxy it.

Originally Posted by Wanderer View Post
MHO, I would look for some thing other than building with JB Weld. Epoxy has tremendous holding power, but sheer strength is next to nothing..... you can knock it off with a screwdriver.........

I've been kicking this idea around since I bought the bike. I'm really pissed about this problem, but the bike as a whole is perfect for my needs. I don't want to forsake the whole bike to solve this one problem. But I hadn't considered pressuring them to pay for modifying the bike.

Originally Posted by Al1943 View Post
Since it is a 2014 bike, have it replaced or refunded under warranty.
That's a really interesting point about moving the brake caliper to the front of the fork. It would be SOOO much safer if the mechanics you're suggesting turn out to be true (and I don't see why they wouldn't react that way).

As for your suggestions, I'll take a look at better quality skewers. Currently I'm using Pinhead skewer locks so nobody steals my wheels. I tried putting the QR skewers back on as a control test to see if the locking skewers were the problem but the wheel moved no matter what. The idea behind using a solid axle was I can still use locking nuts. But if internal cam skewers solve the problem then I'll just adjust the way I lock up my bike.

And thanks for the suggestion about the nail polish and aggregate mixture! That sounds fantastic and super simple.

Originally Posted by FBinNY View Post
First of all the problem is caused by a poor design decision that goes back to the very beginning of bicycle disc brakes. That was to place the brake behind the fork rather than in front. Probably they went this route because discs were installed on mtn bikes first, and they might have thought that this would reduces the chance of a brake being damaged by rocks or whatever.

Unfortunately, with the brake behind the fork, the reaction torque from braking drives the axle down which is the way dropouts are open. (if mounted in front, the reaction torque would drive the axle up, eliminating the problem).

In your case, the best bet would be to buy a new skewer with a serrated steel face which can bite into the dropout providing better grip. This is the same solution that provides enough holding power for rear wheels not to slip with horizontal dropouts. Quality skewers provide the same or greater gripping power than axle nuts, so there's no need to go to solid axles.

If you want more assurance, you can mix some grit, (fine sand, ground glass, or abrasive grit) into nail polish an paint the faces of the locknuts. This will give you grip on the inside of the dropouts more than tripling the holding power of any mounting system.

BTW- since the fork has a stop before the wheel can drop (lawyers' lips), you might consider installing the wheel butted up against the lips, vs. at the top of the slot. That will address the migration problem, by having the wheel start where it wants to go anyway. Alternatively, you can use JB Weld to build the lip up until it touches the QR or locknut with the wheel at the top of the dropout, so there, no possibility of movement in either direction.

In you shoes, I'd start with the better skewer and/or the grit paint on the axle, and let Specialized foot the bill, since the OEM arrangement doesn't work, then modify the dropout only if necessary.

Thanks for the input HillRider. As I mentioned above, the bike came with the crappy external cam skewers but I'm currently running Pinhead locking skewers since I don't want anyone stealing my wheels. The bike is a commuter bike. The solid axle idea was in part a way to let me secure the wheels from theft. When I noticed the wheel was shifting in the dropout I switched back to the crappy QR skewers but they didn't work any differently than the locking skewers. But regardless, if the internal cam QR skewers solve the problem I'll just adjust my locking procedure and live without locking skewers.

I also really like the idea of building up the "lawyer lips" (I hate that term BTW) so the wheel is seated against it. I'm sure the repeated movement of the axle and nuts is causing damage to the whole tab assembly. I keep having this vision of the wheel shifting so violently during some emergency braking that the "lawyer lips" get sheared off.

Originally Posted by HillRider View Post
Nutted solid axles are no more secure than a properly tightened quick release so that won't solve your problem. BTW, what type of quick release do you have? If it's an external cam type, it will not provide the clamping force a good internal cam (Shimano or Campy type). If you don't have an internal cam skewer, get one.

"Through Axles" (closed dropouts with an completely enclosed axle) are the most secure design and are becoming more prevalent but require a compatible hub and fork. Another solution is to design the front dropouts to face forward so the torque reaction tends to seat the axle, not eject it. A moderate help is to make the layer's lips almost completely surround the dropouts to better contain the skewer ends.

At this point, other than a fork and hub change, all you can do is use a proper type of qr, keep it tight and hope the lawyer's lips don't wear off.
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Old 05-12-14, 12:01 PM
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Agreed, they should foot the bill.

While this topic has been brought up, does anybody have any experience or suggestions on getting the manufacturer to pay for fixing a design flaw? I'm certainly not opposed to kicking and screaming at my local distributor's store or harassing Specialized corporate, but the main goal is to get it fixed. I don't want to push so hard that they tell me to kick rocks.

Originally Posted by FBinNY View Post
I offered this as a last resort, and I don't believe it'll come to that. However the build up will be supported by the existing lip, so if the dropout is prepared properly, the fill should hold fine. While I mentioned JB Weld, just about anything, from any of the "plastic aluminum" products, to auto body filler will do the trick.

Either pair of Shimano skewers (front and rear) and/or grit paint will solve it, but since Specialized provided a lousy design combined with a lousy skewer, they should foot the bill.
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Old 05-12-14, 12:05 PM
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Originally Posted by FBinNY View Post
First of all the problem is caused by a poor design decision that goes back to the very beginning of bicycle disc brakes. That was to place the brake behind the fork rather than in front.
Sheesh!
It's been at least ten years since I first read about the problem, and yet the dumb mfgrs are still doing it.

Between this, and making the rotors so undersized that they can't dissipate the heat from a long, steep mtn descent, I doubt that I will ever get disc brakes. And I was really enthused about them when they first came out.
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Old 05-12-14, 12:07 PM
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Originally Posted by alexxander.fost View Post




As for your suggestions, I'll take a look at better quality skewers. Currently I'm using Pinhead skewer locks so nobody steals my wheels.

And thanks for the suggestion about the nail polish and aggregate mixture! That sounds fantastic and super simple..
OK, we now have the crux of the problem --- the Pinhead skewers. These provide the least holding power of just about any option. They're fine for road forks, and maybe even for mtb, but definitely come up short for disc brakes.

The grit paint on the axle face, maybe even combined with some on the static nut of the skewer and on a plain washer under the turning nut may provide enough bite that the Pinheads work. If so, you're home free, if not, go back to a standard skewer.

BTW- this lets Specialized off the hook, since odds are the OEM wheel and skewer probably worked OK.
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Old 05-12-14, 12:23 PM
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Agreed. Running Pinhead skewers lets Specialized off the hook as they (nor I) can properly verify the source of the issue... However, I did several control tests with the external cam skewers that came with the bike and it doesn't hold any better or worse. The wheel still moved under extreme braking and rested against the "lawyer lips" on the caliper side of the fork. I'm confidant the problem can be replicated.

Interesting point about the Pinhead skewers not having much holding power. Perhaps if I over torque the skewers that came with the bike it'll solve the problem. I'm not one to over torque anything and I'm sure there's some wiggle room before the threads start to yield.

Okay, before I go crazy I'll put the factory skewers back, tighten them down beyond the factory torque limit, and see where I end up. I'll do the nail polish next if that doesn't work. Then I'll go cry to Specialized if I'm still having grief and ask for something beefier.

Originally Posted by FBinNY View Post
OK, we now have the crux of the problem --- the Pinhead skewers. These provide the least holding power of just about any option. They're fine for road forks, and maybe even for mtb, but definitely come up short for disc brakes.

The grit paint on the axle face, maybe even combined with some on the static nut of the skewer and on a plain washer under the turning nut may provide enough bite that the Pinheads work. If so, you're home free, if not, go back to a standard skewer.

BTW- this lets Specialized off the hook, since odds are the OEM wheel and skewer probably worked OK.
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Old 05-12-14, 12:32 PM
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Yeah, I'm pretty appalled too. Part of me wonders if this is going to take a class-action law suit to resolve. 10 years is a long time to let a design flaw persist -especially when considering bike models are completely redesigned every ~3 years. That's at least three missed opportunities to resolve the problem. And its not like we're talking about an ergonomic issue or aesthetics. Brake are a big deal. Especially on bicycles.

I'm wondering if the issue has to do with some hidden law governing dropout design specifications for bicycles sold in the US. From what I've seen in my engineering courses, laws governing engineering design are usually ultra specific.

Originally Posted by Shimagnolo View Post
Sheesh!
It's been at least ten years since I first read about the problem, and yet the dumb mfgrs are still doing it.

Between this, and making the rotors so undersized that they can't dissipate the heat from a long, steep mtn descent, I doubt that I will ever get disc brakes. And I was really enthused about them when they first came out.
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Old 05-12-14, 12:39 PM
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Originally Posted by alexxander.fost View Post
Yeah, I'm pretty appalled too. Part of me wonders if this is going to take a class-action law suit to resolve. 10 years is a long time to let a design flaw persist -especially when considering bike models are completely redesigned every ~3 years. That's at least three missed opportunities to resolve the problem. And its not like we're talking about an ergonomic issue or aesthetics. Brake are a big deal. Especially on bicycles.

I'm wondering if the issue has to do with some hidden law governing dropout design specifications for bicycles sold in the US. From what I've seen in my engineering courses, laws governing engineering design are usually ultra specific.
While I characterize it as a poor choice (back mount vs. front), I wouldn't go so far as consider it a defect. The existing systems do a decent jon holding wheels on despite the issue, and there's zero movement with decent axle faces and skewers.

I'm not a big fan of disc brakes, except for the classic ones where the wheel itself is the disc (IMO, all bikes have disc brakes, except those with hub brakes), but experience has shown that existing designs work OK, and wheel ejection is extremely rare -- if it happens at all.

I might point out that while the reaction force from the disc is pushing the axle down, the weight shift from braking is forcing the fork down onto the axle, which mitigates the effect. There may also be other good reasons for rear of fork mount, such as better shedding of dirt from a rising disc, vs. a falling one which would pile dirt atop the brake.

The industry is pretty responsive to problems, and has never been slow to try alternatives. If wheel ejection were even on the radar, you can rest assured that a change to solve the problem would have been by now.
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Old 05-12-14, 02:12 PM
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Fair enough. And good points all around. I guess I'm just a bit frustrated. I'm only an engineering student so I'm far from an authority on the subject of bicycle design, but I get really frustrated when I see engineering designs that are a potential safety problem. Since I started engineering school they've been pounding into our heads how things we will eventually design can kill people and every effort should be taken to protect against that.

In the context of disc brakes, I'm disappointed that bike engineers haven't altered what several people in this thread have already identified as a more robust design. Well designed safety systems should be passive and redundant in nature. This current system instead naturally wants to eject the wheel. The job of preventing this falls on the "lawyer lips" and the skewer's clamping force. A properly engineered system should work with undesirable reaction forces and convert them into an asset. Moving the caliper as you guys have mentioned here would play on the existing strengths of a fork.

Regardless, I'm not trying to argue and I'm sure you're right about the industry being responsive to alternative ideas. I'm more just venting about an otherwise great bike being spoiled by such a basic oversight. Though to be fair, the current disc placement is an ISO standard. Perhaps the case should be made to the International Standards Organization to re-evaluate this standard.

Originally Posted by FBinNY View Post
While I characterize it as a poor choice (back mount vs. front), I wouldn't go so far as consider it a defect. The existing systems do a decent jon holding wheels on despite the issue, and there's zero movement with decent axle faces and skewers.

I'm not a big fan of disc brakes, except for the classic ones where the wheel itself is the disc (IMO, all bikes have disc brakes, except those with hub brakes), but experience has shown that existing designs work OK, and wheel ejection is extremely rare -- if it happens at all.

I might point out that while the reaction force from the disc is pushing the axle down, the weight shift from braking is forcing the fork down onto the axle, which mitigates the effect. There may also be other good reasons for rear of fork mount, such as better shedding of dirt from a rising disc, vs. a falling one which would pile dirt atop the brake.

The industry is pretty responsive to problems, and has never been slow to try alternatives. If wheel ejection were even on the radar, you can rest assured that a change to solve the problem would have been by now.
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Old 05-12-14, 02:35 PM
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Try a quality, internal-cam skewer such as the ones sold by Shimano, et al.
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Old 05-12-14, 02:46 PM
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2 solutions Uncommonly used ..

1 put the caliper on the front of the right fork blade ... some custom builders will ..

and 2, use a dropout that opens to the front, rather than the bottom. .. German Tout Terrain Does this.
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Old 05-12-14, 03:06 PM
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I like that. Perhaps if I'm pissed enough about this to spend a couple hundred bucks I'll invest.

Originally Posted by fietsbob View Post
2 solutions Uncommonly used ..

1 put the caliper on the front of the right fork blade ... some custom builders will ..

and 2, use a dropout that opens to the front, rather than the bottom. .. German Tout Terrain Does this.
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Old 05-12-14, 04:55 PM
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Originally Posted by MileHighMark View Post
Try a quality, internal-cam skewer such as the ones sold by Shimano, et al.
That's what I was going to say. I've actually solved this problem in at least one bike by replacing the Specialized skewer with a Shimano skewer.
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Old 05-12-14, 05:39 PM
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Originally Posted by alexxander.fost View Post
....I'm wondering if the issue has to do with some hidden law governing dropout design specifications for bicycles sold in the US. From what I've seen in my engineering courses, laws governing engineering design are usually ultra specific.
Don't blame the ISO. They don't impose design standards, but rather codify industry standards so all players are using the same playbook.

Originally Posted by alexxander.fost View Post
....I'm only an engineering student so I'm far from an authority on the subject of bicycle design, but I get really frustrated when I see engineering designs that are a potential safety problem. Since I started engineering school they've been pounding into our heads how things we will eventually design can kill people and every effort should be taken to protect against that.

In the context of disc brakes, I'm disappointed that bike engineers haven't altered what several people in this thread have already identified as a more robust design. Well designed safety systems should be passive and redundant in nature. This current system instead naturally wants to eject the wheel. The job of preventing this falls on the "lawyer lips" and the skewer's clamping force. A properly engineered system should work with undesirable reaction forces and convert them into an asset. Moving the caliper as you guys have mentioned here would play on the existing strengths of a fork..
Good engineering involves making trade offs wisely. As an engineering student a phase you'll probably be hearing is "never sacrifice the good on the alter of perfection".

The existing disc brake designs, meet your standards of good design because they are reliable and redundant. The lips, and QRs back each other up, and no the lips do not shear off from wear or stress. While I tend to prefer the front of blade design (especially for road use) it may not be suited for off road use because of mud and dirt accumulation above the caliper. Granted, some fine tuning fo the shape and angle of the dropout slot would add a layer of resistance to ejection, experience shows it isn't necessary if the rest of the retention system is OK -- lips, quality axle and QR faces with bite, and reliable QR lever.

One problem is that there are too many cooks, so what works fine if all elements are in place, can fail when folks make willy-nilly changes without considering the implications.

Ill considered changes to what would otherwise work is something that plagues every field of engineering, at every level. Often a problem item will be referred back to the original engineering team, who'll take a 30 second look before someone shouts out "who the F***, said you could change the .......?!!!!"
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Old 05-13-14, 12:06 AM
  #21  
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Originally Posted by FBinNY View Post
First of all the problem is caused by a poor design decision that goes back to the very beginning of bicycle disc brakes. That was to place the brake behind the fork rather than in front. Probably they went this route because discs were installed on mtn bikes first, and they might have thought that this would reduces the chance of a brake being damaged by rocks.
I'd be more inclined to blame it on a case of unintentional motorcycle mimicry. For any one who's at least accustomed to glancing at motorcycles, front mounted calipers does look quite out of place. A bit like a flag flying INTO the wind.
And now, the bicycle industry, instead of fixing the original error, is instead reaching for another motorcycle feature, the thru-axle.
Luckily enough, this ALSO stiffens the fork up, by improving the mechanical link, which is useful in these days of 29er wheels, long-travel forks and soon even slender disc brake road forks.
Still, if it'd been my call to make, I wouldn't have accepted it. It's in violation of basic safety design principles. Dangerous features should, as far as possible, be removed instead of safeguarded against. Caliper up front, the wheel would stay in place even with the q/r / axle loose. Now, the wheel relies on having the q/r / axle properly done up.
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Old 05-13-14, 03:09 AM
  #22  
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Old 05-13-14, 07:07 AM
  #23  
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So one of our fleet bikes had this issue...

My take on it was,

1. Oil the external-cam skewer so it could be closed tighter.
If that didn't work,
2. Swap it for an internal-cam one.

But! One of the guys pointed out step 2 could be step 3:
2. Scrape the paint off the dropout where the locknuts and skewer sit.

Bingo. The wheel stays put with a crappy external-cam skewer. I was kinda surprised, but also not - the paint (or even powdercoat) can be pretty thick and tough these days.
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Old 05-13-14, 09:25 AM
  #24  
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Originally Posted by dabac View Post
I'd be more inclined to blame it on a case of unintentional motorcycle mimicry.....
This is very possible. I wasn't a party to the design process in the bicycle world, so can't know their thinking at the time.

The MC designers didn't have to worry about wheels dropping since motorcycles didn't have open dropouts. The designers probably decided that it made more sense to have the rotor enter the caliper rising,so it would shed dire and water better. That logic applies equally to bicycles, so the rear placement might also make sense, but the bicycle people didn't consider the other implications. The right answer might have been rear mount, with a redesign of the dropout to counter the torque effects.

In any case, I'm not a fan of disc brakes, which I feel substitute new problems for old ones, but at greater cost and complexity.
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Old 05-13-14, 09:50 AM
  #25  
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Originally Posted by alexxander.fost View Post
I like that. Perhaps if I'm pissed enough about this to spend a couple hundred bucks I'll invest.
Whatever you decide to do, do not on any account read the vast amount of material available on the internet regarding this problem.

That way lies madness.
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