Front disc brake with dropouts

[Adnepos]

I have a Dawes Galaxy (standard, not tandem) that came with disc brakes -160mm. I read with alarm that if the quick release (QR) mechanism becomes loose on these kinds of set-up, then front-braking can cause the axle to jump off the forks.

My front wheel comes off the forks readily when I loosen the QR-no lawyers lips or any other back-up.

I have had just one occasion when I noticed the front QR had come loose whilst on the road and I fixed it immediately! I've done close on 10,000 miles and the disc brakes have functioned well, no maintenance problems (they are cable actuated, not hydraulic) and not caused the wheel to move in the dropouts.

I'm now thinking of upgrading the front wheel, install a magneto for onboard electricity.

Should I be radical and get forks that take a thru' axle? A new fork would also have a 'self-connecting system' -the electrical contact is made when the wheel is secured in the forks, Schmidt SL. But my current forks have given no trouble so the additional expense may not be worthwhile.

What do you think?

[Gattonero]

There had been some reports, and the normal dropouts are not ideal for use with a disk-brake
BUT
the vast majority of people has cycled and raced with such arrangement without any trouble.

The rider's weight and terrain ridden plays a big role in this. Heavy riders and/or journeys on steep roads may benefit from forks purposely done.
Still, I am puzzled that a forks designed for disk-brakes won't have at least the retention tabs

[Valbrona]

1/ If your front wheel only takes 9mm skewer, try a DT Swiss RWS skewer that tightens without the use of a lever. Higher clamping forces are possible.

2/ Or if you can fit one, try a DT Swiss RWS Thru-Bolt. These replace the skewer in thru-axle hubs fitted to regular 9mm dropouts. I use a Thru-Bolt on my bike - 15mm thru-axle hub in 9mm regular dropouts - but with adapters to convert 15mm to 12mm TA. But no need for adapters if your hub is 12mm TA to begin with.

[andrew_s]

Wheel ejection does happen - I've seen it.
In that case, the rider was going slowly enough (pulling into Briancon campsite, having just dropped off the top of the Galibier), that he just about stepped off. The forks got bent though, and he was doubly lucky in that the Briancon bike shop had a suitable spare set in stock.

Factors that make wheel ejection more likely are heavier rider/luggage, braking hard, and smaller discs.
Braking hard was the likely cause in the case of the rider above - he'd been entertaining himself with the power of his new hydraulic brakes, letting the bike run free, and then slamming the anchors on hard for each hairpin.

Until you replace the forks (if you do), try to make a point of checking the QR tightness regularly (at least every week), use a QR with a strong grip (i.e shimano/campag style enclosed cam, or allen key), and I'd recommend putting the adjuster nut on the opposite side to the brake disc, to reduce self-loosening tendencies.

The Schmidt SL connecting system is normal dropout only, though lawyer lips are an option.
As an alternative to SL, Schmidt are bringing out a coaxial cable connector plug for the hub.
If you want a thru-axle generator, there's the SON 28 15 mm, SONdelux 12 mm, or Shutter Precision (SP) P8 in 12 or 15 mm (PD8-X-M, PD8-X, PL8-X-M or PL8-X, where PD is 6-bolt, PL is centerlock, and X and X-M are 15 & 12 mm respectively). The SONdelux is optimised for speed/low drag, and is the least suitable option for generating non-lighting power.

[Brucey]

I have a Dawes Galaxy (standard, not tandem) that came with disc brakes -160mm. I read with alarm that if the quick release (QR) mechanism becomes loose on these kinds of set-up, then front-braking can cause the axle to jump off the forks.

My front wheel comes off the forks readily when I loosen the QR-no lawyers lips or any other back-up....

I think you are very lucky not to have had 'an incident'. There is basically no way I would use the setup you have, and I'm amazed that Dawes would ever sell a bike that was set up in this way. Certainly all the disc braked galaxys I have seen have had lawyers lips; they are necessary IMHO.

To fix the problem, you could buy new forks. Or perhaps you could add your own 'lawyer's lips' to an extant steel fork. A competent welding specialist would be able to add material to the dropouts as a build-up and then dress it so that the wheel cannot be ejected unless the QR is backed off three or four turns.

As it happens I have a new, unused steel fork for a galaxy, which has 1-1/8" steerer, disc mounts and lawyer's lips. PM me if you would like to buy it.

FWIW I think that the special contact system for some Schmidt generators is rather faffy and isn't really a big advantage. I can't help but wonder if the security of the hub fitment is somehow compromised by the extra parts in the dropout, too.

cheers

[tim-b]

Hi
Here's a link to an interesting article. It includes some suggestions to help you
Regards
tim-b

[Adnepos]

Thanks all

There's plenty to think about. I'm minded to get new forks (thru axle set-up) at the time I get my new wheel.I'll not be in a rush to change but in the meantime I'll keep a close eye on the QR lever.

[reohn2]

I have a Dawes Galaxy (standard, not tandem) that came with disc brakes -160mm. I read with alarm that if the quick release (QR) mechanism becomes loose on these kinds of set-up, then front-braking can cause the axle to jump off the forks.

My front wheel comes off the forks readily when I loosen the QR-no lawyers lips or any other back-up.

I have had just one occasion when I noticed the front QR had come loose whilst on the road and I fixed it immediately! I've done close on 10,000 miles and the disc brakes have functioned well, no maintenance problems (they are cable actuated, not hydraulic) and not caused the wheel to move in the dropouts.

I'm now thinking of upgrading the front wheel, install a magneto for onboard electricity.

Should I be radical and get forks that take a thru' axle? A new fork would also have a 'self-connecting system' -the electrical contact is made when the wheel is secured in the forks, Schmidt SL. But my current forks have given no trouble so the additional expense may not be worthwhile.

What do you think?

Simple answer:- http://www.chainreactioncycles.com/mobi ... -prod26621
I have no need for qr skewers as I don't race or have need for rapid wheel changes,and so have these skewers fitted to all my bikes and tandems,all but one have disc brakes.

[rmurphy195]

I thought the retention tabs - "lawyers lips" - had been a legal requirement on the front forks for quite some time?

[Adnepos]

I thought the retention tabs - "lawyers lips" - had been a legal requirement on the front forks for quite some time?

Done a search and not found anything about these tabs being a legal requirement -I don't have a problem with them by the way, I wish my forks had them. How could they be a legal requirement when many bikes have thru' axles so no way of sensibly deploying them -or other secondary retention system?

[PT1029]

I'm sure a bike made for discs would have lawyers lips on the drop outs, unless it was from the early days (1990's) of disc brakes, before the wheel ejecting habit was discovered. In those days Galaxys didn't come in a disc version.
I assume your QRs are original, at one point someone made front QRs with a bigger cam throw, so you could open the QR wide enough for it to slip past the lawyers lips.
In my experience (on customer's bikes), you get a slight warning the front wheel QR isn't tight enough. Put the front brake on hard, push the bike forward hard. If the wheel in the drop out moves to the left while pushing (but re centers when you stop pushing), then the QR is not tight enough* and needs tightening (*but is not yet loose enough to throw the wheel out).

Through axle forks won't have lawyers lips because the design is totally different. Well, they won't have until a real life (American?) lawyer finds a way to make them a requirement....

[reohn2]

Properly desiged frames overcome the problem by having the dropouts facing forward so the wheel axle is forced into them rather than out of under braking

[Brucey]

Properly desiged frames overcome the problem by having the dropouts facing forward so the wheel axle is forced into them rather than out of under braking

they are a better idea for sure but it doesn't stop the hub from moving around, and potentially becoming a slack fit over time through wear on the dropout faces etc.

The reaction force on the axle from a front brake caliper is backwards and downwards, whereas the usual load (arising from the road) is upwards and backwards; if the QR isn't tight enough vs the braking loads then the axle will still move about which (sooner or later) causes trouble.

BTW the tension force in a QR skewer is estimated to be between 500 and 1000kgf (depending on type and method of closure used. A 100kg rider braking hard will manage 100kg at the contact patch which means a 200kg leverage load on the axle (regardless of brake type, by taking moments about the fork crown) plus a torque reaction load that varies with the brake type. The latter load is estimated to be up to ~x5 the load at the contact patch (assuming a 160mm disc and a 700C wheel). So conceivably you could get 500-700kgf load trying to make the hub move in the dropouts.

Debates about the distribution of the load between the dropouts aside, it looks as if the coefficient of friction between the hub and dropouts needs to be between 0.5 and 1.0 to have any chance that the wheel might not move. Between random pieces of steel with a trace of oil present, it is very unlikely that the coefficient of friction will be that high.

My suspicion is that in most disc-braked bikes (with QR wheels and lawyer's lips) the front wheel moves under hard braking and then doesn't always move back again during normal riding.

Arguably the lips are on the wrong face of the dropout, anyway; it would be more secure if the locknuts see the load from the lips, not the QR skewer, which isn't really designed for it.

cheers

[reohn2]

See up thread,I only use hex bolt skewers on my bikes

[Brucey]

See up thread,I only use hex bolt skewers on my bikes

I think they are more likely to get to a decent tension than a cam-type QR, if my experiments are anything to go by. But it doesn't change the basic nature of the argument, only the detail.

cheers