Do disc brakes pull?

[Pale Rider]

Had my first ride on a bike with a disc brake today.

It was a hybrid of uncertain make, but appeared in good order.

When I applied the front disc, I'm sure the bike pulled a little to the side the disc was mounted on.

Is that likely or was I imagining it?

 

[ianrauk]

Not that I have ever noticed.

 

[sabian92]

It shouldn't do, to be honest. I used to have a very similar "hybrid no-name disc" bike and it never pulled.

 

[Pale Rider]

Thanks for the swift replies.

The brake was on the left and I wondered if that fork leg flexed back a tiny bit.

 

[lulubel]

The brake was on the left and I wondered if that fork leg flexed back a tiny bit.

There was a discussion along these lines in the touring forum a while back, about the hazards of retro-fitting discs to forks that aren't designed to take them, but I don't think there was anything mentioned about forks that have been built to take discs. As far as I understand it, the forks have to be stronger for disc brakes because the braking forces are applied near the end of the forks rather than near the crown.

I have a MTB with disc brakes and suspension forks, and it's solid and straight, even under very hard braking.

 

[HovR]

Quick release not tight enough, maybe?

 

[MrJamie]

My front wheel had a bit of an issue where the wheel would tilt left under braking, as the forces on disc brakes try to push down the wheel on the rotor side causing the wheel to tilt/lean in the forks a few degrees, solved by making the QR skewer incredibly tight. The bike itself didnt pull to the left and kept a straight line, although it did kinda look like the wheel was pulling left.

 

[Salad Dodger]

My MTB has discs and I can't say that I have ever noticed them pulling to one side.

Binding a bit, yes, but pulling to one side no......

 

[Pale Rider]

There was a discussion along these lines in the touring forum a while back, about the hazards of retro-fitting discs to forks that aren't designed to take them, but I don't think there was anything mentioned about forks that have been built to take discs. As far as I understand it, the forks have to be stronger for disc brakes because the braking forces are applied near the end of the forks rather than near the crown.

I have a MTB with disc brakes and suspension forks, and it's solid and straight, even under very hard braking.

Makes sense.

Another difference is you have quality kit - I saw your bike buying thread - but you also give it proper use which proves a decent disc set-up works without problems.

 

[Pale Rider]

My front wheel had a bit of an issue where the wheel would tilt left under braking, as the forces on disc brakes try to push down the wheel on the rotor side causing the wheel to tilt/lean in the forks a few degrees, solved by making the QR skewer incredibly tight. The bike itself didnt pull to the left and kept a straight line, although it did kinda look like the wheel was pulling left.

Sums up what I felt.

Tightening the quick release is a good shout.

 

[MrJamie]

Makes sense.

Another difference is you have quality kit - I saw your bike buying thread - but you also give it proper use which proves a decent disc set-up works without problems.

There's also a design flaw with front disc brakes, in that the caliper should be ahead of the fork not behind. With the caliper behind, when the brakes are applied the wheel/axle is pushed downwards, trying to eject itself from the dropouts, particularly on the rotor side, which can (in my case) make the wheel tilt to the left. The lawyer lips on the dropouts and good quality skewers done up very tight are meant to help, as are using bolts rather than QR. Presumably the heavier you are the more momentum and grip and hence force you can put things on under braking too and probably worse on the road than trail, and maybe why a lot of the accounts seem to be from bigger riders. I ended up reading loads about it online as it worried me a bit, this page is pretty informative http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/ If it is just the QR, i was told to do it up as tight as you can with your hands and check it from time to time. IIRC the same physics/forces can cause a similar effect if there is flex in the hub/spokes too.

 

[Pale Rider]

There's also a design flaw with front disc brakes, in that the caliper should be ahead of the fork not behind. With the caliper behind, when the brakes are applied the wheel/axle is pushed downwards, trying to eject itself from the dropouts, particularly on the rotor side, which can (in my case) make the wheel tilt to the left. The lawyer lips on the dropouts and good quality skewers done up very tight are meant to help, as are using bolts rather than QR. Presumably the heavier you are the more momentum and grip and hence force you can put things on under braking too and probably worse on the road than trail, and maybe why a lot of the accounts seem to be from bigger riders. I ended up reading loads about it online as it worried me a bit, this page is pretty informative http://www.ne.jp/asahi/julesandjames/home/disk_and_quick_release/ If it is just the QR, i was told to do it up as tight as you can with your hands and check it from time to time. IIRC the same physics/forces can cause a similar effect if there is flex in the hub/spokes too.

That's a bit worrying.

I've not read everything in the link, but it seems most of the problems were in fairly extreme downhill use.

So (hopefully) the average Joe on his hybrid on the towpath is unlikely to have any problems.

As I mentioned in my OP, the bike I tried wasn't mine, but if I ever get a disc brake bike I shall at the very least keep the quick release tight and check it regularly.

 

[Crankarm]

Storm, tea and cup comes to mind. This is a vicious rumour started by Luddites who still believe that side pull caliper rim brakes are the most efficent brakes ever put on a bicycle. Disc brakes are by far the most superieur, the strongest, most durable and reliable, the most fade fee brakes of all brake types that can be fitted to a bicycle. They work well in both wet and dry conditions.

 

[DiddlyDodds]

The only disc brake i have had was on a "Halfords" mountain bike , it weighed just over 300 tons so hard to tell if applying the braked made it pull to one side, thinking back i am not sure that even a car hitting it would have made it pull to one side, would have probably make the car veer off.