Carbon fork + canti brakes = extreme judder

[citoyen]

Test rode a new bike the other day, which was a hugely enjoyable experience, except for one thing: under heavy braking, the fork juddered alarmingly.

Now, I admit I tend to rely on the front brake rather more than the rear, and I was probably braking more heavily than I needed to since I've mostly been riding the spongy-braked Brommie recently and so I'm not used to such powerful stoppers.

But before I part with my cash and take the bike home, is this something I need to worry about? Is it safe? If I buy the bike, will I just have to learn to use the rear brake more?

I have to say, I've never seen canti brakes on a carbon fork before but I assume it's quite normal for a cyclocross bike, which this is.

I mentioned it to the bloke in the shop (a well-known London chain, ahem) and he seemed completely nonplussed. 

d.

[border-rider]

I don't think it's an inherent property of cantis on a carbon fork

Having said that my (ex-OnceMore's)  TinOne does have a tendency to do this, but I think it's more  a function of brake setup and block type than anything else.

I had Vs on the Pomp when that had a carbon fork, and they were fine.

[Really Ancien]

I've got Campag Veloce V brakes on a cyclo-cross carbon fork. they don't judder. But the reasons why they might are numerous, loose headset, lack of 'toe-in' on the shoes. The canti posts are screwed into an alloy section at the top of the forks, they might be loose. There's no end of fiddling you can do with cantis. They're fine if you keep on top of them, but I still prefer twin pivots.

Damon.

[citoyen]

I was thinking it must be something to do with the fact that with cantis (or indeed Vs) the calipers are mounted on the fork blades rather than the crown, so could cause the fork to flex under heavy braking.

Thanks for the suggestions, Damon. Assuming I do go ahead and buy the bike, I'll try those adjustments.

d.

[Simon Galgut]

A lot of cheap forks with cantis have the judder and/or squeal problem. I have had it with numerous forks on my commuting bikes and it is definitely the forks that are the problem - I think a certain lack of stiffness to resist the outward force on the canti posts is to blame.

I would think twice about buying the bike unless the bike shop can set it up to your liking first.

The only fork I have found that is perfect with cantis is the Easton EC90X, but that may blow your budget.

[ed_o_brain]

Wasn't this a problem with the early Specialized TriCross bikes? I thought Specialized re-designed the forks for their second production year.

[citoyen]

The only fork I have found that is perfect with cantis is the Easton EC90X, but that may blow your budget.

Woah! Just a bit. Maybe I'll save up for one of those for later.

Is it actually dangerous, though? I mean, will the judder ultimately cause the fork to break?

I am definitely thinking twice about buying it, but still leaning heavily towards going ahead and seeing what I can do to overcome the problem. Cos dammit, it's a nice bike and lots of fun to ride.

Given that it's a cyclocross bike, designed to be ridden in wet, muddy conditions, the brakes are probably just a bit too powerful on good road surfaces in the dry, so a lighter hand on the front brake and a bit more emphasis on the rear brake may be all that's required.

d.

[rogerzilla]

There are two things that will reduce the risk:

- Tektro CR520 cantilevers, which are a nice fit on the bosses and don't tend to vibrate much
- A fork crown mounted cable hanger.

[PH]

- Tektro CR520 cantilevers, which are a nice fit on the bosses and don't tend to vibrate much
- A fork crown mounted cable hanger.

An explanation of why the fork crown hanger might work;
BP1272F: KF Kona Design front UpHanger for cantilever brakes

[citoyen]

- Tektro CR520 cantilevers, which are a nice fit on the bosses and don't tend to vibrate much
- A fork crown mounted cable hanger.

An explanation of why the fork crown hanger might work;
BP1272F: KF Kona Design front UpHanger for cantilever brakes

Brilliant. I don't really understand it but it makes a kind of sense. Thanks for that.

d.

[border-rider]

I don't think it's an inherent property of cantis on a carbon fork

Having said that my (ex-OnceMore's)  TinOne does have a tendency to do this, but I think it's more  a function of brake setup and block type than anything else.

I had Vs on the Pomp when that had a carbon fork, and they were fine.

I've now put new brake blocks on and set the cantis up properly.  No judder, great braking.

I'm not convinced that a carbon fork is really any more flexy than some of the lightweight steel ones

[citoyen]

I don't know either way. The fork on this bike is carbon but with an alu steerer. Don't know if that would make a difference. I've bought one of those Kona uphanger widgets but haven't fitted it yet. I'll report back when I get round to it.

d.

[border-rider]

I don't know either way. The fork on this bike is carbon but with an alu steerer

So's mine.

[sam@singular]

The ultimate fix is a fork mounted cable stop as above, another thing which can also help is making your straddle wire longer which reduces the mechanical advantage of the brake.  This can definitely happen with lightweight steel forks as well as carbon. I wouldn't be concerned about it it compromising the integrity of the fork - the forces it faces through general riding will be just as great, if not more so than under braking.

[MacB]

my ill fated drop bar conversion, followed by u-turn, left me with some bits. I've sold most of them but still have an unused Kona DF cable hanger, £5 posted, pm me if you're interested....Al

[border-rider]

Tempted, but my fork doesn't have a hole in the front to mount one

I'm tempted to drill one as the cable mount on the steerer fouls the bars.

[Regulator]

Test rode a new bike the other day, which was a hugely enjoyable experience, except for one thing: under heavy braking, the fork juddered alarmingly.

Now, I admit I tend to rely on the front brake rather more than the rear, and I was probably braking more heavily than I needed to since I've mostly been riding the spongy-braked Brommie recently and so I'm not used to such powerful stoppers.

But before I part with my cash and take the bike home, is this something I need to worry about? Is it safe? If I buy the bike, will I just have to learn to use the rear brake more?

I have to say, I've never seen canti brakes on a carbon fork before but I assume it's quite normal for a cyclocross bike, which this is.

I mentioned it to the bloke in the shop (a well-known London chain, ahem) and he seemed completely nonplussed. 

d.

According to the inimitable Mr Paul Smith SRCC (formerly of Bike+), judder is fairly common with cantilever brakes on carbon forks.  I found this with the Van Nicholas, as have others from the forum.

The trick is to ensure that you use a relatively soft brake pad (OK, you end up replacing them more often) and that you regularly toe the pads in.

[border-rider]

I wonder if there's resonance effect here also...the lower density of the CFRP might make the forks more prone to oscillation at some frequencies, and maybe the stick-slide action of the pads on the rims is enough to excite this.

Just an idea...

[mattc]

... This can definitely happen with lightweight steel forks as well as carbon. ...

Is this related to lightweight forks tending to bladed shapes? So either they're more twisty, or there is a different 'twisting resonance'* to round cross-sections?


*I may have made that term up.

[mattsccm]

this was regarded as almost normal on tricrosses. Not on my Xs but it seemed as if the length of the wire between the cable stop was too long and an up hanger solved the problem.  Other threads, eg STW and Bikeradar have good coverage. It seems as if this is one place where carbon has a weak spot. Stick an alloy fork in with an identical set up and it will stop. Try Canti's if you want but Specialized  now use an uphanger from the bolt hole in the forks.