why are Vs better than cantilever brakes?

SimonAH

New bike looming (CAADX 105, practicality overriding lust for the Cooper as I already have one very pretty fast and simple bike) and the engineer in me is upgrading even before she's ordered.

Is it that with a canti there is more cable between the two (well three really) force points in the leverage equation? Ergo more sponginess due to temporary cable stretch? Or am I missing something fundamental?

davis

When you pull a canti brake, the straddle wire lifts up. This causes the force on the levers to "move" to a more upwards vector -- i.e. it starts to pull the lever up when you want it to pull sideways instead.

There are probably other factors too.

desweller

V brakes are canitlever brakes.

nicklouse

V are Linear pull cantilevers. they can apply more force onto the rim.

nation

With cantis you have to apply progressively more and more force at the lever as the brakes are applied for a given increase in the force with which the pad is applied to the rim. As a consequence, when you have to haul hard on the lever you lose the sensitivity that enables fine modulation.

With Vs the relationship between force at the lever and the force with which the pad is applied to the rim is linear - the same increase in force on the lever will apply the same increase in force at the pad wherever the brake is in its range of movement. You don't have to squeeze as hard to generate bigger braking forces and you therefore have more modulation, which means not only can you brake harder with less effort, you can brake much closer to the limit at which you'll start locking wheels.

cjcp

Leaving aside Nick's post, cantis were designed by Satan for a bit of a laugh, aimed at scaring pedestrians out of their skins and birds out of trees. (They squeal like hell.)

That's the non-engineering POV.

Never had any such problem with the V-brakes on my mtb.

Next CX bike I buy will have disc brakes. End of. None of that faffing around with toe-ing or the position of the cable hanger.

unixnerd

I have V brakes on my mtb, they're great. I have cantis on my tourer, they're no use in the dry and scary in the wet. I'm an engineer and have tried everything to optimise the leverage on them to no avail. I remember coming down the Cairngorm ski road on the tourer once (and never again) almost getting cramp in my fingers I was pulling the levers so hard.

No way I'd buy a cyclo cross bike right now. Since the UCI legalised disc brakes I'm sure all the manufacturers will be coming out with disc options for 2012 models. I reckon most will use cable operated calipers rather than hydro, that's just fine so long as you get the newer calipers where both sides move rather than just one. It may also make a difference to the used value of the bike when you come to sell it.

nicklouse

unixnerd
got all your 90 Degree angle sorted?

jejv

nicklouse wrote:

unixnerd got all your 90 Degree angle sorted?

Not sure about that NL, could you elaborate ? Why ? Which angle ?

If we're talking about braking on the hoods, part of the problem is that drop bar levers aren't designed for that, even though most folks with drop bar levers seem to spend most - or all - of their time on the hoods. For the hoods, we'd really want a dog-leg lever, like an MTB lever, so we can apply force to the brake lever more easily from the hoods.

Suppose the canti is in a vertical plane.

At the biting point (so nothing is moving much), the straddle wire tension is half the brake wire tension, divided by the sine of the angle between the straddle cable and the horizontal. More straightforwardly,if the angle of the straddle cable from the horizontal is less than about 45 degrees, then to a good approximation, the tension is inversely proportional to the angle of the straddle cable from the horizontal: halving the angle (by lowering the straddle) doubles the leverage. What can be done in practice depends on whether you have a shimano-style safety straddle, whether you have mudguards, how much tyre you need to clear. There are different lengths of shimano-style straddle available.

The other factor (for a given brake) is the angle between the pivot, the point where the straddle wire attaches to the brake, and the straddle. Leverage is proportional to the sine of this angle "A" - or the cosine of the difference between this angle and a right angle. So making angle "A" closer to 90 degrees helps. But the sensitivity to this angle is normally much less than the sensitivity to the angle of the straddle wire to the horizontal, because the sine of any angle vaguely near a right angle is close to 1 - for example sine 60' == sine 120' == 0.866.
In practice, with wide cantis, this means that less spacers between the brake and the pad, narrower rims, and thinner pads will all give a little bit more leverage.

If you do this stuff in the second point, the straddle cable can be lowered further (assuming it's not fixed length, like shimano).

So why do Shimano do these funny straddle wires ?
That's so that if the brake cable fails, or the straddle hook fails, the straddle wire doesn't catch on the front tyre and throw you into the road. That can happen.
Are there any production CX bikes with wide cantis that also have something to catch the wire and prevent this happening ?
Mudguards would do the job.

MrChuck

V brakes don't neccessarily work any better than some well set up cantis, but getting them well set up is a PITA and that alone is enough reason for me to prefer Vs.

On CX bikes there's a mud clearance issue as well.

bails87

Why aren't Vs used then?

snailracer

jejv wrote:

Are there any production CX bikes with wide cantis that also have something to catch the wire and prevent this happening ?
Mudguards would do the job.

On older mountain bikes, the reflector bracket would catch broken straddle wires.

MrChuck

bails87 wrote:

Why aren't Vs used then?

Mud for one thing, I think a liitle while back there was more of a problem making Vs work well with drop levers too.

nation

Shimano do Vs with a parallelogram linkage for MTBs that helps with mud clearance. The pads sit further from the wheel rim in their rest position.

Also means that if you prang a wheel out of true mid ride you don't have to disconnect the brake to ride home (as long as it isn't too bad).

snailracer

Cantilever brakes can be set up over an enormous range of leverage, which is good (or bad) depending on how carefully (or usually not) the brakes are set up, and whether you need that versatility. For example, over MTB/cyclocross terrain, you might want different leverage on the front brakes vs the rear. On tour, you might want to set up your brakes so they don’t rub if your wheels go out of true (at the cost of reduced braking power).

V-brakes are essentially fixed leverage/fixed pad displacement, but the advantage is that it’s very easy to compensate for pad wear without drastically changing the leverage and pad displacement. This means less maintenance for everyday commuting use – all you have to do is give the cable adjuster a twist now and then as the pads wear thin.

As Sheldon Brown explained, V-brakes are also better because they use lower cable tension/more cable movement than cantilever brakes. This results in less compression of the cable outer and less stretch of the inner wire, both of which would make the brakes worse.

MichaelW

My touring bike cantis have a huge amount of flex in the whole system and a very tight curve in the front brake cable but getting a solid cantilever hanger is all but impossible for older bikes.
Up-hangers which mount to the fork crown go a long way to eliminating flex. These dont fit older brazed steel forks very well, they work better with welded ones which have more surface area for mounting on the front.

If you want to use road levers with V brakes, you need a cable pull converter such as Travel Agent.

Mr Plum

Just bought some mini Vs for the Tricross. Fitting them next week. Can't wait to have some proper stopping power.

EKE_38BPM

Since my fixie frame broke I'm in the market for a new frame. I only use a front brake so I want that brake to be as good as possible.

I'm considering getting a disc compatible fork and disc front wheel. Any suggestions for a fork?

optimisticbiker

EKE_38BPM wrote:

Since my fixie frame broke I'm in the market for a new frame. I only use a front brake so I want that brake to be as good as possible.

I'm considering getting a disc compatible fork and disc front wheel. Any suggestions for a fork?

Why I understand your logic, surely its flawed in that any brake that can stop the front hard enough to get the back wheel to lift will be the best brake possible under that circumstance... anythign more and you'll be over the bars! A v- or caliper-brake will do that with far less weight than a disc...

desweller

OptimisticBiker wrote:

EKE_38BPM wrote:

Since my fixie frame broke I'm in the market for a new frame. I only use a front brake so I want that brake to be as good as possible.

I'm considering getting a disc compatible fork and disc front wheel. Any suggestions for a fork?

Why I understand your logic, surely its flawed in that any brake that can stop the front hard enough to get the back wheel to lift will be the best brake possible under that circumstance... anythign more and you'll be over the bars! A v- or caliper-brake will do that with far less weight than a disc...

A) Better braking in the wet
Doesn't destroy the rim
C) More control (less hand power required for a given retardation)

Discs are good.

UndercoverElephant

DesWeller wrote:

OptimisticBiker wrote:

EKE_38BPM wrote:

Since my fixie frame broke I'm in the market for a new frame. I only use a front brake so I want that brake to be as good as possible.

I'm considering getting a disc compatible fork and disc front wheel. Any suggestions for a fork?

Why I understand your logic, surely its flawed in that any brake that can stop the front hard enough to get the back wheel to lift will be the best brake possible under that circumstance... anythign more and you'll be over the bars! A v- or caliper-brake will do that with far less weight than a disc...

A) Better braking in the wet
Doesn't destroy the rim
C) More control (less hand power required for a given retardation)

Discs are good.

D) With road levers they generally suck balls.

Jury's still out.

desweller

UndercoverElephant wrote:

DesWeller wrote:

OptimisticBiker wrote:

EKE_38BPM wrote:

Since my fixie frame broke I'm in the market for a new frame. I only use a front brake so I want that brake to be as good as possible.

I'm considering getting a disc compatible fork and disc front wheel. Any suggestions for a fork?

Why I understand your logic, surely its flawed in that any brake that can stop the front hard enough to get the back wheel to lift will be the best brake possible under that circumstance... anythign more and you'll be over the bars! A v- or caliper-brake will do that with far less weight than a disc...

A) Better braking in the wet
Doesn't destroy the rim
C) More control (less hand power required for a given retardation)

Discs are good.

D) With road levers they generally suck balls.

Jury's still out.

Doesn't that just imply that the fault is in the lever? EKE can choose a suitable lever as he doesn't have to worry about gears, e.g. these.

nation

OptimisticBiker wrote:

EKE_38BPM wrote:

Since my fixie frame broke I'm in the market for a new frame. I only use a front brake so I want that brake to be as good as possible.

I'm considering getting a disc compatible fork and disc front wheel. Any suggestions for a fork?

Why I understand your logic, surely its flawed in that any brake that can stop the front hard enough to get the back wheel to lift will be the best brake possible under that circumstance... anythign more and you'll be over the bars! A v- or caliper-brake will do that with far less weight than a disc...

The level of control and modulation you get with discs is far superior to rim brakes. The theoretical braking power you can generate may not be any higher, but you can use much more of it.

Kinesis do a couple of CX forks with disc mounts. Alloy one is about £70 and the carbon one is about £130.

Drysuitdiver

what screws me is the different colour pads , with no explanation of what the colours mean on any of the packaging . leaving the quad tech black pads on daughters till i know better from a chat with tech on Monday

nicklouse

jejv wrote:

nicklouse wrote:

unixnerd got all your 90 Degree angle sorted?

Not sure about that NL, could you elaborate ? Why ? Which angle ?

the 90 degree angle the straddle wire makes with either the pad contact point or the arm pivot point.
one give "better" feel and one gives most braking power.

snailracer

nicklouse wrote:

jejv wrote:

nicklouse wrote:

unixnerd got all your 90 Degree angle sorted?

Not sure about that NL, could you elaborate ? Why ? Which angle ?

the 90 degree angle the straddle wire makes with either the pad contact point or the arm pivot point.
one give "better" feel and one gives most braking power.

I use the angle at the yoke (i.e. the angle between the two symmetrical lengths of the straddle wire) as a reference:

- A sharper angle gives more pad movement, with less leverage. This reduces braking power, making it less "grabby". It is also suitable if your rims are a bit out of true and you don't want the pads rubbing against it, as you can set the pad-to-rim spacing to be quite large.

- A less acute, flatter angle gives less pad movement and more leverage. This means you have to squeeze the lever less hard to get strong braking. Your rims need to be true because that the pad-to-rim spacing needs to be close to avoid running out of lever travel.

On my canti-equipped bike, I set the rear brake to be less strong (i.e. sharper yoke angle) than the front one - a grabby rear tends to lock up too easily.

Counterintuitively, a stronger brake will feel spongier at the lever because it's flexing the pad, brake arms, rim, etc. - assess the strength of the brakes by actually test riding the bike and braking.

On many cantilever brakes, you can't actually adjust the straddle cable length (unless you buy new ones). However, you can still adjust the yoke angle by mounting the pads (which have long pillars for this) further from or closer to the brake arms, and adjusting the amount of main cable to compensate.

sketchley

EKE_38BPM wrote:

Since my fixie frame broke I'm in the market for a new frame. I only use a front brake so I want that brake to be as good as possible.

I'm considering getting a disc compatible fork and disc front wheel. Any suggestions for a fork?

The carbon v-brake compatible fork off my frame might be available soon.