Brake pad length

[George]

Pads for cantilever brakes are usually 55mm. But pads for V-brakes are usually 70mm. The fixings are usually identical.

What's the reason for using shorter blocks with cantilevers? Is there any reason why I shouldn't fit V-brake pads & shoes to the cantilevers on my touring bike? Wouldn't the increased contact area provide better braking, and wouldn't that be useful, e.g. on a laden tourer in the wet?

[petemarshall]

I use them on my tourer. Tight fit on the forks and may be to tight on some otherwise no problem. I fitted them because I couldn't find koolstop pads in the smaller size, only road type pads or long ones.

[Patch]

We only stock the long ones now. So we always use long ones on cantilevers.

[George]

Thanks, both.

[Clive]

Pads for cantilever brakes are usually 55mm. But pads for V-brakes are usually 70mm. The fixings are usually identical.

What's the reason for using shorter blocks with cantilevers? Is there any reason why I shouldn't fit V-brake pads & shoes to the cantilevers on my touring bike? Wouldn't the increased contact area provide better braking, and wouldn't that be useful, e.g. on a laden tourer in the wet?

It might making braking worse? if the same force is applied across a greater area = reduced force per given area = reduced friction ??

On the subject of brakes (1), what are opinions on cantilevers versus V brakes? I test rode a Thorn Mercury yesterday and a popular option seems to be a cable operated rear disc brake with either a cantilever or V front rim brake. Just wondered what the pros and cons of each were?

On the subject of brakes (2), has anyone used Koolstop dual blocks, a combination of salmon and black; salmon for wet and black for dry conditions. I've moved back to Koolstop after finding the previous Swissstop disappointing.

On the subject of brakes (3) the Shimano R450 cantilever brake fitted to the Mercury seems to work so much better than the Tektro ones I have. I didn't realise there could be so much difference?

[George]

It might making braking worse? if the same force is applied across a greater area = reduced force per given area = reduced friction ??

Interesting. I'm afraid that I don't know; that's why I raised the question.

[Andy Terry]

When you brake, the stopping force depends on the coefficient of friction between the brake block and the rim, and the clamping force applied.

Bigger brake blocks do not apply more force - they only apply the same force over a bigger area.

[Philip Whiteman]

When you brake, the stopping force depends on the coefficient of friction between the brake block and the rim, and the clamping force applied.

Bigger brake blocks do not apply more force - they only apply the same force over a bigger area.

Entirely, the co-efficiency is also dependent upon within the brake block. Hence, a cheap block using lower quality rubber is going to be less effective than a more expensive and higher quality version.

I could extend this conversation to my unfortunate knowledge and experience with the braking capabilities of railway carriages, but I won't.

[chris ankcorn]

Entirely, the co-efficiency is also dependent upon within the brake block. Hence, a cheap block using lower quality rubber is going to be less effective than a more expensive and higher quality version.

The amount you pay for a brake pad is not necessarily an indication on its stopping ability.

If the brake compound is too hard it will wear your rim faster then a cheaper softer compound. I would prefer to use a cheap softer compound and be prepared to replace them before their down to the grooves.

Wiping your rims with white spirit on a regular basis makes an appreciable difference too.

I buy my brakes pads from Discobrakes. They are so cheap that you can afford to change them frequently.

I'm not saying I'm correct but this is my opinion and it has served me well.

[Philip Whiteman]

I disagree, Chris. It is not necessarily the softness of the rubber but the properties of the compound. Generally speaking, the more expensive versions such as Koolstop use a higher quality compound than say Shimano or BBB blocks. You can have a soft rubber with a poor coefficiency but have an equally soft rubber with a high coefficiency - as it all depends upon the manufacture crosslinking and polymer chains within the rubber that produce a high or low friction and thereby braking coefficiency. Cheaper types of block tend to use a greater proportion of raw rubber and within the subsequent manufacturing process, use less curing agent and accelerators for setting. As a result, the rubber is insufficiently 'tacky' to produce a good rate of friction. So in short, you get what you pay for.

[chris ankcorn]

I disagree, Chris........................So in short, you get what you pay for.

If I can lock-up the back wheel with my cheapo brake blocks then why do I need to spend more on brake blocks which have a higher coefficiency?

[George]

When you brake, the stopping force depends on the coefficient of friction between the brake block and the rim, and the clamping force applied.

Bigger brake blocks do not apply more force - they only apply the same force over a bigger area.

Andy, clearly that's true, but is it the whole story? If that's the whole story, wouldn't that mean that pad size is irrelevant to stopping power? And, if that's the case, why do mountain bikes have bigger pads than road bikes? Just pad life?

Might the area that the force is applied over influence the amount of deformation of the various components, and might that in turn affect the friction between pad and rim? And might the size of the pad influence the tendency for films of water and dust to get between the pad and the rim? Etc.

The amount you pay for a brake pad is not necessarily an indication on its stopping ability.

I disagree, Chris.

There's no question in my mind that some brake blocks are much more effective than others, and that there is a crude correlation between what you pay and what you get. But not a precise correlation. In some cases (e.g. Campag), you pay an awful lot simply for the name. And brand A may be 10% better than brand B, but 100% more expensive.

[Andy Terry]

When you brake, the stopping force depends on the coefficient of friction between the brake block and the rim, and the clamping force applied.

Bigger brake blocks do not apply more force - they only apply the same force over a bigger area.

Andy, clearly that's true, but is it the whole story?

Yes, I believe so.

Assuming the same materials.

bigger pads = less pressure (same force over more area) = less wear

[CakeStop]

Softer blocks seem to get impregnated with tiny bits of metal and I've always felt that unless one frequently removes the blocks to extract these it is they that are wearing the rims more than the blocks themselves. Koolstop Salmon feel harder than an average block and they seem to last much longer and wear rims less so I reckon they work out much cheaper in the long run.