Disc brakes vs. 'normal' brakes??

[Mad at urage]

Try a steeper alpine descent on a 16kg recumbent! You're constantly braking to keep the speeds in the 50-60mph area. This is where rim brakes lose the plot completely. If the tyre doesn't blow the pads end up a mass of molten rubber in a matter of minutes. The rubber disposed on the rim turns into hard vulcanised plastic coating & not even the pad carrier will help you stop. Once this happens you're out of brakes permanently. At least if a disc overheats you can let the bike roll through & the disc cool off, which at those speeds doesn't take too long.


The answers seemed like basic disc 101.

Indeed they are, including where it says "With rim brakes you already have the biggest possible rotor on a wheel: the rim!"

 

[snailracer]

Indeed they are, including where it says "With rim brakes you already have the biggest possible rotor on a wheel: the rim!"

And if you put a tensioned rubber band on the outside, it stops most of the squealing. And rubber is grippy, perhaps we could use it as a tyre? I reckon it will sell!

 

[GrasB]

Indeed they are, including where it says "With rim brakes you already have the biggest possible rotor on a wheel: the rim!"

But that makes the, incorrect, assumption that larger rotors are always better.

 

[snailracer]

But that makes the, incorrect, assumption that larger rotors are always better.

OK, so how is a larger rotor not always better?

 

[GrasB]

Go too big on the rotor & the friction surfaces stay too cold & you start needing really soft pads & soft rotors to keep performance at the low friction interface temps. Problem is really soft pads get effected by things like water on the braking surfaces more & tend to overhead more readily. Net result, go too big & you have to make compromises on the friction materials which impede brake performance.

Bare in mind that disc brakes are overheating at temps where your rim would have got so soft the tyre pressure would have bend the rim outwards & unseated the tyres.

 

[Smut Pedaller]

Interesting reading for those of us who have thus far assumed disc-brakes are always better than rim brakes.

From what I gather, the article is about someone who uses aftermarket ultra lightweight rotors which look like doilies, a cable to hydraulic converter, then proceeds to drag his brakes down a hill and wonders why they fail further down the hill... Bad technique, mismatched equipment. No surprise there.

 

[VamP]

From what I gather, the article is about someone who uses aftermarket ultra lightweight rotors which look like doilies, a cable to hydraulic converter, then proceeds to drag his brakes down a hill and wonders why they fail further down the hill... Bad technique, mismatched equipment. No surprise there.

Sure.

But equipment manufacturers have to assume that users will do this. Or face astronomical law suits.

 

[Smut Pedaller]

Sure.

But equipment manufacturers have to assume that users will do this. Or face astronomical law suits.

Actually I am being a bit mean, the article was written pretty objectively and he later does admit to poor braking technique and mismatched equipment in the comments. He does let the spokespeople have their say.

Generally though, I'm doubtful that a manufacturer(s) would be convicted of negligence and sued in a scenario like this, particularly when the potential plaintiff is the editor of an online bike website and really should know better! Anyway it's going a bit off topic.

The comments are pretty interesting though, particularly the amount of comments from people who ride tandems and use cable operated BB7's who have never had any problems because they used appropriate rotors and proper braking technique. 2x the power and weight, with only slightly more aero drag.

 

[GilesM]

I'm waiting for the first hydraulic road disc brake....... will it be Shimano or SRAM?

Neither, those wonderful people from Barnoldswick who have been making top mtb hydraulic brakes for a few years now.

http://www.hopetech.com/page.aspx?itemid=SPG343&tab=technical

Aimed at the CX bikes right now due to the changes in regs.

 

[GrasB]

You have a cable in the system... the merits of hydraulics have just been rendered almost completely mute. the SRAM Red solution gives you hydraulics from lever to pads.

 

[Globalti]

I've got BB7s on the cross bike and they are good once they have dried out but cold and wet they squeal like a piggie and vibrate horribly. I am pleased to see that SRAM have done it but don't like their double-tap system so I will also be waiting for Shimano's offering, I think.

Shimano have 4000 employees and 400 of them are in R&D; they might take longer but I'm sure the job will be done right.

 

[ColinJ]

You have a cable in the system... the merits of hydraulics have just been rendered almost completely mute. the SRAM Red solution gives you hydraulics from lever to pads.

I don't think that there would be much friction in the short runs of brake cable to the hydraulic system just under the handlebar stem. The conventional front brakes on both my road bikes feel fine. It's the friction in the rear brake cables that bothers me.

 

[GrasB]

It's not the friction so much as even a short stretch of cable renders the modulation & feel advantages of hydraulics almost completely void as most of the problem occurs in large radius cable bends like handle bar routing.

 

[snailracer]

It's not the friction so much as even a short stretch of cable renders the modulation & feel advantages of hydraulics almost completely void as most of the problem occurs in large radius cable bends like handle bar routing.

Now surely any loss in feel is related to how much tension is transmitted through the cable - if the cable tension is low (i.e. travel is long) then very little feel is lost because the cable friction and compression effects are minimal. This is why V-brakes typically feel much better-modulated than cantilevers or caliper brakes, even with identical cable runs and the same overall mechanical advantage.

IOW, a hybrid cable/hydro disc can still have good "feel" if properly designed.

 

[snailracer]

... At least if a disc overheats you can let the bike roll through & the disc cool off, which at those speeds doesn't take too long...

When a hydro disc overheats, the wheel can lock or skid - you don't necessarily "roll through".