Road Bikes - Why no hydraulics?

[MacB]

It is too easy to skid narrow tyres using rim brakes as it is, they just do not have a large enough road contact point to require any more braking power.

I can hammer my fat tyred bikes brakes and not skid, but on the roadie, braking forces even close to that end up with wheel slip as the tyre loses traction with the road.

I love disks for the wet weather braking and being kinder to rims throughout winter, but thin tyres can't really handle any more power than calipers already provide.

But most of us aren't seeing it as a way to increase braking power, rather a way to get more consistent braking regardless of conditions and to see parts last longer.

 

[threebikesmcginty]

But most of us aren't seeing it as a way to increase braking power, rather a way to get more consistent braking regardless of conditions and to see parts last longer.

That's exactly it. My company bike has hub gear, disc brakes and mudguards - all there so I can cycle comfortably whatever the weather and get consistent performance (from the bike, not me) and longevity of components.

And as a dropbar bike with this stuff on, I think it looks pretty smart.

 

[Piemaster]

Your model is too simple. Rim brakes operate by clamping the rim which is taking the force generated by the tyre on the road. The braking force is transmitted to the bike throught the fork crown - the fork blades are only partially involved. A disk brake is applying the force at the wheel spindle, the fork tip has to take the reaction force from the clamped rotor - this is why they there was a tendency to pop front wheels out when the caliper was on the wrong side of the fork.

Errr.. thats what I posted. Glad you agree with my 'too simple' model This is how both types of brake slow the bike down, regardless of the actually mechanics of the process. The road/tyre friction is transmitted to the bike frame via the crown fork. I don't think we're actually talking about anything too different here, but the medium is making it more complicated than it should be, I'd be happier chatting over a pint with a pencil and back of a fag packet to hand. If we ever meet up.......but until then I'll bow out as I can't see us achieving anything.

The OP was about hydraulics but this has strayed into a discussion about rim v. disk. Disks are a very effective solution for MTB's and Hybrids (in whatever the widest sense is) but they aren't going to appear on race bikes because of thermal efficiency, aerodynamics and because the current solution works as effectively as is required - you can easily lock a wheel already so no extra braking power can help. Apart from some issues with modulation on carbon braking surfaces there isn't a driver to change other than the perennial desire to get rid of drag and weight.

I can't see them happening on road race bikes either (road race deliberate as mtb/CX are raced too). Not as though I think it would make any difference to any but top road riders, but because thats what the pros ride so thats what I want on the road bike too.Nothing wrong with that either.

 

[xpc316e]

It is too easy to skid narrow tyres using rim brakes as it is, they just do not have a large enough road contact point to require any more braking power.

I can hammer my fat tyred bikes brakes and not skid, but on the roadie, braking forces even close to that end up with wheel slip as the tyre loses traction with the road.

The small contact patch of a narrow tyre makes no difference to its tendency to skid, or not. Fat tyres, assuming that everything else is the same, are pushed onto the road surface with proportionately less force, and grip is almost directly related to how hard a tyre is being pushed onto the road. Therefore width of tyre makes no difference.

 

[2Loose]

The small contact patch of a narrow tyre makes no difference to its tendency to skid, or not. Fat tyres, assuming that everything else is the same, are pushed onto the road surface with proportionately less force, and grip is almost directly related to how hard a tyre is being pushed onto the road. Therefore width of tyre makes no difference.

I completely disagree.

If you answer the question 'Why do race cars have wide, low profile tyres but cycles narrow ones?' you may see why I disagree.

 

[Cubist]

I completely disagree.

If you answer the question 'Why do race cars have wide, low profile tyres but cycles narrow ones?' you may see why I disagree.

A bit too simplistic to bolster your argument I'm afraid. Massive differences in friction coefficient from compounds that resemble chewing gum, and major differences in torque. Up to a thousand horsepower transferred through a wide sticky tyre onto a racing circuit doesn't equate with a Bonty hardcase on Clapham High street on a wet Wednesday evening!

 

[Norm]

A bit too simplistic to bolster your argument I'm afraid. Massive differences in friction coefficient from compounds that resemble chewing gum, and major differences in torque.

'tis you who is introducing those differences, Cubist. The reality is that there are indeed many differences between a car racing tyre and a cyclists commuter tyre but 2Loose's point was not about all those.

Strip out everything else, make it as simplistic as it needs to be to make the point and a wider footprint has a greater level of grip.

 

[Cubist]

Agreed Norm, but if you were to factor the contact patch under braking of a F1 car braking from 200mph to that of a bike tyre braking from say 40mph and take into account the friction available between track and tyre per lb etc etc I would say the bike has more rubber per unit of energy, surely? We need someone like Rando or Marin to do the maths!

 

[snailracer]

But most of us aren't seeing it as a way to increase braking power, rather a way to get more consistent braking regardless of conditions and to see parts last longer.

Yebbut hub brakes are even better in those respects, are less likely to get bent by bumping in the bike racks, don't require dished wheels, are cheaper and have long been fitted to bikes.

 

[xpc316e]

I completely disagree.

If you answer the question 'Why do race cars have wide, low profile tyres but cycles narrow ones?' you may see why I disagree.

You might well disagree, and I admit that it defies logic, but here's the reason why tyre contact patch size makes no difference:

Frictional resistance is Coef-of-friction x pressure x contact area.
The area and the area part of pressure cancel, giving:
Friction is Coef-of-friction x force.
Therefore contact area makes no difference to the frictional resistance!

 

[GrasB]

I love disks for the wet weather braking and being kinder to rims throughout winter, but thin tyres can't really handle any more power than calipers already provide.

As someone who has many 1000s of road miles logged with skinny tyres, 700x21 to 700x28c, & disc brakes... erm WTF?! I've consistently found Avid BB7 disc brakes to deliver reduced stopping distances & be far more controllable than any type of rim brake I've dealt with.

The great thing about discs is they are far less prone to sudden increases in braking effectiveness that you get when the pads finally clear all the muddy water off the rim & start to bite properly. This means in bad conditions you have total confidence to pull the bike up at maximal braking from the start.

 

[tincaman]

Is this close enough to a road going bike? Looks good don't it?

 

[2Loose]

As someone who has many 1000s of road miles logged with skinny tyres, 700x21 to 700x28c, & disc brakes... erm WTF?! I've consistently found Avid BB7 disc brakes to deliver reduced stopping distances & be far more controllable than any type of rim brake I've dealt with.

The great thing about discs is they are far less prone to sudden increases in braking effectiveness that you get when the pads finally clear all the muddy water off the rim & start to bite properly. This means in bad conditions you have total confidence to pull the bike up at maximal braking from the start.

I am certainly not disputing the better control and modulation with disk brakes, this, along with instant braking rather than having to clean off the rims all help with reduced braking distances. No disputing that at all, in fact I stated that. I only referred to total braking power causing skids more easily on narrow tyres.

When calipers do bite, they can deliver enough power to lock the wheels and skid. I believe the same bike with fatter tyres will take more braking force before skidding on the same surface , that is all.

This of course is offset by the better modulation so can be controlled more easily with disks, but that wasn't my point. I have owned more than one disk braked bike, so I do appreciate that disks are the better solution.


GrasB, you drive fast cars on a track right? Simple question: Would they drive\accelerate\stop as well with skinny tyres?

 

[snailracer]

You might well disagree, and I admit that it defies logic, but here's the reason why tyre contact patch size makes no difference:

Frictional resistance is Coef-of-friction x pressure x contact area.
The area and the area part of pressure cancel, giving:
Friction is Coef-of-friction x force.
Therefore contact area makes no difference to the frictional resistance!

For bicycles, you also have to factor in the unevenness of the road surface: a smaller, high-pressure contact patch is more likely to skip and thus lose grip, than a larger, low-pressure contact patch.

 

[snailracer]

Agreed Norm, but if you were to factor the contact patch under braking of a F1 car braking from 200mph to that of a bike tyre braking from say 40mph and take into account the friction available between track and tyre per lb etc etc I would say the bike has more rubber per unit of energy, surely? We need someone like Rando or Marin to do the maths!

A F1 tyre runs at amazingly low pressure, something like 5psi IIRC. I would have thought this was to maximize the contact patch area.