Disc brakes on road bikes

[lukesdad]

Sorry, I don't follow Rob?

I was looking for a winter bike and did first consider a disc brakes one, but most are over 10kgs so I decided against it.. As far as I can tell, disc brakes add a lot of weight to a bike. I didn't really spend much time looking at why that is but i'd take an educated guess the increased weight must be the discs and the mechanisms, the heavier wheels and some structural strengthening needed due to increased forced applied with the discs

It seems a bit of an odd thing for you to say, given you do mention a lot here about marginal weight savings (groupsets for example)-so why would you say the additional weight a disc set up carries doesn't matter?

I think he s reffering to top of the range kit .

 

[400bhp]

In what respect? disc brakes or components?

 

[Rob3rt]

Sorry, I don't follow Rob?

I was looking for a winter bike and did first consider a disc brakes one, but most are over 10kgs so I decided against it.. As far as I can tell, disc brakes add a lot of weight to a bike. I didn't really spend much time looking at why that is but i'd take an educated guess is the increased weight must be the discs and the mechanisms, the heavier wheels and some structural strengthening needed due to increased forced applied with the discs

It seems a bit of an odd thing for you to say, given you do mention a lot here about marginal weight savings (groupsets for example)-so why would you say the additional weight a disc set up carries doesn't matter?

Personally, I don't want disc brakes but at the same time I don't really care if they become UCI legal.

There are pro's and con's, weight is a con yes, but it is not as dramatic as people speculate because you save weight in the rims, i.e. rotational weight. You are taking weight from the rim and adding it to the hub. Plus in UCI sanctioned road events your bike can not be lighter than 6.8kg so at present people are adding weight to get their bikes up to this i.e. if they had disc brakes, then they wouldn't have to go dropping weights down the seat tube just to meet spec.

BTW, hydraulic brakes are already making their way onto road bikes (of sorts, as it is on a TT frame), Cervelo are using Magura hydraulic brakes.

 

[400bhp]

Ahh, you were answering from a professional perspective, rather than a ordinary punter.

I understand the dynamics and the physics, but I'd rather have an overall lighter bike. I don't think a lighter rotational mass makes up for the overall heavier bike.

From what I recall reading a few issues of cycling plus back, hydraulic brakes are on a few road bikes.

The biggest plus for me with a road brake with discs is the fact I'd have to clean it less.

 

[earth]

How much does the braking surface at the rim weigh? Far less than the increase for the whole disc setup. It is removing weight from the right place - agree. But I wouldn't want the additional weight of the disc components to put pressure on frame builders to make lighter frames at the expense of stiffness.

 

[lukesdad]

Rim weight is negligble and only really matters on accelleration

 

[Rob3rt]

How much does the braking surface at the rim weigh? Far less than the increase for the whole disc setup. It is removing weight from the right place - agree. But I wouldn't want the additional weight of the disc components to put pressure on frame builders to make lighter frames at the expense of stiffness.

The braking surface of the rim probably doesn't weigh a lot, but considering that the area is much larger than the hub, the weight transfer, would at a guess be roughly equivalent.

Similar with the reinforcing of the frame and forks, the weight would mainly be shifted around from one place to another.

I am not saying there wouldn't be a weight increase, there would, the extent of which depending on the type of disc brakes used, I am just saying, it will not be as much as one might initially expect.

 

[Rob3rt]

Rim weight is negligble and only really matters on accelleration

That doesn't matter, the wheel weight would not be vastly different as the weight would be transferred from the periphery to the centre mostly preserving overall weight whilst producing (however marginal) a preferable weight distribution.

 

[400bhp]

The braking surface of the rim probably doesn't weigh a lot, but considering that the area is much larger than the hub, the weight transfer, would at a guess be roughly equivalent.

1. Similar with the reinforcing of the frame and forks, the weight would mainly be shifted around from one place to another.

2. I am not saying there wouldn't be a weight increase, there would, the extent of which depending on the type of disc brakes used, I am just saying, it will not be as much as one might initially expect.

1. What makes you think that?

2. What would one expect? It was what I expected when I looked into it, which seemed to be around a Kilo, using rough comparatives.

 

[400bhp]

That doesn't matter, the wheel weight would not be vastly different as the weight would be transferred from the periphery to the centre mostly preserving overall weight whilst producing (however marginal) a preferable weight distribution.

I'm not convinced it is. I would guess overall wheel weight is relatively higher for a disc braked bike?

I don't know much about disc braked bikes (even though I have one) but the weight surely has to be greater given the greater stresses applied to the wheel?

 

[lukesdad]

That doesn't matter, the wheel weight would not be vastly different as the weight would be transferred from the periphery to the centre mostly preserving overall weight whilst producing (however marginal) a preferable weight distribution.

You are talking about different materials unless we are using carbon discs. MTB disc wheels are considerably heavier than their counterparts.

 

[Rob3rt]

1) Taking a few punts. You could redesign the fork crown as it won't be subject to the same forces either during braking, or by having a bolt tightened too it, same with the rear end brake bridge as many are reinforced to take the force of the bolt through it. It is a case of scavenging around the frame and seeing where there is excess material they have previously been unable to get rid of, or had little motivation to get rid of because of current weigh limits and then using that material buffer to re-enforce the parts that need it.

2) Well expectations vary, but you have to think, right now, a road bike with disc brakes is going to be less evolved as it is not something widely used, due to regulations in competition. Once regulations allow (if they do so) and people start using discs, then there is much more motivation to engineer frames and forks to suit. Right now, they are essentially clagged on there.


I don't see the need for disc brakes on a road bike, but I also don't think they would be particularly crippling either.

 

[400bhp]

You are talking about different materials unless we are using carbon discs. MTB disc wheels are considerably heavier than their counterparts.

Thanks - as I suspected.

 

[lukesdad]

Braking forces will be increased at the crown as the lever becomes longer have a look at the meat around mtb forks at the crown.

 

[400bhp]

1) Taking a few punts. You could redesign the fork crown as it won't be subject to the same forces either during braking, or by having a bolt tightened too it, same with the rear end brake bridge as many are reinforced to take the force of the bolt through it. It is a case of scavenging around the frame and seeing where there is excess material they have previously been unable to get rid of, or had little motivation to get rid of because of current weigh limits and then using that material buffer to re-enforce the parts that need it.

2) Well expectations vary, but you have to think, right now, a road bike with disc brakes is going to be less evolved as it is not something widely used, due to regulations in competition. Once regulations allow (if they do so) and people start using discs, then there is much more motivation to engineer frames and forks to suit. Right now, they are essentially clagged on there.

1. This is speculation though. Your post sounded like it was a given.

2. Potentially, yes. But again we are speculating.

As it stands, disc braked road bikes for the ordinary punter are relatively heavy.