Road bikes with discs

supersonic

I have enough stopping power ;-). I don't see the need for anymore on the road, my brakes work well with control.

meanredspider

supersonic wrote:

I have enough stopping power ;-). I don't see the need for anymore on the road, my brakes work well with control.

Obviously not going fast enough then

tgotb

meanredspider wrote:

I do find it really difficult to understand why people don't find discs better - for me, there's a clear difference. I would genuinely like to understand why that is.

Because caliper brakes are light, simple, and for some applications they work very well indeed. Why the near-religious devotion to disc brakes for every single application?

Look at it another way: A disc brake operates by pushing pads onto either side of a rotating metal disc; the bigger the disc, the more effective the brake. A caliper brake does exactly the same thing, except that the disc is ~70cm diameter and happens to have a tyre attached to it. The basic principle of operation is the same. Different configurations have different advantages and disadvantage, it's horses for courses. Most times I race on the road, I never even touch the brakes. What advantages will a heavier and less aerodynamic disc setup give me there?

ugo.santalucia

TGOTB wrote:

meanredspider wrote:

I do find it really difficult to understand why people don't find discs better - for me, there's a clear difference. I would genuinely like to understand why that is.

Because caliper brakes are light, simple, and for some applications they work very well indeed. Why the near-religious devotion to disc brakes for every single application?

Look at it another way: A disc brake operates by pushing pads onto either side of a rotating metal disc; the bigger the disc, the more effective the brake. A caliper brake does exactly the same thing, except that the disc is ~70cm diameter and happens to have a tyre attached to it. The basic principle of operation is the same. Different configurations have different advantages and disadvantage, it's horses for courses. Most times I race on the road, I never even touch the brakes. What advantages will a heavier and less aerodynamic disc setup give me there?

None, you are right... discs are not for racing and nobody wins UCI cyclocross races with discs... I suspect they will never make it into the PRO tour, but for the average cycling enthusiast they are the best thing out there. Reliability, stopping power and the fact that expensive rims last forever make them far superior to any other solution in a non competitive environment.
Problem is we all feel we need the lightest, fastest equipment, when really... we don't

Wrath Rob

TGOTB wrote:

meanredspider wrote:

What advantages will a heavier and less aerodynamic disc setup give me there?

In the dry? Better feel and modulation enabling you to brake later into a corner and therefore increase your average speed. But that's a pretty small set of circumstances that many people won't encounter.

In the wet, however, its a different ball game. Rim brakes are cr@p in the wet, relying on several sweeps of the rim to enable effective braking. Either that or you have to constantly trail brake to keep them dry. I think everyone can identify with that heart-in-mouth feeling when you're heading towards something big and solid, frantically grabbing at your brakes harder and harder with nothing happening for an agonising second or 2. You simply don't get that with disc brakes.

And the weight and heat arguments might be valid if you're regularly racing up and down alpine mountains but in the UK are you really going to hit the performance limits of 160mm discs on the road? Or suffer massively up Box Hill from carrying a few 100g's more?

jedster

"Look at it another way: A disc brake operates by pushing pads onto either side of a rotating metal disc; the bigger the disc, the more effective the brake. A caliper brake does exactly the same thing, except that the disc is ~70cm diameter and happens to have a tyre attached to it. The basic principle of operation is the same. Different configurations have different advantages and disadvantage, it's horses for courses. Most times I race on the road, I never even touch the brakes. What advantages will a heavier and less aerodynamic disc setup give me there?"

I think that would be looking at it the WRONG way!

First up, I don't think there is a strong case for disc brakes on a road racing bike. I think there is a big case on a commuter or winter trainer. A lot of that is about not grinding your rims away but also because the braking performance is a bit better. Obviously that is more pronounced offroad when you smear your rims with a grinding paste.

But on your logic on the mechanics, the big advantage of disc brakes is that the disc can be very true - flat and accurate. A rim is never going to be as true because of the greater diameter and the construction (spokes!). This means you can adjust a disc brake so that the pads sit much closer to the braking surface than with rim brakes which means that the pressure you can apply to the disc is huge (mechanical advantage from relatively big finger movement to tiny pad movement) and this means you can grip the disc hard - this more than compensates for the diameter of the contact point. Because the disc is much smaller diameter you can afford to make it thicker and stronger without a eright penalty. Then of course you can redesign your rims to be purely focused on retaining the bead rather than being compromised with two purposes (i.e. weight penalty).

tgotb

Wrath Rob wrote:

TGOTB wrote:

meanredspider wrote:

What advantages will a heavier and less aerodynamic disc setup give me there?

In the dry? Better feel and modulation enabling you to brake later into a corner and therefore increase your average speed. But that's a pretty small set of circumstances that many people won't encounter.

In the wet, however, its a different ball game. Rim brakes are cr@p in the wet, relying on several sweeps of the rim to enable effective braking. Either that or you have to constantly trail brake to keep them dry. I think everyone can identify with that heart-in-mouth feeling when you're heading towards something big and solid, frantically grabbing at your brakes harder and harder with nothing happening for an agonising second or 2. You simply don't get that with disc brakes.

And the weight and heat arguments might be valid if you're regularly racing up and down alpine mountains but in the UK are you really going to hit the performance limits of 160mm discs on the road? Or suffer massively up Box Hill from carrying a few 100g's more?

That comment was specific to (non crit) racing. 95% of the races I do these days are either track (no brakes anyway) or TTs. In a TT I might feather the brakes once, when I get to the turn, and on some courses I literally won't touch them at all, I never even come off the aero bars. No amount of unused superior braking performance is going to persuade me to ditch my aerodynamically superior calipers, it just doesn't make sense. Same applies, to a lesser extent, in a lot of road races; you just don't need the performance that discs give you, so why take the marginally increased aerodynamic drag and weight?

Crit racing is somewhere I can see disc brakes might be an advantage. I'm a big fan of discs for 'cross, but as Ugo pointed out the top guys aren't using them. My point was that it's horses for courses.

meanredspider

TGOTB wrote:

meanredspider wrote:

I do find it really difficult to understand why people don't find discs better - for me, there's a clear difference. I would genuinely like to understand why that is.

Because caliper brakes are light, simple, and for some applications they work very well indeed. Why the near-religious devotion to disc brakes for every single application?

Look at it another way: A disc brake operates by pushing pads onto either side of a rotating metal disc; the bigger the disc, the more effective the brake. A caliper brake does exactly the same thing, except that the disc is ~70cm diameter and happens to have a tyre attached to it. The basic principle of operation is the same. Different configurations have different advantages and disadvantage, it's horses for courses. Most times I race on the road, I never even touch the brakes. What advantages will a heavier and less aerodynamic disc setup give me there?

Not saying they should be used for every single application - for many of the TT races I've seen around Cambridge I can't imagine why you'd want them. But we're talking about road bikes on a commuting forum. But, beyond that, I think I'm reading that people actually don't think disc brakes are better for stopping - that's the bit I don't understand: my experience is that they emphatically are.

And, yes, the calliper brake does broadly the same thing - just with a load of compromises thrown in:
- the braking surfaces are a compromise - one made of a material that you'd want to make a wheel of and the other a material that doesn't wear the first material too badly whilst still providing friction in a predictable and progressive manner.
- the stiffness of the system: the wall of a wheel and callipers that have to reach around a rubber tyre with squishy rubber blocks
- the diameter of the "disc" needs to be the diameter of the wheel whether that makes sense or not (almost no road vehicle has the same sized discs front and rear). And no opportunity to tune for the weight of the rider.
- the position of the disc exposed to all the water and dirt the road has to offer
- adding weight in the braking track precisely where you'd rather not have it
Basically engineering compromise after compromise. And that's fine if you don't brake much.

supersonic

My rim brakes work fine in the wet - the wheels lock up far before I run out of brakes.

I look forward to all the tech quetions when people get hydro disc brakes for their road bikes ;-). No bite adjustment (unless you usually pay more for it), bleeding problems, rubbing, squealing, leaking, sticking pistons etc. Just look in the MTB tech section, some disc brakes with some people cause no end of problems. Don't expect them to be infallible, they ain't.

tgotb

jedster wrote:

But on your logic on the mechanics, the big advantage of disc brakes is that the disc can be very true - flat and accurate. A rim is never going to be as true because of the greater diameter and the construction (spokes!). This means you can adjust a disc brake so that the pads sit much closer to the braking surface than with rim brakes which means that the pressure you can apply to the disc is huge (mechanical advantage from relatively big finger movement to tiny pad movement) and this means you can grip the disc hard - this more than compensates for the diameter of the contact point. Because the disc is much smaller diameter you can afford to make it thicker and stronger without a eright penalty. Then of course you can redesign your rims to be purely focused on retaining the bead rather than being compromised with two purposes (i.e. weight penalty).

In theory you're right, but in practice I disagree. My experience is that it's far easier to true a wheel, specifically because you have independent control of all those spokes I find it easy to get down to sub-millimeter accuracy, and with a decent measuring gauge a good wheel builder probably does better. To straighten an out-of-true rotor, even with the right tools, your only option is a rather crude "grab and bend". On the point of weight, it's theoretically possible to build your rim lighter without a braking surface, but in practice I doubt the gain will be significant; when you retire a rim due to excessive brake track wear, how much lighter has it become?

In any case, my argument was never that discs don't have superior stopping power/control; my point is that in some scenarios the stopping power and control of calipers are perfectly good enough, and other factors make them a better compromise than a discs. I was questioning MRS's assertion that discs are always better.

meanredspider

supersonic wrote:

My rim brakes work fine in the wet - the wheels lock up far before I run out of brakes.

What does that tell you about your brakes? Locking a wheel has nothing to do with good brakes. You can lock a wheel by poking a stick through the spokes. I could lock the wheels on my 1976 Ford Fiesta. Locking a wheel tells you absolutely nothing about anything.

supersonic

Ultimate stopping power is provided by grip of the tyres. I have good tyres. I can lock the bike up with control, as I previously said. So why do I need anything else?

Being able to lock them proves I have enough power, and in reserve. Therefore discs are of no use to me, even if they are more 'powerful' - the ultimate level of decelleration is the same.

meanredspider

TGOTB wrote:

I was questioning MRS's assertion that discs are always better.

That's not an accurate description of my assertion. My assertion is that disc brakes work better. If you don't need brakes, that's hardly of interest. Deaf people don't normally worry about having a great stereo.

tgotb

meanredspider wrote:

TGOTB wrote:

I was questioning MRS's assertion that discs are always better.

That's not an accurate description of my assertion. My assertion is that disc brakes work better. If you don't need brakes, that's hardly of interest. Deaf people don't normally worry about having a great stereo.

What you actually said was:

meanredspider wrote:

I do find it really difficult to understand why people don't find discs better - for me, there's a clear difference. I would genuinely like to understand why that is.

I don't find discs better, for some applications, because they're heavier, less aerodynamic, and calipers provide all the control and stopping power I need. There you go :-)

meanredspider

supersonic wrote:

Ultimate stopping power is provided by grip of the tyres. I have good tyres. I can lock the bike up with control, as I previously said. So why do I need anything else?

Being able to lock them proves I have enough power, and in reserve. Therefore discs are of no use to me, even if they are more 'powerful' - the ultimate level of decelleration is the same.

I'm sorry - that's just not accurate on so many levels. The closest bit is that the tyre might be what determines the stopping power or it might be you going over the handlebars. What really determines your stopping distance though is your ability to brake on the threshold of one or other of these events - constantly maximising the retardation without the tyre locking (but slipping slightly) or you doing a face plant. And this is where rim brakes are poor for all the reasons I listed as compromises.

supersonic

You seem to have just said what I have said! The more grip you have, the harder you can brake. Then I mentioned the control bit - which I have ample of. I can brake right on the limits of traction, in all conditions.

So why do I need anything else? A disc brake WILL NOT alter this for me.

meanredspider

TGOTB wrote:

meanredspider wrote:

TGOTB wrote:

I was questioning MRS's assertion that discs are always better.

That's not an accurate description of my assertion. My assertion is that disc brakes work better. If you don't need brakes, that's hardly of interest. Deaf people don't normally worry about having a great stereo.

What you actually said was:

meanredspider wrote:

I do find it really difficult to understand why people don't find discs better - for me, there's a clear difference. I would genuinely like to understand why that is.

I don't find discs better, for some applications, because they're heavier, less aerodynamic, and calipers provide all the control and stopping power I need. There you go :-)

Fair cop - I wasn't very precise

I'd imagine (but I don't know - this is a commuting forum, in my defence) that weight isn't much of an issue for TT (within the bounds we're talking here). I don't think we really know that they are less aero (the wind tunnel test was rubbish) though it's a fair bet that they probably aren't as good.

meanredspider

supersonic wrote:

You seem to have just said what I have said! The more grip you have, the harder you can brake. Then I mentioned the control bit - which I have ample of. I can brake right on the limits of traction, in all conditions.

So why do I need anything else? A disc brake WILL NOT alter this for me.

Well all I can think is that you're superhuman as well as supersonic. You're right - disc brakes are wasted on you

supersonic

I do have pretty expensive rim brakes mind ;-). And I love them!

tgotb

meanredspider wrote:

I'd imagine (but I don't know - this is a commuting forum, in my defence) that weight isn't much of an issue for TT (within the bounds we're talking here). I don't think we really know that they are less aero (the wind tunnel test was rubbish) though it's a fair bet that they probably aren't as good.

You're right, weight is less of a factor for TTs (take disc wheels as an example) but aerodynamics is everything. I find it hard to imagine that any front disc is going to be as aero as a caliper built into the fork, but at the same time it probably doesn't make much difference at the level most of us race at.

That test really was a load of rubbish. Aside from the fact that they didn't involve a rider, what's the relevance of comparing it with a TT setup anyway? They could at least have compared it with a standard road caliper configuration...

meanredspider

Yes - I'd be the last to suggest putting discs on a TT bike even if I do come across as a disc evangelist. My excuse is that I'm a mechanical engineer and a car racer and I've done a huge amount of reading on brakes and braking. Having run discs on a CX commuter, I'm obviously running them on a road commuter and I've never once looked back. My racing snake colleague refers to me as "Bomber" for my descending - nearly all of which comes from confidence on the brakes.

supersonic

They'll be putting suspension forks on next ;-)

meanredspider

supersonic wrote:

They'll be putting suspension forks on next ;-)

Funny - I was just thinking that. Don't worry, I won't ever be arguing for that

As it is, I want to get around to taking them off my winter MTB!

Kieran_Burns

meanredspider wrote:

Yes - I'd be the last to suggest putting discs on a TT bike even if I do come across as a disc evangelist. My excuse is that I'm a mechanical engineer and a car racer and I've done a huge amount of reading on brakes and braking. Having run discs on a CX commuter, I'm obviously running them on a road commuter and I've never once looked back. My racing snake colleague refers to me as "Bomber" for my descending - nearly all of which comes from confidence on the brakes.

My mate won't cycle behind me in wet weather nowadays. Not because he's concerned about getting wet, as I have full 'guards on the bike; but because he just goes sailing past whenever I put the brakes on. He's grabbing handfuls and not stopping and I'm trying not to lock up.

EKE_38BPM

What a timely thread. Just yesterday I was thinking about reviving my steel framed road bike (set up as a fixie) and changing the fork to a disc equipped one.
My current commuter's (geared aluminium road bike) wheels are showing signs of wear and a heart-in-mouth moment a while ago made me seriously rethink my braking options.

The way I see it, for a commuting bike which gets ridden high mileages in all weathers and carrying relatively heavy loads, disc brakes make perfect sense.
Increased breaking ability: check
Braking ability in all conditions: check
Reduced wear on expensive components: check
Less fettling to keep everything working at 100%: so I've been told

Of course, as it will be used on a fixie, I'll only have a front brake. That should nicely wind a few people up.
My ideal commuter/work bike setup is:
Steel framed fixie
Bull horn bars
Front disc brake, no back brake
Dual sided platform/SPD pedals
Panniers
I'm still undecided about a dynamo rear hub. As a London rider I don't need huge amounts of lighting so battery drain isn't a big enough problem to insist on a dynamo hub and the extra wiring that goes with it.
Mud guards are not a major issue, but I can see, and have expeienced, the advantages.

As DDD says, discuss.

asprilla

EKE_38BPM wrote:

What a timely thread.

Indeed.

I'm currently selling a load of gear, including a bike, to finance and make room for a steel single speed disc braked commute, guards and all.

For winter though, mine will have fat tyres and hydraulic discs.

meanredspider

Sounds fine to me. A back brake on a bike ( especially one with discs) is mostly there as a spare. Hard braking only lightens the load on the back to a point that it can't brake anyway. I almost never use my rear brake except for rolling up to the office car park barrier when I'm fishing for my pass with my right hand.

Initialised

Haven't we missed something here, with rim brakes you can't safely brake under heavy cornering due to judder and the lateral forces deforming the wheel making braking uneven and prone to locking the rear wheel, with disc brakes the rotor doesn't deform while cornering like a rim does allowing the rider to brake through the corner rather than before the corner thus allowing higher cornering speed and the option of adjusting the line through the corner with less risk of locking the wheel. Hence MRS' confidence on descents.

airbag

This and the 'gravel bike' (sigh) feature on the home page seem to point to the same thing.

For TT bikes, and out-and-out race bikes, disc brakes are unnecessary, possibly an aero/weight disadvantage and maybe a hazard. But a lot of people don't need those things, and as things are they're underserved.

Walk into a ferrari dealership and you can't buy a race car, you buy a racing-style car with everyday practical touches. You can even, I believe, currently buy a ferrari with 4wd and a hatchback (the FF?). Same with porsche. Where's the bike with all the race tech you'd want, but a nod to everyday practicality? No, not a 'sportive bike' with the same lack of guards, miniscule tire clearance, but slightly longer headtube. Not the touring bike made of steel (lovely as steel may be) weighing 12 kilos. Not the cyclocross bike with a slack headtube, high bb and still no guards.

Where's a general purpose road bike, with carbon loveliness, near enough racing geometry, but practical nods like guard mounts, bigger tire clearance and brakes that don't eat rims or suck in poor conditions?

Ouija

supersonic wrote:

They'll be putting suspension forks on next ;-)

Mmmmmm........
SWS 700c