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why not disc brakes?(15 posts)

why not disc brakes?kenyee
Jun 12, 2001 12:06 PM
Time for a stupid newbie question since I couldn't find it mentioned in the archives :-)

Why don't people put Avid disc brakes on road bikes? From what I understand, they aren't affected by water, unlike traditional caliper brakes which you have to dry a bit if you hit water puddles. Is it just the weight issue because they are heavier?
My Takegrz mnky
Jun 12, 2001 12:44 PM
First - realize that there are some nice disc brake systems on tandems - they have a real need for increased stopping power. Many feel that road bikes don't need the additional power and modulation control. You could put Magura hydraulic brakes on a road bike with canti bosses right now, but these aren't discs and the weight penalty is huge. 'Cross bikes already take advantage of them.

1. NIH - not invented here. So thus the reluctance - look how long it has taken roadies to go to threadless systems an dremovable face plates. Change comes slowly in the road bike world b/c there are primarily a couple large companies (Shimano & Campy) who make the components. Disc brakes for MTBs didn't come from either of these mfr.s, but now Shimano has both a hydraulic and cable disc system. Even the splined crank design was used first on MTBs (XTR).

2. Problem looking for a solution - many would question why road bikes would ever need disc brakes. Of course many said the same thing about index shifting and then STI. Also, any retro fit will have to be designed around the standard road leverage ratio which is different from MTB (or else use a "Travell Agent" type of device).

3. Weight - in most cases you have to keep the weight at or below the current standard. An exception to this is the STI/Ergo shifting - it weighs significantly more than the old down tube shifters, but offers a perormance/convienience advantage. Disc brakes could fly if most riders agreed that the benifits exceeded the costs.

4. Frames and forks have to be redseigned to accomodate the different loads. Current frame/fork designs are empirically close to their limits - slapping a disc setup on a std. road bike will most likely lead to some nasty failures.

My prediction is that soon road bikes will be using mechanical discs. In ten years we will all look back and laugh at our current set ups and ask our selves how could we even ride with the lack of modulation and all weather stopping power? It's also a great marketing coup to sell more stuff to people who already own bikes instead of trying to lure in new customers.
rain/cross bike of the godsHank
Jun 12, 2001 1:46 PM
I'd like a road/cross version of the Single Malt - single speed w/discs.

http://www.ibiscycles.com/products/bikes/mtb/single_malt/index.html
Something's going on...yapsaw
Jun 12, 2001 2:06 PM
I know I've seen the splined system when I was in Singapore (this was before the introduction of the splined system) and the component was made for bmx. Shimano had release this way back in the mid 80's and probably the time was not right (and compatibility issues). It was never seen again until their release a few years back. Seems like Shimano is recycling their patents and actually earning $$ this time.
Yep, both Bullseye and Redline had spline BMX BB'sJ.S.
Jun 12, 2001 5:49 PM
back in the eighties. These were quite different than Shimano's but spline non the less.
Thankskenyee
Jun 12, 2001 2:37 PM
Wouldn't have thought about the frame/fork stress levels.
You would think better stopping power from disc brakes = more safety since you can stop faster even if the rim is wet :-)
Your Takeskinner
Jun 13, 2001 1:36 PM
Some more of grz mnky's pie-eyed ideas and hypothoses.

"Problem looking for a solution" ??? What?

Where do you come up with these theories?
Duhgrz mnky
Jun 13, 2001 6:07 PM
Excuse the coloquialism - techies toss it around when some one comes up with something cool but it doesn't address a pressing problem.

Let's make it painfuly obviuous to even the most casual observer (that would be Mr. Skinner): So exactly what pressing problem does putting a disc brake on a standard road bike solve? (Hint: none).

FWIW - I wish I did make this stuff up, but it ain't so.
DuhBrit Racer
Jun 14, 2001 4:58 AM
I'd agree that it's not really a very pressing problem but a few years back, Hope (An English company - produce top of the range MTB discs) designed a road bike disc brake at the request of Banesto. Why? Well, Banesto were concerned about the heat generated by lots of braking for hairpins during mountainous descents. The heat apparently softens the tub cement that holda on tubulars sufficiently for there to be a greater chance of them coming off - not desirable at high speed and even less so if Big Mig was on board, in yellow at the time...

In the end they didn't use the discs but I had a go on them at a trade shown and they were very nice.
I believe the saying goes "Solution looking for a Problem"Schicchi
Jun 28, 2001 2:10 PM
.
I agreefreespirit
Jun 13, 2001 1:44 PM
every road bike I've ridden had brakes that could easily out-brake the tires' grip; stronger brakes wouldn't help much; in the rain, except for the first few seconds, the problem is worse

Current road bike brakes are very light, particularly if you consider the whole system, wheel, hub, fork/stays, etc. Plus, doesn't a rim brake have quite a bit of mechanical advantage (or less disadvantage) compared to a hub/disc brake?

Only under the most extreme circumstances have I ever found existing brakes to be marginal, maybe requiring more hand power than I would like - this on the steepest, narrowest, twisty descents. I'll take the light weight any day.

Now, if much grippier tires were invented, that might change things.

Progress doesn't mean that because you CAN do it, that you MUST do it.
re: why not disc brakes?bsenez
Jun 12, 2001 3:26 PM
I have thought about this also, and decided it would be nice but probably won't be seen on production bikes for many years. Our nice ~400 gram all carbon forks would be ripped to pieces by the stress a disk brake would apply. Also I do not think many of the lightweight racing frames could take the stress of a rear brake either. It seems most practical on a touring bike which would most likely be all steel (or at least heavier) and would benefit from additional stopping power. To be honest i would love to have a set of hydro discs on my 20lb road bike, and diamondback even came out with a production cyclocross bike with discs.
Do you like your STI's?Spoke Wrench
Jun 12, 2001 5:35 PM
A couple of years ago I had to make the choice between STI shifters and Magura hydraulic brakes for the tandem I was using at the time. I decided that I didn't want to give up my STI's.

A couple of years ago, I had to make the choice between STI shifters and Magura hydraulic brakes on my tandem. I went with the STI's.

My current tandem has a Formula hydraulic disc brake for the rear, but uses a cable gizmo to connect the STI lever with the master cylinder. It works OK, but we don't have the long downhills here in St. Louis to worry about rim overheating. If it wasn't for the style points, I'd just as soon have a rear V brake.
There's also tranfering Torque to the hub throught the spokesSchicchi
Jun 28, 2001 2:16 PM
Perhaps this is not such an obvious issue, but when you use rim brakes, both the braking force (calipers) and the inertia are applied to the rim, when you use disk brakes you have to transfer that force through the spokes and into the hub.

That's why there aren't any radially laced mountain bike disk ready MTB wheels.

Plus, the radius of road wheels is larger than MTB wheels, which equals more torque on the hubs and on the fork and frame against which they have to brake.

my two cents.
Works Both Waysgrz mnky
Jun 28, 2001 2:30 PM
Good point about the spokes. However, even with rim brakes there is load transfered through the spokes - the rim uses the rim brakes as a pivot point, and the hub resists the force from the contact patch (or vice versa depending on your frame of reference). The disc is obviously all torque through the spokes wich is larger and is your point. It wouldn't take much to beef up the road bike hubs and spokes for the disc loadings. Ultimately it's all do-able and currently being done on tandems. It just comes down to a cost/benifit ballance - taking all factors into account. Road wheels are slightly larger in diameter, but a fat MTB tire reduces the total difference.