It 's always seemed inevitable to me that one day disc brakes would be standard fixtures on all high end road bikes. After all they just work so much better. Dave Moulton in his blog http://davesbikeblog.squarespace.com/ gives some good points as to why I'm completely wrong...again:I fail to see the point of a disc brake on a road bike. A conventional caliper brake is a disc brake, with the rim being the disc.
The rim is the largest possible diameter and therefore has the most leverage when the braking force is applied.
With a disc at the hub the braking forces are transmitted through the spokes. What is more the driving stress is in one direction, followed by the braking stress in the opposite direction. Stressing spokes in this manner could possibly lead to breakage or coming loose.
With a normal caliper brake acting on the rim there is little or no stress on the spokes, (Apart from the normal weight bearing stresses.) the stress is directly from the rim to the tire.
A disc brake means you can’t have radial spokes. Not only must there be crossed tangential spokes on the non drive side of the rear wheel, you must also have tangential spokes on the front wheel.
A disc brake means you can’t have radial spokes. Not only must there be crossed tangential spokes on the non drive side of the rear wheel, you must also have tangential spokes on the front wheel.
Tangential spokes are longer, therefore more weight; remember also this is spinning weight which is more important. A radial spoke wheel has marginally less wind resistance.
The disc and its caliper has to be heavier than the conventional brake, and more expensive to produce.
I can see an argument for a disc brake on a mountain bike or a cyclo-cross bike, because it would possibly collect less mud than a brake that operates near the tire.
But on a road bike; I just don’t get it.
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Thanks Dave.
1 comment:
So that's why motor bikes use them then :-)? They stop you better, even in the wet. Also bike rims now free for redesign as they don't need to provide a braking surface, jut somewhere to stick spokes and a tyre. Discs on a road bike can be smaller than on mountain bike. I think it is like using Di2. You can snear but find me someone who has used it and then doesn't want them. Use disc brakes for a week and same deal. Instead of descending a mountain in the wet on your race carbon wondering if you can stop, you can descend so much faster and safer.
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