Dan Daniel wrote:
>> Advantages of single-pivot types:
>> 1. Pads can be set further away from rim (for the same lever
>> travel) -- more useful at rear because of greater wheel flex there.
>
> Ok. Is this a real problem? Are racers rubbing brake pads in sprints?
It is a real annoyance for me. Dual-pivots require minimal pad clearance
to work comfortably, ie. without having to move lever a long way before it
does anything. In order to have a DP rear working to my satisfaction, the
pads have to be very close, meaning centering and wheel trueness is highly
critical. This is a PITA. Then the rim rubs as the wheel flexes!
Racers have been known to undo rear brake quick-releases on climbs because
of rubbing.
I'm sure many people get round the problem by having more pad clearance
but the extra lever travel required doesn't feel ergonomical to me.
>> 2. Harder to lock-up accidentally.
>
> So one can 'slam on the brakes' with equal force on the front and rear
> lever with less concern over a rear wheel skid?
That's one aspect, although you can just to use more front brake instead.
> I thought that a big
> part of a rear wheel skid is lifting from the ground because of the
> weight shift forward under front braking.
Sometimes you want to use the rear brake as much or more than the front,
say on loose or slippery surfaces. I find it all too easy to skid the
rear tyre with a DP.
>> Disadvantages:
>> 1. Trickier to centre (sometimes).
>
> But you can leave the pads further away, so centering is less
> critical!! 
Anyway, I would hope that someone who knows enough to
> want two types of brakes front and back can figure out how to center
> a brake.
>
>> 2. More lever force required -- but that shouldn't normally be an
>> issue for rear braking.
>
> And it lessens the chance of lockup, so it's actually an advantage,
> yes?
Yes indeed for rear braking if all is well. Some users claim they can't
lock up their rear brake even if they tried and actually want stronger
rear brakes than they have now, so /some/ people on some bikes may not
want less rear braking "power". I was also thinking about the
disadvantages for front brakes, while we're on the subject.
> So in a way, both of the disadvantages are pretty minor.
Absolutely, which is why I'm not bothered by them and use an SP rear on my
road bike. I like to point out disadvantages just to be fair, sorry if
they confused you.
> Anyway, what I am really after is an explanation of the advantages of
> a single pivot brake on the rear compared to a dual pivot brake.
Explained above.
> Is it
> simply 40 grams of weight combined with the rear wheel being less
> important in braking, or is there more to the idea of putting a single
> pivot in back and a dual pivot in front? Sorry if I am missing the
> point of your plus/minus listing above. Maybe a simple sentence or two
> explanation? Thanks.
For me, the advantage is a brake that requires less fussy adjustment and
provides braking that is easier to control and just feels better. The
weight saving is a mere bonus (although I put it in front of pad
adjustment due to wear in my list because I don't mind adjusting pads once
in a blue moon). Campagnolo emphasise the weight difference more,
however.
I started off with a pair of Avanti dual-pivots, then replaced the rear
caliper with an older single-pivot version of the same model, on the same
bike, so I am comparing "like with like".
~PB
