A question of brake reach ~
 

This morning I read this posting by a member on the CR list, and it got me to wondering.

"One critical variable that people don't discuss is brake reach. The "same" Record brake run as a long reach caliper at the bottom of the slots and a short reach run at the top of the slots brake nothing alike. The former is a classic "speed modulator" while the latter is a powerful, effective brake that is capable of stopping as quickly as the tires and conditions allow."

I was wondering about how two different sets of Record brakes might differ on the bike I was working on at the time. I tried both a set of short reach Record brakes on it, and a set of "long", or regular reach Record brakes. Both fit. And work. The shoes were near their lower limit in the slot on the short reach set. Closer to the top of the slot on the standard reach set. I didn't have the chance to test each fully.

What do you say about the theory mentioned in the quote? Is it a wash? One set-up preferable to the other?

Boulderdash!!!

What you end up with in the two examples is the same "lever" length achieved with different starting points. It doesn't matter if there is a lot of brake arm sticking out below the pad or very little. The geometry of the lengths of levers and pivot points involved hasn't changed. If the distance from the pivot to the points where the cable meets the arms differed, the guy would have a point. I don't think Campy changed this on the different reach brakes. The other lever, from the pivot to the brake pad can't change unless you are willing to have the pads miss the rim.

Was the cable adjusted so the distance of the pad to the rims was the same in 'relaxed' position for both top and bottom slot trials?

I doubt it was a design, if it is indeed true it is likely a case of the arms flexing in the slot area.

The farther the pad is from the caliper pivot point, the less force you can cause the pad to apply to the rim, for the same hand grip force on the lever. However, the difference isn't huge - roughly proportional to the change in caliper pivot-to-brake pad distance. Most people have enough additional hand grip power available, some women and children might be the exception. For them, better pads and cleaner rims should mostly offset the larger brake reach. Also, adjusting the brake pads to run close to the rim will help.

It seems to me that if braking power was really a problem, some enterprising company (probably French) would have developed a brake caliper where the cable runs through a pulley (like a compound bow, or a block and tackle).

Mafac did this essentially with the Top "63" centerpull. The pivot to block dimension had no adjustment. The adjustment was part of the interlocking "saddle" that had two halves fitting on a radius held by the brake fixing bolt, you adjusted that to reach the rim. A cool idea I thought, but for cost or weight it was abandoned in favor of the Dural Forge, which became the Racer.

Braking performance was one of the items that the shop rats while working would discuss long ago, the mechanical advantage of shorter reach was self evident. Bicycling magazine in the early 70's even did a technical article on the formula to show relative advantage, the differences are quite small though.
Rear calipers were often set with larger reach for possible fender use, wheel removal and adjustment of the axle that might effect the placement of the brake pads. There has been a long held belief that the rear brake should not be so powerful to avoid locking up the rear wheel during braking, longer reach less power. Universal supplied their calipers with different reach front to rear.

(one of those reasons that rear dropouts by Campagnolo were angled as they were, as the axle moved to shift the Cambio mechanism, a slot angle was needed to reduce the rim to brake movement as the bike was shifted)

What JYL wrote is true but the example is two brakes with different reach installed in the same position on the same bike. The distance from pivot to pad doesn't change, only the amount of metal hanging down past the pad.

edit: at least that's my interpretation of what's being said in the original quote.

Right. So what's said in the original quote is true, at least in theory; but I suspect the actual effect is somewhat exaggerated.

No. It's not even theoretically true. If the distances from the cable to the pivot and the brake pad to the pivot don't change, the geometry hasn't changed and therefore braking power hasn't changed. Any amount of metal hanging past the brake pad doesn't matter.

Let's look at the physics. The extra metal hanging down below the pad adds inertia to the movement of the caliper arm. That means it will be slower to engage and slower to disengage. So theoretically it does make a difference. And if you think you can measure that effect, then go ahead and waste your time trying. :D

Actually, there is one possible difference between the two. They may have different springs or different spring anchor points on the caliper arm. If so, they could require different hand strength to apply the same pressure at the rim. I don't know that they do or they don't, and I wouldn't place any bets on them being different that way; I've never looked. But it's possible.

Interesting. In my example, it does make sense that there would be no difference, as the distance between the pivot point and brake pad would be the same. I suppose a truer test would have to be between short and standard reach with the brake pads set at the same point relative to the slot. Or, a test between the same reach caliper, with the pad set at its uppermost setting in the slot, and the lowest point. In which case, if I understand this correctly, the closer the brake pad is to the pivot point, the greater the mechanical advantage.

Perhaps we are reading the quote differently. In your hypothetical situation, "if the distances from the cable to the pivot and the brake pad to the pivot don't change, the geometry hasn't changed." This is exactly right. But as I read it, the quote envisioned the opposite hypothetical situation: If you put the brake pads as close as possible to the pivot, you have a strong brake. If you put them as far as possible from the pivot point on the same caliper, you have a weak brake. Even if the brake in question is a Campy NR. This explains why opinions about this brake vary so widely.

But the original quote was talking about long reach brakes at the bottoms of the slots vs short reach brakes. The pads of the long reach brakes would indeed be further from the pivot point, and so would not have the same stopping power as the short reach ones.

Right. His example, quoted, and my example, represent two different things.

Didn't mean to confuse the two. Only that it got me thinking.

In practical terms, it is a wash if the geometry is the same, and I think it is.
There is a difference between the long and short Record calipers beside the length of the arms: the long ones use a longer spring than the short ones. I haven't checked this, but I suspect it makes a slight difference in brake feel.

Getting theoretical for a minute...
A more important consideration, especially for people with small hands, is the shape of the levers and their distance from the bars. Your grip strength changes as your hand closes, increasing as your fingers curl more. The brake lever's ratio (lever-to-pivot/cable fulcrum-to-pivot) matters a lot as well. Classic era Campy Record levers have a high ratio, which helps deal with the calipers' muscular return springs. I believe that lever ratio, fit, placement and adjustment matter a lot more than most people realize, and at least as much as the design, configuration and construction of the caliper.

Oops, I read it as the opposite. "reading is FUNdamental"

Aesthetically speaking, if you can run a shorter reach caliper I would, because I think it looks better.

I dont have much choice in the matter. With short reach brakes my pads are clamped near the top of their slots. With a 28 tire I have about 1/4 inch from tire to brake bolt.

+1 and we all know it is better to look good than to stop good. fwiw I don't believe there's any difference, and any test of the two brakes would have to take user bias out of the equation.

Pads and braking surface make all the difference.

Campy Record brakes are made of a very stiff aluminum. My old McLean racing bike has the long variety. I have big strong hands, and I'm using Gran Compe aero levers which might have more leverage than original Campy levers. Both brakes work extremely well. They are not drag brakes.


Cheap brakes made of flexible material would, I expect, work badly if the reach is long and might be decent with a short reach. In theory, Campy brakes would see a difference with a difference in reach, but the stiff material lessen the difference, possibly to the point of immeasurability.

You're saying that the difference in mechanical advantage between long and short reach brakes would be negated if the calipers are made of stiff material?

This is an interesting observation. The bike in question came originally with 700c tubulars, which were long gone and it had 27 inch clinchers on it. And, different brakes. Kind of surprised the standard reach brake set worked but there is quite a bit of clearance on this bike. I figured I'd keep one set of Records and sell the others. Now I'm not sure which to ditch.

Sell 'em? You nuts? Buy another frame!

My favorite enabler strikes again! :)

I know…the minute I did sell them I'd no doubt find another use for them.