Braking…Pivot Points

from Rookie’s keyboard

Hello, friends

Today, we are going to talk about pivot points and bicycle brakes. There are two types – single pivot (SP) and dual pivot (DP) brakes.

SP are caliper rim brakes equipped with brake arms rotating around one (shared) pivot point. You can find them on retro road bikes as well as on some entry-level models.

DP brakes use two “independent” pivot points for each arm. The brake mechanism is still similar to that of SP brakes. The cable pulls the arms which then rotate/swing and grab the brake track of the rim to create friction and slow down or stop the wheel.

Understanding SP and DP Brakes

The strongest point behind DP brakes is that each arm has a larger mechanical advantage/leverage in comparison to SP models.

The two types of DP brakes are classified as asymmetrical and symmetrical.

• Asymmetrical DP brakes have a center and a side pivot point – thus the name.
• Symmetrical DP brakes have both of their pivot points positioned on the right and left sides.

The distance between the pulled ends of the brake arms and the pivot points determines the mechanical advantage. Longer distance = longer lever = better leverage. 

Let me present you three graphs that will make the idea easier to understand: 

The first shows an SP brake. Notice the distance between the brake arm ends and the pivot point.

The next illustrates asymmetrical DP brakes. One of the levers is as long as that found on SP brakes but the other is much longer – thus more leverage.

Finally, we have symmetrical DP brakes. Those models offer the greatest leverage as both pivot points are further down the brake arms. 

More Leverage = More Stopping Power? (not really)

At this moment, many rookies may conclude that DP brakes offer more stopping power thanks to their additional leverage, but that wouldn’t be a fully accurate conclusion.

The leverage doesn’t determine the maximum stopping power. It only influences the amount of energy (pull) needed to reach that high point. 

Let me say that with different wording – the greater mechanical advantage of DP brakes offers greater stopping power for the same amount of force applied to the brake lever. 

But if you were to grab the lever harder when using SP brakes, the degree of braking would be the same or greater. 

So, in practice DP brakes are not stronger, they simply make it easier to generate maximum stopping power.

The quality is a deciding factor too. A high-end SP brake will outperform a low-quality DP brake regardless of leverage. 

Modulation

Modulation is a short and fancy way of saying “control over the braking force”. 

If the brakes have too much modulation, they will take too long to bite. If the brakes have too little modulation, you won’t have a lot of control as the brakes with start catching the rim too quickly. 

Single-pivots have better modulation because they have a lower mechanical advantage. Of course, the settings of the particular brake model can change that.

Interesting Fact

Some bikes are running a DP brake at the front and an SP at the back to benefit from both systems. 

The DP takes the front to maximize the total braking power of the bike. The front brake is more powerful because the friction of the front wheel increases during braking whereas that of the rear drops.

The SP brake is installed at the back to take advantage of its higher modulation. The rear brake is used primarily for slowing down rather than stopping, and it makes sense to augment its technical capabilities.

Centering = Potential Nightmare

Centering is the process of positioning both brake shoes at an equal distance from the rim. In an ideal world, every brake is centered. 

If there’s a major disbalance, one brake shoe will reach the rim before the other. The result is less-than-ideal braking and unequal wear of the pads.

SP brakes are more frustrating to center for two reasons:

• Both brake arms operate around a shared pivot that also connects the brake body to the fork/frame

• SPs don’t have a dedicated centering screw. (Meanwhile, DP brakes have a centering screw, and that makes the process a lot simpler.)

Low-end SP brakes are destined to be out of center no matter what. But even high-end models go off-center eventually.

I can give you one “ghetto hack”, though. It’s a bit drastic and can leave a scratch on the brake, but I’ve tested it and it works.

Put the end of a flathead screwdriver on the spring section of the brake arm that has to go closer to the rim and then hit the handle of the screwdriver with a light hammer. 

It’s not in the manual, but it works. The tap should be firm, but not insanely aggressive.

Price

SP brakes cost less but are becoming harder to find due to the low demand and the market domination of DP brakes. 

I have a set of Dia-Compes from the 80s and they work just fine apart from the centering issues (it’s not that bad). 

But ultimately, the price difference is small. We are talking about bicycles after all – not Ferraris.

Weight

Logic says that SP brakes should be lighter and sometimes they are, but ultimately weight depends on the model. Some DP models are lighter than the SP versions. 

The table below will give you some ideas.

SINGLE PIVOT	WEIGHT	DUAL PIVOT	WEIGHT
SRAM RED Brakes Aero Link	132g	Dia Compe MX806	211g
Dia-Compe BRS200	138g	XLC BR-R03	156g
Campagnolo Veloce D-Skeleton	174.7g	Campagnolo Record Dual Pivot Skeleton	158g
Shimano Dura-Ace B-210	185g	FSA K-Force WE	151g
Dura Ace BR-7400	190g	Dia Compe BRS202	201g
Shimano 600 BR-6400	181g	Shimano Dura Ace BR-R9200	163.2g
Average:	168.2g	Average:	172.1g

What to choose?

Here’s the deal. 

First, go for a reputable brand. Before all, you need a quality brake. I’d choose a high-quality SP brake over a lame DP brake any day of the week.

However, when all things are equal, I’d go for the DP models (preferably symmetrical). 

Why? I like the ability to center the brake easily. Yes, I am running an SP brake and routinely use the screwdriver tap method to center it, and that’s annoying. But otherwise, the brakes are just fine. They stop as good as I need them to. 

Ok, fellas.

I hope that this lesson was useful (I know it would’ve been when I was a rookie myself.)

Until next time, 

– Rookie