What's the deal with compressionless brake cable housing?

Question

Ok folks, I'm confused and in need of advice. On my commuter (touring) bike, I just upgraded my BB5's to BB7's. In the process, decided/realized that I also need to replace my cables and housing (@mikes was right in his answer to a past question of mine).

In surfing the 'net I see that I can get compressionless cable housing or "regular" cable housing. Compressionless seems to be preferred by folks interested in higher levels of performance.

That said, I have always trusted Sheldon Brown's advice on a variety of bike related topics. He seems to say that compressionless housing is made for (and should only be used for) indexed shifters and it might be dangerous to use it for brakes. However, there are several vendors (1),(2) who sell compressionless housing made specifically for brakes.

So, is Sheldon wrong? Will I be introducing additional risk in my braking system by using them? Will compressionless cable housings make a significant difference in the performance of my mechanical disc brakes?

Answer 1

I recently upgraded my brake cables with some Jagwire of the compressionless variety. jm2 is correct in saying the steel housing is reinforced with kevlar to prevent the longitudinal wires from buckling. The performance is very good and my brakes are far more responsive than with the old, traditional spiral-wound housing that was there before.

That said, installation is made a bit more tricky because:

1. The cable is not as flexy (it's a lot thicker than gear housing) so lengths must be cut appropriatly and secured well with the correct ferrules/end caps.
2. It is very difficult to cut. I tried first with a proper, full-size hack saw to get a smooth cut and it was immediately blunted. They must use very hard steel. I then just used some high-quality wire cutters which just about did the job and I smoothed up the cuts with a file. Make sure you have decent cutters if you're using compressionless.

It's also debatable whether compressionless is needed for brakes. It's needed for gears as they are indexed so need precise cable draw for a given shifter movement. Brakes have no such need, if you need more caliper movement just squeeze the lever a bit more. It probably gives some finer modulation but I reckon most of the improvements I experienced were just due to new cable vs 8-year-old ropey cable.

Answer 2

I believe Sheldon wrote this before there was brake specific compressionless housing available on the market. My understanding is that brake specific compressionless housing is reinforced with Kevlar, not plastic, and it has certainly been rigorously tested to work as expected.

The folks I know that run compressionless housing on their mechanical disc brake setups seem very happy with it, so if you're not completely happy with your current setup it may be worth a shot.

Answer 3

This can be confusing, especially if you are not new to cycling. Let me explain. Regular brake housing is spiral metal, looks like a compressed spring, with a slick lining. This has been around a long time. But, like the spring it resembles, when you brake and put a load on it it compresses a tiny bit.

With the advent of index shifting, which requires precise cable pull, manufacturers came out with compressionless casing for shifters. The casing is made up of thick wires that are spiral wound, think of a helix, along the length of the cable. When you pull the cable, the wires cannot compress.

In the past you had to be very careful never to use the compressionless housing with brakes as the spiral wound casing was only held together by the plastic outer casing of housing. Shifting did not put enough stress on the housing to split the plastic outer, but braking definitely could cause the housing to split leaving you with no brakes. That could be lethal!

Then someone clever figured out that if you wrapped the spiral wound wire with a material that could withstand braking forces then you would have a braking system that would give better feedback. Now you can buy this as compressionless brake housing. There are also other compressionless housing systems, like Nokon.

My comment about confusing to old timers has to do with being warned to never using spiral wound casing for brakes because it could fail. Now the reinforced spiral wound casing can be used for brakes. You just need to be very careful that the casing is reinforced for use with brakes.

Another thing to note is that compressionless housing is not as flexible as spiral wound casing, so you need to account for that when you route it and cut it.

Given a choice, compressionless is the way to go as there it less slop in the system. You will pay a premium for the housing, but it is worth it. Hope that helps.

Answer 4

Yes there is a difference between traditional gear & brake housing. And no you shouldn't use standard gear housing for brakes as it can split right down the middle.

The true compressionless housing available for brakes these days is like nokon, i-link and vertebrae. They all use a segmented design and can be used safely for both gears and brakes.

Answer 5

Normal fluid driven disc brakes are engineered to use the non-compressible nature of the fluids to drive the caliper. Cable driven disc brakes for bikes use an almost the same mechanisms but instead of driving the caliper by pushing it (compressive force), they pull it (tinsel force) with the cable.

Derailleurs movements need to be more precise than traditional brakes. So, shift cable housing is for bikes is more rigid than typical brake housing for bikes. It deals with much less force than the brakes, so it can be made thinner than on brakes and save some weight.

A shift cable isn't strong enough to handle the forces used with disc brakes and would snap. We need the precision that the rigidity of shift housing with a diameter that can handle the thickness of a brake cable.

Compressionless brake housing gives us that by taking the rigid design of shift cable and scaling it up to handle brake cable thicknesses. But if that was all the cable manufacturers did it wouldn't work. The extra thickness would prevent the cable from snapping but, under these higher forces the steel strands that make up the wall of the housing (housing, not cable) would "mushroom" through the outer plastic jacket like a loose sock.

Imagine holding a fist full of drinking straws. You can balance a plate on top of them and place a lot of weight on top that. If you let go of the straws, they'd collapse. The plate is like the pulling force on the cable, the straws are like the steel strands that make up the housing wall. The wall in compressionless brake housing is wrapped in telfon, kevlar, or steel coil to keep them from deforming, just like your hand keeps the straws together.

Anyway, without this additional rigidity, or more specifically "this lower tolerance for changes in force", the caliper would "float" against the disc and be less efficient. They'd feel squishy and have less power.

I have the BB7 discs like you on one bike and cantilever brakes on four others and compressionless housing (Jagwire Road Pro) on all of them. I definitely do not have the "spongy feel" on the cantis that people often complain about. They are rock solid.