Bicycle Mechanics - routing of cable

I have a somewhat unusual question, why do some frame's have it so that the route of the cable to say the derailleur has like 1 foot of cable then on the top tube it is exposed and then sealed againf or 8 inches and so forth. Why not just have the system totally sealed?

The cable housing is used to support the cable when it's pulled and is only necessary where curves in its path are required. The frame already supports straight runs against its tubes. The less cable housing the less weight, cable friction and cost.

The cable housing is used to support the cable when it's pulled and is only necessary where curves in its path are required. The frame already supports straight runs against its tubes. The less cable housing the less weight, cable friction and cost.

You have obviously never ridden a bike with full housing! The difference is night and day since the cable is then sealed from any invading dirt or gunk. Also, with brakes, you get less housing compression and a firmer feel running full housing typically. My SS uses full housing front to back and the brake feel with V's is pretty incredible.

I would imagine full housing would be better, i mean its pushing it saying the routing many frames use is for weight saving it. Well could i take a drill bit and drill a hole so that the cable guide is large enough to fit through entirely, i would imagine it would be like butter with an AL frame, or i could take the easier route and use zip ties. What do you recomend?

I would not drill out the stops until you determine that you really do want to use full housings. The tie wrap approach would better for a test period. If you like the full housing then you could modify your frame as you suggest.

Doc

well what are disadvantages to full housing?

Also, with brakes, you get less housing compression and a firmer feel running full housing typically. How do you get less compression with more housing?

I would imagine full housing would be better, i mean its pushing it saying the routing many frames use is for weight saving it. Well could i take a drill bit and drill a hole so that the cable guide is large enough to fit through entirely, i would imagine it would be like butter with an AL frame, or i could take the easier route and use zip ties. What do you recomend?There is no pont. You are kidding yourself.

You have obviously never ridden a bike with full housing! The difference is night and day since the cable is then sealed from any invading dirt or gunk. Also, with brakes, you get less housing compression and a firmer feel running full housing typically. My SS uses full housing front to back and the brake feel with V's is pretty incredible.




If you go back and read the original post you will see that he asked why it was so on some bikes. This is the question I answered. And gave the reason why it was done that way.

It pisses me off that you are trying to insert modern technology concepts into an explanation of a design element that was utilized before the advent of modern compresionless housings.

And as an aside I never said I thought it was better.
But At this point I will.
It IS better for a rigid road bike to have free run cable routing.

Your monkey motion bike is a whole different thing.

Also o-ring seals in the feral ends of housing keep out dirt and grime. And dirt on the bare shift cable has no affect.

And you have never felt the brakes on one of the bikes I have built.

Want full housing.....heh heh get Hydrolic disc brakes! Go with what you want! You want full housing! Get full housing or make it yourself!

Pedal On,

Bob

Gear cable transmits information as well as force. Modern index gearing systems need to be very precise and you just can't get that precision using full housing which flexes.
Brake cables just transmit force. Full cable housing is a bit spongier, but saves on maintenance if you use your bike in foul conditions. This is what I use on my commuter and touring bikes.
Internal cable routing is another option.
With a steel bike, you can alter the cable routing however you like, adding or removing brazeons.

The best discussion on cable routing I have seen is the book Touring Bikes by Tony Oliver. The name is a bit misleading, its about the principles and practice of bike design and fabrication (road,touring and MTB)

Gear cable transmits information as well as force.
WHAT??

Gear changing is an analogue information system with 8 states (or recently 9 and 10), rather than the 2 states of a binary system.
The analogue information is transmitted in the form of a certain length of cable which is pulled by the lever. This length is translated into a horizontal throw of the derailleur.
If you use fully shrouded cable, this is increasing noise in the system. The theories of Shannon still hold no matter what type of information we are talking about.
Mavic transmit the gear changing information by electrical cable or infra-red.

http://en.wikipedia.org/wiki/Claude_E._Shannon

For gear cable the force doesnt matter - the distance moved is however most important and must be the same at both ends

Gear changing is an analogue information system with 8 states (or recently 9 and 10), rather than the 2 states of a binary system.
The analogue information is transmitted in the form of a certain length of cable which is pulled by the lever. This length is translated into a horizontal throw of the derailleur.
If you use fully shrouded cable, this is increasing noise in the system. The theories of Shannon still hold no matter what type of information we are talking about.
Mavic transmit the gear changing information by electrical cable or infra-red.

http://en.wikipedia.org/wiki/Claude_E._ShannonWhy try and make it rocket science. Index shifting is just precise cable pull.Once it gets to the derailer,that's another story.Certainly the less interference and slop the better. A good reason for downtube shifters.

Spoken like a true engineer, MichaelW.

No differential amplifiers needed here.

WHAT??
I guess he meant: position matters with shift cable, but not so much with brake cables. That's why compressionless housings are used for shift, but not brake. I don't say I agree, I just think that's what he meant. This being said, long housings are the pits for a) shift precision (housing compression+ deformation, friction), b) brake feel (internal friction), and c) maintenance (a gunky cable by itself is ugly, but works, a gunky cable in a long housing is a non-shifting/non braking bike).

Full housing is probbably more expensive to install. It looks also less neat because the housing never travels in a perfect straight line, and there usually is more friction in it. Even with "non stick" housing or cables, cables in full housing tend to rust in place over the years.

As for problems with short sections of housing getting dirty, a lot depends on how each section of the housing is designed. The bicycles I have don't show any problem with exposed cables; they are touring bikes which aren't used too much in mud, but they are ridden a lot in snow, ice, slush, etc. The guide under the bottom bracket is easy to pack with grease before winter comes.

Even with "non stick" housing or cables, cables in full housing tend to rust in place over the years.

Not with stainless cables. That was a problem in older days of steel cables and unlined casing.

I'll rephrase: "there will be rusty spots in the casing. It is true that modern cables tend to stay in good shape, but if you pull out an enclosed cable that has spent the entire winter outside, there will be red/rusty spots inside. Been there, done that.

Want full housing.....heh heh get Hydrolic disc brakes! Go with what you want! You want full housing! Get full housing or make it yourself!

Pedal On,

Bob
Are those similar to hydraulics? Not to pick on you, but a cop that claims to be a retailer of some sort ought to be able to properly spell.