Exposed control cables versus fully enclosed cables

[Dan79]

I have noticed with our new(ish) Dawes tandem, the rear brake cable of which is exposed for much of its length, that the rear brake is more spongy than i would expect. There is nothing apparently wrong with the set up of the brake cantilevers or pads; is this just something to be expected with cables as long as are found on a tandem, or is the fact that the cable is exposed contributing to this? If I were to replace the cable housing with a fully enclosed outer, would that make any difference (it is obviously only exposed on the straight runs along the frame tubes so I wouldn't anticipate much additional friction resulting from curves). Presumably exposed cables are more prone to deformation along their exposed parts / more breaks in enclosure present more opportunities for ingress of dirt and other contaminants?
Is there a performance-based reason, other than cost/weight saving/aesthetics for the prevalence of exposed control cables on bikes these days?

 

[Ian H]

You'll get more compression, not less, when the cable runs in an outer.

 

[raleighnut]

^^^^^^^ Wot e said

 

[Racing roadkill]

Make sure someone hasn't used gear cable instead of brake cable. This sounds like a massive dumb assed mistake, but I had it happen to me once, when I let someone else re cable one of my bikes.

 

[mjr]

Either buy stainless/coated cables or keep the exposed bits lubed/greased but routing (no tight turns!) brake and lever type are as likely to blame for slop IME.

 

[Mobytek]

you will only be able to go point to point exposed, need an outer to get it round corners.

set up is the cause of your spongyness

 

[Cyclopathic]

All cables have a certain amount of stretch in them and being a tandem rear brake there will be more play as it is quite long. Calliper brakes also sometimes have a bit more play and stretch in them.

 

[Dan79]

Thanks for all the responses, however I'm not clear as to whether compression in this context is a good thing or a bad thing - are you talking about compression applied by the outer cable on the inner causing friction, or compression applied as desired on application of the lever? Basically, whether or not it is better performance-wise to enclose cables or to expose them where possible. The routings of the parts of the cable where an outer is necessary to negotiate seatposts etc looks tight, but being a Dawes would expect them to have decent engineers who would have thought about where the lugs go so am assuming that's not the problem unless their standards have slipped.
Also I would suppose that an exposed cable will be more liable to stretching than one that is enclosed?

 

[fossyant]

It's fine. It will be worse if fully covered. If it's new, there is always a chance the cable is slightly corroded/grubby as they can be in storage. I had to change a cable on my daughter's bike, brand new.

 

[RichardB]

Think of it this way: the movement you get at the brake end of the cable is the same as the movement at the lever end, minus any compression of the outer that happens when pressure is applied. The longer the length of outer, the more compression is possible. The length of exposed cable is braced against the frame of the bike, and you would have to pull the lever pretty hard to compress that! The more exposed cable you have the less spongy it should feel. A fully-enclosed cable should be worse, not better.