Cycling UK Forum

Hi All
I've just received some gear outer (SP40) from Chain reaction, I cut the first one to length and noticed that the core was spiral rather than strands which run the length of the outer. I thought all gear cables had strands, certainly all the ones I've used over the last 25yrs, which provide better indexed shifting The outers are marked 'Shimano SIS' so have things changed or have I bought the wrong thing?
This is Chain reaction's description:

Shimano SP40 Road-MTB Outer Gear Casing(Pre-Cut)

Presumably the *pre-cut* SP40 should be used as is. The SP41 is the non-spiral cable outer that I cut to length.

IIRC SP40 isn't recommended for every system; it isn't quite compressionless so adds to the errors in the indexing system. However it is (I think) the lesser of several evils if you have a MTB with a short cable run that bridges across a suspension movement; the spiral windings make the housing more flexible.

You may find the SP40 housing works for you but later, it might be straw that breaks the camel's back, as it were.

cheers

I suspected that might be the case Brucey, I'll get some sp41.

Many thanks for the replies.

NB there is often a length of housing to the RD which has about a 180 degree bend in it. This is easily accommodated by spiral wound housing but SP41 (and similar) are better for the indexing, but also stiffer and tend to spring back at the RD in such a way that the B tension adjustment is interfered with. My approach to this is to set (permanently deform) SP41 housing into a curve that is about right, so that the housing isn't trying to spring the mech in one direction.

Then I grind the ends of the housing so that they are square; often they are quite a long way off square once the housing is deformed into the curve. Other lengths of housing o the bike don't have such abrupt bends in and/or the springing is of less consequence. These housings don't need to be permanently deformed into a new shape. However they also can have ends that are not quite square once they are formed into a curve. Thus I check the ends for square and regrind them whilst holding the housing in the appropriate curve.

Grinding the housing ends square raises burrs on the plastic parts that you need to trim off. But it helps SP41 type housing in two important ways;

1) the end of each wire reinforcement strand is often like a little chisel if you use cutters on it; this helps to cause wear inside ferrules, especially plastic ones. (check the appearance of the cut ends using a strong magnifying glass, and check the insides of used plastic ferrules)

2) if the ends are ground square when the housing is the correct shape, the load is better shared between the reinforcement strands; again this helps with ferrule wear/damage but it also helps the housing to survive; it is less likely to become springy, go a funny shape or to burst open than it would be otherwise.

The net effect of being a bit more careful with cable prep is that the cable installation is liable to last longer before it goes wrong in some way, such that the indexing starts to become unacceptable.

cheers