Hi guys,

This weekend I broke open what very much seemed to be an original Shimano package labeled "Shiman SIS shifter cable set", which to my surprise contained spiral-wound outer cables.
I've always thought that for SIS shifting the cable sheaths with the lenghtwise strands were pretty much a must.
So what's this?
- is there a Shimano spiral cable that is SIS compatible and which I've simply haven't heard of before?
- have I been ripped off and bought some counterfeit/embarrassingly old stuff?
- Was the lengthwise strands for shifters not that required actually?

So basically, can I use it with no detriment, can I use it with some degradation of performance, or should I get some new cable and leave this aside?

I think on older index shifting Shimano still used the sprial wound housing. It works ok for lower gear count systems where the spacing between the cogs is still pretty wide or on bikes with frame shifters where there is just a short piece of housing. On a bike with higher gear count or if you have long runs of housing, you're probably better off getting some of the 'lengthwise' housing.

some shimano shift housing is like that, the stuff that comes with the shifters usually. impossible to run a brake cable through it if you tried

The functional difference between long helix (index) and traditional spring wound (brake) housing is how they flex. In technical jargon it's related to the location of the neutral axis.

In a brake housing the coils of the spring lay against each other and cannot be compressed, so when the cable is flexed the inside of the curve remains a constant length and the outside of the curve opens up becoming longer. (imagine a Slinky flexed into an arc) This means that the distance down the center of the housing gets longer also, which could be problematic for index which requires a constant length housing.

Index housing is wound the long way, and flexes like a solid tube, compressing on the inside of the curve and stretching on the outside (and usually ovalizing somewhat) so that the neutral axis (place of no length change) is right down the center, assuring a constant length for the inner wire to run through.

In practice I'm not sure that it really makes a world of difference, because there isn't that much change in the curvature of the housing once the bike is set up, though with suspension or other sources of housing flex while riding the type of housing becomes more important.

In your shoes, I'd email the Shimano or the source and ask if it was a mistake. If not, I'd go ahead and use the housing and see how it performs. No sense, spending dough to replace it unless you have to.

It does make a difference.

The effective length of the housing changes if you are using spiral wound as you turn the bars. When did shimano introduce SIS housing? 8 speed? Earlier? I highly doubt you can get away with using 4mm, brake housing as a substitute for 9+ gear systems.

Good winter experiment.

The housing that came with my SIS shifters looks spiral wound, is thinner than brake housing, and works fine. It is marked "Shimano SIS" on the outside.

I just replaced cables/housing and used the Shimano SIS. Normally I use the Dura-Ace but went with something cheaper this time. I also noticed the spiral wind. I'm not too worried about it. If my shifting suffers (which I doubt it will) I'll be using something different next time.

The point is well taken, Yes, it can make a difference when steering changes the curvature of the housing, which is why I preferred to explain how it might make a difference, vs. stating that it did, or didn't.

The question is whether it makes a material difference or not, which given that Shimano now uses spring housing in some kits, might be in doubt. Considering the small amounts that the handlebars are turned while riding, and therefore the small change in neutral axis length, I think that whatever difference there is will be probably be within the working tolerance of the system. But it might make the position of the handlebar when the derailleur trim is adjusted more significant, so I'd do so with the front wheel straight.

Also make note that this seems to be 4mm housing so any change in neutral axis length would be 25% or so less than with 5mm housing.


BTW- let me remind folks that while it might be OK to use spring (brake style) housing for the derailleurs, it definitely is not OK to use index housing for brakes. Index housing lacks sufficient compression strength for the brake lever forces and may burst in an emergency braking situation.

I got one of the first Dura-Ace SIS drive trains (6-speed, downtube levers) in North America during the winter of 1985 as a pre-production sample for Trek to evaluate. I remember looking at the derailleur housing and thinking "WTF is up with that?" because it had longitudinal strands rather than spiral wound. Then I read the directions...

Lower end index shifting groups (Tourney level) use spiral wound housing. When fractions of yuan count for OEM sales, a couple pennies here and there add up. It's a stiffer steel, and the plastic outer casing is also stiffer than regular brake housing.
Its fine on lower end systems, but you'd get better performance from SIS-SP derailleur housing for sure.

sis housing was on my 6 sp, all original 105. I would think spiral stuff would only make frustrations for anything more than 8 cogs..

I disagree.

Shimano 9 speed sytstem pulls about 2.5-7mm of cable per rear gear shift. You're telling me that you're not going to have anywhere close to 2mm (less? see below) of effective housing length change as it flexes? With non sis housing? Not to mention the fact that you're constantly countersteering to keep the bike upright. And that people don't only shift gears while riding in a straight line?

Sram 10 speed pulls around 1.6mm of cable.
Shimano 10 speed around 2.3mm (not 6700/7900 series)
Shimano 10 speed around 1.3mm. (6700/7900)

That's for a FULL shift, you and I know it would take much less than that for the gear to not be engaging correctly in it's cog. Unreliable shifting with tighter cog spacing is why shimano introduced SIS housing. It's made because it makes a difference.

My first experience with Shimano's SIS was on an early '90's Trek with 7-speed downtube shifters. The shift cable housing was so short (only from the chainstay stop to the rear derailleur) that the type of housing probably didn't matter at all and I didn't pay attention to what was there as OEM.

My next experience was with 8-speed STI's in the mid-'90's and the cable housing that came with it definitely had longitudinal (or more correctly, a long pitch spiral) reinforcing wires. For the long houing runs that STI's require, I'm pretty sure it matters.

I think I would debate this point. In higher end brake housing or spiral wound housing for shifters, they do try to wind the spiral very tightly to minimize compression. But I have seen lots of brake housing that clearly compresses under the pressure of braking. This gives cheaper cables that 'mushy' feel and will mess up index shifting when brake housing is used by mistake. I've caught this on several bikes as the problem when shifting will work fine at one end of the range, but gets increasingly bad as there is more tension put on the shifter cable. I assume you were referring to spiral wound housing specifically for shifters and in that case you're probably right that the changes in the cable path are the critical issue. But just to be nit picky...

Yes of course, there are probably poorly made brake housings out there, just as there's poorly made anything. But the design of brake housing calls for the coils to lay against each other like a new unkinked Slinky. In that condition they are highly non-compressible. Usually, when you see spongy housing it's because someone kinked the housing permanently separating the coils. In the old days of road bikes, before aero levers this usually happened when people turned the bike over to work on it.

Keep in mind that brake cables operate at vastly highly tension/compression loads than gear cables.