Rear Mech Cable Outer Length

[Tomba]

Anyone know the optimum outer cable length for a 105 rear mech on a Cannondale Synapse aluminuim?

I changed from a MTB SLX rear mech at the end of last year which had a shortish outer or I would have measured an old one.
Since I changed back I've had problems changing round about the middle of the cassette. Tried every way of adjusting to get it right but its still a wee bit jumpy. The cable outer at the moment is 350mm

I've seen cable kits that have a 320mm section for the rear mech, and wanted to know if that is the optimal length outer.

 

[mrandmrspoves]

I stand to be corrected. ..but don't see how the cable length makes any difference. You should keep the length as short as you can but long enough to avoid tight curves. If you have indexed correctly and still can't get the gears smooth across the range, take a good look at the gear hanger because if it is loose or damaged you will not achieve a full indexing

 

[Tomba]

I stand to be corrected. ..but don't see how the cable length makes any difference. You should keep the length as short as you can but long enough to avoid tight curves. If you have indexed correctly and still can't get the gears smooth across the range, take a good look at the gear hanger because if it is loose or damaged you will not achieve a full indexing

Thanks for that. I've checked the mech and hanger and all seem fine. I'll cut it at 350mm and see how it looks before installing the inner cable.

It also looks like I used ferrules that are meant for brake cable housing so there is a wee bit of movement. I wonder if this could be the cause of the problem?

 

[mrandmrspoves]

If the ferrules are stopping the gear outer cable bedding down correctly - it could cause the problems you're having - but most ferrules are a standard 5mm and interchangeable between brake/gear outers so unlikely to be the problem. Another area to check is that you have connected the cable to the derailleur correctly - usually there is a small groove to indicate the correct route.

 

[Tomba]

If the ferrules are stopping the gear outer cable bedding down correctly - it could cause the problems you're having - but most ferrules are a standard 5mm and interchangeable between brake/gear outers so unlikely to be the problem. Another area to check is that you have connected the cable to the derailleur correctly - usually there is a small groove to indicate the correct route.

Just checked again and they are 5mm ferrules and according to the info they are supposed to be for brakes. Apparently its 4mm for gear cables?

Yes the rear mech cable is connected correctly.

 

[MattHB]

You don't want it too short or there will be more friction through the outer which can impair smoothness.

 

[P.H]

Good article here about cable sizing, with clear photos to give you an idea of how it should and shouldn't look;
http://www.parktool.com/blog/repair-help/cutting-cable-housing

Basically you want the cable to leave the mech straight, within reason a bit too long is better than too short.

 

[screenman]

When did you last change your chain or cassette?

 

[Hacienda71]

Sram have a specific length, not sure if Shimano are the same but I did cut my last Shimano build to the same as my Sram and it works fine

 

[Tomba]

When did you last change your chain or cassette?

About 300 miles both new.

 

[screenman]

Well that takes care of that idea then, I asked because changing a chain without a cassette can make it feel like they are not indexing in those gears, mainly due to the middle one's being the most used a worn sprockets. Is it bang on at either end of the range?

 

[Tomba]

Well that takes care of that idea then, I asked because changing a chain without a cassette can make it feel like they are not indexing in those gears, mainly due to the middle one's being the most used a worn sprockets. Is it bang on at either end of the range?

Yes all good at both ends.

 

[screenman]

Am I reading this correctly? you changed your mechs is that right. If so what did you take off and what did you put on.

 

[Tomba]

New cassette, chain, rear mech and cable.

 

[screenman]

All the same brand as before? Sorry about all the questions but without all the information it is hard to be specific. Any chance of a spacer left out when fitting the cassette?

This guy tells it as I would if everything you have there is compatible.

http://www.bikeradar.com/gear/article/workshop-troubleshooting-shimano-gears-18244/