Chain Tension - too much or too little!

russello

Afternoon workshop....

Looking for some advice re: chain tension, after putting together my first build, a Kinesis Crosslight FiveT. The build includes a Tiagra group, with 10spd compact gearing. Rear cassette is SRAM 11-28t. Chain is a tiagra 10 spd chain.

My problem is re: chain length and tension.

Options seem to be that big-big works, but I then get chain slap on the lowest rear cog when in the small ring or little ring. Too little tension. The chain stay is horizontally higher, as this is a cross frame, but this still does not account for all the slap....

Alternatively, I take out another link, oversome the chain slap, but big-big means that the RD is sort of shuddering, and the chain under far too much tension. The RD angle is just plain wrong. I appreciate the big-big is not recommended, but even 1 cog down on the casette is not good.

I have tried adjusting the RD B limiter screws in each of the above scenarios to either increase tension and reduce the chain slap, or reduce the tension when in big-big. The B limiter helps a bit, but not enough.

I just cant seem to find some middle ground where I can avoid the chain slap when using the small cog, whilst at the same time being able to use big-big.

I do not have this problem on any of my other bikes when running compact and up to 28t rear, and I am trying to sort myself before I shuffle down to the LBS!

Any wisdom would be really appreciated, especially by my drive side chain stay!

Russ

smidsy

Shimano Tech docs are helpful

e.g.

http://techdocs.shimano.com/media/techd ... 607047.pdf

drays

It sounds like you might need a longer cage rear mech to take up the slack in little-little rings.

smidsy

Not necessarily.

You size the chain for big front small rear as per shimano tech docs (with jockey wheels vertically in line at 90 deg to the floor).

If you do that and still have an issue then maybe you need to look at other options.

russello

Thanks.

Tech doc printed off for some reading tonight, as Mrs O'Hare is out with friends.....

Immediate observation is that I have 28t at the back, and tech doc recommends max 27t. I have a spare 11-26 at home, so some fettling later on!

Cheers - Russ

styxd

drays wrote:

It sounds like you might need a longer cage rear mech to take up the slack in little-little rings.

Pretty much this.

If you're using a compact (34/50) up front, then I'd guess the rear mech won't be able to cope with the difference.

You'll need a long cage I reckon. There's calculators online that'll help you work it out.

I just avoid the big/big combo.

smidsy

Russ

The tech doc I linked to was an example - as I do not know which rear mech you have.

Go to the tech docs site and get the correct one for the model you have.

I run 28t rear on a normal short cage mech no trouble (although mine is Ultegra 10 speed)

russello

Just reading the doc, with ipad on, and just sussed the generic doc.

Will let you know how I get on.

Thanks. Russ.