Chain length Problem

Huck Finn

Got an issue with new chain. Bought a bike which needed serious work but old chain worked perfectly in all gears. Stripped bike and cleaned and replaced everything I had to.

When I installed new Sram chain, checked length over two largest chainrings with shock bottomed, split chain, then installed. Chain rides perfectly in two largest chainrings but when put into smallest front and small rear, hangs at an impossibly slack angle.

I thought it must be an overly long chain so cut another link but this makes it too short in largest chainrings. My rear dérailleur is set up correctly and the cage is not twisted.

I'm stumped as to what this could be.

ride_whenever

When you measured chain did you put it through the rear dérailleur?

Huck Finn

No. Measured it the normal way. It's almost as if the derailleur isn't taking up the slack but the b screw is in the right place I think.

cooldad

You shouldn't be in that combo anyway.

Huck Finn

I know those combos are not to be used but that isn't the issue. When in the smallest front cog and smallest three cogs, the slack in the chain would suggest it is 2-3 inches too long! My only thought must be the derailleur or gear hanger.

I'll post pics tomorrow afternoon.

nicklouse

so what mech?
what range on the cassette and crankset?

sounds like the wrong mech.

supersonic

How many chainrings are you using?

YeehaaMcgee

Mech cage not long enough.

Huck Finn

Thanks for replies. It's a sram xo dérailleur with a triple shimano xt chainset on front. The cassette is a sram pg990.

Mech cage looks to be a medium compared to my shimano long cage on other bike. The strange thing is that i'm sure these are the standard parts which came with the bike. 2010 Specialized Stumpjumper Expert.

supersonic

This is not uncommon. You have three option:

1) Shorten the chain. You will then be able to use that gear, but not the large/large combos. Hit them, and you'll rip the mech and hanger off.

2) Change the mech

3) Don't use the small/small combos.

I'd go for 3 - there is no need to use these combos, and if you do hit the small/small, no damage will be caused. Unlike 1.

Huck Finn

Thanks SS. As the bike is great when pointed downwards, i have a mind to eventually go to a 2x10 setup or similar.

Could i try an option 4 then and perhaps buy a double crankset, shifter and mech to match? I assume the larger tooth combos on a double setup may give me the right tension with the medium cage RD.

Huck Finn

Ah, i see. I can buy single rings with different tooth ratios can i?

nicklouse

Huck Finn wrote:

Ah, i see. I can buy single rings with different tooth ratios can i?

Ok I deleted that reply as I have no idea what you have as that info has not been provided.

You don't need anything special to run one or two rings on the front just change the rings you have now to suitable ones or do as many have been doing for year take the big ring off and add a bash and set the outer stop to stop the third click.

As to a 2X10 do you have 10 now? If not see the FAQs.

YeehaaMcgee

Huck Finn wrote:

a triple shimano xt chainset on front.

I'm a bit lost now, but is that the info you were after, Nick?

RevellRider

Just a quick thought, does the chain hang slack when it's in the smallest cog on the cassette and the smallest chainring with the suspension bottomed out?

nicklouse

YeehaaMcgee wrote:

Huck Finn wrote:

a triple shimano xt chainset on front.

I'm a bit lost now, but is that the info you were after, Nick?

He was on about going to a 2 x 10.

Does he have a 3x10 or 3x9 now?

The answers would be very different.

YeehaaMcgee

The cassette is a sram pg990

They're 9-speed only, right?

RevellRider

The Op has a 3x9 set up but is considering 2x10 in the future.

The problem with the chain being slack, I reckon, is due to chain growth in the suspension system.

supersonic

Chain growth is when the rear axle gets further from the BB - it actually tightens the chain! Though looking at it the other way, if measured at full compression in an extensive system then it may cause it (if the mech is on the limit), though we are only usually talking 10-20mm.

The simple answer is not to use those gears in the small chainring.

RevellRider

Supersonic, I'm fully aware of what chain growth is. I didn't make myself clear enough in the last post. What the OP should do, is go out and ride his bike with the chain at the original length as once he's sat on his bike the suspension compresses and the chain slack disappears

YeehaaMcgee

That doesn't solve the problem. We know the chain is too long at rest.
The solution, I'll bet you a pint, is a longer cage mech.

Huck Finn

Thanks for all replies. Ended up confusing myself with this one yesterday. Done my head in. I was convinced something was amiss. Fitted my long cage xt mech today and problem disappears. Thanks all

Huck Finn

Yeeha. If i were a betting man... I'd be down a pint

supersonic

XT mech? If you had a SRAM X0 then you'd need another SRAM, unless you replaced the shifter too.