Wrong BB axle length...
 

So, after putting the drivetrain on my new bike together today, I realised that the BB axle is too short.
The inner ring (on a triple) is so far in that it's in line with the inner plate of the front derailer cage!

Current axle length is 113 mm.
Should I get a 118 mm one, or maybe something longer still, if that even exists...?

Until I get a new one, I will have to stay out of the smallest chainring, I guess... :(

Well, what is recommended for the crankset?

No idea. Doesn't say, either on Shimano's website or on the online store's website, where I ordered from.
It came in a sealed plastic bag with no "manual" or anything like that.

How was I supposed to find out?

I asked in here before, but didn't get much of a reply...

Depends on the make/model of crankset, which you have not revealed.

I have a couple of Web pages that should help you get this sorted out:

http://sheldonbrown.com/bbsize

http://sheldonbrown.com/chainline

Sheldon "Numbers" Brown

Yeah, forgot that.
Shimano FC-M540 crankset - it's a triple. In this case a 26-36-48 (for the time being...).

The only BB sizes available to me are 113 and 118.
(Shimano ES71)

So, will those extra 5 mm be all on the drive side, or just half of it?

(Edited the crankset name - forgot the "M"...)

Hmm, this is strange...

I just found the same crankset on a Swedish online store.
There, they recommend using it with a 113 mm axle...!

The recommended spindle length is 113 or 118,depending on seattube diameter. Longer one with 11/4" or larger.

Tube dia is 28.6 mm (or 1 1/8 in).

Is this actually a problem?? Can the derailer be adjusted inward further?

Not that I can see...
The limit screws are all the way out.
I even tried to see if rotating the entire cage inwards (clockwise seen from above) helped, but not even that allowed the chain to run without significant rubbing.

The only thing I can think of that could help a little bit more, is to use a thinner spacer in the derailer clamp. Would gain 3-4 mm. Could lose stability and function...

So, will the extra 5 mm of axle (113 -> 118) be all on the drive side?

if i'm reading this right, you've probably effectively got an 31.8 seat tube and should use a 118 BB. or buy a 28.6 deraileur.

He said it was 11/8". New shimano mtb derailers come with 13/8" clamps and shims for 11/4 and 11/8".I'm windering if that mickey mouse shim business isn't the problem?

that's kind of what i was getting at... i said effective, not actual

I believe if you have a 118mm, the 5mm means 5mm in total length of the axle so 2.5 on each side

I've tried to find this info using Google and using this forum's search function, but no luck.

I really need a definitive answer to whether the extra 5 mm will be all on the drive side or half on each side for 113 vs 118 mm.

Should I maybe get the (LX) ES51 68-121 instead?

It seems as if the chainline is 42-44 mm as it is now (from tube centre to centre of middle ring).

I'd get the best measurement you can of what chainline you've got right now, then go with a new bottom bracket to correct it. Not to second guess you, but are you sure the current spindle length is 113mm? If so, and if 42-44mm is an accurate chainline measurement, I'd go with a 121mm spindle, recommendations be damned. And yes, the spindle length is the total length, so any change will be half on each side (assuming a symmetrical spindle, the most common type).

This is a 7-8-9s frame with 135mm dropout spacing, right?

Yeah, 135 mm spacing.

I do know it's 113 mm. That's what I ordered. If it had been the wrong length, it'd been a 118 mm - the only other size.

Guess I'll have to downgrade to an LX BB then...

Measured chainline properly now.
It's 42.5-43 mm.
With a 121 mm axle, it should come to 46.5-47 mm, given a symmetrical axle.
That's still a bit short of the 47.5-50 mm recommendation on Sheldon's site.

By the way, the frame is a Surly LHT.

Go for the 121. BBs are pretty cheap anyway; might as well get it right.

They are pretty cheap, all right. The ES51 costs UK£17 (US$30).
Will order it tomorrow! :)

Same thing happened to me with my Nashbar Trekking crankset. Recommended 113mm, but it truly needed a 118mm...

But even 118 mm wouldn't bring the chainline up to the 47.5 mm recommended.
I wouldn't be surprised if I need a 126 mm at the end of the day!

I just went through the BB size fiddling too. How far from the centerline is the middle cog on your rear cassette, and what's the difference in chainline between the middle cog and middle chainring? I had the opposite problem, starting out with about 46mm in back and 52mm in front, so I had to find the smallest BB possible. I ended up with 46mm in the rear and 49mm in the front and things seem to be working fine so far. Maybe 46-47mm will work fine for you. There's only one way to find out...

The rear chainline is a secondary concern.
My primary goal is to make the inner chain ring come inside the front derailer range... :)

The rear cassette is a Shimano 11-34 with 9 cogs. I would guess chainline is the same for all similar cassette/rear hub combos.

Unfortunately I don't think they ever publish numbers for the front der range anywhere. I have no idea why.