Mountain Bike Reviews Forum banner
1 - 13 of 13 Posts

·
Registered
Joined
·
163 Posts
Discussion Starter · #1 ·
Hi folks. I've only ever had a couple of mountain bikes since the early 90s and these were both 24 and 27 speed, square taper bottom bracket, all Shimano affairs.

For '09 I'm hoping to build a new bike. It'll be my only bike and will replace my dedicated hardtail mtb and my Trek commuter. What I'm hoping to build up is an Alfine driven Niner SIR9.

But now I find I'm so confused over chain line and BB choices. I've read everything I can find on these forums but still confused. If someone knows of particular threads I've perhaps missed please post a link.

Other than that I'd like any recommendations on BB/cranks to match to the Alfine that are in the middle of the price range. I guess I'm confused by the different BB types and how they affect chainline and Q factor. I know the rear cog is dished so you can flip it to adjust the chainline but is there any adjustment available at the chainring? Or do you just have to buy a crank that matches the hub chainline?

Ok, I'll leave it it that before this post get's any longer. If I build the bike I'd like to use something other than the Alfine cranks. Just looking for lighter weight and a tiny bit of bling factor.

Thanks:)
 

·
Frt Range, CO
Joined
·
2,576 Posts
Alfine chain line is 43mm or 47mm depending how you flip the cog. More applications require you run the 47mm chain line. It's easy to make 47mm chainline with any 68/73mm combo bottom bracket.

- Do you want to run the crank's chainring on the outer on inner chainring lands?
 

·
Registered
Joined
·
163 Posts
Discussion Starter · #3 ·
Hi Pursuiter,
Well, that's another thing I'm weighing up - should I get a dedicated SS crank like the FSA V-drive? For example I know the V-drive has a 50mm chain line so does that mean it isn't compatible with the Alfines 42/37mm?? So, back to your question, I'd also consider for example, an XT crankset with the granny and big ring removed. I don't know where that leaves me in regards to the chain line! More confusion... hehe

What tolerance in chainline is recommended?
 

·
Frt Range, CO
Joined
·
2,576 Posts
I've got the FSA V-Drive Megaexo cranks on my 73mm Jabberwocky with a 49mm chainline on the inner ring (IM9). I've got Shimano LX cranks on my 68mm diSSent with a 47mm chainline on the inner ring (Alfine). I've got a Shimano DX cranks with a 47mm chainline on my 68mm Outcast29 on the inner ring (Nexus).

68/73mm combo BBs are very easy to tweek the chainline. Cheaper cranks with square tapper are harder but is can be done, might buy and extra $20 BB (don't ask how I know).

Bottom line is it's easy if you know what you want.

- What BB width is your frame?

- What cranks do you want to run?

- Bash ring makes you use the inner lands, no bash ring, use the outer lands, looks cooler. Which way will you run?
 

·
Registered
Joined
·
163 Posts
Discussion Starter · #5 ·
Well, instead of posting a bunch of "maybe I'll get these..." I'll leave it for the time being and try to do more home work and get a more of a definitive list on what parts I want. All I know is I want a rigid steel 29er with IGH and disc brakes. Hoping I can get the new 09 SIR9 when it releases here in Japan. Thanks for your help Pursuiter and maybe I'll get back to you asking for more help in a month or two!

Cheers!
 

·
Registered
Joined
·
163 Posts
Discussion Starter · #6 ·
Ok, sorry to bump this back up. If there's another thread on this somewhere I haven't found please post me a link.

So - how do you actually measure chain line? I have an older (maybe 6 or so years old) STX square taper crank and BB that's hardly been used. How can I measure it's chain line? Might be able to save a few dollars and use it instead of new cranks to begin with.

Thanks.
 

·
Frt Range, CO
Joined
·
2,576 Posts
I measure the CL with a set of plastic calipers.

Assuming your STX cranks were on a MTB with 135mm rear hub spacing the CL should be 50mm CL on the inner ring. If you're running an Alfine with 47mm CL, you'll need to buy a new BB with 6mm narrower spindle to get 47mm CL. This is why I like the combo 68/73mm BBs, they can be set up the run 47mm on either 68mm or 73mm BB by playing with the spacers.
 

·
Registered
Joined
·
163 Posts
Discussion Starter · #8 ·
Hi folks, I'm back and can finally say my bike is taking shape and my questions are now legitimate!:thumbsup:

So, I have a beautiful new Sir9 frame and matching Niner fork. I bought my Alfine hub and am in the middle of 1st wheelset build lacing it to a Salsa Semi 29er Dsic rim.

My current 26" commuter runs 48/38/28 up front and 11-28 out back. What Alfine cog size and chainring size would be recommended for me? I don't mind pushing slightly higher gears as I'm mainly commuting and don't get to see too much dirt action.

Thanks for any input! (I did run a search looking for info but didn't find anything that helps me)
 

·
Frt Range, CO
Joined
·
2,576 Posts
komekomegaijin said:
...My current 26" commuter runs 48/38/28 up front and 11-28 out back....
What gears do you normally cruise in? How low a gear do you need?

I pick my primary gear ratio (the frt chainring x rear cog) by the lowest gear I'll need. On my commuter I run a 34x18, gives me these gears (with 29er wheels):

88.5
77.7
67.0
54.8
46.6
41.0
35.3
28.9

On my mountian bike I need as low a gear as I can get, I run 32x22:

68.1
59.9
51.6
42.2
35.9
31.6
27.2
22.2
 

·
Registered
Joined
·
105 Posts
My Genesis Alfine equiped IO ID came with a FC-M545 Shimano crank. Its listed as a non series item, looks much like a Deore crank but has a 46.8 mm chain line, matches up perfectly with a Nexus offset rear sprocket. The only negative is the lack of location tabs to centralise the front chain ring which means you rely on the bolts to hold it concentric.
 

·
Registered
Joined
·
163 Posts
Discussion Starter · #11 ·
Hi again everyone :)

Well, after way too many delays I've finally built the wheels for my Sir 9 and have started to assemble the beast.

I have two questions I'd love some help with.

1st: How do choose the correct chain length with the Alfine hub and Eccentric Bottom Bracket? Should I start with the the EBB in the 6 o'clock position or 3 o'clock position? Do I then just wrap the chain around and join it at the first link that fully wraps around?

2nd: Chain line! I went with current model XT 44/32/22 cranks and just used the 32t with shorter chainring bolts. The Sir 9 BB is 68mm and with the EBB becomes 73mm. This results in a 50mm chainline at the front with only about 3 - 4mm clearance between the chainstay and chainring.

Next, the rear. 135mm hub divided by 2 = 67.5 Measuring from lock nut to cog is 26mm, 67.5 - 26 = 41.5 rear chainline.

The cog is the standard Alfine 18t with plastic guard attached to one side.

How do I get the right chainline?

Thanks, as always, for any help.
 

·
Registered
Joined
·
376 Posts
I have not done it but...

komekomegaijin said:
Hi again everyone :)
Next, the rear. 135mm hub divided by 2 = 67.5 Measuring from lock nut to cog is 26mm, 67.5 - 26 = 41.5 rear chainline.

The cog is the standard Alfine 18t with plastic guard attached to one side.

How do I get the right chainline?

Thanks, as always, for any help.
I have read in this forum that you can take off the plastic guard and reverse the cog.
 

·
Registered
Joined
·
163 Posts
Discussion Starter · #13 ·
What is the usual way to adjust chainring chainline? My XT BB on the 73mm EBB has one 2.5mm spacer on the drive side. So, if I were to remove that that would get the chainline to 47.5mm but means the drive side crank arm is 2.5 mm closer to the bike centerline than the left side. Is that an issue? Is that one way to do it?

Another way, I guess, would be to put 3mm spacers between the crank arm and the chainring. Is this is normal practice? Can I buy specific spacers for this?
 
1 - 13 of 13 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top