Cassette chainline rework

Show off your E-bike creation here.
Post Reply
dirtgoon   10 µW

10 µW
Posts: 6
Joined: Oct 08 2019 9:31am

Cassette chainline rework

Post by dirtgoon » Oct 08 2019 1:32pm

Hi all. I have just ordered a BBS02 and a Luna mighty mini ring that will go on my fat bike with 100mm BB and 197 rear hub spacing. From what I have been researching, the mighty mini ring is going to put my chain line way out of whack.
My bike will be used for singletrack riding mostly in the snow so top speed isn't a priority and I don't think I will need more that 5-6 gears but want my biggest cassette cog to be at least 34t maybe 36t.
Can anyone recommend a rear cassette that can be easily reworked to move the largest cog as far out on the freewheel as possible to improve chainline?

flat tire   1 MW

1 MW
Posts: 1662
Joined: Feb 26 2014 12:20am

Re: Cassette chainline rework

Post by flat tire » Oct 08 2019 1:43pm

Choose an inexpensive cassette compatible with your drivetrain with as few useless stock ratios as possible. The geometry of your bike is unknown and will restrict how far a given size sprocket can be moved outboard by an unknown amount. Also, the biggest cogs are generally attached to each other for support otherwise the mechanical advantage from large radius and bad chainline can deform them. You probably want a more moderate sprocket for your riding as the largest gears on a mtb cassette will be too slow.

Anyway you can move the group of biggest gears down and simple pack the back with the smaller gears you don't plan to use. Obviously you don't want to shift past the hump you've now created, but it won't necessarily ruin your ride if you do.

Balmorhea   10 mW

10 mW
Posts: 24
Joined: Oct 01 2019 8:30pm

Re: Cassette chainline rework

Post by Balmorhea » Oct 08 2019 1:48pm

Any inexpensive cassette that doesn't have a spider for the large sprockets can be reshuffled to put the larger sprockets closer to the outside end. You might have to grind or drill the heads off of some rivets to separate the sprockets. Use the derailleur's limit screws to keep it from shifting past the biggest sprocket.

For the outermost sprocket position, you can do one of three things. You can use the 11-13t sprocket that came with the cassette originally. You can find and buy a special larger size sprocket (intended for Junior racing) and use that instead. Or you can substitute a metal spacer from a cassette, freewheel, or bottom bracket for the outer sprocket.

To make the derailleur work right, it may be necessary to use a Wolf Tooth RoadLink or similar hanger extender to keep the derailleur from crashing into the sprockets.

dirtgoon   10 µW

10 µW
Posts: 6
Joined: Oct 08 2019 9:31am

Re: Cassette chainline rework

Post by dirtgoon » Oct 08 2019 2:13pm

I already have a 10 speed shifter so preferable to get a 10 sp cassette. Problem is I can't find one that the two larger gears aren't riveted to a central spider. The only thing I've found is a 9 speed Sunrace CSM98 that all of the gears can be separated.
I'm riding mountainous terrain in Colorado, pedal assist only and no throttle so I'm thinking I will need the 36t large sprocket.
Would like to arrange the gearing something like this, 36-28-21-17, maybe 13 and stack the unused sprockets behind the 36. I currently ride this bike legs only with a 28t front ring and very rarely shift into anything smaller than 15t in the rear.

Balmorhea   10 mW

10 mW
Posts: 24
Joined: Oct 01 2019 8:30pm

Re: Cassette chainline rework

Post by Balmorhea » Oct 08 2019 2:31pm

If you take out the spacers from the 9sp cassette and substitute 2.2mm thick spacers, you can probably make it compatible with 10 speed shifters, at least across a half dozen gears.

Dura Ace 11 speed uses 2.18mm spacers, or you could stack a 1mm spacer with a Shimano 1.2mm spacer in between each sprocket. For 10-speed, each sprocket plus its spacer should be as close as possible to 3.95mm thick.

c.price   100 µW

100 µW
Posts: 7
Joined: Sep 21 2018 5:01pm

Re: Cassette chainline rework

Post by c.price » Oct 08 2019 11:48pm

Have you looked at the Shimano xtr m980 the 6 largest rings are riveted in pairs the rest are individuall.

User avatar
HolgiB   1 W

1 W
Posts: 50
Joined: Oct 02 2018 2:58am

Re: Cassette chainline rework

Post by HolgiB » Oct 09 2019 7:25am

@dirtgoon:
You might want to check out the webpage of electroncycles.uk:
https://www.electroncycles.co.uk/produc ... -90a-peak/

They give some nice informations on setting up a good chain line together with a BBSHD using a standard Shimano 10 speed cassette.

User avatar
fechter   100 GW

100 GW
Posts: 14173
Joined: Dec 31 2006 3:23pm
Location: California Bay Area, USA

Re: Cassette chainline rework

Post by fechter » Oct 09 2019 1:57pm

I'm running a 30t chain ring on my BBSHD fat bike and had the same issue. I spend a lot of time in the lowest gears climbing hills. I took apart the cassette and reconfigured the gears:
Cassette Edited.jpg
Cassette Edited.jpg (113.63 KiB) Viewed 128 times
Now the lowest gear is where 4th used to be and the chain line is acceptable. I adjusted the stops on my derailleur so it doesn't go past the largest gear. On flat ground, I find my top speed is the same in the top 3 gears as it is power limited. The downside is you can't pedal fast enough for human input above about 15mph.

Taking apart the gear cluster required drilling out some rivets and the two largest gears were riveted in a way that I didn't want to disturb, so they stayed together.
"One test is worth a thousand opinions"

dirtgoon   10 µW

10 µW
Posts: 6
Joined: Oct 08 2019 9:31am

Re: Cassette chainline rework

Post by dirtgoon » Oct 09 2019 2:56pm

I found a 10 speed XT (I think) cassette in my spares bin that I can mod to suit my needs pretty easily. Found quite a selection of cassette spacers on eBay that should make for a tidy modification. Will post some pictures when I get it all set up. :thumb:

User avatar
fechter   100 GW

100 GW
Posts: 14173
Joined: Dec 31 2006 3:23pm
Location: California Bay Area, USA

Re: Cassette chainline rework

Post by fechter » Oct 09 2019 11:21pm

I think it's good to have a cog that's not used on the spoke side of the cluster just to catch the chain if it comes off the low gear. It's never happened to me, but a chain in the spokes generally produces a bad outcome.
"One test is worth a thousand opinions"

User avatar
amberwolf   100 GW

100 GW
Posts: 27538
Joined: Aug 17 2009 6:43am
Location: Phoenix, AZ, USA, Earth, Sol, Local Bubble, Orion Arm, Milky Way, Local Group
Contact:

Re: Cassette chainline rework

Post by amberwolf » Oct 09 2019 11:34pm

That's where those plastic deflectors inboard of the sprockets, usually clipped to teh spokes, can help; you'll know really quick when the chain comes off so it doens't have to survive very long, just long enough to stop moving the chain.

mystryda   1 W

1 W
Posts: 64
Joined: Jul 11 2017 10:39pm
Location: Northern VA (metro DC)

Re: Cassette chainline rework

Post by mystryda » Oct 12 2019 8:00pm

Balmorhea wrote:
Oct 08 2019 2:31pm
If you take out the spacers from the 9sp cassette and substitute 2.2mm thick spacers, you can probably make it compatible with 10 speed shifters, at least across a half dozen gears.

Dura Ace 11 speed uses 2.18mm spacers, or you could stack a 1mm spacer with a Shimano 1.2mm spacer in between each sprocket. For 10-speed, each sprocket plus its spacer should be as close as possible to 3.95mm thick.
He's right, assuming that...

The question nobody asked you (but was probably assumed): which 10-speed groupo are you using? If Shimano or SRAM then 3.95 is the pitch. If Campy, well, it's complicated...
https://www.sheldonbrown.com/cribsheet-spacing.html

With Shimano 9-speed space gears, the exact spacer needed to get to 3.95mm is 2.17mm. 2.2mm will work fine if you tune it for the center of the (gear 5). Using the Dura Ace 11 speed spacers is definitely the easiest approach. If you end up needing 0.1mm then you can cut them out of a Coke can; it's tedious but it works.

Post Reply