b1983

Hi,

I wondering if someone can explain what something means.

The backstory is I bought a fixed gear bike about 6 months ago and recently looked at the reviews for it from the site it was bought.

One of the reviewers said the below should be done to the stock bike...

"Flip the chain wheel so that it sits on the inside of the crank arm bolts (on the stock bike, it is opposite, so the chain is warped and under unnecessary torque). When you flip it, the chain will sit perfectly straight."

Can any explain way the reviewer means by this? Maybe explain it in different words

Cheers

J.Higgins 

Here ya go: https://www.sheldonbrown.com/chainline.html

b1983

Thanks but I think there are too many gaps in my knowledge to understand the information from that link.

What I hoping someone can tell me is something like you need to use tool 'x' to remove part 'y' then do 'xyz'

Once I get a bit hands on I think the sheldon brown info would make sense

easyupbug 

Probably dozens of videos on You Tube that will help, search:

How to Replace a Chainring

JohnDThompson 

It would help if we could actually see what you're dealing with.

I think what you're asking is how to optimize the chainline when using a road-type double crank for a single front ring. It is often enough to mount whatever ring you intend to use on the inner plateau of the crank arm rather than the outer plateau.

First, does your crank actually have a removable outer ring? Some low-end cranks have the outer ring permanently swaged onto the arm. If that's the case, game over. Run the chain on the inner ring and ignore the outer ring and live with what you have, or buy a different crank.

If the ring is removable, you'll need tools to fit the mounting bolts. Usually a 5mm Allen key for the front of the bolt and a special spanner to hold the back.



Remove the mounting bolts, then remove the rings from the crank arm. Mount the ring you intend to use on the inner plateau and secure with mounting bolts. You may need to use shorter mounting bolts or spacers.

b1983

I would need to find a video showing someone 'Installing a chain wheel so it sits on the inside of the crank arm bolts' as opposed to my current setup which guess is a chain wheel on the outside of the crank arm bolts

b1983

I have that tool and will post some pics once I have 10 posts

b1983

Here are some pics





I still don't know what 'Flip the chain wheel so that it sits on the inside of the crank arm bolts' means though. Maybe I need to take it apart to find out..

Jonneh

​​​​​​Undo the bolts using your tool and a 5 mm allen key, remove the ring, thread it back over the spider (fiver-armed thing) such that the indentations around the five holes sit on the inside (towards the frame), put the bolts back in the original orientation.

b1983

Thank you Jonneh,

I just gave it a go but could not get the bolts loose.. However I now totally understand what I'm trying to do.

I will try again

_ForceD_

What all the above are trying to explain is that the holes on the chainring, and on the crank spider are drilled so that the chainring nut and bolt are seated. You’ll need to flip the chainring over…so that the side that would normally be facing away from the bike is now in the inside, where the small chainring normally goes, but facing against the frame…so that the seat holes are facing the nuts/bolts properly.

Dan

jasoninohio

It's a shame it's not setup properly stock, because it doesn't look as nice with the chainring on the inside, but it also looks like he can't go any narrower with the bottom bracket... Oh well, happy riding!

CliffordK

Good point.

If the current chainring comes within 1mm to 3mm or so of the chainstay, you can't move it in any further. Ignore all the above.

It is possible to dimple the chainstay for more clearance without harming structural integrity, but that is another project.

If the chainline is a problem, I'd look back at the rearend.

alcjphil

Good point. What cannot be seen from the photos the OP sent is how close the chainring is to the chainstay. If the gap is too small, installing the chainring on the inside of the crank spider will result in the chainring rubbing the frame, not a good result

CliffordK

Another tradeoff is chainring size and rear sprocket size.

So if your current chainring is too close to the chainstay, you could get a smaller chainring, and move the sprocket in closer by either choosing a narrower bottom bracket, or moving the chainring to the inside of the crank spider.

If you can adjust both the chainring size and rear sprocket size, you may not impact gearing very much.

70sSanO

If the “new” bike is a fixed gear, the first thing to do is to eyeball the chain to the rear hub to see if it is perpendicular. If it is close, just ride it.

Can the rear cog be moved in or out to improve the chainline?

If you can add/remove a spacer, that is the way to go.

Sorry, but I don’t have any experience with a fixie.

John

_ForceD_

My thoughts too. But…wondering if the freewheel/cassette (or whatever he has back there) could accept a spacer so that the gear is just far enough to the RIGHT to accomplish alignment and thereby allow him to keep the chainring on the outside.

Dan

79pmooney

Finally someone asking the real question. I was wondering this morning when I saw this thread but I didn't have time to reply.

So, OP, stand behind your bike (elevated on a stand or kneel on the floor) and line your eye up with the chain. Does it run straight from the cog to the chainring or does it have to jog over because the chainring doesn't line up? (3mm or less is as good as dead on straight.)

Until you do this with your bike, not an "identical" bike you saw on a U-tube, you have no idea whether you are better off with the chainring inside or outside.

DonTx

Yep all this. You may not have a problem at all.

Litespud

below is the crank from my fixie. It's a standard double crank (Campag Daytona), but as you can see, the outer larger chainring has been removed, leaving only the smaller inner ring. The rings are detached from the crank arm by unscrewing the 5 allen-head screws, which screw into cylindrical nuts on the "inboard" side of the chainring. For a fixie, you want the chainring to be perfectly in line with the sprocket (ie, a straight chainline), for efficiency (a straight chain is a longer-lasting smoother chain) and safety (a straight chainline reduces the risk of the chain coming off either the sprocket or the chainring - something you absolutely don't want to happen on a fixie). For me, simply placing the chainring on the inside position of the crank arms gave me a very good chainline without any messing around - YMMV, in that you might find that the outboard position might be better, or you might need to play with things like spacers or altering BB spindle length to get a perfect chainline.
Bear in mind also that using a single chainring on a double crank will likely require new chainring screws/nuts - the original nuts are long enough to accommodate two rings and the crank arm, but will likely be too long for only a single ring and the crank arm. You can get a set of shorter "single stack" chainring screws/nuts from most bike shops

SoSmellyAir

Since your chain ring is solid, you have to remove both the right crank arm and spider as well as the chain ring.

With reference to the above photo, the chain ring is mounted in front of, i.e., closer to the viewer than, the spider.

Another option is to mount the chain ring behind, i.e., further from the viewer than, the spider.

SoSmellyAir

Sorry, you are right, I did not think of moving the inner edge of the chain ring between two spider arms to get the chain ring around the opposite spider arm.

70sSanO

To sum up the advice…

First check the chain angle from the chainring to the cog to see how straight it is running.

If it is not exactly how you want it, measure the distance from the current chainring to the chainstay at its closest point. Moving the chainring from the outer position to inner moves it 5mm closer to the chainstay. I would think you would want to have at least 8mm from your current ring setup to the chainstay so you end up with 3mm after moving the ring.

John

Jonneh

Oops! I deleted my post by accident while trying to edit it, and now you're quoting a non-existent post. Anyway, it's true that the solid ring has a narrower inner circle than a typical 38T chainring, but yeah, the triangles being deeper than the stepped extensions of the arm that the ring bolts to mean that the ring must pass! ;-)

70sSanO

Also, Race Face sells chainring tab shims to fill in the shoulder where the outer ring mounts. I haven’t used them, but I made my own tabs from a worn ring.

It does look better with them than without. But if you have 1x bolts with a double crank, you’ll need longer ones.

John