Emergency SS conversion - Possible on oval chainring

[hboli4]

Hallo Hubbers,

To all the tech-guru's out there. Is it possible to do an emergency ss conversion with a oval chainring on your mtb?

The bearing on my top jockey-wheel seized during an event over the weekend. I tried to make the bike ss just to try and make it to the CP where I could get some tech assistance. I shortened the chain and gave myself a sort-off middle gear with the chain lined up as close as possible with the chainring. After two pedal strokes the chain jumped to the next bigger cog on the cassette and tightened to the extent that I could not loosen the thru-axle and it sort of pulled/bent the chainstay that it touched my crankarm.

All I can think is that due to the oval chainring not being, well uhm round, the chain jumped when there was slack before being pulled tight again when it reached the 'fat' part of the chainring?

Hope this makes sense?

[Jewbacca]

So, in short, you can. BUT you have to set the chain tension with the oval chainring at a very specific position.

The 'longest' ends of the oval ring need to be vertical so the chain is long enough. It will go slightly 'slack' when not at that exact setting, but as it's a retainer ring in a straight line, you shouldn't drop your chain

 

[hboli4]

10 minutes ago, Jewbacca said:

So, in short, you can. BUT you have to set the chain tension with the oval chainring at a very specific position.

The 'longest' ends of the oval ring need to be vertical so the chain is long enough. It will go slightly 'slack' when not at that exact setting, but as it's a retainer ring in a straight line, you shouldn't drop your chain

 

Thanks Jewey,

I guess it is something I will need to practice and not try and attempt in haste. The sweep who picked me up mentioned that the cassette is machined to shift easily and this might be why it shifted/jumped up.

[Jewbacca]

5 minutes ago, hboli4 said:

Thanks Jewey,

I guess it is something I will need to practice and not try and attempt in haste. The sweep who picked me up mentioned that the cassette is machined to shift easily and this might be why it shifted/jumped up.

Yeah

If the chainline isn't straight it will catch the ramp teeth and try to shift up or down.

It's always tough in a race situation. I hope the frame isn't ruined but it seems less than ideal currently.

If you can understand my relatively poor description, the oval ring needs to be at it's longest/tallest perpendicular to the ground.

See below my old SS with an oval chain ring

[droo]

You also need to reconnect the chain with as much slack as you can and pedal a few strokes to allow the chain to find which gear it'll settle in before you shorten the chain.

The chainline and shifting ramps will decide this for you, and if you attempt to influence it the system may destroy itself.