Chain tube position

[deejayen]

My LWB Peer Gynt bike has a power-side chain tube which is suspended from a short keychain which is secured to a small post on the frame. I'm not really sure how long to make the suspending chain. The bike has a triple chainring and a wide-ratio cassette. Is there a certain cog/chainring combination which is used to set the drop of the 'floating' chain tube?

At the minute the chain tube is roughly horizontal when the chain is running between the 2nd largest cog and the middle chainring. I suspect that if I were to run the bike in the small cog then the chain would deflect upwards to where it enters the chain tube. Perhaps it would be better to drop the chain tube by extending the suspending keychain... I imagine there's a scientific method to set this, but it's beyond me!

[[XAP]Bob]

Worth a photo?
Sounds like the chain tube is effectively free floating, which is useful with a chain that moves…

[KM2]

Do you need a chain tube to keep the oil off your calf muscle? You could use a cover made from sheet plastic to protect your leg. Tubes not required.

Doesn’t have to be enormous.

[deejayen]

Thanks!

Yes, my explanation wasn't great! I'll struggle to get a photograph, though.

Edit: Thanks also to KM2! The bike came with the chain tube, so I thought it might benefit from it - maybe stop the chain from slapping against the frame etc. I don't think I need it to keep oii off my leg.

[hercule]

From the dim recesses of my memory (I seriously thought about buying one in the early 90s) they came with a fabric protector as per KM2’s photo originally. I have a similar design of bike (an Easy Racer copy) and it doesn’t need any chain protection or support, apart from an idler on the return side.

[a.twiddler]

No chain tubes, idlers rollers, or anything. Just a simple short aluminium guard fixed to the frame behind the chainwheel. The chain is the correct length, big/big + 2 links, looks a bit saggy, but doesn't flap about or touch the frame, and works fine.

But if you must have them, it's better that they're straight.

It's the wrong side, but they're clearly outlined.

[[XAP]Bob]

Do you need a chain tube to keep the oil off your calf muscle? You could use a cover made from sheet plastic to protect your leg. Tubes not required.IMG_1334.jpeg

Doesn’t have to be enormous.

That's quite neat - I wonder if I can make something similar for my velo.
What material have you used?

[KM2]

It’s original, some type of strong reinforced plastic . It works.
Chaintubes always rub, but probably better in a velo because the water spray can’t get away so easily.

[[XAP]Bob]

I wonder if an additional really thin CF guard would work well... There are two CF guards which deal with the chain behind the seat, but nothing up front. A vertical section which folds over and meets the frame could be quite nice, though also has the potential to be *very* loud.

[KM2]

I would have thought that the chains would maintain their line until the seat area, pulleys?? Perhaps you could make an elongated J structure out of plastic sheet rising from the floor and curving over to the central boom. If you’re getting marks from the chain.

[[XAP]Bob]

That was my thinking, but CF is more in keeping with the machine... I might do some CAD later (Cardboard Aided Design)

The chain is generally very well controlled, though the return side can get displaced from the idler pulley under the seat (which is annoying, because that means getting out and removing the seat).

The section forward of that does result in some chain marking which means I can't wear normal trousers (not very often I want/need to), but not all that much. It's really not a huge issue, but could be quite nice.