Rat Bikes! Pub Bikes Beaters! Frankenbikes!

'Snow problem

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^ same

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23c tyres fun

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I think it's actually the other way round. You'd risk overtightening the left pedal if the bearings bind.

I see your 23c tyres and raise you 20c! Lunchtime 10 to Windsor and back.

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Is that a really long wooden saddle you have?

Your NDS pedal could possibly unscrew while riding.

Loctite!

@frankenbike

I also expect that even the most miniscule mismatch in gear ratios would eventually lead to the wheel locking up

Chains have links and you don't suddenly get 1/64 a link less or something, meaning your ratio will always be exactly the same. Even when your chain stretches.

Right. But if they're both fixed, a slight mismatch in cog diameters or chain link length might mean that one chain might moves through 18.01 inches of chain whilst the other moves through 18.02 inches (per wheel revolution). Since the cranks are also fixed together I think you'd gradually accumulate slack on one side of one chain until it falls off or the wheel locks up.

This is just guesswork base on my intuition, I haven't done any calculations.

No, it's not the cog diameter or chainlink length that determines the wheel speed.

If you have a 40t chainring and a 20t cog a full revolution of your crank would move the chain 40 links. Those 40 links turn the 20t cog 2 full revolutions, which turns the wheel 2 full revolutions.

You can easily see there is no diameter or link length in this equation, they really don't matter.

Hmm. My brain disagrees but I can't articulate why - I'm sure you know the feeling as an engineer. I need to see one working I think.

I mean what about the case of two 18t cogs with a 50t chainring on one side and 51t on the other? That's surely going to break, right?

I mean what about the case of two 18t cogs with a 50t chainring on one side and 51t on the other? That's surely going to break, right?

Exactly, no matter what's the link length. Chains are somewhat free to move on a cog or chainring taking up slack.

Chains are somewhat free to move on a cog or chainring taking up slack.

But what if on the chainring the pins are pressed against the leading tooth and on the cog the pins are pressed against the trailing tooth, and vice-versa on the other chain? So the top side is taut on one and the bottom taut on the other? There's slack, but nowhere for it to go without the cogs or chainrings rotating relative to their opposites on the other chain.

Well first of all, you need to replace your stuff. They are badly worn.

But you would be able to turn your crank and as a result your wheel, just when your pedalling all the forces will be on the chain where the top side it taut and when you're braking all the forces will be on the chain where the bottom side is taut.

But you would be able to turn your crank and as a result your wheel

Right, but if we assume that every revolution of the cranks increases the tension and slack on the taut/slack bits of the chain - just go with it for the sake of the argument - then eventually they'll be too taut to move and one chain will pop off or slip back a link or break. Yes?

Obviously the key bit is whether or not rotating the cranks increases the tension/slack on the chains though.

Obviously the key bit is whether or not rotating the cranks increases the tension/slack on the chains though.

Turning the crank never increases tension, you're still moving the same amount of links. Have you ever turned the cranks on your track bike and seen the bottom of the chain tension up?

I'm not continuing this discussion since it has nothing to do with Rat Bikes anymore.

Right, normally it doesn't. But in this case we've got two drivetrains that are fixed together at the hub and the cranks, each with a chain connecting the chainring to the sprocket. It's a closed loop, there's nowhere in the system for the slack to be taken up or tension to be relieved.

Magnets

haha!!! this is awesome

thats great patina. whats the make of the frame and the finish?

Ah it’s just an old Langdale lightweights track frame 531c. Originally a light blue but the paint has fallen off and it got spray painted one time...

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Fellow rumrunner! First time I’ve spotted one on the forum.

Nice bikes just not well stocked in the UK.

Yo! It has served me well over the years, got it from Goldsprint in Berlin while I was there. Think I’ve only seen one other while out and about in London, possibly with neon yellow forks...?