Basically, I’m struggling to work out the best way to do a little job.
Making a new frame for my daughter and want to use a single-sided swing arm with a rear disc and single speed freewheel.
I’m planning on using a front hub, in reverse, with the disc and freewheel on the same side.
My initial idea was to make a ‘carrier’ for the freewheel that is bolted onto the disc tabs (with the disc) and have a shaft that runs through the hub, bolted onto the swingarm, with a bolt on the free end of the hub.
This would, basically, really on the 2 bearings in the hub.
This is what I’m thinking:
Is there anything I could do better?
I need to be able to move the whole wheel to allow for chain adjustment as I’d like to be able to do that without tensioners ets.
I’m at work so can’t spend much time on this, but couple of points-
How old is your daughter/how large is the load?
The force from the hub is now cantilevered instead of being simply supported at both ends – the axle has to be much harder. An old 20 mm though hub might be up to is with a steel axle. The clevis for the axle to fit in to would have to be quite wide to carry the moment from the axle. How wide is the mount for a Lefty?
The disc would be susceptible to contamination from oil on the chain.
You want a simple sliding/swinging dropout – there’s loads of these around to copy take inspiration from.
It seems generally accepted that the drive cog and and wheel itself should be split across each side of the swing arm. That way, under drive, the pull of the chain on one side, is balanced by the resisting grip force of the tyre – making the net twisting of the axle on the swing arm much more balanced. So you diagram would read from left to the right
bolt – hub – disc – arm – freewheel – bolt
I’d also agree with the comment of an EBB. A sliding dropout is reducing your ability to stop cantilevering of the axle – it simply cant be supported all round if there is a cut out of the support. It also means you dont need to have sliding mounts for the brake caliper either.
As a separate issue I didn’t see mentioned in a skim-read through the above, be wary of having something oily right next to, or in the centre of a brake disc. You’re going to have to keep the chain very clean or provide some means of catching the tiny oil droplets flung out from that chain, or otherwise protecting the disc, to keep the pads from becoming contaminated very quickly.
As a separate issue I didn’t see mentioned in a skim-read through the above, be wary of having something oily right next to, or in the centre of a brake disc.
What about a left field idea, as someone else said I’d be concerned about grease/oil from the chain and freewheel contaminating the disc so with that in mind what about going belt drive which would also reduce the danger of any finger/spiky cog interaction.
Secondly instead of having the freewheel at the rear ,have a fixed cog/pulley at the back which should be easier to mount and figure out how to have a freewheel mounted on the chainset instead.
For a small child the gearing shouldn’t be too much of a issue.
Thanks for the responses, some useful things to thing about.
How old is your daughter/how large is the load?
She’s a slight 5yo, 16.5kg at the mo.
The disc would be susceptible to contamination from oil on the chain.
Indeed, hadn’t thought of that. Belt drive might be the way to go..
Forgot to ask, why not an ebb?
Will look into that.
like this
Yeah, that’s the sort of idea. Is there just a bolt going through the hub?
split the disc and freewheel either side of the swingarm
That could work. I was thinking of having the swingarm on the right side but could do left with brake left. Only issue could be the exposed drive on the right?
Have you actually done any calculations of force then? She might be slight, but if the parts are designed to be supported on both sides then you really should establish that the forces in this usage case are comparable.
Having the brake and the drive on opposite sides of the arm will help the forces, but one of them will be much more exposed to damage and possibly snagging fingers. If you put the drive on the hub and the brake outside, it would be easier to enclose/guard the brake somehow and have the drive protected inside the arm. The main problem with this is that the axle then has to rotate in the swing arm, rather than being rigidly fixed/pressed in place.
Could you used a fixed sprocket at the back, and move the disc brake to the cranks?! It would simplify your back end loads, but there are downsides to having a disc by your ankles. Not sure if you could apply a brake to the chainring, but have the cranks on a freewheel. I guess your daughter doesn’t want a fixie?
Giant did a folding bike a few years ago called the ‘Halfway’ that had monostays front and rear, might be worth tracking one down or doing some research on them.