Cycling UK Forum

Possibly mad idea of the day! .....

I have an On-one Inbred sliding dropout frame. With the standard sliding dropout I can vary the chainstay length from 425mm to 435mm. Both the V brake and disc brake fittings can accommodate this change.

The dropout looks like this;



In theory it looks like a revised shaped dropout could be made to extend the chainstay length to say 460mm, which would be better for carrying loads and pannier heel clearance. I would need to accept the limitation that I'd need to use a drum rear brake, rather than a disc or V.

Would it work in practise or would the forces involved no longer be in the 'right' places,

If it could work in practise would it be a step to far to shape the new dropout plates to give an additional 20mm of bottom bracket drop. To retain current geometry there I would also need to use a proportionally shorter fork.

Forgive me for being stupid, but surely simply moving the rear wheel won't help with pannier heel clearance? You need a way of moving the pannier rack, not just the wheel.

The pannier fixings can be adjusted, so whilst the rack stays in the same place the panniers can be moved forward or back on the rack. I can set the panniers further back on the rack to give more heel clearance, but doing so puts more of the weight behind the rear axle which isn't so good for stability.

Looks to me like a steel frame with slots in, and two M6 bolts each side which thread into the alloy sliding dropouts.
The wheel slots are currently between the two M6 bolts, you would want them behind both bolts.
Whereas it strikes me as being sub-optimal, if you think the original frame will put up with people doing drop-offs, your modification would probably survive.....unless, of course, you want to do drop-offs, when the shear on the back bolt and the forces on the dropout would be a bit of a worry.....I suppose your new dropouts could be steel, and you could go up to M8 bolts....do the new dropouts need to slide?.
But dropping the BB by 20mm will require raising the wheel a fair bit.....will it get past the seatstay bridge, assuming you have one?
If you raise the rear wheel by 20mm, you will slacken the head angle about a degree with the existing forks, which will give you more stability.

But why would you want to do any of this?....would you want to un-bolt the new dropouts, re-fit the old ones and use the bike in its current form?
Because if you don't want to do that, it might be more satisfactory to get a frame made, or an old steel MTB frame and forks modified by a frame builder.

IIRC those droputs have a raised portion that engages with a recess in the frame. This means that the shear loading is not borne by the bolts alone; they just hold the spigoted joint together.

If you remake dropouts to fit, I would consider it mandatory to make them with similar upstands on them. I also wouldn't see any harm in adding a third bolt, belt n'braces and all that...

cheers

Ah, yes, I see a recess on the "inside" of the dropout

Thanks Brucey and 531Colin,

There is a spigot which engages with the frame and no doubt that would mean that making new dropouts would be more difficult.

There are plenty of steel MTBs that could be suitable, but I'm not sure many have longer chainstays or lower BB. The correct answer to this is probably a Long Haul Trucker which already has 460mm chainstays and lower BB, or possibly a Thorn Sherpa (not sure of BB height on that).

But if I had the dosh for that I'd probably live with the limitations of the Inbred as utility bike and get something nicer for other riding

Probably cheaper to buy a Trucker than to have somebody put a new rear triangle on a MTB frame (and possibly) shorten the forks.
An engineering machine shop could machine you some dropouts, but I would be inclined to look hard at the steering geometry to check the likely effect of raising the rear wheel, and make a fairly careful mock-up to make sure the tyre will still clear the seatstay bridge.
If you raise the wheel 20mm, you will slacken the head angle roughly a degree....to drop the BB 20mm may not be possible without also shortening the forks, or sourcing other shorter forks.....I'm not sure its all worth it, with a back brake to work out as well.....

I wonder if you could do some backyard fabrication here?

I reckon you could most easily make new dropout plates from steel, and fabricate the necessary spigot by adding weld metal to build up and then grind back.

I have a hunch that if you position the axle about 20mm further back and 7-10mm higher up, you will be able to retain the use of your disc mounts. The consequent (small) BB drop won't hurt the steering too much, either.

cheers

Brucey wrote:..............I reckon you could most easily make new dropout plates from steel, and fabricate the necessary spigot by adding weld metal to build up and then grind back...................

Or silver solder a bit of thinner sheet steel in place? (maybe hold it with a self-tapper or two so the blowtorch doesn't blow it away....

Or use a bit of "T" shaped stock, cutting the shape on the back of the profile, and reducing the sticking out T bit for the locating spigot.

Thanks for the creative responses. I'll see if I can source a local metal worker.