Re-spacing the rear axle

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531colin
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Re: Re-spacing the rear axle

Post by 531colin »

Anglian wrote: ..................if there's enough clearance after removing 2.5mm (or 2mm, since I'm proposing swapping the 14mm spacer on the drive side for the 12mm one from the idle side) of spacing, then (approximately) symmetrical removal of spacing seems to be a technique which involes less work and adjustment (no re-dishing, minimal derailer adjustment).................


Yes. Provided the chain in top gear clears the dropout, you can remove 2, 2.5, or 3mm of spacers from either or both sides. It doesn't matter at all if you remove 4, 5, or 6mm of spacers in total, or which side you remove 3mm and which side 2mm....its not that critical.
My "counsel of perfection" would be to get the block as close as practical to the dropout and reduce wheel dish....but perfection is not for a hack bike!
reohn2
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Re: Re-spacing the rear axle

Post by reohn2 »

georgew wrote:
breakwellmz wrote:In the time since my last post,i`ve gone out to the shed,found a bit of timber and widened the back end of a frame i use as a wheel jig.

It really is that easy! :D


OK. And has each drop-out been moved out by exactly the same amount?

If not then the wheel will not be equidistant in the drop-outs. When cold-setting a frame it's important that the frame is then checked for trueness.

Spreading the dropouts as per my first post can result in at most 5mm off centre,that's if only one dropout moves.
Whats the chances?
Statiscally 50/50,practically there's a good chance it'll be OK and after all it's a hack!
BTW I've seen "quality" frames out by 5mm when checked and no one was the wiser,until it was checked that is.
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"All we are not stares back at what we are"
W H Auden
reohn2
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Re: Re-spacing the rear axle

Post by reohn2 »

Anglian wrote:
reohn2 wrote:B&Q or hardware shops have a good selection of washers.Replace the 12mm on the none driveside with the appropriate number of washers to give 130mm spacing.Alternatively cut or grind 5mm off the 12mm spacer on the none driveside.
You may need to redish the wheel which is easily done with the wheel in the frame by slacking off the spokes on one side and tightening the other in half turn increments until the wheel is central in the frame.


Hello reohn2,

Thanks, that was quite a thought-provoking reply.

Currently, the 5mm-too-wide wheel is pushing out the rear triangles, presumably by approximately the same displacement each side (since they're roughtly the same strength). If the wheel is centred in the frame in this situation, then removing 2.5mm of spacing from each side (down to 130mm) would mean it should still be centred.

However, you're suggesting removing 5mm from one side only, which presumably moves the centre of the hub about 2.5mm away from its previous position, closer to the non-drive side dropout, meaning the wheel needs to be re-dished, so that the rim is moved away from the non-drive side to compensate for the shift in the hub's position. The sprockets, on the drive side of the wheel, will now also be displaced towards the non-drive side, meaning that the chain-line changes slightly.

I'm inferring (and perhaps I'm wrong) that you're suggesting this approach because you want to maintain the distance between the sprockets and the drive-side drop-out. I can see that it's important to have enough clearance here, but if there's enough clearance after removing 2.5mm (or 2mm, since I'm proposing swapping the 14mm spacer on the drive side for the 12mm one from the idle side) of spacing, then (approximately) symmetrical removal of spacing seems to be a technique which involes less work and adjustment (no re-dishing, minimal derailer adjustment).

Did I overlook something about your assymmetrical spacing-change proposal?

I did exactly as I advised on a bike of mine not long ago.
135mm MTB 7sp hub,130mm Alu frame.I removed a 5mm spacer from the none drive/lefthand side of the hub spindle/axle and was willing to redish the wheel.
Put the wheel in the frame and found a needn't have worried too much as it only 2mm offcentre to get it dead centre it needed about a two turns of the spoke key for each spoke(driveside slackening,the other side tightening) the rim remained within 1mm of truth.
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"All we are not stares back at what we are"
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breakwellmz
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Re: Re-spacing the rear axle

Post by breakwellmz »

Hi

It reminds me of dealing with design engineers when i worked in an engineering workshop,who would talk at length about the pros and cons of doing the simplest of tasks various ways,whilst us`hands on`technicians just got on and did it :lol:

Cheers
reohn2
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Re: Re-spacing the rear axle

Post by reohn2 »

Anglian wrote:
breakwellmz wrote:Surely it LESS faff to spread the frame,non?


Hello breakwellmz,

I don't think so.

Although I'm having to think about the consequences of respacing, and understand how various aspects of the bike's geometry will be affected, if it can be done this way, then I think it's not much work to unscrew the locknuts, replace the spacers with differently-sized ones, and refit the locknuts again. It just needs some appropriate wrenches.

The approach of cold-setting the bike frame to a wider spacing would require (if Sheldon Brown is to be believed) removing various bits of hardware from the bike frame (in particular the derailer), protecting the frame paintwork from scratching, then getting an appropriate lever, and applying force in a trial-and-error basis until the rear dropout distance is respaced (in a balanced way, same displacement on each side), then re-assembling. If I then needed to go back to the 130mm wheel which used to work on this frame, it would no longer fit.

The spacers seem to be on wheels so that the same hubs can be fitted to different frames, by changing them.

I appreciate that the situation for non-solid (that is, QR) axles is different, as meic pointed out above. in that case, axle length needs to be close to the dropout distance. However, for sold axles, and nutted wheels, it the OLD which counts, and the spacers offer an easy way to do that (presuming I can understand the geomterical consequences well enough).

Regards,
Anglian

If the frame is steel(please let us know)you're getting hung up over something that's not rocket science.
An 8mm threaded rod,with nuts on and big penny sized washers(all availlable at B&Q) on the insides of the dropouts,wind the nuts outward thus spreading the dropouts.
Wind it to 135mm and then slacken off the nuts and check how wide they've become.
Do it again but this time a little futher keep going through the process until the d/outs are 135mm with no pressure on them.
Put the wheel in,check if the rim is centred,I'd guess it's not more than 2or3mm out,if any.
You do not need to strip anything off the bike except removing the rear wheel and holding the bike up,say by hanging it over the washing line with the saddle.
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"All we are not stares back at what we are"
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reohn2
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Re: Re-spacing the rear axle

Post by reohn2 »

Ayesha wrote:The important distance is the inside face of the dropout to the shoulder where the freewheel or cassette closes up to on the hub. It should be such so a factory built replacement wheel with the same freewheel or cassette fits straight in and the rear mechanism does not need adjusting.......

The OP already has the correct distance on the driveside,if he does either of the two things I advise in my first post,he'll lead an uncomplicated and happy life henceforth.

Why does anyone want to make uncomplicated things so complex :? .
There's a simple problem.
There's a simple solution!!!!!!!!!!!
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531colin
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Re: Re-spacing the rear axle

Post by 531colin »

reohn2 wrote:.................
The OP already has the correct distance on the driveside,................


Well, I'm not sure he does......won't a modern 135mm screw-on hub be spaced for a 7 speed....even 8 speed?
OP has 6 speed.
But it doesn't matter a hoot, as I don't expect the OP will cycle from Cambridgeshire to Wales to borrow one of Meic's spare wheels... :D
(and even if he does, it means 5 minutes setting up the gears.)

I think the job is to get the bike going with the minimum of fuss....OP says he can lose a few mm. off each side and get chain clearance from the dropout, so thats what I would do.
reohn2
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Re: Re-spacing the rear axle

Post by reohn2 »

531colin wrote:
reohn2 wrote:.................
The OP already has the correct distance on the driveside,................


Well, I'm not sure he does......won't a modern 135mm screw-on hub be spaced for a 7 speed....even 8 speed?
OP has 6 speed.
But it doesn't matter a hoot, as I don't expect the OP will cycle from Cambridgeshire to Wales to borrow one of Meic's spare wheels... :D
(and even if he does, it means 5 minutes setting up the gears.)

I think the job is to get the bike going with the minimum of fuss....OP says he can lose a few mm. off each side and get chain clearance from the dropout, so thats what I would do.

If he takes the spacer(12mm) off the non driveside and replaces it with 7mm of spacer(washers?) all will be well with the world,albeit that the wheel will be slightly off centre, with a spoke key and very little science,the wheel could be redished.
the whole operation would take 1 hour max,if you don't count shopping for the washers :)
If he has a grinder he could grind the 7mm off the existing spacer to save shopping time :wink:
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Brucey
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Re: Re-spacing the rear axle

Post by Brucey »

reohn2 wrote: Spreading the dropouts as per my first post can result in at most 5mm off centre,that's if only one dropout moves.
Whats the chances?
Statiscally 50/50,practically there's a good chance it'll be OK and after all it's a hack!
BTW I've seen "quality" frames out by 5mm when checked and no one was the wiser,until it was checked that is.


actually the maximum error in wheel centre position is 2.5mm, (if only one dropout moves), i.e. stuff-all.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
reohn2
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Re: Re-spacing the rear axle

Post by reohn2 »

Brucey wrote:actually the maximum error in wheel centre position is 2.5mm, (if only one dropout moves), i.e. stuff-all.

cheers

:idea: Correct! :)
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crimble
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Re: Re-spacing the rear axle

Post by crimble »

I confess I haven't trawled through all the replies, but I have had similar experience recently. Some points to consider.
1. Maintain the centre line of the wheel wrt to the bike frame, this will maintain chain line. So any change in dimension on the drive side has to be equal to that on the other.
2. make sure any adjustments don't move the sprockets into contact with the frame or force the chain against the frame.
The hub I had used fat locknuts [7 or 8mm] I replaced these with thinner ones [ 4-5 mm] from a local engineering suppliers, this gave me the clearance I needed.
nez
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Joined: 19 Jun 2008, 12:11am

Re: Re-spacing the rear axle

Post by nez »

531colin wrote:
Anglian wrote: ..................if there's enough clearance after removing 2.5mm (or 2mm, since I'm proposing swapping the 14mm spacer on the drive side for the 12mm one from the idle side) of spacing, then (approximately) symmetrical removal of spacing seems to be a technique which involes less work and adjustment (no re-dishing, minimal derailer adjustment).................


Yes. Provided the chain in top gear clears the dropout, you can remove 2, 2.5, or 3mm of spacers from either or both sides. It doesn't matter at all if you remove 4, 5, or 6mm of spacers in total, or which side you remove 3mm and which side 2mm....its not that critical.
My "counsel of perfection" would be to get the block as close as practical to the dropout and reduce wheel dish....but perfection is not for a hack bike!

Hi Colin,
This implies the wheel wouldn't 'track'. Can I ask in a non loaded way, given your experience, i wonder what offset you reckon is significant? It's not something you find in bike books, but must at some point make a difference to the handling.
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531colin
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Re: Re-spacing the rear axle

Post by 531colin »

Taking 2mm off one side and 3mm off the other will theoretically offset the wheel 0.5mm....except stuff isn't made to that sort of tolerance.
You can put a "normal" back wheel in an Orbit frame with 4mm offset back end and not feel a difference riding no hands.
4mm error in a front fork is noticeable riding no hands, but not (to me) with hands on the bars.
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breakwellmz
Posts: 1982
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Re: Re-spacing the rear axle

Post by breakwellmz »

"I then built a shopper in answer to a request from Jim McGurn who, at the time, was editor of ‘New Cyclist' magazine. He actually only wanted me to write an article on city bikes, but I was not in writing mood. And so ‘Amsterdam' was built, brazed from largish steel tubes and with the most offset rear wheel yet – 60mm. This you could notice when you first rode it, but after 10 minutes or so it was just like a bicycle"

Guess who?
Brucey
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Re: Re-spacing the rear axle

Post by Brucey »

I agree with Colin; a small error in wheel offset isn't noticeable by most people, most of the time. I've seen so many bikes set up with moderate tracking faults; the riders are in most cases quite oblivious to them. If they try at all, they assume that the bike doesn't ride well no-hands for some other reason. I also see very badly out of track bikes -where the front wheel doesn't even follow the back wheel any more- being ridden by casual cyclists, and they seemingly don't care either.

Quite a lot of mass-produced (and some handbuilt) frames are out of track on the day they are made, or get that way through use/abuse. Oddly enough one of the bikes I own with really good tracking is one that had been in a prang, that I took extra care over to see that it came back exactly right.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
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