Hi, just wondering if it's advisable or not to try stretch this from 120 to 135 so I can put a rear motor on.

If it's steel there should be no problem. Go vary carefully if it is aluminium.

If it's steel there should be no problem. Go vary carefully if it is aluminium.

I'm not sure what it is, I assume steel, it's this, as you can tell I'm not very clued up on this . It's one of these, no idea of model or make though

Probably steel. Hold a magnet to the frame; it it reacts its steel, if not aluminium.

Steel is easy. Aluminium is a bit harder, especially on frames for 20" wheels, but still can be done. Two planks of wood shoved in and pulled apart normally does the job. You have to go about twice as far as you need, then let it spring back.

The way I do it. First test with a magnet to be sure it is a steel frame. I use a threaded rod, some wooden blocks, two washers and two screws. The rod goes through the blocks and the dropouts. There is some spring back, to get a permanent 135mm from 126mm I had to stretch to 170mm. Could be a good idea to add a clamp at the brake bridge on top of the seatstays .

After stretching I check for the symmetry with a string : tie it to one dropout go around the headtube and back to the second dropout.The distance between the string and the seat tube should be the same on both

sides.

The distance between the string and the seat tube should be the same on both

sides.

Wouldn't you want some off-set for the gears, to save having to dish the wheel?

Wouldn't you want some off-set for the gears, to save having to dish the wheel?

Yes, you are right, but being unable to lace or redish a wheel I stay on the safe side and try to keep the frame as symmetrical as possible.

Everybody probably already know this link :

https://www.sheldonbrown.com/frame-spacing.html

Yes, you are right, but being unable to lace or redish a wheel I stay on the safe side and try to keep the frame as symmetrical as possible.

Everybody probably already know this link :

https://www.sheldonbrown.com/frame-spacing.html

Thanks for the Interesting link I'd not seen that before. I've had easy success dishing wheels by just slackening spokes on one side and tightening them by the same amount of turns on the other side.

Dave.

If it's steel there should be no problem. Go vary carefully if it is aluminium.

Actually simply don't do it to an aluminium frame, unless you are prepared to risk having it fail immediately or shortly after.

Actually simply don't do it to an aluminium frame, unless you are prepared to risk having it fail immediately or shortly after.

Just to emphasise this. Aluminium frames must never be bent, ever. They will fracture catastrophically, more than likely when you are riding.

Just to emphasise this. Aluminium frames must never be bent, ever. They will fracture catastrophically, more than likely when you are riding.

 

How I change tubes and tyres, even a Marathon Plus once!

 

 

And here reshaping an aluminium rear frame to substantially widen the dropouts while keeping them parallel:

 

 

Agreed it does take care and one needs to know what one is doing and have the required sensitivity, but having done it successfully a few times it is definitely possible.

.

Yes on reflection what I should have said.

Just to emphasise this. Aluminium frames must never be bent, ever. They will fracture catastrophically, more than likely when you are riding.

How I change tubes and tyres, even a Marathon Plus once!

 

[ATTACH=full]32421[/ATTACH]

 

And here reshaping an aluminium rear frame to substantially widen the dropouts while keeping them parallel:

 

[ATTACH=full]32422[/ATTACH]

 

Agreed it does take care and one needs to know what one is doing and have the required sensitivity, but having done it successfully a few times it is definitely possible.

.

You have got away with it, so far... but aluminium will suffer micro stress cracks when bent, then stress corrosion can eat into them propagating further cracking, the process can take time but then one day it will fail suddenly. Steel can take much more bending and even when it does fail it does it slowly, the cracking happens gradually and you get warning through the feel of the frame being 'not right', creaking etc. plus the obvious open crack.

 

EDIT: and as for your wheel removal technique- why on earth are you doing this, wheels should drop out of the dropouts- clue is in the name! BTW I am a trained and qualified cycle mechanic.

Edited October 11, 20196 yr by niggle

We have solid evidence from many of us who have done this successfully and have used the bike for several years afterwards without problems, some have done it more than once.

We haven't heard from anyone who's damaged the frame in attempting to do it.

In a perfect world we perhaps shouldn't bend aluminium but I'm quite happy to do so with care.

 

Dave.

You have got away with it, so far... but aluminium will suffer micro stress cracks when bent, then stress corrosion can eat into them propagating further cracking, the process can take time but then one day it will fail suddenly. Steel can take much more bending and even when it does fail it does it slowly, the cracking happens gradually and you get warning through the feel of the frame being 'not right', creaking etc. plus the obvious open crack.

 

EDIT: and as for your wheel removal technique- why on earth are you doing this, wheels should drop out of the dropouts- clue is in the name! BTW I am a trained and qualified cycle mechanic.

 

Lecturing the wrong person, I first joined the trade in 1950!

 

Re: your edit, it's not a wheel removal technique, it's a way of simply and quickly changing a tube or even tyre.

 

As for your micro-cracking, those bikes in the two photos are still in use far beyond a decade later, the top one from 2003 and the lower one from 2006. There are no micro cracks since , as said, I do know what I'm doing. When I widened one 20" wheel frame it wasn't going to be possible just by distortion so I separated two frame joins and re-welded them afterwards.

.

Actually simply don't do it to an aluminium frame, unless you are prepared to risk having it fail immediately or shortly after.

Did you ever stretch an aluminium frame? I've done loads! I call what you wrote theoretical ball cox!

Sorry it's an old thread but, what happens on aluminium dropouts if you prize apart the dropouts on a 135mm and put (for example) something like a 148mm hub in there?

 

I mean without opening it to 170mm and letting it spring back, just putting the wider hub straight in?

 

The only reason is to tighten the NDS spokes more. My DS spokes are as tight as I dare take them, while the NDS are still too loose, while I have the smallest possible gap between dropout and cassette lockring on the DS, while I have about 5mm of spacers on the NDS axle - it could do with 5mm more but I think the hub is already at about 143mm as it is, so it would be taken to 148mm which is 6.5mm wider each side than the 135mm the dropouts were originally.

 

I just thought adding spacers to the NDS to allow me to tighten the NDS spokes would be a good way to solve it.

By the grace of god, my dropouts are 137.2mm when nothing is in them. Adding 5mm of spacers isn't going to stress them much. Put it this way, I was riding around for at least 1,000 miles on a 135mm hub crammed into a 130.5mm dropout (that was meant to be 135mm I might add) and never had any problems.

 

Also, to negate setting the disc rotor in by 5mm with spacers (which means it's nowhere near lined up properly with the brake pads anymore), I am going to space the rotor itself out by 5mm (evening it all out) with a handful of these, bloody ingenious actually...

 

https://www.sjscycles.co.uk/brakes/100-mm-hope-6-bolt-hub-disc-spacer/

 

Bafang typically has 8mm disc rotor bolts, I'm adding 5mm so needed 13mm bolts but no such length exists, so I got a pack of 14mm and will put 1mm washers under the bolt heads. I cannot see why this won't fix it but I'll believe it when I see it!

 

Buying two 2mm and one 1mm means it can be spaced any way (1/2/3/4/5mm).

 

I will have tighter NDS spokes come hell or high water!

With disc rotors, one has no choice but to start on the DS and line up the rotor/caliper first and space accordingly so not to create issues. The NDS is then what it is and may or may not need spacing or stretching a little.

I will have tighter NDS spokes come hell or high water!

Putting lighter spokes on the NDS is also an option that I have tried and works well. The original 13g stainless steel spokes were too rigid for the lighter tension on the non drive side. I fitted cheap galvanized 14g on the nds side only which were far more flexible and bedded in nicely at the lower tension.

All my builds use 14g spokes, my first and only bought motor wheel I rebuilt with new spokes as I had issues with the build using 13g ones.

All my builds use 14g spokes

 

Ditto

.

When you add so much stretch to the rear dropouts, you might find that the rear wheel might need to be "dished". Spacers at the brake disk can make this even worse, so be prepared for geometry adjustments.

All you need to do is put M6 washers between the caliper and the frame to make it line up with the disc. When you spring the frame out, the disc mounting becomes a little bit out of line, so you might need some thin and thick washers and juggle them around until you get perfect alignment. I have a jar of M6 washers, and they're all different thicknesses, so no problem for me. Normally washer thickness doesn't matter, so have a look around and see what else uses them and swap some around to see if you can get the right thickness you need.