Rear Hub / Dropout spacing…..

[sevenfourate]

Tyres went on wheels today; and then slotted into frame / forks accordingly.

Front hub width to inside of fork dropouts is lovely and snug 👌

Rear has approx 2mm gap either side between cone nut and inside of dropouts as pictured. **I believe eternally common BMX rear spacing is 110mm. This frame is more like 114mm. Which would clearly indicate frame is a little wide…..

Just crank it up ? Or I do have some nice sized / thin Aluminium washers I could put on the inside to take up the slack. Just slightly ‘concerned it’s a very beefy / strong BMX frame; not a flexible Aluminium Road-bike frame. And will be under a little stress to get back to 110mm.

Thoughts ? Cheers in advance 🙏

 

[Ratchet Cat]

Hello. I have been following your bmx build with interest. What is the frame made of? If it’s only a small gap, I’d go with the spacers, as long as the wheel doesn’t move when you pedal.

My 80’s bmx bikes used to have adjusters on the dropouts to stop any movement of the back wheel. Hope this helps 😺

 

[sevenfourate]

Hello. I have been following your bmx build with interest. What is the frame made of? If it’s only a small gap, I’d go with the spacers, as long as the wheel doesn’t move when you pedal.

My 80’s bmx bikes used to have adjusters on the dropouts to stop any movement of the back wheel. Hope this helps 😺

Hi ! 👋

Frame is 4130 CroMoly Steel. Supposedly the lightest / strongest seamless tubing available. Much sought after when building / buying a bike to this day by serious BMX’ers.

I have / may fit chain adjusters as yet - if nothing else it makes chain tension and alignment simple. Of course they are used to mainly control fore and aft movement. I’m looking to understand if it’s ok to pull in laterally as such (Because of short chain stays, strong material etc - it will require more cranking on the axle nuts than a road bike - if the same gap appeared - imo).

I’m not sure it matters either way regarding cranking up or fitting washers. I’d just be really interested to hear any other opinions……😁

 

[si_c]

I’m not sure it matters either way regarding cranking up or fitting washers. I’d just be really interested to hear any other opinions……😁

I would probably see where the wheel sits between the drop outs - a 2mm washer either side isn't much so would be my choice. The risk with just cranking it up is that you get a wheel which isn't centred properly.

 

[All uphill]

As above I'd prioritize wheel centring and chain line using washers.

If you decide to tighten the nuts until the frame and hub match that would probably be OK too. I've cold set a good few frames, and realigned lots of derailleur hangers on steel frames without problem in the past. I'd be much more wary if the frame was aluminum alloy.

 

[sevenfourate]

As above I'd prioritize wheel centring and chain line using washers.

If you decide to tighten the nuts until the frame and hub match that would probably be OK too. I've cold set a good few frames, and realigned lots of derailleur hangers on steel frames without problem in the past. I'd be much more wary if the frame was aluminum alloy.

Chain-line is marginal !

I’ve got one thin spacer I think I can get away with removing on drive side of crank - as that needs to come closer to BB ideally to get a good chain-line.

And putting an Aluminium washer inside at hub end to make the above better - would then make chain-line worse again. *The rear sprocket needs to be closer to the dropout. Not further away…..

So - to prioritise chain-line: ignore putting Hub washer in and just ‘crank’ the axle nuts up as-is ?

 

[figbat]

Try with washer(s), see how it looks/goes/measures. If off, remove washer(s) and try again.

 

[si_c]

Chain-line is marginal !

I’ve got one thin spacer I think I can get away with removing on drive side of crank - as that needs to come closer to BB ideally to get a good chain-line.

And putting an Aluminium washer inside at hub end to make the above better - would then make chain-line worse again. *The rear sprocket needs to be closer to the dropout. Not further away…..

So - to prioritise chain-line: ignore putting Hub washer in and just ‘crank’ the axle nuts up as-is ?

I wouldn't worry about chainline, I'd first make sure that the wheel is centred in the frame. Using washers inside the dropouts to centre the wheel shouldn't impact chainline significantly, if at all. If the chainline is problematic then I would expect that it's likely that and adjustment to the position of the cranks is needed (BB axle length for example).

If you think about it, if the wheel is centered properly then the hub should be in the right position and so the chainline at the rear should be correct.

 

[raleighnut]

I'd use 'chain tugs' that sit on both sides of the axle,must be about 2mm thick.

 

[sevenfourate]

Thanks Gentlemen 😉

In the end; and in order to firstly get cranks / spacing / chain alignment set - I did the axle up without spacers when in the middle of the drop-outs.

It did up no problem and drop-outs / rear stays pulled in the few mm I needed easily.

Chain-line looks good. And freewheeling / pedalling backwards the drivetrain sounds good……..

 

[Ratchet Cat]

Looking good. When’s the test ride?

 

[sevenfourate]

Looking good. When’s the test ride?

Thanks very much 🙏

I’m on vacation tomorrow. So unless the Gyro cabling fairy turns up and works through the night…….

…..it’s going to be once I’m back. When in truth I’m them taking to my LBS for brakes / Gyro to be done. While I watch and learn 😉