Cycling UK Forum

I have been considering....for a while..... knocking up a town/shopping bike based around a 1990's steel mountain bike frame, using a SA FG converted to 5 speed with a drum brake instead of the dynamo......but I am not now sure this is a goer with 135mm drop outs..... so I may need to source another frame ?

The FG axle is 6 1/4" ( 158.75mm) the dropouts 6mm thick each. So this leaves just 11.75mm for the securing nuts !

The OLN is 120mm . I should be able to use anti-rotation washers on the inside of the dropouts and then add whatever spacers needed under the hub locknuts to make the 135mm.

( it'll be a 40h hub to 32h rim....dished.....so 2 lengths of spoke each side !...I think....which will be fun)

BUT less than 6mm of axle outside the dropout seems too little for the wheel nuts ??

So how much thread is enough?

Is cold setting an option ? or should I look for a narrower frame ?

Advice welcome.

( but note the FG conversion and hub brake part is just something I fancy doing for the fun of it ....and I will be using 2nd hand bits n pieces, not new, as far as possible)

I asked a similar question about using a threaded hub with only 6mm of axles protruding through the drop out. The consensus was it wouldn't be reliable and risked stripping the threads of the nut.
I recall from my apprenticeship that 90% of the load would be carried on 2 full threads of a fastening. Not sure the theory would stand up in practise miles from home on a rainy night.
Can you cold set the rear end to 126mm and use your anti turn washers internally thus leaving a full nuts worth of axle protruding.

You need 8mm for the axle nuts and 2mm for the anti-rotation washers - each side. Use a torque wrench with cleaned greased threads and 20Nm will usually be enough. The partially-threaded axles mean the nuts are easy to strip.

I run a 5 3/4" axle AM in nominal 120mm spacing but the frame has thin plate dropouts, not forged, and the hub is actually spaced to 118mm.

When I first read the original post I wondered whether the OP was going to be successful or not. To me it all seems a bit too marginal, but I suppose it’s easy enough to offer the hub up to the drop-outs and see if it’ll fit and (reliably) secure.

I used to think it the case but whether or not sufficiently long axles (for 135mm spacing) are available for the SA AW hub I’m no longer certain. It’s not what the OP wanted but I suspect that he would find an AW an asset; whilst they’ve just three gears and have a limited ratio range they still deliver great utility.

How much thread is needed on the SA nuts is a bit uncertain, but pretty much the same as would be supplied on a traditional installation is my best guess and anything less is pushing your luck - some will be lucky but others won’t and failures are rarely convenient. If the FG is going to be used then a narrower spaced frame would be my route.