Dynamo Hub Dilemma

[amasidlover]

That german PDF was very interesting; I've seen comparisons of the SON and Shimano hubs before, but not the SA or SRAM - The SA comes out very badly for resistance when switched off, but given that I don't switch my lights off that doesn't really bother me... However, the odd thing is they listed the SA X-FDD for €30 but I can't find it in the UK for much less than £70!

I'm going to get myself a rim guage and once the rim is close to worn I'll order another wheel and take the mallet to the old one; I can always reuse the hub if it survives! I can't really afford to be without it at the moment as I've given up the car...

 

[amasidlover]

Well, I bought the SA hub and built it into a wheel (my first!) and have fitted it, unfortunately as with everything I seem to do to my bike there has been a small snag... I have some very unusual 1" threaded carbon fibre forks which smooth out general road vibration very nicely, unfortunately they seem a totally inappropriate size and shape to fit the reaction arm clamp to. SA have assumed that you have a fairly narrow fork leg diameter that is tapers up to the fork crown rather less steeply.

I don't want to 'bodge' a fix as this is my front brake and because carbon fibre failures tend to be spectacular rather than gradual - I don't mind replacing the fork with a reasonably cheap 1" threaded fork, but have no idea what I'm looking for; I don't know how to make sure it will be the right form for the SA reaction arm to use and I also don't know whether I just buy a fork and cut the steerer tube to size (I've read that you can't do this).

Any guidance would be much appreciated!

 

[andrew_s]

Cheap 1" threaded fork from here

The steerer is quoted as being 240mm, with 130mm of thread.
The steerer has to be cut down to a length that fits the headset in use. You need to fit the forks with uncut steerer using the headset you intend to use, but omitting the top locknut, then mark the steerer for cutting so that the top would come just below the top of the locknut if fitted. It's usual to allow for a spacer between the threaded top race and the locknut, both to allow a little leeway for cutting errors, and to allow for the possibility of fitting a different headset with a slightly taller stack height when the first wears out. It's always possible to add an extra spacer or trim the steerer a bit more if it's too long, but if it's too short for the new headset, you need new forks.

I would look around at what 1" threaded headsets are available, and make some judgement as to future availability, with due regard to stack height.

I take it that an extra big hammer failed to get the stuck QR out?

 

[amasidlover]

Thanks - That looks like a plan! I found that fork, but had no idea if it would fit...

And unfortunately the extra big hammer only succeeded in slightly bending the QR without any sign of movement...

 

[andrew_s]

Step 1 is to measure your existing steerer, to make sure it's between 240mm and something like 140mm.
You need a minimum of about 30mm threads for the top race & locknut, and hand-cutting extra threads is hard enough that most bike shops don't like doing it.

 

[amasidlover]

Well, the new forks are on and a quick test ride has shown both dynamo and hub brake seem to work... Will see how I get on tomorrow on the first proper ride!