Thinking of converting rear drive to an XRF-8 advice please

[shouldbeinbed]

on my 18 inch wheel Birdy, the dualdrive (3*8) hub has bitten the dust, it
A) costs silly money to replace
B) gave me far more gear options than I actually need for this country.

Its a 12 year old bike that owes me nothing and I'm thinking of a conversion to as simple and clean a likes as possible rather than a like forlike fix or retiring it. So am thinking of going for the full hub route and quite like the look of the SturmeyXRF-8 with the 70mm drum brake option at the back.

A few of questions to help me decide if its viable to find the cash for it.

• What tooth cog is best for a 13 stone rider who happily pootles along at 15mph in moderately hilly Lancashire?
  My Alfine 8 standard cog (700x38 wheels) was either a 20 or 19T, I dropped it a couple of teeth and am still happily pulling up hill.
  
• Will a 70mm drum brake be sufficient to stop me as well as a good set of rim brakes?
  
• I'm thinking of doing the front hub too, to an x-fdd (70mm drum) or xl-fdd (90mm drum) at the same time. (only a couple of quid difference so cost isn't a consideration between the 2)
  Do I need to match the front and rear drum brakes to save me faceplanting if I grab a handful of both in an emergency?
  
• If I did go for the dyno-hub would I need to step the output down at all to account for the faster rotation of the little wheels? or is here a small wheel specific front hub that I could consider?

thanks in advance

 

[TheDoctor]

That hub looks good for small wheels - first gear is 1:1 and it gears up from there.
I personally would pick the sprocket and chainwheel to give a low gear of around 30 inches, which will give a top gear of around 100".
Assuming you're using your current chainwheel, that's a sprocket with half the number of teeth or so.
On the brake front, a rim brake and hub brake should be plenty good enough. No need to match the front and back, unless you really want to.

 

[shouldbeinbed]

Thanks.

The current chainwheel is relatively huge to accommodate the smallness of the wheels I'll count the teeth when I get the bike back tomorrow and have to do a bit of maths to figure what it equtes to in normal wheel sizing.

I'm keen on drum brakes front and rear just for the aesthetics as much as anything, I have a bit of a foible for things matching - front rim and read drum or vice verca would annoy my picky sensibilities.

 

[TheDoctor]

The largest Sturmey rear sprocket is 25T IIRC.
I'd be looking around a 40-oddT chainring myself. My Brommie (6 speed with the BWR wide-range hub) has gears from 33" to 99" IIRC, and I've never needed one higher than that.
37mph on little wheels is...interesting.

 

[StuAff]

DualDrives are indeed silly money in this country (glad I had the one that broke on me sorted under warranty). Much cheaper in Germany (€120 instead of £250....)
http://www.tretwerk.net/Markenshop/...html?utm_source=googlebase&utm_medium=organic

Apologies if this muddies the waters a bit, but that little box of bits you're talking about isn't going to be cheap so bears careful thought. Shutter Precision & Schmidt (among others, if memory serves) both do dynohubs for 20" and other small wheels, arallsopp has a SON on his velomobile (and you aren't likely to be reaching his speeds....). Schmidt actually do a SON XS with 100mm hub for Birdys (etc).

 

[GrumpyGregry]

I run an XRF-8 on Rhubarb the Brompton. Two things to note...

The further you get from 1st gear the more inefficient the hub becomes, and you can feel it in your legs.
The gearing is weird. Basically six gears 2 - 7 you use all the time. An overdrive 8th, which I've only used 'in anger' once, down a very long hill, and the resulting speed wobble at 40+mph on a B will remain fixed in my mind for a very long time, and 1st is only useful if you're really unfit or need to climb up walls and cliffs

 

[shouldbeinbed]

DualDrives are indeed silly money in this country (glad I had the one that broke on me sorted under warranty). Much cheaper in Germany (€120 instead of £250....)
http://www.tretwerk.net/Markenshop/...html?utm_source=googlebase&utm_medium=organic

Apologies if this muddies the waters a bit, but that little box of bits you're talking about isn't going to be cheap so bears careful thought. Shutter Precision & Schmidt (among others, if memory serves) both do dynohubs for 20" and other small wheels, arallsopp has a SON on his velomobile (and you aren't likely to be reaching his speeds....). Schmidt actually do a SON XS with 100mm hub for Birdys (etc).

thanks for the info, I'd rather have too much to consider than not enough - I'm hoping to budget £500 or so for the full project if I do it.

The bike is a 2001 model, it owes me nothing in terms of the initial outlay and riding it's had - TBH I'm amazed its taken this long to go wrong, the frame and hinges are still in superb condition and its just too much fun and a genuine all rounder that I can't begin to think of getting rid, so it's ripe for a major overhaul and conversion to give me another decade or so out of it. I think to replace it with a similar quality ride/fold combo would cost me more than I'm looking at spending on converting it.

 

[shouldbeinbed]

I run an XRF-8 on Rhubarb the Brompton. Two things to note...

The further you get from 1st gear the more inefficient the hub becomes, and you can feel it in your legs.
The gearing is weird. Basically six gears 2 - 7 you use all the time. An overdrive 8th, which I've only used 'in anger' once, down a very long hill, and the resulting speed wobble at 40+mph on a B will remain fixed in my mind for a very long time, and 1st is only useful if you're really unfit or need to climb up walls and cliffs

helpful, thanks. I've speed wobbled coming down off the Pennines once or twice and its a good cure for constipation.

The lowest gearing combos on the dualdrive are similar super granny's, I couldn't use 1*1 or 1*2 without the front wheel lifting & I barely touch 1st on my Alfine 8 big wheel bike for much the same reason.