Tech advice for Automatic hub upgrade of Brompton
 

So I have my Brompton S2L about a year and I love it. I have been thinking recently about going for the upgrade that I was reading about pre-purchase, namely an automatic hub.

Having read around a little, the hub I'm looking at is a Fichtel & Sachs Torpedo AUTOMATIC (A 2110) Blue Band - I've read hear that the OLD is better suited to the Brompton rear triangle. I am a little concerned that the Blue band is designed for a larger diameter wheel. Has anyone any experience with calibrating the spring for a 16" wheel? Also the one I'm looking at is a 36H model. I think I read here a while ago that 36 spokes are difficult to accommodate on such a small wheel. Has anyone any thoughts on this?

I've seen some commentary that coaster brakes aren't ideally suited to the fold but that a derailleur chain-tensioner such as the one on the S2L is the least-worst option.

Lastly, the model I'm looking at looks to be 18T. Are there any physicists out there who can tell me what the difference would be between a 12/16T rear cassette on the bike now and an 18T with 1:1 and 1:1.36 ratios would be in terms of performance. I'm pretty sure I have the standard sized front chainring (44T). I'm embarrassed to say I can't say for sure!

Any advice gratefully received.

Here is a gear calculator from Sheldon Brown.
http://sheldonbrown.com/gears/
Check out the 2 speed automatix from Sram.

Brompton with an Sram A2
http://www.bikeforums.net/showthread...n-a-Brompton-)

You may wish to check out my thread. I used one of the new 28h SRAM Automatix hubs.

Needs a few mods i.e. modify the change up speed and take off a locking nut/mill one down.

http://farm8.staticflickr.com/7107/7...5da520c5_z.jpg

You need a dished rear sprocket to get the chain line right. The smallest dished one you can get is 16T and with a 54T main, it will give you 56" and 76".

I modified mine to auto change up at 11 mph.

Regards

Jerry

Thanks Jerry

For the time being, the hub I'm looking at is an original Fichtel (sp?) & Sachs Torpedo Automatic 36H 'Blue band' which I think has a much more favourable OLD. It's a coaster brake model too so there's that to consider. I really need advice on changing the changeover speed of that to 16" wheels. I know someone posted a bit about one before - I'll spend a little time later chasing that post down.

Thanks again for your interest.

Des

I believe Sesamecrunch used that hub on a Moulton.

S/Crunch had a kickback Sachs duomatic on his Moulton ... I still run the Sachs Automatic on my Mu Duo as well as my Titanium 700c road bike..


http://bikeforums.net/attachment.php...hmentid=279154


http://bikeforums.net/attachment.php...hmentid=279155

The shifting mechanism is basically the same as the new SRAM Automatix (and uses many of the same parts) and is adjusted the same way.. either through spring manipulation, winding your own springs (what I did), or modifying the flyweights.. I also run the SRAM Automatix on a belt drive Moulton TSR-2..



Moulton

Dahon

Titanium 700c

Thanks Bruce. As you say you wound your own springs, I'm guessing you're reasonably 'pro' at this. Can you advise if I can adjust a blue band sufficiently to cope with a 16" wheel? Is the only difference between the blue and red the spring - i.e. there's nothing stopping me considering this for a Brompton?

Thanks for your input.

You don't have to wind your own springs (I did because I had never tried it before and i wanted a selection of springs to work with), I wrote about some options HERE in the post about my 700c conversion.. one of the followup posts was from a guy who put an extra wind on his and it worked out... When I had a blue and a red Automatic on my bench, I didn't see any difference in the springs, but then, one or the other could have been worked on long ago before i got the hubs .. it's a bit of a hit and miss proposition to get what you want shiftwise, but the hubs do come apart easily to experiment with..

Thanks. I may have rambled a bit in my question. I guess what I really want to know is can I get a blue bad hub to work with my 16" wheel or should I wait to see if I can if a red band hub becomes available?

Apologies for harassing you!

I found this the other day. Could help people adjust.

http://mccraw.co.uk/sram-automatix-review/

A Sachs Blue Band will work fine .. either one (if bone stock) in a 16" wheel will shift early .. most likely in the 5mph range .. one nice thing about the much newer SRAM A2 is the brake is a nicer, more powerful unit.. Jerry fitted one to his Brompton with a little massaging of the lock nuts (narrowing a 120mm hub to fit the Brompton spacing).. I like the looks of the older Sachs units more, but that's just me .. If I didn't have a perfectly fine working SA 3speed in my Mercton, I'd switch it to a 2 speed and run the 36 hole Sachs unit laced to a 24h rim and jettison the rear caliper brake, lever, shifter, etc. to get rid of the cables to the rear, as I fold it quite a bit .. and I could easily get by with a 2 speed where I normally ride it... heck, I may do that anyway .. also, just re-read your original post query again.. your 12/16 gear is 133% range, so almost identical to the 136% range of the duomatic, meaning, if you wanted the same gearing you have now, you would use a 16t gear on the duomatic and when it automatically shifts up, it will be the same as your 12t...