Has anyone used one of these Spa Cycles super-compact doubles on their Brommie? I've just changed the BB for a Shimano UN55 118mm so would prefer to not have to replace it again -- but how to know if the Spa double will work out ok (ie not interfere with folding etc)?
I may be able to offer advice, though my details could have differed. I managed to refrain from extending the length of BB axle by putting a spacer onto the BB on the drive side and keeping the original Brompton crank on the left non-drive side. A cassette spacer can be used as a BB spacer. Keeping the fold neat may require reshaping the left fender/mudguard stay. By now, I already upgraded to a triple, all with a 119mm BB axle.
Thanks for the input everyone... still a head scratch as to whether the Spa Cycles double will be a hassle-free fit. I could live with the chain falling off if folded on the small ring, but am worried about the inner fouling the fold or the chain line being horribly compromised.
Browsing further at Spa I've come up with an alternative to the Spa double... what about one of these Stronglight adapter chainrings? It'll fit the stock 130BCD Brompton crank and has integral mounting for a 74BCD inner. Thoughts anyone?
I used such an adapter chainring too at some point. It worked. There are many ways to get there. It is a tad less rigid solution. Think also about giving up on a chain guard now, not only after finding out that you are staining your clothes.
I have a Sugino 110 BCD with a 58 and a 38. I actually tried a 28 as a 3rd chainring but the chainring prevented a proper fold. At the moment I have a 13 tooth sprocket on the back but also a 177% SA IGH wheel so I can switch between the 2 rear wheels fairly quickly. I will set up the single sprocket wheel with a studded Schwalbe tire and have an extra front wheel with a studded as well.
Bikegang gave me a trial 3 sprocket setup with 11, 14 and 17 tooth sprockets which works very well but I was concerned the winter salt and sand would wear out the 11 tooth sprocket so I'm back to a single sprocket for now. The 13 tooth sprocket with the 58 tooth chainring yields about 72 gear inches and the 38 about 50 for hills. If dry weather will be on hand for a while I will return to the 3 speed SA setup with Marathon Racers.
Hopefully all this isn't too confusing.
I have 3 rings on some rare Shimano crank. The fold is slightly bulkier than for a single ring, but you need an A/B comparison to really see it. I had to modify the mudguard stay that I mentioned, and that was it, in my memory.
This is all very encouraging, and at the same time not very conclusive with regards the particular adaptations highlighted at Spa. Will just have to take the plunge and see how it turns out.
The idea being to swap a double on and off as and when required (ie very long and/or particularly hilly rides) -- so no worry about oily clothing due lack of chain guard as I'll be wearing shorts or tights when the double is on.
The adapter ring with a 28 inner appeals as it allows me to keep the stock cranks... the Spa Cycles double as it'll probably be quicker to swap cranks on and off than chainrings.