Thanks a lot.

For others' benefit: On a 2021 Brompton, the Litepro B-series clamp didn't work with a "9 Speed Front Derailleur Folding Bike Double Gear" LitePro derailleur, because on a double crankset, the fork sat too far outward and wouldn't reach the inner chainring. It might be because I turned a triple into a 46/30T double with the outer ring removed.

I had better luck with the NC-100/Meijun/Mi.Xim clamp, but still had to install the derailleur a bit astray for the fork to reach the inner ring.

So, it's really a combination of a crankset, a clamp, and a derailleur. YMMV.

https://cimg1.ibsrv.net/gimg/bikefor...eeabd80296.jpg

Its because you kept the middle and inner chainring of a triple crankset instead of keeping the outer and middle chainring or used a real double or compact crankset.

Because the middle is a BCD110, which can only go down to 34T while I wanted a 30T.

I found no affordable 46/30T double, hence the hack.

Yes, that's a reason, but it causes the derailleur problem because the inner chainring is too close to the frame.

Maybe an old front derailleur for a triple chainring could do the job ?

I didn't have any, but I'll try a triple derailleur next time.

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Edit: Because of its flexibility, would it be a good idea to always get a triple derailleur, regardless of the crankset — double/triple chainring —, and use the high/low screws to limit its run?

Thanks for the info. As to the chain going down to the inner ring. I modify the derailleur cages, in particular soldering a stainless strip to the outer plate of the cage, to push the chain in more convincingly when the cage moves inwards. The Mi.Xim clamp is the one I had problems with due to the vertical finger, on which the derailleur mounts, holding poorly with just one bolt. However, with two rings only on your bike, maybe the forces that the finger needs to withstand are still low enough for it to hold.

I'll ask the user for feedback in some weeks/months.

From what I could tell, and like on my own Brompton, shifting down is no issue, but shifting up requires dialing the shifter in one frank move; Otherwise, the derailleur sometimes doesn't have enough power to pull the chain up.

On modern bike gearing, upshifting with the front derailleur is helped a lot by pins and grooves on the bigger chainring (each brand has its own tricks and commercial name for that).

If your biggest chainring doesn't have these pins and grooves, it results in a slower sometime difficult upshifting.

For shifting up, I expand the lower lip of the inner cage, by soldering a stainless piece there. In the end, I tailor the cage to the rings and the derailleur mounting. The manufacturers may market a derailleur and rings as a set. I make a set out of whatever I want to put on for whatever reasons. I used to put in pins for upshifting on the rings that lacked them, but these days I achieve smooth upshifting by manipulating the cage only. My pins did not work that great anyway.

The pins aren't enough.

The two chainrings are specially designed in a pair to make the chain mount on the bigger chainring easy and ultra fast.

Its not only marketing, it works amazingly well.

The drawback is that changing the chainring sizes isn't possible, you must stick to the standard pairs 53-39, 52-36 or 50-34.

As said all big brands, Shimano, SRAM, Campagnolo have their own commercial name for that, example: latest Campagnolo XPSS

But then, we're talking about a folding bike used to commute/tour, not riding in the Tour de France.

Besides, while shifting down fast is important, in practice, it matters a lot less if shifting up takes ~a second.

Next time I have a chance, I'll experiment with the Litepro B clamp and yet another derailleur, making sure to match the number of speeds for the derailleur and the crankset.

When the number of teeth is not a whole multiple of the number of arms, you can rotate the rings to get a good match for the climbing of a chain. I cannot remember a case where I would not make a ring and derailleur combination work. On my Brompton I currently have 50-34-20. Before I had 50-32-20 and earlier 50-34-24. On the full-size bike I have 4 chainrings and again I experimented with a multitude of combinations. You could make all of them work.

Yes, they work, but not as well as these matched chainrings !

With these matched chainrings, upshifting is so soft that you do not even feel that the chain is moving to the bigger chainring, no shock, no noise, just a progressive change of ratio.

Yes, orienting and profiling the teeth can help greatly. One way I found it was when trying to put 3 cogs on Brompton sourced from a cassette where the cogs were not in the same sequential order as needed on Brompton. I could not make the pusher shift properly over these with an indexed shifter no matter what I did. After I went back to the cogs from another cassette, where they were in the same order as needed on Brompton, the indexed shifting went to uneventful. However, the pusher is as primitive system as it can get. With a contemporary front derailleur you get well more flexibility. Incidentally, in my perfecting the match between the rings, I may shorten some teeth, but this for downshifting rather than up.

This discussion makes me think whether I should try the profiling for an upshift on an occasion. In the end, I just watch how the chain behaves during shifting and I decide how I can help.

Yes, the same exist for cassette, for example the Shimano hyperglide and hyperglide plus.

Why does it make a difference?

What do you mean with "in the same sequential order as needed on Brompton"?

The cogs sequence is important because the grooves of the hyperglide system (or other brands similar system) follow each other on every cog.

If non sequential cogs are used, these grooves do not match each other.

The same apply for the chainrings that must be placed adequately.

In the upshift, the chain still on the smaller ring, but pressed against the larger ring, must grab a pin or tooth tip with the opening in the link, to climb up onto the larger ring. If the opening does not fall where the grab needs to occur, the chain will just continue to rub against the larger ring and the upshift will not take place. You have a potential to change where the opening in the link falls, by changing the orientation of one ring against the other, through rotation over the arms. However, if the number of teeth is a whole multiple of the number of arms, such a rotation does nothing.

I got a new bottom bracket for my Brompton to replace the one I've been using for some years now and was making creaking noises on one side — trying another crank + pedal didn't solve the problem, so it looks like it's the BB.

The local Brompton store was out of Thun BBs, so I got a cheap, no name BB that was available in another store.

Unfortunately, it doesn't say if it's ISO or JIS, while the crank expects JIS.

Confusingly, some sites say it's important to match crank and BB, while others say cranks can take both these days.

Both shapes look very similar: Is there a sure-fire way to tell if a BB is ISO or JIS?

Thank you.

Sheldon-Brown has an article on square taper BBs. I have myself used an old Stronglight ISO spindle with a Shimano Biopace JIS crankset. It worked fine for years. Not ideal but possible. It was not a Brompton and I do not know if the required chain line on a Brompton would be a problem. Sheldon-Brown, in the last two lines of the square taper BB article states:


I generally avoid mixing sizes on customers' bikes, but I have a lot of experience mixing ISO/J.I.S. in both directions on my own personal bikes, and it has never given me a lick of trouble.


My experience with the Brompton is that it is a bit tight or demanding with regard to the chain line. Especially when using a brand new chain.

If you can mount the spindle on the crank arm without bottoming out the square taper, then I think you will be OK. Not taking the chain line in

to account.

A cheap no-name BB will be nearly for sure JIS. Distinguishing the tapers with calipers is very hard. Angling the calipers a bit will give a bigger error than the difference between the tapers.

Thanks for the infos.