The Rehook is a hoot. Merci. Their site is good and the Amazon reviews hilarious.
You and Bob have inspired me to rubber band a baggie of gloves on all my bikes,
So, change does happen,
Except maybe from vending machines
Appreciate your discussions on gearing, one and all.
It has also taught about the bikes, with good colateral effect

Frankly, installing a front derailleur is a no-brainer, and is really a nice improvement for not much money (~ $£€100 total.)

"40mm SP8 Foldable Bike Front Derailleur Adapter Single Disc Crankset to 2/3 Disc"
https://www.ebay.com/itm/132321125608

"LitePro Braze-On K-Series Front Derailleur Clamp Adapter For Dahon K Frame"
https://www.ebay.com/itm/222154907485

This is very informative.


Rest of his vids:

https://m.youtube.com/channel/UCs0FV...rUCSNuA/videos

Well, I differ with [MENTION=258041]Winfried[/MENTION] on this and I find the suggested LitePro Clamp for Dahon K Frame, also there in the video, to be poor. Also I find the mounting of a double chainring to be a moderate to challenging project depending how closely you want the shifting to work as compared to that on a regular bike and how compact you want the fold to stay. The suggested SP8 Adapter is crude, but nonetheless fine for double ring. On the other hand the LitePro adapter meant for Birdy works fine both with double and triple ring on Brompton.

https://www.ebay.com/itm/323777622883

Mounting of a triple ring is a challenging project.

With my two left hands, it took barely 15mn the first time to install the Litepro clamp + double chainring + shifter, and I've been using this solution for over three years now with total satisfaction.

Provided it would even work because of the chainline… is there even the need for a triple chainring on a Brompton?

So the Litepro clamp for Birdy works better? No filing, no funny tinkering compared to the Litepro Dahon K? Ok. Thank you for that info.

Life is not that easy :D - all of them involve some tinkering, but the Birdy one is more robust and more durable.

The rundown is as follows. All 3 mounts are out of alu and consist out of a clamp and an arm that attaches to the clamp, on which the derailleur is mounted. All 3 clamps are a bit oversized relative to Brompton seatpost, so a shim is needed - I glued rubber from a tube to the inside of the clamp. In each case, the clamp contains a cable stop and LitePro reuses clamps and/or parts of their design between different models.

In the case of the Birdy adapter, the derailleur's mounting point is right by the clamp. The arm is short and sturdy and the derailleur cage moves below the clamp so interference between the clamp and derailleur body is reduced. There is enough swing there available even for a triple derailleur. One poster on the forums 3D printed an arm that puts the derailleur mounting point even below the clamp, giving the derailleur even more swing space - that worked on his Dahon, but on Brompton you then run out of space for the clamp.

In the case of SP8 and K-frame mounts, the derailleur mounting point is above the clamp, hence the cage hits the clamp when swinging to low gear. This reduces the swing space for the derailleur. Still enough space is left for a double derailleur but not for triple. Both in SP8 and K-frame the arm onto which the derailleur mounts is extended, but in SP8 case it is thick so the derailleur is held fine. In the K-frame case the arm is thin and flexes during shifting. If there is a hiccup in shifting, such as of chain getting stuck, there is a high likelihood of the arm getting bent permanently. This is alu, so it cannot take many such bends before it fails.

In each case, to align the curvature of the derailleur cage with ring curvature, you need an asymmetric washer for braze-on mount derailleurs from Sram. Finally you may need to play around with the bottom bracket spindle protrusion to the drive side, either changing spindle length or using a spacer for bottom brackets. Some filing in the derailleur or mount can help to increase the derailleur swing.

All mounts may be cheaper on AliExpress than Ebay - for vendors from China you can expect slow shipment on both, with fake tracking number put in to create impression that the item shipped - part of life now.

Oh ... Blimey!! :cry: :mad:

You can do it step by step. First you just mount a double crankset on the drive side, see whether it fits an move the chain by hand and look whether you like the improved gear options. Then you mount the clamp without the derailleur and play with it. Each time you leave yourself the option to go back :).

Thanks for the infos.

In case I meet a Brompton user who's interested in installing a double chainring, I'll recommend getting the Birdy version of the Litepro clamp, even though I've had no problem with the Dahon K version.

[MENTION=258041]Winfried[/MENTION] I have all 3 discussed clamps + CM Wasson. The last one is fine too, but it is not available anymore and it is heavy and bulky with the extra baggage not quite adding to strength. Personally I prefer solutions that can be carried to other bikes rather than one-offs.

Since we are on the topic of mounts, I wanted to share a washer solution for derailleur. When you pile up all washers including the asymmetric one from Sram, you make the derailleur more likely to slip down the mount. To prevent that I replaced the standard outside washer with a one with a hook, out of a metal strip, preventing the downward movement.

Incidently, Ridea also offers a front derailleur + clamp. The clamp looks like Litepro's

RIDEA Headquarter Oval chainrings Crankset CNC lever are Upgrade Component for bikes and motorcycles

There seem to be 2 mounts there of interest, one dedicated for Brompton and another for Birdy. The Brompton one mounts the derailleur above the clamp, like in Litepro for Dahon, and the Birdy one by the clamp. The Ridea Birdy clamp is available from bikegang, meaning that you can actually get this item shipped relatively quickly.

https://cimg0.ibsrv.net/gimg/bikefor...ad445e1f36.png
I remember that I was agonizing over it compared to Litepro, but in the end went with Litepro. It might have been the location of the cable stop, farther away in LitePro than in Ridea. When the cable stop is closer, you need to apply a higher tension in the cable to move the derailleur into the high gear position. Also the arm that holds the derailleur is bolted to the clamp with one bolt in Ridea and with two in LitePro. There is not a lot of material there for the threads to grab onto so a couple of bolts may be claimed to work better. Incidentally, my LitePro Birdy mount came with just one bolt, but there was a threaded hole for the second, so I added that second. The Dahon version had both bolts there from the start.

As to the dedicated Ridea Brompton mount, I have no idea how to get hands on one. Ridea does not seem to pay much attention to the markets outside of Asia for one. Maybe even the bicycle market is secondary for them to motorcycle. Also, in a sense I do not need another mount anymore.

Facebook Brompton hacks video has a demonstration of using your foot to shift _ up and down, a double crank.
with the smaller ring on the outside .. adding a backstop behind the big ring is part of the hack..

It may be open accessed via YT for non FB users..

I have a 58/38 chain ring combo using a 110 cranks which has the drillings for a 3rd chain ring, say 22 teeth. I did have it set up with the 38 on the outside but the angle of the 58 caused some rubbing of the chain on the 38 so I reversed them and it works fine. However, since I greasy finger shift, and a 22 tooth chain ring weighs next to nothing, I was wondering if the 2 speed shifter chain tensioner can deal with that range (22-58) on the front. Have those of you with 3 chain rings had any issues with that? I don't have many grades where a 22 tooth chain ring would be needed but it would be nice to have for a few.

I had a double derailleur mounted for shifting 24-34-50. I had to modify the cage a bit. It worked but was not very stable. The derailleur was stretched to the limit and the shifting was easily thwarted by this or that getting knocked. Life got easier for me when employing a dedicated triple derailleur. However, the cages of the latter are bulkier. In particular you have to accept the bottom bracket spindle sticking out farther,

A friend might get a Brompton, and would then want to install a double chainring.

Based on the above, I will recommend getting the LitePro B-Series Braze-On Adapter For Birdy instead of the K-Series I've been happily using for a few years now.

As for the front derailleur, and an alternative to the Shimano Tiagra (FD-4600?) I used… are there yet cheaper options I could use? I'm just curious.

If the friend were to stay with double then the cheap SP8 adapter should be enough and still preferred over the K-Series. If the friend ever went to go to triple then the Birdy one would be preferred.

As to FD, the friend might consider a used Ultegra off Ebay, though they might be more expensive in Europe. I would just make sure that the cage is bolted rather than riveted to make experimentation with settings easier. In addition, I would advise getting the Sram adjustment washer to perfect the alignment of the derailleur cage with chainrings. It costs around $10, but once you try to make something similar yourself you are likely to decide that this $10 is a worthwhile expense.

Thanks!

Incidently, on a stand at least, shifting works fine with the triple-turned-double 46/30T I just installed to get yet smaller gears in hilly areas :
https://cimg4.ibsrv.net/gimg/bikefor...f3cce21857.jpg

Is the folded bike size increased for you because of the triple? Does the folded bike lock fine? At some point I tried to limit any increase in the width of the folded bike due to the front triple, as much as possible, but it started bringing in other problems and I just went with the flow, tolerating a slight increase, and it seems OK.