Changing folder chainset from 50/34 to 40/24 with braze-on FD

[horizon]

I'm resurrecting this post but also the project as I'm using my Tern again for overnight work trips. What I got stuck on of course was finding smaller chain rings for the existing 110 BCD spider (Spa's go down to 33T). This means (I presume) changing the whole chainset. Two runners have emerged. Neither give their BCD but I assume it must be 74.

This is the one I flagged up last year:
https://spacycles.co.uk/m2b0s109p3383/S ... cral-Rings
and this is one I found recently (I won't be buying it):
https://www.renehersecycles.com/shop/co ... ble-crank/

Before parting with the £69 for the Spa, I have a couple of questions:

1. Why don't I just fit a triple (as suggested above)? Answer: because the FD is a double?
2. Why can't I find a cheap double like Spa's but say £40 cheaper? Answer: because it's really a triple?
3. Will whatever I fit be a 74 BCD? Answer: Yes?
4. Why doesn't my folder have a triple anyway? Indeed why have Tern dropped the D16 and now only do the D8 without the FD? Answer: no idea.
5. Are these questions related?

All help and suggestions appreciated. All my other bikes have triples so this is new territory for me.

[Brucey]

1) you could fit a triple but without the outer chainring
2) you could buy an XD2 triple (currently £35. 110/74 BCD) see above
3) no, you could buy something which you can't get chainrings for instead
4) most folk don't ride folding bikes far enough, or with enough load on, or up big enough hills to need a triple
5) you are trying to optimise a bike for your own purposes; no-one ever said this was going to be easy or inexpensive.

FWIW the more expensive chainset is more expensive because it is fitted with better quality zicral rings and a chainguard; all parts that cost a bit more than the basic (softer) chainrings fitted as standard on the XD2. The basic chainrings -of which you don't have a choice in sizes at the bargain price28,38,48 is your lot- won't last that long but maybe you don't plan to do mega-miles on this machine, so maybe that would be OK.

If you remove the outside chainring from an XD2 you will need shorter(or shortened) chainring bolts or spacers, or a chainguard.

cheers

[UpWrong]

On my bent I use an old Ultegra triple with a Sora compact double FD. Have a Spa guard as the outer. Standard ring bolts. Shifter is a gripshift triple. Rings are 30\42.

[rjb]

I've hacksawed the teeth of a very worn outer chainring to convert a triple into a double with a chainguard. It was a steel outer and was not as difficult as I expected. About 1/2 hours work and included finishing with a file to smooth the edges off.

[horizon]

4) most folk don't ride folding bikes far enough, or with enough load on, or up big enough hills to need a triple

cheers

I agree, they're obviously used (or maybe not even used) as local runabouts. But look at the thread that's running ATM about crossing the Alps on a folder! You can clearly do a lot on a folder: even the manufacturers must think so as it is they who put the rack braze-ons on (front as well!). The irony is that a folder is probably the right bike for touring: after all, it is touring that usually involves some interaction with public transport, whether that be buses, coaches, planes or trains and the inevitable negotiation with hotel keepers as to how and where the bike gets stored overnight. I still find it hard though to accept that Tern have simply deleted the option, even of a double.

I'm going to have another think about the options and probably bite the bullet and get the Spa. I still have to work through any implications for the BB and the shifters but these should be OK.

Thanks as well to rjb and UpWrong.

[Brucey]

oh yes, I didn't say you couldn't, or shouldn't do that if you want to, just that most people don't.

cheers

[NickJP]

Sugino and Wickwerks both make adapters for lowering the FD on a frame with a braze-on mount. Here's the Sugino adapter in use on one of my wife's bikes with a 39t big chainring:



Sugino adapter: https://www.suginoltd.co.jp/store/products/detail.php?product_id=76

Wickwerks adapter: https://wickwerks.com/products/fit-link-adapter/

Unless your frame has a dropped drive side chainstay, you'll also need an FD with a fairly short cage to avoid having the bottom of the cage foul the chainstay when you try to shift to the small chainring. As you can see from the photo above, a standard road FD intended for use with two chainrings often does the job. A triple FD usually will not work as the cage is too long. Genevalle make a nice short cage braze-on FD intended for CX use: https://www.gevenalle.com/product/burd-front-derailleur/.

On steel frames with a braze-on FD mount, you can sometimes mount a clamp-on derailleur below the existing mount if you are using small chainrings. One of my wife's other bikes which has a mid-1980s De Rosa SLX frame is setup this way. Modern MTB 2x FDs are good for this, as they have really short cages.

[horizon]

Thanks NickJP, that's really helpful. I'm wistfully hoping that I can just stick a new crankset on and it will all work. There is some downward adjustment possible on the braze-on (it's on the highest setting at present) but if that isn't enough then an adaptor could be the way forward - at least it's there as a backstop.

I do know that I'm prevaricating on this. The bike is only used for work trips and even then I'm umming and arring as to whether I could just get used to booking a bike on the train. It also does the job with the existing gear (it's 27" which isn't actually too bad anyway) so whether it's worth potentially £120 to lower what are fairly adequate gears I don't know.

PS Just reading this:
https://road.cc/content/feature/246424- ... adventures
It's quite incredible that a serious website like road.cc can say baldly, "Gravel bikes are over-geared". There seems to be quite a disconnect betwen Shimano (and their bike-maker customers) and the real world of human beings.

[Brucey]

bikes have always been overgeared for 'normal' cyclists. Non-cyclists often want high gears when they start and racey types don't really need low gears. Folk consciously (or unconsciously) want to look like racers and part of the look is what size and how many cogs you have and how big they are. For many years if you used a triple chainset on a road bike (actually anything that wasn't 52-42 in fact) then this would be noted...

Do you really need low gears? Walking up the occasional hill isn't the end of the world, is it?

cheers

[horizon]

Do you really need low gears? Walking up the occasional hill isn't the end of the world, is it?

cheers

Fair point. While I've been chewing this over, I've reflected on it on a couple of my regular trips with the bike (fully loaded). Basically it does the job: I've had it three years now and it hasn't let me down. On my regular run from the station home (about 10 miles) there are only two hills that it won't go up but I wouldn't cycle up them anyway even with lower gears. But I've wanted occasionally to combine a short work trip with a longer ride over a couple of days (Dorset is often the venue). I know then that there will be a few hills that I can easily cycle up in say 22" or less with luggage but not with the gears as they are. Any of the Spa super-compact combinations would make this bike very handy and versatile indeed.

I think if someone said, here's the stuff (chainset, adaptor, FD if required) for free, it's a no-brainer. But it's a lot of cash (and some work) at present for a slightly uncertain outcome and, as you say, all to avoid a few walk-ups. Hmmm.

[horizon]

A quick update for anyone who wondered where I got with this:

A Spa super-compact touring double 42/26 (as linked to above) came up on Ebay unused. I snapped it up for £28.00 as opposed to the £69.00 new price. So that sorted the choice of chainset.

I found I needed a longer BB (116 instead of 113). I had a 122 in my spares box and tried that. That all worked.

The last step was the front derailleur. I moved it down to its fullest extent, tightened the cable tension and adjusted the H screw. It all works. A neat, inexpensive solution and the difference in gearing is dramatic. AFAICS from road testing the FD works absolutely fine. I don't see any other problems at present (e.g. from the longer BB). The chainrings were one step larger than I wanted (42/26 rather than 40/24) but this might have helped the FD position.

"Sea trials" begin later this week so I'll see if it really is all 100%. Thanks to all who helped.