650b conversions, some new bikes, all nonsense

After attempting a 650b conversion on a slightly too small Spa a few months back, the itch to cut up something and try again has come back. Throughout my relatively short life, I have been (maybe fairly) unkind to Jan, Grant and anyone that believes the pinnacle of cycling technology was around 1940's french bikes, yet I find myself more and more attracted to the idea.

I stand by my criticism of Jan's rolling resistance test, and the boasts he makes because of it. I should say, I have owned a few of the tyres over the years and while they were nice, they were way too expensive and punctured if you liked at them too long. While the lab tests are not analogous to real life, they don't need to be, that's the point, you are comparing on a level playing field, so your measurements mean something relative to each other.

After watching the Frink bike video the other week, the bug to try my hand at a conversion bit, and I found myself trawling for old Treks. Not being in the continental USA, prices for these old bikes was more than I was willing to pay (and I don't like the square lugs) so I started having a look through here, only to find this:

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It's perfect. It uses a weird seatpost size, is threaded and has a 130mm rear end already. As a total bonus, it fits a 650b x 42 out of the box!

It's also ratty, so I don't feel bad chopping it up. It does have a super weird BB shell, it's id is 35.5mm dia and has no threads, but also doesn't have the massive lead in chamfer old Mavic bb's used. The original owner had used a Mavic BB in the 80's but recently has been using the damaged thread bbs, which is what I intend to do.

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The plan for this bike is as follows:
-2x 11 - 105 which I'm stealing from my other bike. Oddly enough, I'm running 46-30 rings and it always feels under geared so I might try a compact double, but that can happen once the bike is built.
-Wheels are the cheapest 650b rim brake wheels I could build and aren't worth writing home about, but get the job done. Ended up getting some thorn rims to make them okay.
Tyres. After my short but heavily opinionated diatribe above, I usually end up with gravel kings. I did notice a strange sensation on my other conversation, which I shall call ghost steering. It's odd, but fine. Might try something else, but we will see. Ideally I would like the frame to clear 47's for full effect.
-Brakes. I have tried everything else and really wanted to try boss mounted centre pulls. Mafacs are too hard to source and to expensive so I've gone for dia compe 610-N. While they don't have the sharp lines of the cnc'ed counterparts, they are cheaper and way stronger (look up drop forging Vs CNC from billet, the grain structure makes all the difference). I had planned to make my own mounts for the frame for them but ended up just buying them, which after recieving then I now regret, as they were comparatively expensive for how simple they are (brake calipers were £80 for the pair, the mounts came to £60, but I was quids in by this point).

Otherwise, a cockpit and other ods and sods will be pinched, plundered or ploined from other bikes as needed. I would really like to make myself racks (the constructor esq ones that velo orange make) at some point but we will see how motivation goes.

First things first, after test during the tyres, the frame needed to be dimpled. So I ignored that and moved into the brake bridge. As the frame was designed around 28inch tyres, it's high, even with a 42 in there so, I made a quick jig out of some steel stock and got it roughly where I wanted it:

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The brake bridge was then mitered and the tube beaded brazed in place. Luckily I have access to a mill, so that made most things easier, but in reflection, I wish I had just cut it by hand and filled it:

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The old bridge was then cut out and the tube filed away. I then turned my attention to the brake mounts. Originally, I had planned a complex setup in the mill to mitre then at the 16deg the seatstays were at, but that took to long, so I ended up just fileing then to shape and then brazing them on. I made the jig out of the same piece of bar stock at before but with different holes, and guessed the location by offering up the brake to the frame, and measuring the centre distances between the bolts. It worked!

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I was a bit chuffed with the mounts, and was waiting on the springs (for some reason they are sold separately from the bosses, and very hard to find) which turned up yesterday. With the springs installed, they feel solid as! So stoked. Plan is to tackle the fork mounts this weekend, and if I have time, internal cable routing for the rear brake though the top tube and sti bosses on the down tube.

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👍
Good this

Following

Things left to do:

1. Dimple stays.
   
2. Brake mounts for the fork
   
3. Cable stops everywhere. The frame has band on everything, which is fine, but not what I wanted. Plus they are mega rusty.
   
4. Find a external BB that will work
   
5. Pump peg
   
6. Mudguards
   
7. Paint. There's a mob in Surry which offer Cerakote (stronger powder coat) and sand blasting, so will have that done once I've done tinkering. As the bb has no threads, I don't really need to mask anything, as I can run traps through it (headset will be fine, it's approx 15um of paint max, willing to bet the range cups from the 80's went controlled that finely)
   
   

Bonus

1. Racks. Maybe. Might just buy something. Unsure.
   
2. Headtube badge/down tube decal. Unsure what to do here, the frame is a no name with no serial number, so I was going to make my own. I really like the raised lettering I've seen around (most recently on August) but I seem to remember geekhouse doing it in the early 2000's. I was thinking about calling it Allora, which is kind of Italian for "what now" but I'm not Italian, and when I mentioned it to my Italian mate she said it was wasn't quite the pun I thought it was.
   
   

Otherwise, I'm getting pumped. It looks cool and I'm excited to ride it.

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Very cool.

Sub’d

Top tinkering here

I feel at home in here

Arse bracket wise, I have found this: https://www.sjscycles.co.uk/bottom-brackets/yst-bb0901-threadless-external-bottom-bracket-68mm-black/

Which after emailing SJS, they informed me it doesn't work with road cranksets as it's too wide, which leaves me with three choices.

Mod the frame. Already doing this else where, but it will mean I'm stuck with this BB for life (or at least this brand). Not totally a bad thing.
Mod the bb. Prefer this option, but it will depend on how much material I have to remove.

My plan is to measure the bb on my other bike that works with the cranks I want to use, then use that as my max limit. I reckon I'll have to skim about 2mm of material off something, so we will see when I get around to ordering it.

Necular option is make my own pressfit BB. I like this idea the most, the BB shell is well within bb30 tolerances, but upsettingly not diameter) so making something would be easy, it's more if I have to replace it, I would have to make another. That being said, now that I have typed it, it does seem fun.

Silly question, why braze on a new rear brake bridge and then ignore it and braze on the centre pull bosses. Is it just for mudguards?

Nice
sub’d

Totally fair question, it mostly boils down to two things:

1. Stiffness. This term gets thrown around, but in this instance its correct. the bridge mount for the caliper adds an extra ~30mm to the distance from the pads to the mount, and therefore will decrease stiffness. As the brake arms are at the end of the day, quite thin, increasing their stiffness (and hopefully reducing the posibility of the dreaded howl) is only positive. The bridge will be used for a mudguard, I had the nice machined one left over from a previous project, and to be frank, the old location made for a weird looking gap from tyre to bridge.
   
2. Vibes. Nuff said. (It will be used for mudguards, and possibly even a Brompton esq light mount, not sure yet, the square edges might mess with the organic shape.
   
   

See badly annotated attached image. Please ignore the homage to Tom Sachs.

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Thanks for the kind words all, I cant promise consistant updates, for that I appologise, but I have another bike I need to build up by Septmeber (preferably earlier- Im planning on doing the Dolomites trip on bikepacking.com with a pal and maybe should ride the bike before then) so it will be at least rideable before that. I hope.

Great project! As an italian myself, i'd suggest you to keep the naming and add a question mark. "Allora?" in italian is much more similar to "What now?" when posed as a question.

Complimenti!

Thanks, was just curious. What make is the frame by the way?

I have a tendency to over explain, appologies if offence was caused.

I got the frame from @Rhodrich, I was under the impression he got it new (but I cant remember where from) but I could be wrong. Otherwise its unidentifitable. Its well made, the fillets are nice, if I had to guess I would say its 531, but could be extremly wrong. There are no cable stops or anything, it was all band on if that makes it any easier to guess?

@Marcootsee Im into that! awesome.

No offence at all, please explain away :). I just love these threads as it's something I just don't have the skills to do.......

Wow - so good to see my old frame get some love! Sorry I can't tell you any more about its origins. I bought it second hand in the mid 90's as a bare frame from a guy in Tolworth, already sprayed up in the weird copper colour it is now. I built it up as a touring bike (pic below), and used it for riding to and from school. Seem to remember that the Mavic bottom bracket that my local bike shop fitted costed me £50 at the time, which was a lot of paper round money!
I used it on and off for the last 30 years or so, including most recently for commuting, and it rode really nicely. I only took it off the road when it started to get a bit too ratty for my liking.

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Fun project

Very cool. Interested to see how you‘ll do the internal routing and the dimpling.