On One Pompino owners...

It's pretty normal on bikes designed with mudguards in mind, and there's no centre seatstay bridge brake hole, so it's the most logical place to put it.

Cheers, so hopefully room for 650b x 42 with guards...

Someone needs to make a U-brake to convert 700c frames to 650b ... or maybe someone does?

Or some kind of adapter ...

U brake boss ≠ v brake/canti boss.

U brake bosses are shorter and fatter iirc.

You could make a ubrake that fits on canti bosses but probably a bit too niche.

Is that adapter to convert MTBs from 26 to 29?

True but

Someone needs to make a U-brake

I'm talking about something specifically for converting from 700c canti bosses. Why couldn't this be made for conti bosses?

@fizzy.bleach yeah thats right.

It is a brake adaptor that can reposition cantilever brake bosses on a BMX frame.

Don't see why it couldn't be inverted. Might need machining to work but an option.

Couldn't you just fit those upside down/on the other sides?

Exactly ...

They're for converting 20 x 1-1/8” wheel standard (ISO 451) to accept the 20 x 1.5” (ISO 406) standard .. which is similar to the radius difference between 700c and 650b (19mm) ...

So...problem solved?

Actually scrap all of this the brake boss would need to be removed as it would be in the way of the brake arm. Something with a deep cutaway and long arms like a Paul canti might work with a bit of fettling

Not sure on the above ... retracted.

So — old posts off, tap the recess for M1 and you're golden.

It's a one-way conversion (albeit with no brazing).

Retracted

Seen on pedalroom

It's for frames with thread in posts.

Unscrew the posts, boltnon the adapter, screw posts into adapter.

I don't see any reason the wouldn't work to drop the posts down just as they fobto raise them up.

That looks like only a 650b front ... and think it's a 650b fork?

I assumed both wheels were 700c, just think it looks a fun bike

I need some helps. I'm venturing into my first build, and I'm acutely aware that there's loads of shit that I don't know shit about. I'm new to all sorts of things, but I'll just pester you all with one thing for now. Specifically, I need your collective knowledge, advice, and patient explanations, regarding chainline:

I bought a pair of MTB wheels second hand recently for a pompetamine. By my crude guesswork, the wheels look like they have a chainline of 46.5mm. I got that number because the hub is 135mm. The sprocket is 21mm in from the outside of the hub, so the chainline is (135/2) - 21mm = 46.5mm. See bad photo:
angle of photo is a little off, as I didn't have a third hand available for photography, but I think the sprocket is 21mm from the end of the hub. Am I calculating this correctly?

The hub has a freehub and spacers, so I can shuffle the sprocket out a bit, but I think the chain would foul on the spokes if I brought it any further inward.

I heard vicious rumors that a shimano alfine chainset wasn't a bad place to start, but this says it has a chainline of 42.7mm.

4mm doesn't seem like a lot, but I'm guessing that this is beyond what is recommended?

What do people suggest? Getting the alfine (or similar) with a different BB with a wider spindle? (not sure what BB this Alfine comes with). Or do I get a different chainset and bottom bracket?

This isn't going to be a fancy build, so recommendations of fancy parts might be awkwardly ignored.

Thanks for the helps.

get the chainset, ditch the chainguard and mount rings on outside of tabs. Et voilà, 46mm chain line.

The spindle is part of the Alfine crankset, so no adjustment there.

I assume as you mention a Pompetamine this wheel is said bike and not a Pompino. If it is for a Pompino you need a wheel with an OLD of 120 mm. From the picture it looks like there are some spacers after the cog on the outside which could move to the inside. The chainline needs to be much closer otherwise the drivetrain will be really noisy and will wear fast.

Thanks for the replies. @JesperXT thanks, good to know
@Cranky It's for a pompetamine, which is 135mm OLD. I do have some flexibility with the sproket on the hub, so I can hopefully fine-tune it. But not sure if I can get the chainline any lower.

@drøn that's a good point, but I was also tempted to make things more complicated for myself in the future: One reason why I thought about the alfine, or maybe go for a road double chainset, is to go for a double/double set-up. Something not dissimilar to this: there are 2 pictures of his/her chainlines (sorry for links within links. I'm not so hot at this stuff).

I was thinking of having rear sprockets of 21 and 17. And having front chainrings of 39 and 43. Hopefully with somewhat-functioning chainlines. And then I can chainge gear fairy easily*. I don't mind being a little off on chanline if it means slightly higher degradation of parts. I do mind the increased probability of my face hitting the dirt (or some other such painful malfunction), but but I don't really know what the parameters are for such happenings.

Also thought about White industries, http://www.whiteind.com/double-double/ but I'm incredibly (embarrassingly?) tight with money, so would like to consider less spendy options first. Also, I've already got these wheels, which have a free hub. But I might just start simple, get the bike on the road, and then think about overcomplicating things in the future.

Help and advice welcome. Derision and piss-taking discouraged, but tolerated if constructive.

Links within links:

Had a mental block, moving the cog further out is the opposite of what you want to do. Sorry.

That's OK. One day I'll forgive you.

@T4NY4 uses one on a cross-check. Might have some advice for you.
See:
https://www.lfgss.com/comments/13463919/

I have the SA 3 speed fixed hub. It's quite enjoyable. The only thing i would note is that it does feel like you're riding with a slack chain, but i got used to that quite quickly. Mostly I just ride in the top gear, which is 48/18 or something (same as my regular fixed), then use the other two for hills.

Ask me any questions you like and I'll attempt to answer.