After studying this for a week or so, I took the plunge and started to build up my homebuilt minivelo from junk bike parts. I started thinking that I wanted to build a bike that could easily be put in a suitcase by using sleeves as referenced in another thread, and I still intend to do that. But I decided I would build it up this way first just to make sure I like the ride before I cut the frame.

Here is where I'm at now. It will be a 52 chainring/16 freewheel single speed bike with front and possibly rear caliper brakes. I figure the less stuff I add to it the easier it will be to pack. I know the handlebars will probably have to be dropped some more.

I like it.

That's an impressively long seat post. And is that a quick release on the stem?

First of all, lucky little me, I would not need such long seatpost and stem. And this build is giving me ideas!...
Second, a question. Do you consider 451 mm wheels?

Cheers

you might want to put the saddle as far forward as you'll be more over the cranks then
will be steadier to climb then

have you got a close up of the stem?
did you cut the quill tube from a stem and then clamp a plain tube onto it?

Yes, it is a seatpost clamp and quickrelease.

Yes, I did exactly as you said, clamped as scrap seat tube cut from a frame onto a quill that had the stem cut from it, then filed flush. Works beautifully. And allows use of a quick release.

Does the seatpost flex much?

Not that I have noticed- I have only ridden this bike for a short distance but I have not noticed that seatpost flex would be an issue. The wheelbase seems a bit short but nothing insurmountable.

The way I see it, this seatpost is no longer than a Bike Friday and some folders?

The wheelbase could stand to be a bit longer, that would open up the "cockpit" for easier standing sprints and hillclimbing, but again, it's usable as-is.

i was thinking of the cockpit as well. the top tube seems too short for someone with legs long enough to justify that seatpost. of course its a scrapbike project, so understandably you use what you lay your hands on. please update us on how it goes!

I added chain, front brake, and am now able to take this bike on short rides. I think this will be quite a nice little bike for short trips. It took a short while to get used to, but nowhere near some other bikes (like some recumbents).

I am still waiting for the chain tugs to arrive in the mail. I used a cheap v-brake lever for the front brake, I was able to expand the plastic clamp enough to fit over the larger diameter handlebars. I will add the rear brake later for safety. The foam grips are not permanent, eventually if/when I decide this one is a keeper I will strip it all down, remove the decals, clean everything up and paint the currently painted parts. I think I will leave the chrome as-is since it is so durable.

There's alot to like about this bike- low step over height, extreme portability, very nimble handling, low weight (for what it is).

cool bike. Ive modified some kids bikes, and rode them.

very nice build. i have been toying with the idea of building a formula 1 BMX too. this diamondback BMX will be the guide.

Nice build!

I've been hunting Craigslist for a 24" tire BMX for a good price for the same project build. No luck so far.

Put a straight edge, on that seat post.. so you are able to compare it as it bends a little bit at a time.
to plan replacing it , before its too bent.

Is that one using chromoly steel ?

Hey, that's my bike! haha. Well, it WAS my bike. This thread is 5 years old, and many things have changed during that time.

As I recall, the bike's handling was very nimble. It was simple, relatively lightweight, and fun to throw around.

My plan was to keep the frame intact, but braze in a second top tube and second set of seat stays along with a seat tube extension to stiffen the seat area. Similar to how some F1 bmx bikes were designed. In the end, I disassembled the bike and stored the frame and other parts for years, only to have recycled them about a month or two ago.

Here's what I like about the concept: compact frame, bottom bracket in "correct location" for 20"wheelset, if you get a bmx frame with a long enough top tube (~21") the bike is OK for adult size riders.

The challenges: the seatpost (as already discussed), need a riser for the handlebars, rear dropout spacing not correct for geared wheel.

I say if you can find a geared 20" mountain bike with a 21" or longer top tube, you might have something. Similar to the F1 bmx bikes that marxmini is using.