ChiapasFixed

I think this could be a really great way to recycle discarded BMX frames and make nice little commuters that can go on the train or in the trunk of a car.

Also a great way to experiment before going ahead and investing in a smoothound, bianci, or quoroz freedomwon (man I like that bike!)

The major challenge I think is sourcing the super long seat posts and making sure they dont break.

If you have made a mini-velo like this in any config. pls post your picks and share your advice!

I know there was an earlier thread sort of about this, I really think this has potential!

griftereck

I built a 3 speed BMX a few years ago.

I had some steel tubing in my garden. was some kind of frame for a green house or something. I put another steel tube inside it. It was a tight fit inside the seat tube. Its stuck in there now. I stripped the bikes components. The frame went rusty. Crummy cheap paint I used.
I used a seat pin I bought in town on my Puch Minisprint. Its a regular BMX seat post. Cant remember the brand, probably DB as they have a lot of DB parts in that shop. The Puch is a little bigger than most BMX frames though.
Im 5 foot 8, or 1.7metre tall. The bikes fit me ok

ChiapasFixed

cool man, thanks for that!
i am thinking something like this:
https://www.fixedgeargallery.com/2005...hrisThomas.htm
and this is just the most beautiful conversion I've seen:
https://www.fixedgeargallery.com/2004/g/skid10.htm

gnome

Sorry for the non-drive side shot and not quite a BMX conversion.

My fixed gear min-velo is built up on a Healing Cruiser (locally made Raleigh 20 copy) which has a nice tall seat-tube. In high gear it's geared 52/14 for 69 gear inches. I think my seatpost is just a regular 400mm one.

gnome

Found a drive side shot in it's current configuration. I blame it being late at night and my brain turning off for the night an hour ago for the previous Non-Drive side shot.

Swapping the flexy long reach caliper for the sturdy black BMX one and fitting KoolStop pads has improved the braking considerably.

ChiapasFixed

hey gnome, that is nice!
advantage being that bike was intended to be ridden over long(ish) distances, hence the adequate seatpost, unlike a BMX...
I still think using BMX frames is fine, and am decided to try it. I am thinking about seatpost isssues mainly such as:
-is there generally a size (diameter) BMX seat tube, or do they come in a wide variety as most bikes do?
-what materials and gauge of tube would best ensure safety with an extra long seat post?
where can I source said seatpost/tubing?

other concerns also come to mind such as:
-will most BMX frames accommodate a standard cartridge bearind square tapered bottom bracket?
-will I be able to fit the right stem to a standard BMX fork, or will I be better off fitting a road-type 20" fork from another source?

all these questions will be answered by doing, but if anybody can share some of their experience it would sure save me some time and effort!

thanks!

NormanF

I think you'd want to use a non-racing frame. A BMX frame is just not designed to be a commuter.

LittlePixel

Actually - this sort of topic has come up before - lots of info on this thread...
https://www.bikeforums.net/showthread.php?t=396754

If it were me I'd look into (rarish) F1 BMX frames, and 'Tall' adult sized frames like the Mongoose moosgoose as a starting point - the geometry might work better without need for a really long seatpost.

F1 BMX:



Another:





Moosegoose- look at the height of the top tube compared to a 'normal' bmx...


Moosegoose:


...compared to 'Normal'

NormanF

I concur that a Moosegoose or F1 type adult frame is the best way to build a comfortable mini velo. At least it doesn't look ridiculous on an adult and the geometry will be suited for long distance riding. A BMX frame is typically used in stunts and dirt jumping and it doesn't really lend itself for the road.

griftereck

older BMXs will probably have a 22.2mm = 7/8" diameter seat pin. these will be constant thickness.
the newer ones are going oversize. But this ussually means 25.4mm = 1" diameter. these will step down in thickness at the seat clamp
this is quite common size. so you could easily get an alloy 400mm post in that size.
I geuss there are BMXs that use different sizes of post. For instance Mark 1 Raleigh Burner BMXs used the 28.6mm seat posts. Thats the same post that fits in a Twenty. Think they used some of the tubing to make the different bikes
If you get an old BMX. It will have a treaded headset and a 21.1mm = 3/4" diameter quill stem.
Some american road and MTBs have this size of stem. Also late 80s early 90s low end Raleigh MTBs had that size. Ive got some old Kalloy and SR stems in 21.1mm diameter quill
Newer bikes are likely to have an 1 1/8" Aheadset. This is the same as MTBs and road bikes. So is easier to swap stems. Thought you might have problems with the bars. As a lot of BMX bars are constant 22.2mm diameter along the tubing. Where as MTB and road bikes often have a centre bulge on the bars to fit in a larger hole in the stem.
BMXs ussually have a smooth large diameter bottom bracket. This is for 1 peice cranks. You can get either a special axle that has the BMX style cones screwed to it. Or special cups that push into the frame and are held together by long bolts. DMR make those. A screw in BB cartridge would go into there.
Ive got the special axle in my City folding bike just now. I got it from a Raleigh Dakota. But have a set of DMR cups. So will swap them into the City, as I want the special axle for an old MTB build.
You get BMX 3 peice cranks. They use special axles. Some of them have hexagonal ends, instead of square tapers or splines.

griftereck

if you want a nice bit of strong tubing you could look in a custom/chopper motorbike shop.
some chopper builders fit dead straight bars to there bikes. Ive seen them called Broomstick bars. Sometimes called drag bars, but sometimes drag bars have a slight bend, so they arent so uncomfortable to grip.
Most motorbikes use 22.2mm bars. But Harleys and some bikes from Japan use the thicker 25.4mm bars.
Motorbike bars are made of thicker metal than bicycle bars. So are strong but a little heavy. Though you can get Broom stick and drag bars in nice coloured alloy.

rench123

My neighborhood ride. Singlespeed. Lugged frame and fork from a "mini-racer" - small wheeled road bikes common in the Philippines in the 80's. Wheels are 451. Seat and seatpost from are standard mountain bike parts, Handlebar and stem are BMX parts.

I still see a few of these around the city, used by couriers with the drop bars turned upside down. I like the extra height and stiffness provided by BMX bars.

ChiapasFixed

great guys! thanks for all the responses and the great info Grifterek!
I do like the f1's, although my original intent is to see if one can build a little urban commuter from discarded frames with virtually no money...
I am now armed with more info to try a prototype! will keep posting once I find a frame to start on.

NormanF

The parts are cheap and readily available so one is out not too much money. If you don't have too much to spend, build a single speed little urban commuter. It will be fast enough.

Arrowana

Any idea how these compare to normal bikes? I've been wanting to get something to replace my Sears 3-Speed that is lighter, and has a wider range for the gearing. I was going to get a decent road bike and a Nexus 8 hub, but after finding out about these and the Sturmey Archer 8 Speed, I realised I could probably have a complete bike for less than a Shimano Hub. I've read a bit on folders, and it sounds like the good ones can ride as well as a normal bike. These don't have to worry about folding, but they also aren't designed to be used like this.

Maybe I'll have to get the bits and peices to get my BMX working and try it.

rench123

the ride is a bit harsher because of the smaller wheels. I ride my mini more than my 26" wheeled commuter bike. I like its responsiveness.

NormanF

That can be compensated with medium width to fat tires. Skinny tires are unsuitable unless one has a suspension fork installed because of the harsh ride. Big Apples on my Raleigh Twenty are comfortable and it still rolls fast.

Arrowana

I suppose I could also throw my Velo Webspring Saddle on it too. It made quite a difference on my 3-speed.

8-Speed hub will have to wait awhile though, I need studded tires and fenders for my MTB first.

NormanF

I got the Schwinn Qualifier today and being a one sized fits all frame, the problem of the bars being too low was solved with a stem swap and installing a Wald 8069 high rise bar. It felt good!

fiberunner

Hello.
Sorry about ask after so many time, but I´ve just found this post. I would like to do something very similar to your conversion.


So I would ask you some questions.


First of all, Did you finish your project? How was? Did you enjoy the result? Did you enjoy it for much time?


How did you solve the problem with the extralarge seat post?
- What was the measure of the diameter of it ?
- How long was it?
- Did you strengthen it? How?




Thank you very much.
PD. Sorry about my awful english

bhkyte

Telescopic posts are available on ebay for a varity of sizes. I found race bmx bikes not too bad for medium rides with the seat post fully up. Modern bmx bikes tend to be stunt bikes with lower seats and heavy frames and rubbish (no) brakes.

If you find a modern race bike it will be expensive.

fiberunner

Thank you for the answer.
The problem with the most Telescopic posts I have found in internet is that they are for folding bike and they have a very big diameter. The bike that I have needs a 26 mm diameter seat post, 26 or smaller with an adaptator. The longest that I have found is 540, I think it will be a little just, I prefer a bit longer.

fietsbob

actual BMX rases , as seen in the last, London UK, Olympics are fast sprints over a course with a Lot of bumpy rollers and corners .. Moto-cross with a Bicycle.

so even the non trick skate bowl X Games Riders dont sit down, other than when stopped .

fiberunner

Will not be my case, because I usually ride more relax than the examples that you have said. For this reason I need a extralong seatpost.

bhkyte

its not quite true that bmx racers never use their seats during a race.
most don't but i raced against a nationally ranked racer who had his seat at a regular height and peddled around some corners. on pro modern courses yes riders never sit down unless well infront in a qualifer or maybe in muddy conditions.