Mini-velo conversion?
 

OK, so I've loved the looks of the minivelos for a while now, that Japan market Bridgestone, the Dahon Hammerhead, and the like. Pacific Reach. Tyrell (yowza!). If cost were no object, I'd already have one.

Trouble is, cost is always an object, so I've put off any minivelo purchase. To tell the truth, if I was going that way, I'd probably go with a Swift and add folding to the mix as well. But still out of reach at the moment.

However, in my stable of bikes is an early 90s Cannondale "Beast of the East" M800 mountain bike currently set up as a commuter. The canti studs are positioned for BMX or roller brakes, which were cheap or obsolete at that point, so when I built it up, I had wheels made with Sachs drum brake hubs. Been a great commuter setup--the bike was named "Beast of the East" because it is great on trails in the east, with tighter steering than usual for a mtn bike and a way-high bottom bracket. That got me thinking and I'm looking for some confirmation.

I was thinking I could easily have the hubs relaced to 20" rims. The bottom bracket, measured from the ground to the center (crank bolts) is 13". On our tandem, the height is 10.25". Difference of 2.75", 70mm.
Going from rim size 26 (ISO 559mm) down to 20 (ISO 406mm) gives me a difference in diameter of 153mm, radius 77mm difference. Compared to difference in bb heights, 20 wheels on the C'dale would put the bb center 7mm lower, about 1/4". (Uh... (26-20)/2-2.75=.25 ..note to self: Duh!)

So I'm thinking this has a good chance of working out. Yes?

Reference bb heights:
Swift: 11.5"
Trek 520: 10.9"
Converted M800: 10"

Seems like it would be a bit low. Currently running generic Kenda 1.5" slicks, would go with Schwalbe Big Apple 2" on the 20 rims. Starts defeating the purpose of a low cost conversion, but I suppose I could go from current 170mm cranks to 165 for a bit more pedal clearance if need be.

Hmm...

I think you could do this - I think it'd need shorter cranks to be safe but it does start with a high bottom-bracket and the height (based on looking at the just-off-horizontal chainstay) looks similar to my Raleigh Twenty which went from 451 to 406s.

I took the liberty of doing a fast and dirty photoshop so you can see what would happen. This *is* to scale based on ISO sizes [406, 559] of the rims, the new ones with Big Apples taken off a 2008 Speed P8 Dahon

You might gain a couple of mm in the BB dept if you ran an ENO singlespeed eccentric hub in the rear as you'd be able to rotate the axle downwards in the dropout and effectively hoist the rear up by a few mm. You could also try longer forks but this would dick around with the geometry.

I say give it a go. It's a cool idea and one I'd definitely try. One avenue of exploration might be to go for 451 sized wheels - there will be a gain of a few mm in rim size (22.5mm) but a loss when you try to find a big tyre like the Big Apple so you might end up with the same effective diameter. I think it'd be sweet on slicks. But then I always do - tyres have to look like elastic-bands stretched over the rims in the Littlepixel house Lol....

Hope the image helps with the plan... (I left 'ghosts' of the original wheels to help see the two sizes)

http://www.littlepixel.info/twenty/Cannondale_M800.jpg

Ok so who wants to fit 349s to a Badboy Ultra? :)

Maybe you could go for a 24" wheel instead and gain some of the advantages of a smaller tire and avoid some of the disadvantages? Then you'd have no clearance issues on the BB/cranks and the derailer would have better ground clearance too.

Regards
T

Wow, LittlePixel, thanks for the photoshopping and sorry I didn't see this sooner. Kinda looks more like a BMX bike with gears, but no real getting around that. This really gives me some inspiration and impetus to get the ball rolling. The aluminum frame is pretty jarring, as is, running the Kendas around 80-90 psi, so I'd definitely be looking for some cushioning tires, especially at smaller diameter.

timo888--derailleur clearance. Right. Forgot about that. How big an issue is it with 20" wheels? I see bikes with Capreo drives (mostly 16" wheeled bikes?), also regular derailleurs. Dunno if it matters, but existing derailleur is a Sachs New Success mtn unit.

Other things to consider: It's currently set up as a decent commuter with fenders and rack--if I make the change, I'll need to rig something up for fenders, and the rack is going to look pretty silly way high above the rear wheel. Also, winter's coming and I was thinking of getting a set of studded tires to use it as a beater. This might become a springtime project....

I think it looks pretty good - nicer than a Cannondale Hooligan (see other current thread).

You shouldn't have problems as long as it's not a loooong derailler. Just avoid tree-stumps... ;)

Fenders - how about some crud-catchers fitted to the frame? Rack - same really. The gaps will be bigger but I don't think you'd find a rack for a 20" bike that would fit the bosses on that frame (ie it would have to be fitted well below them and then somehow extend upwards to fit the fitting spots)

I have one seating here. Disk brakes, even easier. Not on my list of priorities right now though, but I will give it a shot. It's only a set of wheels after all.

EDIT: It might be a good idea to consider shorter crankarms as well...

I want to see this! ;)

Right, so I don't really want to convert a pair of perfectly good 26" wheels to 20" on just a whim--too much work for not enough return. Next best thing? Find some donor 20" wheels for a bit of proof of concept prototyping.

Got a kids bike from the dump for free, with 20" wheels. I tell you, this bike is perfectly fine except for rusty chain, flat wheels, and a broken front brake lever (at the clamp--entire lever and CLAMP is made of plastic). What some people throw away... The really great part is that the wheels have white tires and screaming metallic magenta (girl's bike) rims, which will look *****in' on my basic blackout commuter. The clip on sun and moon spoke tchotchkes had to go, however.

Wheel spacing is about an inch short to make the rear wheel fit. I threw the wheels under the bike to see what it looks like. Remarkably like the photoshop workup above... except with fenders and a rack that now sit about a mile above the tire. BB height worked out exactly like I thought, 10" off the deck, a bit low but hopefully not too low. Last night I disassembled the coaster brake hub--wonderfully crude tech there--today I got a longer axel. Tonight, I'll rig something together and take it out for a couple of test rides. My wife actually likes the idea and if I go that way, may indeed lose the bike to her.

Once I'm done with testing, I'll rebuild the girl's bike and drop it back off to the "free for the taking" part of the dump, only it will actually be ridable. Win-win situation.

Thanks for the update. If you get a chance, post some pics so we can see your progress.

--sam

I love the bit about taking the bike back fixed up - Pay it forward.
Yes - pix please!

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I could just as easily post this in Alt Bike... or SS/FG, heh.

OK so here's the bike set up with 20" tires. These are 406 rims, tires are 1.95 wide. BB is 10" high.

Looks like a very strange BMX bike...

Rides amazingly well. And fun? Woah, let me tell you it is way fun just to throw this thing around, hop curbs, cruise. When I think about it, it's still going to be a pretty twitchy bike, and shortening the trail probably doesn't help with that, but the steering didn't feel as different as just the lighter weight and accelleration of the wheels. 20" bikes are fun. Didn't go for a big ride, and it wasn't the best test without shifting. And only a coaster brake, so basically all the controls up there are dummies that I just didn't want to disassemble. What can I say, I'm lazy. Seems like I got a way tighter turning radius. I keep the inside pedal up, outside pedal weighted when turning anyway, so pedal strike in corners wasn't an issue. They are somewhere between .5-1" lower than where they are on my other bikes, but the only time I hit was when I was intentionally trying to, doing very tight circles at increasing speed. Otherwise, no pedalstrike. I could live with that.

Digging into a coaster brake hub for the first time was fun. Brutally simple and elegant mechanism. This hub was a Chinese YCC knockoff of a Shimano hub and the exploded diagram from Sheldon's site helped. The axel swap was a piece of cake. Took off the fenders and rack. I was off by a half link trying to run it off the 36 middle ring, but the 48 big ring was perfect... just had to swap them around for some kind of chainline.

Pretty goofy, but enlightening. Going with 20" wheels is certainly a possibility. Still not sure I want to tear into a perfectly good 26" wheel setup. But maybe an excuse for another set of drum brake hubs... Only thing keeping me back at all is the thought that it takes away the utility and turns it into merely a wicked fun bike--I'd have to do some serious rigging to get fenders to fit. Although just the rack would turn it into a nice fair weather commuter... which is just the opposite of its role as a winter beater... although part of the whole reason you got your uber commter with IGH and tire clearance to fit studded tires was for possible winter duty...

Neat - I'm looking forward to seeing the evolution of this project.

Looks seriously cool.

I love that on so many levels - bravo!

Yeahbut here's the conundrum: New drum brake hubs (good luck finding used drums...), plus spokes, plus rims, plus tires & tubes, plus freewheel/cassette, plus labor for the build = used Swift, Dahon/new DownTube price range.

This current conversion cost me $12.99 for a new axel, all told. To tell the truth, if I hadn't just completed another coaster brake bike build based on an old cruiser frame, I'd be tempted to run this setup for a while. Who am I kidding, the pink wheels will stay on for at least a few rides this weekend.

You can get new Sturmey-Archer drum brakes at a reasonable price. The rear can be with a single speed, 3, 5, or 8 speed hub. The 3 is the best geared one - simple and lighter. Get the hub with the least amount of spoke holes you can. They are very large flange which makes building a 20" wheel with more than 32 spokes a hassle - go for 28 hole if you can get them.

They are great hubs, really free spinning. (I use a set on my mud bike) They are also shiny and pretty IMO :)

What price an original work of art, eh? More personal satisfaction than a used Swift etc. In any case you can always transfer the bits over later.

That might be the motivation I needed to start my 20" wheel search for the Bad Boy Ultra. Good job!

Thanks! Check BB height on your bike first--Beast of the East has stock 13" BB height as one of it's features, and the height with the 20" wheels at 10" is on the very much lower side of where usual BB's are located. I'd not want to be pedalling through a turn on the new "Slumber Party Beast." Pix show the bike standing on its own, on a slope. I can't do that with most bikes I own--like I said, even with the elevated BB, the pedals are still lower than usual for me.

what about using sidepull calliper brakes. Maybe from the donor bike.
make a bridge out of thick steel. with 3 holes on it.
one in middle for the brake spindle. The ones at the end.
then bend steel round the seat stays or fork legs
then bolt it to the thick steel bridge.
if you slot the end holes you can have some adjustment, as the frame tubes might not be parralell

Cheap workaround, have spare hubs, would look totally kludged. Hmm. Might even be able to use existing canti mounts to facillitate this. Double hmm. Cheaper still if I delve into my first ever wheel build. Donor bike sidepull front caliper is absolute pot-metal *****, unusable; rear is coaster brake/non-existant--would have to buy new/used sidepull calipers. Or pick usable items off another dump bike, which might include usable rims.

Thanks for the idea! Sounds like a wicked cheap solution, if not 100% elegant. But who am I kidding, elegant has nothing to do with this bike...

I'm just starting on a similar project, also trying to do it on the cheap. Clearly the BB height and the brakes are the challenges with the mountain bike to velo conversion. I think $300 is the starting price of a commercial mini-velo, so once my parts list exceeds about $150, I will probably just go with an off-the-shelf bike. Another option I'm considering is to starting with a kids 20" multi-speed bike; extend the seat post and stem. I'm wondering about the minimum wheelbase I can get away with: 36"? Robert