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Old 04-18-11, 11:25 AM   #1
Pukeskywalker
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BMX to mini-velo conversion suggestions?

I have a question for you... I'm thinking about taking a bmx and converting it into a higher, more-upright bike similar to a mini velo, like this:

http://www.fixedgeargallery.com/2004/g/skid10.htm

This bike, however,would have brakes and a front derailleur (I think a 2 speed bmx with a fd and tensioner is possible)

can anybody recommend a certain brand/decade of bmx to look for on CL and ebay? Something that is aluminum or 4130 cromo... decent BB heights for 170mm road cranks... and not too expensive? Budget for this project is around $100... conversion parts are going to be at least $35 of that.

Thanks

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Old 04-18-11, 12:20 PM   #2
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Just me, but I restored a 20" BMX at the beginning of the year. I'm relatively disappointed in the speed of it and distances that I can ride it. But that has to be qualified too, I like you am an atb & roadie that decided to dabble into bmx. To me, the bmx I have is a non-foldable that behaves like a single speed foldable for what I use it for. In fact I see old retirees riding their Wal-Mart bmx's like foldables all the time. I think they ride theirs that way, because a foldable is still expensive and these bmx's are a cheap alternative. Throw a cruiser seat on one and it's comfortable, slow, you can even add a basket and do light grocery shopping.

The bmx frame is rock solid and that's an advantage because I'd think even a hi-ten bmx frame is going to be virtually indestructible provided you don't do the tricks. And that link you have, you aren't going to be jumping in a fixie's/roadie's crouch anyway. But the tires, frame and speed of the bmx is probably going to leave you thinking why you tried to make it a commuter ? I mean the fat tires aren't conducive to getting anywhere fast as well because of contact and rolling resistance of a 20" 2.10 or fatter tire. The bmx I have isn't anything I would ride out of the neighborhood. I'm fortunate that I have a couple of parks with trails that I don't have to load the bmx in a truck or suv to get to & ride. But again, that's as far as I'm going to ride the bike.
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Old 04-18-11, 12:42 PM   #3
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fuji, do you have a picture of your bmx? I was expecting it to be slower than my road bike, but not super slow with this set up. The gallery I linked to above is a guy using his as a courier.. so that has to be worth something.

I was thinking slick tires, pumped up a little to high, and as aero of a seat set up as possible given the short seat-to-handlebar distance (I was thinking a layback seatpost to help with that one)

I know the ride would be really harsh on 20" wheels... factoring that in.
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Old 04-18-11, 02:52 PM   #4
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Your idea isn't that original. Huffy made a Pro Thunder Z2 in the 80's that was a two speed. What was kind of unique is the shifter. The right grip twisted like a motorcycle throttle to shift.
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Old 04-19-11, 02:38 PM   #5
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Your idea isn't that original. Huffy made a Pro Thunder Z2 in the 80's that was a two speed. What was kind of unique is the shifter. The right grip twisted like a motorcycle throttle to shift.
wow. Crazy chain line too..
http://bmxmuseum.com/bikes/huffy/17815

I'm a little confused about the tension relief happening on the top on the chain... I'm guessing that portion of the tensioner was fixed to the frame and stationary.

Edit: I think the bmxmuseum guy has his derailleur set up wrong, it should look like this:
http://i616.photobucket.com/albums/t...s/100_2516.jpg

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Old 04-24-11, 02:42 PM   #6
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I would look for an old race frame with a "euro" bottom bracket. that's a standard BB for road/mtb. it will be the best thing to make it compatible with a double-ring road crank.

the hard part will the chain tension. you can't put a rear derailleur on a bmx bike easily. you might be able to use a der hanger from a cheap bike with semi-horizontal dropouts. also, how do you plan to put cable stops on the frame for the FD?

I think your best bet is to get a long bmx frame (a 21" top tube is considered pretty long) and run it as a single-speed with a tall seatpost (qr clamp for ease of storage) and some tall bars and run it as a single-speed. bmx frames are spaced at 110mm, so a 130mm road hub or 135mm mtb/hybrid hub will not fit in your frame. the FD fitting will be even more difficult.
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Old 04-24-11, 05:34 PM   #7
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Done it:

It's totally doable and the the bike rides really well. (Not to mention a great conversation starter)

Mine started off as a low end kids bike I picked up for $10. ( I later found it might have been a Formula One bmx).
I ripped everything apart, installed a euro bb converter, put on 165mm cranks and 451mm wheels.
Because my headset's inside diameter was 21.1mm (which a lot of bmx are), I had a really hard time finding a long quill stem. Finally settled on a quill stem extender.

It's really nimble, and not that different from riding a road bike. My longest ride was a 70km round-trip from Baltmore to Anapolis. A plus is I've packed it into a cardboard box within airline's regulation size, so I can take it on trips with me!
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Old 04-24-11, 07:40 PM   #8
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An acquaintance of mine fitted a bmx bike with a long seat post similar to the velospace bike. He says it's very easy to lock up the rear wheel due to the way his weight is distributed.

Cool project though, be sure to follow up with your progress,
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Old 04-25-11, 01:09 AM   #9
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Quote:
Originally Posted by Pukeskywalker View Post
fuji, do you have a picture of your bmx? I was expecting it to be slower than my road bike, but not super slow with this set up. The gallery I linked to above is a guy using his as a courier.. so that has to be worth something.

I was thinking slick tires, pumped up a little to high, and as aero of a seat set up as possible given the short seat-to-handlebar distance (I was thinking a layback seatpost to help with that one)

I know the ride would be really harsh on 20" wheels... factoring that in.
This one has the 44/16 single speed setup and with 20" wheels is roughly 55 Gear inches. I find my SS/FG with 700C x 25 pushes 76 GI. So relatively speaking the bmx spins like crazy in comparison, but sure doesn;t feel like it because the tires are balloons and simply don't feel nimble even aired to the 65 psi max. My front tire is a 2.25 and the rear is 2.10. Most bmx today are 2.10 front 1.95 rear. I can ride it for 45-60 minutes, but it's mostly standing up and that takes it's toll on the back and legs. I don't think I've gone more than a mile and a half with it away from home. But riding it within that area in a local park that had a combination of asphalt & trails and weaving thru the park. I can put on a good 5-7 miles with 3-4 laps around the park. As for the track, road and atb bikes that I have, I can ride those 15-20 miles depending upon traffic conditions in about the same time the bmx gets a park workout. I guess I could throw a 50+ tooth front and maybe a 14 on the rear and get more power GI, but I'd also think more about going with a 24" wheel bmx ? And this thing weighs 31.2 lbs (mines a 2003, but the 2002 is essentially the same thing):

http://www.bikesdetails.info/Haro_Ba...l_X1_2002.html

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Old 04-25-11, 01:58 AM   #10
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That Huffy Pro Thunder Z2, 20 x 2.125 wheels, 32T/40T front with a 13T on the rear. GI is only 61.5 in the high gear, 42.9 for the low gear:

http://bmxmuseum.com/bikes/huffy/37409

The 44T/16T and 20" setup I have is 55 GI. Most new bmx are 25T/9T with 20" tires that's 55.6 GI. Special_k going 70 km round trip that's 43.5 miles, I'd like to know how long that took, because that kind of mileage on a 20" bike, I doubt I'd even try that if I were still a pre-teen or even teenager ? I'm impressed, must be an animal cranking that bike long distance like that. Heck of a commitment to go 20+ miles away from home in one direction. Because once you're there, it's 20+ miles back. But I guess if one could get the GI to approach 44/18 and 700C wheels (that's roughly 63-65 GI), maybe it's not as hard as I think it would be ? More like running an 26" atb at a lower gear setup for a couple of hours ? The 24" wheel bmx with 25T/9T is 66.7 GI. That's why I suggested that.
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Old 04-25-11, 05:10 PM   #11
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I have a 53t chainring and a 16t freewheel in the back, on 451mm tires = 65.9 gear inches
I don't remember exactly how long I took, but probably around 3.5 hours. I had to admit I was dead tired on my way back though.
I'm putting some gears on it this summer.
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Old 04-26-11, 08:22 PM   #12
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Get one of these http://www.bikesdirect.com/products/mercier/nano.htm
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Old 04-27-11, 05:20 PM   #13
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I just want to say these bikes are awesome. And you can find some cheap 56t chainwheels around...
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Old 04-27-11, 11:49 PM   #14
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Those look pretty neat and beating the 2.10+ tire width issue with 1.5's" on it, 16 speed (42/52 crank & 12-25 rear cluster). The frame on that isn't the fat bmx, so it's not gonna feel as solid, but probably more like a 26" atb/mtb with 26 x 1.5's on it ? Price is pretty reasonable for 100% chromoly. Building one of those from a frame up will probably get you to the figure modifying a bmx without the headaches of solving where to get the parts, cost & thinking out the resolution ? Just my experience with a refurb bmx, if you get one for $ 50-100 or so, expect at the least to throw another $ 50 in tires and whatever a seat post will run ? This link actually has a nice tip at the top of it for understanding bmx tires generally needing 406's. I know I'm going to need new tires soon for the bmx I fixed up. Hard part is finding really budget & economical 2.10 & 2.25's like what are OEM, I may have to go 1.95 & 2.10 going foward, perhaps just 2.10's front & rear ?

http://www.everybicycletire.com/Shopping/c-15-20.aspx

These definitely are the Shetland ponies of commuting.

Funny, the more I look around the area and see others using bmx as alternatives for commuting transportation, I see retirees using their bmx's for a cheap alternative to a folder. Then I see the young hood gangsta's riding their bmx's for short commutes. They probably see me as some where in between ? Or maybe they just don't see me or give it any thought ?

Last edited by fuji86; 04-27-11 at 11:56 PM.
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Old 05-05-11, 10:38 PM   #15
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here I was thinking I had an original Idea and then I come across this.
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Old 05-08-11, 04:21 PM   #16
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You might want to try this to get the two-speed gearing, assuming you can lace up a wheel using one. I know that they've become common on folders again, and on urban commuter bikes like the Torker KB2. Worksman has them available on their bikes also.

http://www.sturmey-archer.com/products/hubs/cid/7/id/55
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Old 06-02-14, 03:58 PM   #17
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Quote:
Originally Posted by Pukeskywalker View Post
wow. Crazy chain line too..
1982 Huffy Pro Thunder Z2 - BMXmuseum.com

I'm a little confused about the tension relief happening on the top on the chain... I'm guessing that portion of the tensioner was fixed to the frame and stationary.

Edit: I think the bmxmuseum guy has his derailleur set up wrong, it should look like this:
http://i616.photobucket.com/albums/t...s/100_2516.jpg
Hey that's mine, the photobucket one. Surprised you found that pic, I forgot about it. I really need to get that bike out of the attic someday and clean it up.
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Old 06-08-14, 01:44 AM   #18
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I have adapted BMX and kids bikes into Mini velos.

Heres my Townend Megaforce 1 F1 BMX that I have.


F1 BMX was a short lived race series, for geared BMXs. A few manufacturers built bikes for it. Ive seen photos of a bike with full motorbike style fairing.

Try to get a bike that has a 25.4mm diameter seat pin. So that the seat tube has an outside diameter of 28.6mm. So you can easily mount a front mech. I tried to fit a front mech to a bike that had a thinner diameter seat tube, using home made shims. Never worked.
Front mechs are rated for a certain angle of the seat tube to chainstays. Bmxs with high BBs often have the chainstays pointing down to the wheel axle. where as bigger wheeled bikes have the bb lower than the wheel axle. It might cause problems.

You can fit internally geared hubs to BMXs quite easily. Shopper/ folding bikes often have the same wheel size, and the hub width is similar. Well for the old/low end 3 speed bikes.

Modern...er new school BMX, well the better models, might have a cassette hub. some have a really small cog. 9 tooth. And are to be used with a front cog of around 25 tooth. So giving a near 3 times gear ratio. Over 50 gear inches. I don't think theres any reason they cant be used with bigger front cogs, to get higher gear ratios. Might have problems using them with a tensioner. The hubs will likely have a thick, 14mm diameter spindle, instead of the older 9 to 10mm...er 3/8" diameter. So would need a suitable frame to fit, probably a modern one, upto about 10 years old. Older frames might be able to be filed, ground out to fit a thicker axle in the drop outs.

Ive had the idea of fitting road or MTB chainrings to a BMX crank. Ive not seen it done. Maybe theres problems. I thought one of those solid chainrings could be modded, cut off the teeth so that the diameter is less than the new chainrings. Then drill the holes in it for the chainring bolts. So would get round the cost of changing the whole cranks.

If you do want to change the cranks. You can get adaptor axles. That have all the bearings and cups that the BMX axle had. They have a square taper on them, to fit 3 piece crank arms. There ok. Im gonna fit that to my Townsend. But a lot of crank manufacturers are making cranks that don't have square tapers. You can get adaptor cups. That push into the BB shell. And have the standard English BB threading in them. I had a pair of cups from DMR, never got round to using them tho

If your wanting to fit a chain tensioner, or a rear mech to tension the chain. You can get a claw, that bolts onto the axle. Often seen on cheap bikes that don't have the gear hanger as part of the drop out. Ive managed to fit a claw backwards, so it more easily fitted on a rear facing drop out.

Modern multispeed bikes often have a removable gear hanger. So if you bash the mech it doesn't damage the frame. Theres seemingly hundreds of these. some might suit being bolted to a BMX drop out.

Last edited by alecw35; 06-08-14 at 01:56 AM. Reason: spelling mistake
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