Problems w/ Single Speed Conversion
 

I bought an old small frame to build into a SS for my 10 year old. The guy that flipped the frame had it sprayed so I don't know the make/model exactly, but he said it was a Schwinn. It's just a low-end lugged frame but the small size made it attractive. Here are my issues:

Frame sized for 27" wheels. Going to use 700c, so I had to buy some long reach brakes (Tektro R556 should make the 70mm reach). Can I drill out the back side of the fork to accomodate the recessed Allen head for the front brake?

There are no braze-ons for typical rear brake cable routing. I am debating just leaving the rear brake off. Is this a bad idea for a kid's bike? Is there an alternate way of running the cable/housing in absense of the braze-ons?

The rear drops are 126mm. I can either use a freewheel hub rear wheel with a thread-on SS freewheel or a 130mm freehub wheel with a SS cog/spacers. I assume i can spread/cold set the rear with out any problem, but I'm wondering if anyone has advice/preferences?

Thanks!

Yes, you can drill out the back of the fork crown with a 5/16" drill bit to allow a recessed nut brake mounting.

For any freewheeling bike, I consider a rear brake a necessity. You could buy two front brakes and use one in the rear so it has a long enough mounting bolt to go through the rear brake bridge and accept the nut. Drilling out just the forward side of the brake bridge to accept a recessed nut brake is possible but tricky. You can run the rear brake cable housing full length along the top tube and either do positioning crudely with zip-ties or buy clamp-on cable guides fo a neater job.

Either of your rear hub choices are fine. Cold setting 126 mm dropouts to 130 is no problem but generally a 130 mm hub can be made to fit 126 mm dropouts with only a little force so there is no need to cold set the frame except as a covenience. Use what ever hub and wheel combination you have or can get at the lowest cost.

+1 to all of Hillriders suggestions, except for the part about drilling out the fork. Drilling the back of the fork to enlarge the hole is easy, but you won't be able to do the counter bore to recess the head of the nut. That doesn't matter, it can sit outside without any problem, though you might have to buy a longer one. (they're available inexpensively in a variety of lengths)

The 130mm hub will work fine. You will need to spread the dropouts a little bit to get the wheel in but this is easily done by hand, especially with old flexy steel frames.

single speed
 

I would run the 27 wheel with the threaded hub as it is cheaper to buy, unless this makes bike to big. This will give good cornering clearance for the cranks. If the cranks are 1 piece then you can replace them with kids cranks in a shorter length and sprocket size for the 700c wheels. If you run 27" you would also be using a shorter reach brake for more power.

Some advice/opinions:

Get the widest tires you can fit in the frame. Most kids are pretty rough on stuff, especially bikes. Maybe yours isn't, but someday when some dumb friend borrows it and starts smashing into curbs the wide tires might protect the rims from getting dented.

I don't know how much you want to spend on this project, but IMO the best choice would be a 7-speed 126mm Hyperglide cassette hub (nothing wrong with a 130mm hub either.) Cassette hubs make SS projects so much easier because it's just a matter of adding spacers to get a perfect chainline. Or you could go with a flip-flop hub in case you ever want to make the bike fixed gear.

Most (all?) of my bikes as a kid only had rear brakes and I survived, but they weren't road bikes. Since your bike may be capable of faster speeds than most BMX bikes can reach, I'd definitely put two brakes on it.

I (tentatively) decideed on the freehub wheel 700. I built one from an old Ultegra 7 speed hub so it's 126mm. The problem I'm now having is that the skewer won't clamp down properly in the drops. I've never had this problem. The skewer ends are tightened all the way, but it's not enough on the clamp side. I'd rather not have skewers because it's a kid's bike so I'm getting some bolt-on skewers. I do have a 7 speed rear wheel in a freewheel. I could put that on, but there are no braze-ons for shifters. I want to keep it simple and light so will probably stay with a SS.

Next issue is bars. I have some old road bars but they are kinda wide (42). I also have some bullhorns, but I was thinking about a riser comfort bar. Problem with that is then I need new brake levers (I have plenty of road levers).

I will post some pics. Thanks for the feedback!

A couple of thoughts on this:

1. If the threading on the skewer stops too soon that the nut won't tighten, look around for a shorter qr. You may have one intended for an MTB (135 mm) hub and it's too long for a 126 mm hub. Even try a front skewer.

2. Possibly the dropouts on that frame are so thin the axle ends stick out beyond the dropout faces and won't let the skewer bite into the dropouts. Or, the axle is off center in the hub so one end sticks out too far and causes the same problem. Check if this is the case and, if so, either file a bit off of the axle ends or add a thin spacer to shorted the amount sticking out or center the axle so both ends stick out the same amount. .

This is what I suspected. I've had this problem before on an old mountain bike with thin dropouts. If the axle sticks out too far the QR will grab the axle instead of the dropout.

I'd ask the bike's future owner their preference on bars, unless this is going to be a surprise. I'm looking forward to seeing pictures!

I suspected both the issues mentioned with fitting the rear wheel in the drops (this drops and skewer bottoming). I think adding a knurled spacer/washer between the non-drive drop and the skewer will do the trick. I am using a skewer from a 126mm hub so I don't think that's the issue.

I have decided to go with a 45 deg stubby stem (Nashbar $5) and moustache bars. These bars give good control and an upright position while allowing me to stay with road brake levers which I have in stock rather than have to spend more on mountain-type levers.

The issue of ground clearance is interesting because of the 700c rims on a 27" frame. I am using Michelin 28mm tires so this helps raise the frame a bit. But, the shortest old stock cranks I had were Stronglight 170's. The platform pedals are also a bit wide. So, I am concerned about this. I suppose I could try to find a 165 crank on ebay.

On gearing selection, since the smallest chainring i had was a 42, I thought it would be good to go with an 18 tooth cog on the freehub for appropriate gearing for a 10 year old. I had some old Hyperglide cogs so I swapped out the Nashbar 16 tooth cog for the 18. The Hyperglide is cogs are thinner so swapped out one of the thin spacers for a slightly thicker one. When I clamped it all together the freehub was prevented from spinning. Somehow the lockring is pressing up against the freehub body I suppose, but the spacer seems right. I may just try to find a proper 18 tooth cog.

Because it's a kid's bike, I am thinking about additonal add-ons that will appeal to a kid. I have a nice LED light for the seatpost. I was thinking about a horn too. Anything else? I will post pics tonight.

The radial difference between 27" and 700C rims is only 4 mm or less than 3/16" so that won't change the ground clearance by any significant amount. I'd consider 700x32 tires, not for ground clearance issues, but for rim protection. 10 year old kids have been known to be a bit rough on equipment and those rims could use all the help they can get.

True, but I'm not going to spend any more $ on tires and since 10 year olds don't check air pressure anyway, it won't matter! The Michelin 28's seem pretty fat (more so than the Conti 2000 28's) and he's pretty light so hopefully the rims don't get too beat up. I did use an older front wheel so I won't be disappointed if it gets damaged.

This is why narrow tires are more problematic. Narrow tires have less air in them, so when they lose a little air the pressure drops significantly (compared to a fat mountain bike tire.) When tires don't have enough air the rims are more easily dented when hitting curbs, etc. If your son doesn't trash the bike I'm sure 28s will be fine, but if it breaks you've been warned!

If you can convince your son that fenders are cool, they can be a nice addition, especially shiny chrome ones.

recessed nut brakes are overrated, get the Nut fixed center bolt model..
it makes fitting fenders on it a piece of cake.

Freewheel SS needs 2 brakes ,run continuous housing to the back one .

Fit 2 brakes !

a 32 wide 700c is nearly same as 27x1.25" you may have room for a 35 tire , the chainstays & fork blades at the crown, are the inside clearance limit .

126 is a 6 speed spacing , If you get a freewheel hub . you just re center the hub with spacers on both sides of the axle . I'd use a solid axle secured with nuts.
then you build a wheel that is centered between the hub flanges..

it should be fairly easy to take the 130mm hub and replace/remove the spacer between the cone nut and the lock nut, then dish the wheel to center it again. if it's a quick release hub, you will need to get a shorter axle or just cut down the existing axle by a few millimeters. it's kind of a crude mod, but it should work fine.

This project is coming along. The issue with the rear skewer is the thinner drops combined with more axle sticking out the ends. I will add spacers on each side beneath the locknuts. Here's the current build spec. Pics to follow soon. Not all parts have been delivered to me yet. Gearing may be too tall.

Single Speed Project

Frame – Schwinn Varsity? Lugged, Horizontal Drops, 19”
Front Rim – Wobler Alpine 700c, 32 spoke
Rear Rim – Mavic Reflex 700c, 32 spoke
Front Hub – Shimano 105
Rear Hub – Shimano 600 Hyperglide Freehub (7-speed)
Single Speed Kit – Nashbar, spacers & 16 tooth cog
Skewers – Nashbar Bolt-On
Tires – Michelin Dynamic Wire Bead, 28mm
Tubes – Presta, Slimed
Cranks – Stronglight 103, 122 BCD, 170mm
Chainring – 42 tooth
Chainring Bolts – Single Speed/BMX type
Bottom Bracket – 105 square taper cup & cone, English thread
Chain – 3/32”
Pedals - platform
Seatpost – SR Sakae 25.8mm
Saddle – Fuji, chromo rails
Bars – Nashbar Moustache 52mm
Stem – Delta 45 deg rise quill
Headset – 105, 1 inch for threaded steerer
Brake Levers – BRS400
Brake Calipers – Tektro R556 Long Reach Dual Pivot
Kickstand – Greenfield
Bar Tape – Cinelli Cork
Bottle Cage - Blackburn
Light – Knog Gekko3 LED

Looks pretty good.

One thing I noted was the Mavic Reflex rear rim, I assume it's the clincher version, not to be confused with the tubular rim which is still in Mavic's line.

These were the successor to the Open 4 rims and proved quite fragile. They were rapidly replaced by the Open Pro in Mavic's rim line up. Given your son is 10 years old and light it should last ok unless he rides like a lot of 10 year olds, i.e. with little reguard for equipment care.

Yes, it's an old Reflex clincher. These had issues with eyelets breaking. The rim is a bit older, but it's 32 spoke and he weighs 90 pounds at most. I think it will be OK so long as I keep air in the tires. He doesn't ride over curbs or off road. It's basically just for burning down the block or for taking short rides with his old man.

http://bikeforums.net/attachment.php...hmentid=182936http://bikeforums.net/attachment.php...hmentid=182935http://bikeforums.net/attachment.php...hmentid=182934

Nearly finished with the bike. Here are some pics. Still need to add the chain but waiting on a larger cog.

Really nicely done. Maybe post a group of pics on the ss/fg sub-forum. I especially like the white calipers and bottle cage. Nice touch. :thumb:

Thanks, will post some pics soon to SS/FG.