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Road conversion to fixed, Bodge ?

Ste_SSte_S Posts: 1,173
edited October 2007 in Road general
I'd like to convert my Carlton road bike to fixed. Forward facing dropouts, and rear hub is a campag screw on type.

Should i get a new rear hub and track specific chainset, or can I get away with spacers and loctite'ing a sprocket onto the screw on hub ? Will have both front and back brakes, although getting used to back pedalling to brake may be nice if i get around to entering the local track league next year.

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  • BronzieBronzie Posts: 4,927
    I converted an old 1960's frame to fixed last year - didn't bother with a track chainset, just using an old Shimano 105 chainset and 3/32" chainring (works OK with 1/8" chain). I did get a 107mm bottom bracket to give the correct chain line*. Using a Miche rear track hub with 1/8" sprocket.

    Not sure about using a screw-on road hub - will probably be ok as I rarely find backpedalling necessary with front and rear brake.

    * - but make sure that there is still enough clearance between the chainring and the chain stay - may limit what size chainring you can fit - I'm using a 42 front on mine
  • What you need to buy to make a fixed gear bike depends on how fussy you are, what bits you have lying around and how much you can afford to splash on 'proper' gear. Try this for the 'economy version', which I've used for the Carlton Corsair I'm running as my fixed wheel bike. I've made mine a cruiser style with sit up and beg handlebars and fat 42mm hybrid tyres and it's a real hoot to ride.

    The crankset is now a biopace era Shimano 105 with a 48 tooth chainring (not biopace!) mounted on the inner position on the crank. With the same BB the original Raleigh branded Suntour crankset had the 52T chainring on the outer position for the same chainline. I only changed the cranks because the gearing was slightly too high and I had a 48T chainring that fitted a Shimano crank, but didn't fit the Suntour cranks. Large chainrings won't fit on the inner position if the BB is too short as there isn't enough clearance at the chainstays. You need to fiddle with cranks and BB axle lengths until you get it right, depending on what kit you have, there are no rules just trial and error.

    Out back there is a standard screw on freewheel hub, without the left hand thread lockring you get on proper track hubs. I use the right hand thread lockring off an adjustable bottom bracket tightened up against the fixed sprocket and it works just fine. Tighten up the fixed sprocket and lockring as much as you can, then go for a ride up a steep hill applying constant pressure on the pedals, but when you slow down use just the brakes and take your feet off the pedals so you don't put any unscrewing torque on the sprocket. Then retighten the lockring to take up any slack from having tightened the sprocket on the thread and you shouldn't have any problems with the fixed sprocket working loose, especially if you make use of the back brake too. At least I haven't in 3 years.

    I swapped spacers over on the rear hub to centre it more and move the sprocket over to the right, which is essential to give it chance of lining up with the chainring. I think there was a 20mm spacer fitted to make room for the original 6 speed freewheel. I replaced this with a 10mm one on each side of the hub. When you have done this, the rim has to be recentred as it will now be 10mm off centre to the right. Just loosen all the right hand spokes by one turn and tighten the left hand ones by the same amount and it will be pretty close to central. This is made easier if you have box section rims as you won't be troubled by protruding spoke ends. Otherwise you might have to file them down.

    The only specialist part needed is the fixed wheel sprocket (mine is 18T) which was £6 from Spa Cycles. Everything else can be from the donor bike and old bike parts cluttering up the garage.

    Good luck...
  • Ste_SSte_S Posts: 1,173
    Thanks for that another jacko, seems simple enough in theory. I have the same Raleigh/Suntour chainset that you have and three spare bottom brackets so hopefully will have something that works. Getting the chainline right seems the most fiddly bit
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