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3 speed freewheel on a fixed hub?

Gavin GilbertGavin Gilbert Posts: 4,019
edited July 2007 in Road general
Possible? Wise?

Playing with my mictometer this evening tells me the average ratio of thread to 5 speed freewheel width is 38% - i.e. 38% of the freewheel is supported on the hub.

With the fixed FB hub I want to use on the '47 Claud/Osgear, a 3 speed freewheel gives a 33% ratio.

I'm not good on the engineering side of things - is the 5% difference going to be significant and would mounting the 3 speed unit be safe?

Posts

  • Random VinceRandom Vince Posts: 11,374
    if your proposing haveing a mech on there and running a geared fixed then, as was pointed out to me when i was considering doing the same with a 5 speed, when you put resistance to the pedals, you'll have to take up the slack in the mech first, it laying out allong the chainstay and when you pedal it moving itself back to its normal positon before it affects the rear wheel.

    your actual question is are you able to mount a 3 speed freewheel (and due to how long i've been awake and driving for i missed what you were asking) i'd guess it'd be ok, how many mill is it out?
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  • Gavin GilbertGavin Gilbert Posts: 4,019
    Not running fixed - running one of these:
    www.classiclightweights.co.uk/designs/osgear-hs.html :shock:
  • DickieDickie Posts: 1,489
    Gavin, it is possible but I wouldn't myself.

    Though having said that I bought a Carlton Gran Sport years ago and the freewheel thread was shot. The chap had just fitted it on the fixed side and ran it like that for 5 or 6 years. The hub was a steel barrell l/f campag.

    I threw it out because it was rusty! DOH!

    The minimum thread engagement needed for safety is 3 full turns, this is a general workshop rule of thumb so not gospel. Are the freewheel threads a good fit or piss fit on the hub?

    Can you measure the amount of thread on the hub and freewheel and let me know.

    I said P I S S fit not wee wee fit!
  • pete.whelanpete.whelan Posts: 788
    what you really need to do is build up a wheel with a Sturmy-Archer ASC hub - 3 speed fixed.

    mine rides ever so smoothly
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  • Gavin GilbertGavin Gilbert Posts: 4,019
    pete.whelan wrote:
    what you really need to do is build up a wheel with a Sturmy-Archer ASC hub - 3 speed fixed.

    mine rides ever so smoothly

    ASC? It's a bloody Osgear project :roll: I chose a fairly bland luggless Claud Butler to show off the gear!

    Dickie: the hub thread measures 6mm but I will need lose 0.5mm of this to fit the alloy spoke protector disk. The freehub is 18mm.

    It's not looking likely is it :( Hope I can pick up a rear Blumfield at Ripley in October....
  • NorwegianBlueNorwegianBlue Posts: 484
    Am I missing something here? (Quite possible.)

    Why not just use a hub designed for a freewheel.
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  • Gavin GilbertGavin Gilbert Posts: 4,019
    NorwegianBlue wrote:
    Am I missing something here? (Quite possible.)

    Why not just use a hub designed for a freewheel.

    because a period correct matched pair of 'racing' freewheel hubs are as rare as hens teeth - but it looks like I'll need to keep on looking :(
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