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Converting SS to fixed - Will the chainline still be right?

smurfylicioussmurfylicious Posts: 96
edited October 2011 in Road general
I bought my bike as a ready to ride SS, now I'd like to try fixed. The chainline is already perfect with the freewheel it came with. Will that change if I fit a fixed sprocket? I notice that fixed sprockets have a shoulder on one side. Is the shoulder the exact width to give the same chainline as the freewheel it came with? Or, will I need to muck about with a spacer between the fixed sprocket and the hub body.

If it helps answer the question, it is a flip-flop hub, the freewheel that is fitted is a Shimano one, and I was thinking of buying a Surly 3/32 fixed sprocket.

Thanks for any help


  • No solid answer i'm afraid, in theory yes. But most often in my experience no...

    Try it and see.
  • No solid answer i'm afraid, in theory yes. But most often in my experience no...

    Try it and see.

    Oh dear! Where can I buy spacers if I need them? Is it normal to buy a pack containing several different thicknesses?

    I can measure the freewheel quite accurately with a digital vernier. If someone knows the dimensions of a Surly 3/32 fixed sprocket I'd know if I needed a spacer. Of course I'm assuming my flip-flop hub is symmetrical (and it might not be), as I'm going to leave the freewheel where it is and put the fixed sprocket on the other side.
  • People worry too much about chainline. My fixed bike was 5 speed hub, then singlespeed, then 3 speed, then fixed and they all worked fine without me ever thinking of chainline.
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    Gears - Obscuring the goodness of singlespeed
  • mz__jomz__jo Posts: 398
    1. Normally a flip-flop hob will give the same chainline both sides (otherwise there is nonpoint to the beast, because you can't turn your wheel on the road without respacing) but single freewheels don't necessarily have the same width as fixed sprockets (and the concept works best fixed/fixed)
    2. I used to think the same as Stickman but now I have come to the conclusion that it does matter having the chainline as close to right as possible, to cut mechanical losses. However it makes more difference to the running of a fixed wheel than to a freewheel, because you can generally run the chain a tiny bit slacker on a freewheel, and because where you notice the error on a fixed wheel is going between forward pedalling and holding back (which you don't have with a single freewheel)
    3. Measuring. Start with your hub. Measure the distance from washer or locknut that contacts the fork-end to the shoulder of the sprocket thread (the part that the sprocket threads up against). It should be the same both sides. Note this dimension for each side on a piece of paper. Now measure the dimension from the contact face to the teeth of your fixed sprocket (outside to outside or outside to inside, doesn't matter but note which because you want to measure this on your freewheel). Measure the same dimension on your freewheel (remembering that the adjustable cone, normally with two dimples for undoing and with maker's name or similar goes to the outside so you want to measure the other side).
    4; If everything is the same, nothing to worry about. If not return to your measurements and do the subtractions. If you have less than 2mm difference I wouldn't worry. If the error is 2mm and over go to the site of Velosolo Bikes (sorry I don't have the link on this computer) where you will find various spacers for going behind sprockets or chainring bolts, depending in which direction you need to correct. Spacers may well be available elsewhere but I am ppretty certain that Velosolo will have what you want.
  • mz__jomz__jo Posts: 398
    Normally a fixed sprocket will be about the width of its thread (so that the lockring comes up against it correctly. I can measure one of mine but it won't be a Surly (probably won't make enough difference to throw the calculation out significantly but if you are really serious you need to go into a shop which has your chosen sprocket and measure before buying). Mine are mainly TDC and over 35 years old.
  • mz__jomz__jo Posts: 398
    Thinking about this you shouldn't need to respace your chainrings because otherwise you would have to respace every time you turned your wheel. Measure to be certain. I have a fixed sprocket one side and a freewheel the other on my bike and I don't have any worries when turning the wheel in the middle of a ride. I can always check my wheel to see exactly what it gives. Normally everything works around a chainline of 42mm from the centreline of the bike.
  • Thanks for all the replies. After visiting the velo-solo website I followed a link to Sheldon Brown:

    About halfway down the page is a tabulation of shoulder-to-chainline measurements for sprockets and freewheels, including my Shimano freewheel, and the Surly fixed sprocket I was thinking of buying. If anyone else has the same question as me then this website has all the measurements you need to find out if you'll need spacers before you buy. :D
  • mz__jomz__jo Posts: 398
    That is a page of Sheldon's site I have never looked at. Thanks for the information. Don't forget, if you need to run a slight error, it is better to have the fixed right and the error with the freewheel - but your flip-flop hub is probably designed to be useable both ways round.
  • I'm almost ready to go fixed :D

    Measured all the chainlines very carefully

    Chainring: 52mm (very large, I know, but I have 135mm spacing at the back, and my frame can accept cyclo-cross tyres)

    Freewheel: 54mm

    Fixed sprocket: 51mm

    I have a 1mm spacer which could be used to move the fixed sprocket to 52mm. I'd rather not use the spacer because it will significantly reduce the amount of thread available for the lockring.

    I'm guessing that the 1mm error is good enough. Of course, my measurements could be out, but I don't see any deviation when I look along the chainline.

    Need to decide whether to ride fixed tomorrow or carry on with single-speed. Anyone got any opinions?
  • mz__jomz__jo Posts: 398
    Go for it :D:D
    What's your hub, using mtb spacing like that? I didn't know that there were any mtb specific flip-flop hubs; I thought they were all ss conversions on standard cassette hubs (with Velosolo discmount sprockets for the fixed side). You live and learn.
    Of course, unless you need to alter the length of your chain (or you run with only one brake) there's nothing to stop you flipping the wheel whenever you want, even in the middle of a ride.(Best avoided if you are racing though).
    Don't do anything to your chainline, it will be just fine as it is.
  • stickmanstickman Posts: 791
    My flip flop is 135mm
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    Gears - Obscuring the goodness of singlespeed
  • My rear hub is a no-name aluminium thing with sealed bearings, it looks quite robust, and the wide spacing should give a very strong wheel. The 135mm spacing is probably because it came on a bike which is also supplied as an Alfine equipped model. The manufacturer (Genesis) probably uses the same frame jigs to make both bikes.

    I've had a quick go at riding fixed. My thoughts so far:
    1. I'm glad I've got two brakes, stopping without using brakes takes forever.
    2. My legs have now gone faster than I ever thought possible.
    3. The seat is much too far forward to enable efficient braking just using leg power.
    4. I rode half as far and less than half the height gain as my last ride on S/S, but felt much more sore the next day after riding fixed. Why?
    5. I still don't understand why people rave about the rider/bike connection when riding fixed. What am I missing? Does it take a year of riding to 'get it'?
    6. Only forgot to pedal a couple of times. Fortunately I've ridden S/S for a while so I'm used to spinning, but I saw a bump coming up and stopped pedalling, the reminder from the bike to 'just keep pedalling' was very abrupt.
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