Crossed up and singled out lugged Italian steel road bike- Mtbr.com
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  1. #1
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    Crossed up and singled out lugged Italian steel road bike

    Oh the horror! Lucky I'm not posting this over on rbr, but this is what I'm riding at the moment.

    On the weekend I ditched the derailleurs and cables and am running 48-21 with 35mm tyre on the rear and 40 on the front. The clearance is damn tight through the road brakes, have to steer clear of any seriously sticky mud, but no big issues so far.

    The gear is a bit of a compromise, a bit small for the road, and a bit big for the trail, but it goes ok. Tried a new commute in this morning which takes me through some nice woods, and then a bike trail along the river into the centre of town. Very nice not to think about shifting and just cruising along. Couple of dropped chain issues, but this seems to be due to the ramped cogs, only comes off on the back.

    I'm thinking a flip-flop hub will be my salvation. My question is what is the biggest BMX freewheel you can get? I'd like to run 38-20 for the dirt, and 38-16 fixed for the road - I think my semi-horizontal drops will give me enough adjustment for a four tooth change. Is there such a thing as a 20T freewheel? What other options might I have?

    Thanks for any tips,

    Sam

  2. #2
    drev-il, not Dr. Evil!
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    Quote Originally Posted by Kolo
    Is there such a thing as a 20T freewheel? What other options might I have?

    Thanks for any tips,

    Sam
    Yes, ACS and White Ind make a 20T. Shimano may as well.

  3. #3
    I am the owl
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    I can get a 4 tooth change on my Surly Crosscheck, but it's limited to certain gears and the one position is WAY far forward, although I haven't had any problems. 42x17 and 42x21 for anyone interested. Tried to go to a 5 tooth change with a 42x16 but had too much chain slack.
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  4. #4
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    Thanks for the responses guys. I will check out the ACS, according to my sources the biggest Shimano make is an 18.

    Riderx, how long are your drops? My thinking goes something like this - 4 tooth difference = 2inch difference in chainring circumference. The chainring only has about half the teeth engaging the chain at any one time, so the difference between the two using the same length chain should be about an inch - which is probably about right....

    Am I way off? Is there a recognised formula for working this out or is it just a try it and see sort of thing?

    Thanks,

    Sam

  5. #5
    I am the owl
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    I think you are about right. Check sheldon Brown's site, he's got some info, I think 1 tooth change = 1/8" movement in chain.

    Pic of my drops.
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  6. #6
    voodoo child
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    an alternative

    If your dropouts end up being too short for the 4-tooth difference, running a 16t/20t flip-flop is still possible. I had the same issue and solved it by using a chain with two powerlinks and either 3 or 4 links in between. 42x16 combo used one less link than the 42x20 combo and puts the axel in the exact same spot. (This might be important for you since you said clearance was an issue -- you might not be able to move the axel very far forward in the dropout.) On my SS CX bike, I stored the extra links inside my drop bars.

  7. #7
    mtbr member
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    Quote Originally Posted by Kolo
    Riderx, how long are your drops? My thinking goes something like this - 4 tooth difference = 2inch difference in chainring circumference. The chainring only has about half the teeth engaging the chain at any one time, so the difference between the two using the same length chain should be about an inch - which is probably about right....

    Am I way off? Is there a recognised formula for working this out or is it just a try it and see sort of thing?
    Also the extra 1 inch chain length is spread between the upper and lower runs of the chain so the axle only has to move 1/2 inch. So common sense gets you the same rule of thumb of 4 teeth = 4(1/8) = 1/2 inch.

    (minutely less than 1/2 inch because the chain is not exactly half around the cog.)

  8. #8
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    Hmm, I would have thought that accounting for half the the chainwheel already takes care of the upper and lower length of chain.... Anyhow, I guess I'll try it and see.

    Pauly, you're right, my clearance issues at the chainstays will probably prevent me from going all the way forward in the dropout using the tyres I am currently, extra links of chain is probably the best answer.....

    Thanks for the help guys, when I get this all sorted I'll get some pics up.

    Sam

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