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Singlespeed gearing: help please.

jonny_trousersjonny_trousers Posts: 3,588
edited October 2010 in The workshop
Okay, I'm getting really confused with gain ratios and whatnot here and not being the most mathmatically minded person in the world I thought I might seek out the advice of you guys.

The bottom line is I am running 50/17 at the moment and I would love to gear my bike the tiniest bit higher without needing to change the chain.

Would 50/16 be a little tough for the commute? Might 51/17 require a change of chain? Does 49/16 sound like a reasonable option? Any thoughts would be appreciated.

Posts

  • Buckled_RimsBuckled_Rims Posts: 1,648
    Depends on your drop outs, or if you're using a tensioner.

    The question can only be answered if you know how much tightness or slackness there's in your chain. It's a "how long is a piece of string" question otherwise.

    If for example your chain is stretched to the limit on the dropout, then putting a 16t on is going to need a link taken out.

    Personally speaking, if you change the ratio you might as well change the chain as you'll have new on new.
    CAAD9
    Kona Jake the Snake
    Merlin Malt 4
  • Depends on your drop outs, or if you're using a tensioner.

    The question can only be answered if you know how much tightness or slackness there's in your chain. It's a "how long is a piece of string" question otherwise.

    If for example your chain is stretched to the limit on the dropout, then putting a 16t on is going to need a link taken out.

    Personally speaking, if you change the ratio you might as well change the chain as you'll have new on new.

    Thanks! It's a Pearson Touche and there is quite some distance in the horizontal drop out. I don't suppose there is a great deal of space left for using a much bigger chainring, but I could probably get away with going smaller - 49/16 for example. Do you think 49/16 would give me a noticable, but comfortable up shift from 50/17?
  • SalsaSalsa Posts: 753
    We don't know things about your bike like tyre size/crank length etc, as you do know these factors use the rabbit single speed calculator to easily find your gear/gain ratios.
    That will let you see what your existing ratio is & what effect changing cogs/sprockets will have .
    http://software.bareknucklebrigade.com/ ... pplet.html
  • I already checked ratios on the Sheldon Brown site, but the figures that came up didn't mean a great deal to me in a practical sense. I was more looking for someone to say something along the lines of, 'Yes, 50/16 would be a killer' or 'No, moving up to a 51T chainring probably shouldn't require you to buy a new chain.

    Thanks anyhow, I guess I'll just have to experiment.
  • Buckled_RimsBuckled_Rims Posts: 1,648
    I already checked ratios on the Sheldon Brown site, but the figures that came up didn't mean a great deal to me in a practical sense. I was more looking for someone to say something along the lines of, 'Yes, 50/16 would be a killer' or 'No, moving up to a 51T chainring probably shouldn't require you to buy a new chain.

    Thanks anyhow, I guess I'll just have to experiment.

    Forget the price of a chain, it's only a tenner. What you want to worry about is your knees and can they cope with that gearing? Your commute might be flat but as soon as there's a head wind or there's lots of start/stop traffic, your knees might pop.

    I couldn't in a million years use a single speeder on 50/16. I still say for myself the Langster type gearing of 42/16 is just about right for me. I can bike up hills, power into winds and still be pedaling.
    CAAD9
    Kona Jake the Snake
    Merlin Malt 4
  • 50/17 actually seems to handle headwinds well and is not too sluggish at the offset so perhaps I should just stick with what I have. Thanks for the advice!
  • Tom ButcherTom Butcher Posts: 7,137
    Seems a massive gear to me - depends what you are using it for I suppose but I used to do a fairly fast chaingang on 39*16 - OK I did half of it - I got dropped on the descent. Of course only you know what gear suits you best - but for a commuting bike it wouldn't suit me.

    it's a hard life if you don't weaken.
  • vorsprungvorsprung Posts: 1,953
    I use sheldon browns gear inch calculator to convert the ratio I have into gear inches
    And then see what other combinations will give me a similar ratio
    And then try it

    So I started on 42x17 which is roughly 67" with 28mm tyres

    This seemed a bit pedestrian so I had a few days with 52x19 or 73" and that was too much ( I was doing a 70 mile round trip over Exmoor at the time )

    I stuck with 42x17 for a year or more and then found a 16T sprocket and did 42x16 which is 70"...this I found to be an excellent ratio
  • Sounds like you've been tinkering already. The Pearson SS bikes usually come with a 48/18 setup which on a 25mm gives a pretty standard 72 gear inches (if my maths is correct).

    Dropping to a 17T rear gave me about 3-4 mph on the flats and a few more drops of sweat on the climbs. I was going to go for a 16T initially but am relieved I went for the 17T as a tester.

    A single tooth drop at the rear shouldn't cause any issues in the drop outs. Give it a whirl and see. What's the worst that could happen? :roll:
    .
    Beep Beep Richie.
    .

    FCN +7 (Hanzo Fixed. Simple - for the commute)
    FCN +10 (Loud and proud PA)
  • Harveytile wrote:
    Sounds like you've been tinkering already. The Pearson SS bikes usually come with a 48/18 setup which on a 25mm gives a pretty standard 72 gear inches (if my maths is correct).

    Dropping to a 17T rear gave me about 3-4 mph on the flats and a few more drops of sweat on the climbs. I was going to go for a 16T initially but am relieved I went for the 17T as a tester.

    A single tooth drop at the rear shouldn't cause any issues in the drop outs. Give it a whirl and see. What's the worst that could happen? :roll:

    The tinkering was already done for me. I bought the Touche second hand and it'd had a lovely Sugino 75 chainset added. The bike came with 50/17 fitted and I have 16T and 15T cogs spare (not tested either yet as I do not have a lock ring removal tool).

    According to the Sheldon Brown Gear Calculator, with 700 x 25 tyres and 165mm cranks I am given 77.6 gear inches, which sounds quite high, but it really doesn't feel that bad.

    My commute's pretty flat really and the 50/17 does feel good most of the time. There are just a couple of points where I feel my cadence is a touch too high.

    Thanks for all the replies!
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