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Gear Ratio Question

ed1973ed1973 Posts: 219
edited August 2018 in MTB workshop & tech
So to cut a long question short, I used a gear calculator to work out the difference between running a 32t chainring and 30t chainring with a 42t rear cog:
32t is 0.83
30t is 0.78
So anyone know if 0.05 will have a big difference on a tough climb?
Also are the ‘Snail’ narrow wide chainrings on the ‘Wish’ app any good they are £9 plus p&p or will it just get chewed up after the first ride?

Posts

  • steve_sordysteve_sordy Posts: 2,240
    Ed1973 wrote:
    So to cut a long question short, I used a gear calculator to work out the difference between running a 32t chainring and 30t chainring with a 42t rear cog:
    32t is 0.83
    30t is 0.78
    So anyone know if 0.05 will have a big difference on a tough climb?
    ..........

    I'm puzzled how you get 0.83 and 0.78

    A 32t driving a 42 is 32/42 = 0.76
    A 30t driving a 42 is 30/42 = 0.71

    But if all you are changing is the front ring, you only need to consider the difference between the 30 and the 32.

    I'll assume that you are going from a 32 to a 30. So the change is 2/32 which is a 6.25% difference.

    I agree that this is a small change, in fact it is less than half the gain you get by changing one gear on the cassette. Some shifts will make it less than one third.

    But the key question is will you notice it?

    If you ride very steep hills and/or need to climb out of steep bomb holes, and/or have dodgy knees, then yes you will see the benefit! But you will also spin out a little bit sooner when accelerating downhill.

    You could always change to a cassette that has a 46T. That will give you an extra 46/42 = 1.095 or 9.5% extra lower gear. That is better than the 6.25% from swapping the front ring. And you won't be spinning out sooner at the other end of the cassette because your front ring will still be a 32t.
  • ed1973ed1973 Posts: 219
    Ed1973 wrote:
    So to cut a long question short, I used a gear calculator to work out the difference between running a 32t chainring and 30t chainring with a 42t rear cog:
    32t is 0.83
    30t is 0.78
    So anyone know if 0.05 will have a big difference on a tough climb?
    ..........

    I'm puzzled how you get 0.83 and 0.78

    A 32t driving a 42 is 32/42 = 0.76
    A 30t driving a 42 is 30/42 = 0.71

    But if all you are changing is the front ring, you only need to consider the difference between the 30 and the 32.

    I'll assume that you are going from a 32 to a 30. So the change is 2/32 which is a 6.25% difference.

    I agree that this is a small change, in fact it is less than half the gain you get by changing one gear on the cassette. Some shifts will make it less than one third.

    But the key question is will you notice it?

    If you ride very steep hills and/or need to climb out of steep bomb holes, and/or have dodgy knees, then yes you will see the benefit! But you will also spin out a little bit sooner when accelerating downhill.

    You could always change to a cassette that has a 46T. That will give you an extra 46/42 = 1.095 or 9.5% extra lower gear. That is better than the 6.25% from swapping the front ring. And you won't be spinning out sooner at the other end of the cassette because your front ring will still be a 32t.

    Thanks for the detail. I’d considered changing from 42 to 46 at the back but it’s a difference is £50 odd for new cassette to £9 for new chainring. Perhaps the answer is more training to get stronger legs plus a weight loss ha ha!
  • JBAJBA Posts: 2,772
    For the sake of 9 quid I'd just give it a go and see how I got on.
    “Life has been unfaithful
    And it all promised so so much”

    Giant Trance 2 27.5 2016 ¦ Sonder Broken Road 2021¦ Giant Revolt Advanced 2 2019 ¦ Giant Anthem 3 2015 ¦ Specialized Myka Comp FSR 2009
  • ed1973ed1973 Posts: 219
    JBA wrote:
    For the sake of 9 quid I'd just give it a go and see how I got on.

    Very true!!
  • trek_dantrek_dan Posts: 1,366
    Ed1973 wrote:
    Also are the ‘Snail’ narrow wide chainrings on the ‘Wish’ app any good they are £9 plus p&p or will it just get chewed up after the first ride?
    I've bought a few unbranded chainrings direct from China, all have been spot on. Exactly the same as the likes of Superstar Components sell, just with different logos.
  • kajjalkajjal Posts: 3,380
    I would just give it a go and see what you think.

    When going for a single chainring the thing to avoid is struggling with gear ratios that make it very hard going but promising yourself I will get fitter and lose weight. When you do get fitter and have lost the weight, that is the time to make the change and the main thing is to enjoy your riding.
  • steve_sordysteve_sordy Posts: 2,240
    Kajjal wrote:
    .............

    When going for a single chainring the thing to avoid is struggling with gear ratios that make it very hard going but promising yourself I will get fitter and lose weight. When you do get fitter and have lost the weight, that is the time to make the change and the main thing is to enjoy your riding.

    I entirely agree. I first went to 1x11 from 2x10. The 1x did not replicate the range and I had to compromise, so I chose to have the easy gear replicated and left the harder end to look after itself. My priority was always climbing and not going fast. I started with a 32t front ring and I still struggled in some places, so I fitted a 30t, the smallest gear I could fit on my crank. OK it was only 6.25%, but it made a difference!

    A year or so later, I can get up that slope with a few gears lower down the cassette, but I still don't want to go any faster, so I can't be arsed to refit the 32t, or even opt for a 34t. :lol:
  • kajjalkajjal Posts: 3,380
    Kajjal wrote:
    .............

    When going for a single chainring the thing to avoid is struggling with gear ratios that make it very hard going but promising yourself I will get fitter and lose weight. When you do get fitter and have lost the weight, that is the time to make the change and the main thing is to enjoy your riding.

    I entirely agree. I first went to 1x11 from 2x10. The 1x did not replicate the range and I had to compromise, so I chose to have the easy gear replicated and left the harder end to look after itself. My priority was always climbing and not going fast. I started with a 32t front ring and I still struggled in some places, so I fitted a 30t, the smallest gear I could fit on my crank. OK it was only 6.25%, but it made a difference!

    A year or so later, I can get up that slope with a few gears lower down the cassette, but I still don't want to go any faster, so I can't be arsed to refit the 32t, or even opt for a 34t. :lol:


    I have been there with the wrong gear ratios on long steep hill climbs and that is why I am still a mountain biking neanderthal on 2 x 11 and 2 x 10 to give me all the gears I need :)
  • trek_dantrek_dan Posts: 1,366
    A year or so later, I can get up that slope with a few gears lower down the cassette, but I still don't want to go any faster, so I can't be arsed to refit the 32t, or even opt for a 34t. :lol:
    I put a 28t (oval) ring on for a 24 hour race last winter and I've never bothered refitting the 32t (oval) I had on before. Its nice to have a bail out gear and do less cross chaining under normal conditions. I never find I miss the higher top end other than when its totally flat, which isn't very often,
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