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i need help with choosing what to change on my groupset. when i am going down hills or on flats i seem to be spinning when i am in big cog and top gear. my bike is a dawes giro 300 with a 7 speed shimano sora. i am confused what i need to update can some one help me please?


  • tony btony b Posts: 57
    Hi ben

    You need either a bigger chainring, although I'd be surprised if the one on there at the moment was too small, or a smaller 'low gear' cog on the rear freewheel.

    Count the teeth on all the back and the front cogs. What are the numbers?
  • yeah thanks for the help. i have counted the cassette and its 13-28 and the front is 52-39. do i need to change my cassette or is it just me? although saying when i go down hills i seem to be spinning all the way down when in the smallest cog at the the back.
  • rpopper65rpopper65 Posts: 171
    It seems like a lot of the racing cassettes are smaller than yours (see this link to the Dura Ace 10-speed and the various sizes it comes in), with the smallest at 11 or 12 teeth. And the only major difference I can see with the chainsets is that most of the shimano racing sets are 53-39.

    I am not sure that the extra teeth are going to make a huge difference to you, and if you decide to upgrade you will have to upgrade the entire gearset, since your sora 7 speed rear derailleur will not work with an 8, 9 or 10 speed cassette (and your front derailleur cage may not be able to cope with a much wider range of chain movement, especially if you jump from 7 speed to 10 speed on your rear). Then, you will need to change your shifters (unless they are not at all indexed), and you will have to have a chain specific to your cassette size, too. So, before you do any or all of that, I would just take a minute and re-visit your original post: "when i am going down hills or on flats i seem to be spinning when i am in big cog and top gear."

    My first reaction is to say that I don't often see racers pedalling all the way down every hill they come down, and I wouldn't say that you should expect to be pedalling hard all the way down. What sort of hills are you experiencing this on? If it is a really steep descent, then the best thing you can do is get some good speed going after you reach the peak of the hilll, then when you reach the point where you are spinning and not getting any resistance from the pedals you shold tuck down in a good aero position, rest your legs and maintain good technical control of your bike.

    My second reaction is to ask what speeds you are reaching on the flats when you are spinning, and what sort of cadence is it when you feel you are spinning? If you are reaching a cadence of 100-110 rpm, then that may not technically be "spinning", but just moving your pedals a lot faster than you are used to. If you are reaching a cadence of 120+ in your fastest gear on a flat stretch (or going faster than 50 kph/30 mph) for long periods of time, then (a) you must have massive legs and (b) you may just be a natural-born cyclist who needs a custom built gear set to keep up with your charmed abilities.

  • When i am going down hill i am doing about 120+ rpm, also i do think that i am a natural born cyclist because i have actually been cycling for nearly all my life.
  • rpopper65rpopper65 Posts: 171
    Wow! 120+ rpm in your heaviest gears? What kind of speed do you get up to? What about on the flats? What sort of cadence do you get to, at what speed, and for how long do you typically stay at that pace? Have you done time trials and/or races? What times have you done there?

    You may need to approach a specialist bike shop about having something special built for you in the way of rear cassette and front chainring. You may also want to find some professional, elite level coaches you can talk about specific training to support that level of ability and see where you can go with it.

    At the very least, it might also mean that you don't have to worry too much about the bike section of the triathlons and you can concentrate on the swim and run sections more.
  • JonesJones Posts: 4
    I'd turn pro mate [:D] if your spinning 120 rpm in a 52x13 your doing 37.5 mph [:D] so your going a fair speed on the flat to [:)]

    Pro riders are only riding a slightly bigger final gear 53x11 ish, I haven't looked but I'm pretty sure you could still buy a 7 speed cassette with a 11 to 23 spread try somewhere like Edinburgh (spelling ?) bicycles [:)]

    You cetainly don't need that 28 cog with legs like yours [:D]

  • Yeah i wish i could!!!!! thanks for your help as i have just ordered a 11-23 cassette so hopefully it should be better!!!!!!!
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