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Gearing advice and musings

Discussion in 'Bicycle Mechanics and Repairs' started by Crackle, 22 Nov 2007.

  1. Crackle

    Crackle Pah Staff Member

    Location:
    Wirral
    I think I need the benefit of some other opinions on this.

    Waffle (go to The point: to avoid)
    Having been back into using my bike after a 10 year lay off, give or take the odd mtn bike session I've now had about 10 months to establish a pattern and analyze my riding style, which has changed, as has which gears I now use.

    I now have a Dawes Audax, prior to this, apart from the mtn bike, I had an old Rotrax which I had bought in a shoddy state and fixed up. For some reason I got rid of that about 12 years ago - wish I still had it.

    Anyway, my previous riding style was basically to choose a gear, normally 75" and ride it. Only changing for big hills and wind assisted straights. I was much more of a 'balls out' rider than I am now.

    The Dawes came with a Tiagra chainset 52/42/30 12-25(10 spd). I changed the 52 to a 49 immediately as i knew I would never use a 52.

    So: Where I live is quite bumpy, mostly singletrack with some quite challenging hills in the vicinity. There are no flat rides within a 30 mile radius.
    My riding style is much more fluid than it used to be and because of modern STI's it's quite easy to maintain that fluidity, so I tend to ride, on the flat, at about 90rpm, dropping into the 70's and 60's for hills and into the 50's for 10% and all bets off for greater than 10%!.
    To achieve this I now ride a 64-68" gear, except on long flats when I get into the 70"s. If I go past 22mph then I'm going downhill. I'm also a crap climber, always have been, so I need low gears.

    The point: I don't use the lower half of my rear cassette. It might as well not be there. Instead I'd like a lot more choice around the 60-70" gear range and some lower gears around 27" for when I tour around here. I also need some more in the 70" range for when I am on the flat.
    I like the triple and I'm thinking of setting it up thus:

    outer ring - bigger 70-80" range for flatter longer roads - top gear 100"
    middle ring - so named my singletrack ring for 47-65" range perfect for around here, usable top 71" (=20mph at 90rpm)
    inner ring - for climbing only, once it gets past 1/4 mile 7% it would be engaged.

    So with a 12-25 cassette this would mean a 46/38/26 on the front which at 90rpm gives me a speed range of 26-12mph for the outer and middle and at 55rpm 9-4.5mph on the inner.

    For this I'm looking at a Stronglight chainset to replace the Tiagra.

    So I'm just looking to bounce this off people and get some opinions on the gearing and Stronglight chainsets and rear/front mech compatibility i.e. will I be able to keep the existing rear 105 short mech and the front Tiagra. Also BB, will that need to be different for a Stronglight?

    Just to be clear I don't race nor do Sportives or Audax events. I ride a modest 250 miles a month and consider a good ride out to be 40-60 miles, with an occassional 80 (I get bored and fidgety after that). My average speed really varies with the terrain but on a flat ride I do about 16.5mph average; this is adequate for my purposes.
     
  2. TheDoctor

    TheDoctor Man-Machine Staff Member

    Location:
    Stevenage
    46-38-26 130/74 BCD rings should go straight onto your Tiagra chainset. I'm currently running a Sora on 48-38-24 with a 13-26 cassette, which is a little overkill but goes up mountains nicely.

    If you've got a square taper Tiagra, the Stronglight Impact chainset should go straight on. I believe they're both 110mm. If it's hollowtech / splined it won't. BBs are hardly expensive, so that's no great problem.

    Just my 2p worth.
     
  3. OP
    OP
    Crackle

    Crackle Pah Staff Member

    Location:
    Wirral
    So you're running pretty similiar to what I'm thinking about.

    Do you think the Stronglight is better than the Tiagra or as you suggest, just buy the rings for the Tiagra?
     
  4. TheDoctor

    TheDoctor Man-Machine Staff Member

    Location:
    Stevenage
    I've no idea TBH. I changed the rings on mine because it was cheaper and I wouldn't need to get the BB out. Certainly the Stronglight has a good rep, but I've not heard any complaints about the Tiagra one either. I know that as standard, the Tiagra's a bit heavier, but that may well be down to the steel rings which you're getting rid of.
     
  5. OP
    OP
    Crackle

    Crackle Pah Staff Member

    Location:
    Wirral
    Right: Going for a 46/38/24 on original 12-25. Just going to get the rings and stick with the Tiagra. 24 is better than the 26 as it gives me two distinct extra gears on what I have now. It should get me up anything unloaded and most things loaded.

    Do you think I'll have to take some links out of the chain?
     
  6. TheDoctor

    TheDoctor Man-Machine Staff Member

    Location:
    Stevenage
    I'd have thought so. Read Sheldon for chain length. If the new chain doesn't run smoothly on the new rings then a new chain will be needed. You'll also want to lower the front mech - essentially, look at how far it is above the big ring now, and then try and get it that far above the new one, if that makes any sense. About a 2-3 mm gap as it swings across the teeth.
     
  7. MichaelM

    MichaelM Veteran

    Location:
    Tayside
    I've been in a similar situation to you. I changed cassettes, chainrings, put on a compact chainset and then changed the cassette again. Whenever I'm out, I always seem to be thinking about ratios and whether or not I've got it right.

    So, my advice (FWIW - and this is what worked for me) is............

















    Get a fixie :biggrin:
    you'll never wonder whether or not you're in the right/wrong gear again.
     
  8. Blonde

    Blonde New Member

    Location:
    Bury, Lancashire
    It can be a bit of a faff to adjust the front mech to work with the smaller outer ring - not only does it need to be a little lower, you may well need to tweak the angle of the mech as well to take into account the different curve/shape of a smaller outer ring. I had trouble for a few weeks when I changed from a 52 to 46 and could only use either the little, and middle rings, or the outer and middle. Using all three rings just wasn't possible at first till I fiddled round with the mech and eventually got the angle spot on.
     
  9. OP
    OP
    Crackle

    Crackle Pah Staff Member

    Location:
    Wirral
    MichaelM - a fixie around 'ere!:biggrin: I should Coco. I already have dodgy knees.

    I've already had to faff with the setup when I had the 49 put on. Despite spending ages at it, the bikeshop couldn't get it right. It took me about an hour of fiddling to sort it. They hadn't moved the derailleur down far enough. So am expecting some fiddling but thanks for the heads up. Apart from that and the chain, can't see anything else I need to think about and I've spent ages fiddling the spreadsheet I've made, to make sure the spreads right but I'm quite sure it is. Luckily (or sadly), I have every gear combination on every bike I've had for the last 20 years so I can easily analyze my gearing choices over the years.
     
  10. NickM

    NickM Veteran

    Difficult, isn't it? (fun, nevertheless). I've never thought about this logically before, but having been prompted to do so by your thread, this is my approach:

    1. Decide what bottom gear you need. This is by far the most important decision. Don't be vain!

    2. Decide whether you want a double or a triple chainset. A triple is unnecessary unless you want a bottom gear smaller than 32". Whatever chainset you choose, unless you are racing, select the smallest available inner ring. If it's the popular 130/74 or 110/74 bolt circle, that will be a 24T.

    3. Decide how close together you want your gears - 1 tooth increments? 2 teeth? For non-racing bikes, I like 2-tooth gaps in the most used part of the cassette.

    4. Decide what your biggest sprocket will be. Let's say that you have decided you need at least a 27" bottom gear, that you have no objection to a triple chainset and like 2-tooth jumps in the middle of the cassette. To get a sub-27" bottom gear with a 24T ring requires a 25T big sprocket. You could choose a 12/13/14/15/17/19/21/23/25 cassette.

    5. Consider your [middle and] outer chainring choices. Your decision will be influenced by whether you prefer to avoid changing chainrings, doing most of your gear changing on sprockets. I think sensible people prefer to avoid using the inner ring of a triple unless they really need it, which means having the middle ring fairly small.

    I like an outer-to-middle chainring change to be equal to either 2 or 3 sprocket changes in the most used part of the cassette. I don't care about duplicating gears; but I do like not having to think much about how to get to the gear I want. A simple rule like "a chainring is worth two sprockets" helps me.

    6. Decide what top gear you would like. This tells you what the big ring should be. The decision depends mostly on whether you pedal down hills - I don't, so I don't feel any need for gears higher than 100". Like you, I can't see the point of carrying sprockets around that hardly ever get used. Since 100" at 95rpm is good for over 28mph, I can't imagine ever needing a gear higher than that except for racing.

    It sounds to me as though you need a triple, because to get a 27" bottom gear with a double while still having a reasonable top gear requires either a tiresomely big gap between rings, or bigger jumps from one sprocket to the next than most people would want for road riding.

    I've arrived at a 12-25 cassette with a 45/36/24 triple chainset. The small outer ring should help make chainring changes between middle and outer as slick as they can be.
     
  11. OP
    OP
    Crackle

    Crackle Pah Staff Member

    Location:
    Wirral
    Ahhh! I'm gonna have to re-evaluate the whole thing now.........I'll be back.
     
  12. OP
    OP
    Crackle

    Crackle Pah Staff Member

    Location:
    Wirral
    Right. I've run it through the spreadsheet. The rear block has the spacing you put down with the addition of a 16 as it's a 10 speed - very important that 16. Otherwise I'd agree with your jump assessmnet. When you reach a certain point (on a hill) you need a meaningful jump! This is actually why I want the smaller rings because the meaningful jump is at the back of the block already.

    Firstly, you're right it has to be a triple. If I didn't live here I would consider a compact (had one previously 50/36) but I have, in the space of 20 miles, four climbs over a mile long at 7-10%. On a tired day the 30" comes into play on the last hill. Another ride with a 10% gradient for two miles and some ridiculous 2 mile 20% climbs which I haven't ventured over yet - Triple!

    No ride has less than 250m of climbing but in little lumps, up down, up down kinda thing.

    The middle is definetly being designed as my main ring around here. It has to cope with gentle downhills, flats and sudden short 20/25% ups or longer 7% drags without me resorting to the inner. Running your 36 gives me gears too low at the back, though the mid to high range has merit but the top gear is a tadge too low and I feel I would spin out on occasion. The 38 has a marginally inferior mid to high spread but is a bit higher at the low end and still has a high enough gear that I won't spin out.

    There's not a lot of difference on the 45/46 choice. The 46 is slightly closer to a sweet spot for me but hmmmm, maybe, maybe.

    I wouldn't be jumping between middle and outer very often. It's designed to ride either, outer only, inner only or middle to inner and back but apart from that we're not far away in our musings.
     
  13. NickM

    NickM Veteran

    Your bike - your choice! It took 20 years to find out what really suits me, anyway :biggrin:
     
  14. OP
    OP
    Crackle

    Crackle Pah Staff Member

    Location:
    Wirral
    Ahh I see! No fair dinkum, I though you were recommending it for me :biggrin:xx(

    Remarkable then - it's taken me 20 years too (I hope :biggrin:)
     
  15. NickM

    NickM Veteran

    Well, I was... unless you thought something else would be better for you!

    I just wish I could have had 20 years' worth of Scottish mountains to experiment on.