general advice about lower gear ratio

Discussion in 'Cycling Equipment' started by WKB, Nov 21, 2006.

  1. WKB

    WKB New Member

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    I purchased a Novara touring bike about 18 months ago and am generally happy with it. It has a front chainring with a 52/42/30 gear ratio in front and a cassette of 11-28 in the back. This makes for a good combination of gear ratios that is more than enough for the flatlands of the US Gulf coast, which is where I live.

    After 18 months, I've noticed a couple of things. I rarely use the 52/11 combination, even on flatlands while unloaded. My legs aren't that strong and I really don't want to go that fast on this particular bike. Also, while touring fully loaded in the central Texas hill country, I often used the lowest gear ratio (f:30/r:28) and on occasion wanted something a little lower. So I put these two together and decided that I can live with a slightly lower gear ratio.

    I'm a little uninformed about the best way to do this. As I understand it, I can get another chainring with fewer teeth in front or a bigger cassette with more teeth in back. Which route is best?

    Thanks, Keefe.
     
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  2. daveryanwyoming

    daveryanwyoming Well-Known Member

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    Keefe,
    That depends on a couple of things like the cage length of your rear derailleur since that puts a limit on the largest rear cog you can mount and the total amount of chain slack it will take up. Given that you bought a stock touring bike I assume you have a long cage rear derailleur. If that's the case I'd go to a 12-34 cassette. It sounds like they mounted a mountain bike rear cassette (11-28) which means you're carrying around the nearly useless 11 tooth cog at the expense of lower end gearing. All in all changes to the rear cluster give you more bang for your buck than changes to chainrings. You can play with different gearing combos here: http://www.sheldonbrown.com/gears/ to see the net effect of different chainring / cog combos.

    You can, of course, do both, change the cluster and the chainrings. For instance you could go to something like a 12-30 rear and drop the size of your granny chainring up front. That would give you a bail out gear for those Texas hills but keep your higher gears closer together for your more typical flat riding. As long as your rear derailleur can handle the max teeth on the rear cluster and the total chain slack from your large ring - large cog to small ring - small cog combinations you're good to go.

    Personally for a touring bike I'd probably just go with a larger cassette, maybe even one of the touring specials made by Harris Cyclery: http://www.sheldonbrown.com/k7.html which sacrifice the 11 or 12 tooth small cog for more reasonable touring gears.

    Good luck,
    Dave
     
  3. Strid

    Strid New Member

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    The easiest route is to swap the cassette for new one. With that said, I'm not sure if you can get a road bike cassette with more than 28 teeth. I don't think they're made for road bike gear sets. Then your other option is to swap the inner chain ring for something smaller, obviously.

    Do you know the brand of your gears? It is probably Shimano something and there are probably decals on the rear derailleur and shift levers.
     
  4. carpediemracing

    carpediemracing New Member

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    If you get smaller chainrings in front (say, 46T or smaller, which reduces your top gear by the equivalent of about one cog), you can get correspondingly smaller small chainrings (say a 24T instead of a 30T).

    This will give you the broadest range of gears. By keeping your current cassette, you will not be creating bigger jumps between gears.

    Smaller rings weigh less, allows for less chain, and if you are touring, you can carry more spare links for repair.

    They do wear a bit quicker though, but this is over hundreds or thousands of miles.

    However, you will need to get a derailleur for that - either a mountain bike derailleur or a compact (road) crank derailleur. Otherwise your front derailleur won't shift as well.

    Just as a note - the 52x11 is typically used for downhills (unless you are a superb sprinter). You'll find that on flat terrain you won't need the highest gears, but if you are softpedaling down a long descent, you may find the 11T to be nice. A 46x11 is higher than a 52x13, which I would guess to be your second highest gear.

    To calculate relative gear size, do the following:

    chainring/rear-cog x wheelsize

    I use 27" for wheel size just for consistency, if using the same size wheels/tires.

    52/11 * 27 = 127
    52/13 * 27 = 108
    46/11 * 27 = 113

    More accurate would be to multiply by tire circumference but that is a lot of work for rough calculations. It is necessary to use circumference when comparing different tires, wheel sizes, or measuring for racing gear limits (i.e. legal restrictions).

    hope this helps
    cdr
     
  5. gclark8

    gclark8 New Member

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    Can you give us a little more information:
    A link to the web page for the bike specs,
    how many speed is the cassette,
    is it a CS cassette or a spin on MF freewheel?

    To change either we also need to know the rear derailleur, bottom bracket and shifters types.
     
  6. Retro Grouch

    Retro Grouch New Member

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    How many cogs do you have on your rear cassette?

    If it's a 9-speed, the quickest and easiest solution is to install a mountain bike 12/34 cassette. You'll also have to install a mountain bike rear derailleur to handle the 34 tooth big cog and you'll need a new, longer chain.
     
  7. WKB

    WKB New Member

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    I am grateful for all replies. The bike is a Novara Randonee touring bike. I cannot find a link with the current specifications, and I think that's because it's out of stock at the moment.
    The rear cassette is not labled, but it appears to be one from Shimano. It has 8 speeds with the following numbers on each cog: 11,12,14,16,18,21,24,28. The rest of the bike is equipped with Shimano Tiagra components, so I have to assume the cassette is the same. The arm on the rear derailler is considerably longer than the one on my road bike, and it is labled "9 speed." The shifters are built into the brakes and are also made by Shimano. The front right one is labled "8-speed." In the event that I have left out any relevant information about the components, I have uploaded a few photos here: http://www.pbase.com/keefeborden/bike_photos

    I'm still not sure of the best option, but based on the replies so far, I'm inclined to remove the 11-tooth cog and put on one with 32 teeth on the big end. Maybe I need to replace the entire cassette with one that is 12-32. This would keep it at 8 speeds, which appears to be the maximum the shifting can handle. Would this require a larger chain? Any other advice? Again, I'm grateful for all replies.

    Best, Keefe.
     
  8. alfeng

    alfeng Well-Known Member

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    As suggested, you can get a smaller granny ring -- a 28t 74BCD will only cost you ~$10 (steel is "OKAY!"/better/cheaper), I would think, at your bike shop (if they have one to sell you) ... it shouldn't more, AND you shouldn't spend more than that because I believe your Tiagra crank currently uses a square taper BB ...

    So, the options are legion with regard to alternate cranksets ... a USED (or, new if you can find one) Shimano MTB crank (42/32/24 is common with 4-arm 104BCD cranks ... a 44/32/24 would be better ... a 46/32/24 would probably be best ... AVOID "compact" 5-arm cranks with 94/nnBCD as replacement chainrings are not commonly available ... 5-arm 110/74BCD cranks are an excellent option) which has a square taper is easily bought for under $30 (+ local sales tax OR shipping) ... check eBay ... BE PATIENT ... unless you were doing another loaded tour in the next few weeks.

    You'll need a crank puller if you don't already have one ... either to remove the current crank to change the granny OR to swap cranks.

    The Tiagra rear derailleur MAY be able to handle a 32t, but maybe not (the Shimano ROAD rear derailleurs can generally handle a 30t cog despite what Shimano suggests ... 32t is a "maybe" with the Shimano ROAD rear derailleurs).

    FWIW. I would simply change the granny before I changed the cassette -- your cost would be the chainring + crank puller (you should be able to get them through mail order places like Nashbar for ~$30, shipped ... or, probably about the same price separately through eBay auctions ... heck, they may have the "stuff" at REI, but the crank puller will probably be a PARK, and they'll charge you ~$15 after tax & the gas it takes to get there.). OTHER changes will probably have unforeseen & escalating costs ...

    Buying separate cogs for your cassette can be very expensive ...
     
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