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I'm putting together a gravel bike from parts. It will be for mechanical brakes -- cantilever at first and maybe mechanical disc later. I will be buying new shifters, derailleurs, cassette, and chain. The question: Is there a good reason to consider Tiagra 4700 2x10 instead of 105 R7000 2x11? Both offer clutch rear derailleur options (GRX400 for the Tiagra). Cassette options are good for both, 11-32 or 11-34 for Tiagra, and 11-34 for 105. A strange thing to me is that there is very little difference in price.

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  • With the 2x11 you can have closer gear spacing (smaller steps between gears). Apart from that there probably really isn’t much difference. Can’t you go for a GRX groupset with smaller chainrings? The 50/34t chainrings on the Tiagra and 105 make steep climbs really hard.
    – Michael
    Commented Aug 1, 2022 at 16:59
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    Do you have a particular reason to not go directly to disc brakes? Asking because large tires are appreciated in gravel bikes, and rim brakes will be very constraining on that matter. Also, going to disc directly will allow you to install GRX components, are more suited for gravel riding.
    – Rеnаud
    Commented Aug 1, 2022 at 17:09
  • @Renaud Cantilevers work just fine with large tires. V brakes would work too, but the awful shifter/lever combinations today don't allow you to choose separately a shifter for the desired number of gears, and a lever for the desired pull ratio, independently from each other.
    – juhist
    Commented Aug 1, 2022 at 17:23
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    Going for disc brakes straight also means you don’t need brake mounts for both.
    – Michael
    Commented Aug 1, 2022 at 18:38
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    In answer to the above comments ... (1) I am using very small chainrings, not groupset -- 40/24 or 42/26; I have experience doing this on other builds. The small front / large rear combo will thus have a very low gear ratio of 0.8 or less. (2) I am starting with rim brake wheels and Tektro cantilever brakes that I have in order to make best use of my parts inventory; I already have a frame and fork that accommodate both cantilever and disc brakes for QR wheels.
    – Old95rpm
    Commented Aug 2, 2022 at 1:38

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There are several benefits of Tiagra:

  • Cheaper initial investment, yet still probably good enough for actually using it regularly
  • Cheaper wear parts
  • Thicker chain and sprockets so with similar materials you get more wear life out of the wear parts, all else being equal (although more expensive 11-speed chains and cassettes could obviously use better materials, so not all else is necessarily equal if you are comparing for example Dura-Ace 11sp with Tiagra 10sp)
  • Larger jumps in cassette, meaning you have to do fewer gearshifts to get the desired change -- today, most systems have way too densely spaced gears
  • 11-speed cassettes may not be compatible with all Shimano freehub style hubs since you need special 11-speed hubs, 10-speed cassettes on the other hand are with 8/9/10 speed and also 11-speed hubs with a spacer (unless you are considering some really old freehub like 7-speed) -- you didn't mention what hub you have but it may force you to use 10-speed cassettes

Also something to consider:

  • With Tiagra 4700 the rear derailleur pull ratio is the same 11-speeds, so when it will no longer be possible to buy 10-speed parts you can still buy rear derailleurs that are compatible with your system, and also the pull ratio of Tiagra 4700 and 11-speed systems allows smoother shifting than the old pull ratio, even if you run full-length housing
  • With 11-34 tooth cassette, the 11-speed system doesn't add anything really apart from way too densely spaced gearing, since the low and high gears are the same
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    define "too densely spaced"?
    – Paul H
    Commented Aug 1, 2022 at 22:34
  • I agree with @PaulH, this is mostly a reasonable answer apart from the contention that 11s systems are too closely spaced. I find this assertion to be odd. 9s and 10s drivetrains generally were very much more closely spaced when they were introduced, e.g. the default cassette was 12-23 or 12-25.
    – Weiwen Ng
    Commented Aug 1, 2022 at 23:46

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