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I want to build a genesis croix de fer bike. The usage of this bike will be touring, with rear and front panniers, for an approximately 6 month autonomy travel. I am starting from zero, so there are no constraints of preexisting parts in my inventory.

My goal is to have road shifters, with a double crankset. Since I will carry around some weight, I'd rather have a small crankset; a deore 38 / 24 seems ideal.
Now I am kind of lost on how to achieve this.
What cassette should I get ? A deore too or can any 10 or 11 shimano cassette fit ?
Which derailleurs do i need to get; do i need the mtb rear and front ? Or can I mix both ?
And lastly, which shifters would be compatible with all this ?

I know that's a lot of questions, but I'm kind of lost on all the possibilities. Thank you !

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  • What total bike weight are you aiming for? Whats the low gearing you ride at the moment?
    – Criggie ♦
    Sep 12 '20 at 22:28
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What you're describing is a "mullet drivetrain", that is, road shifters with mountain derailleurs & gears. There are a lot of variations on this. Here's a guide. Note that some of these require third-party adapters to make them work.

Some of these permutations offer a lower gear than you might need or want. Another alternative would be a gravel drivetrain. Shimano's 2x11 GRX, for example, could be used with a 30x46 low gear, which is very low for riding on pavement, even fully loaded.

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  • Thank you for your answer, I will look into mullet drivetrains. Shimano GRX seems like a good option, but very pricy. So, you are saying that a 30x46 would be enough to climb anything fully loaded ? I was under the impression that it might not be enough, after reading this : cyclingabout.com/gear-ratios-how-to-select-touring-bike-gearing
    – aguilbau
    Sep 12 '20 at 19:33
  • A 30x46 gives you a low gear of 18 gear-inches. At a cadence of 90 rpm, you'd be going about 7.5 km/h. If your gear is much lower, you'll hit stall speed.
    – Adam Rice
    Sep 12 '20 at 20:08
  • @aguilbau it all depends on how "strong" of a cyclist you are, and the steepness of the hills you will be riding. On your current bike, calculate the lowest gear ratio you use to go up really steep hills. On your new bike, you will want your lowest gear ratio to be at least that low, because you will be riding tired, and loaded down.
    – sam
    Sep 12 '20 at 21:17
  • Having looked more closely at the Cycling About article, an 18" low gear is exactly what he recommends for "off-road touring," and the lowest low gear he recommends. That article was written in 2015, and is a bit out of date. MTB cassettes now have low-end sprockets as big as 50 teeth, which he doesn't account for.
    – Adam Rice
    Sep 12 '20 at 21:48
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A low gear of 24:50 would be 15.4 gear inches, which is low and should get up most paved roads eventually. However its slow and spending hours slogging away at a climb is no fun, so your endurance is important. You'd be doing 4.4 km/h at 60 RPM.

At the other end, don't discount the importance of some high gearing too. For every climb there is a descent, and a 38:11 would hit 100 RPM at 45 km/h.

https://www.sheldonbrown.com/gear-calc.html is a handy resource for exploring combinations of chainring and cassette options.

I suggest you ride a few combinations of bike gearing. Borrow or hire bikes, just to get an idea of how a particular gear setup feels in action.

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