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I am a newbie enduro rider and also i love riding rough terrain uphills, my question is which set of cogs will be more efficient on my riding dicipline. 11-42t or 11-51t 11 speed cassette. Also, I am currently using 34t chainring.

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  • This is quibbling really, but there isn't an 11s Shimano rear derailleur that is spec'd to handle both a 51t max low sprocket AND a 42t max low sprocket. The RD-M5100 spec sheet reports 51t is max and minimum low sprocket and other 11s RDs spec out at 42t or 46t max low depending on cage length. Personally I've had excellent shifting on an 11-51 using RD-M9000 (XTR) without a link extension. Just had all but 3 threads of the B screw full in.*
    – Jeff
    Nov 18, 2022 at 3:33
  • *Shifting was excellent with this set up and remained so for many weeks of daily riding single track. I decided to change things up after reading a few different anecdotal reports of slowly degrading shift quality. Evaluation of the 11s XTR rear derailleur used long term with an 11-50t Sunrace cassette revealed lots of slop had developed in the linkages. Couldn't see any value in letting that happen to mine.
    – Jeff
    Nov 18, 2022 at 4:13

3 Answers 3

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A typical enduro bike spends a lot of time winching up steep but relatively smooth fire roads. That's the terrain where super-low gears come in most handy, because you can stay in the saddle and get the necessary power out of a high cadence rather than grinding torque. Besides comfort&endurance, staying in the saddle also has the advantage that you don't much need to worry about suspension bob or wheel spin. So if you expect to use the bike on such fire roads, I'd definitely go for the 11-51t.

If you use the bike more as a trail bike, i.e. shorter but more technical climbs, then there's not much point. On technical climbs, it helps to keep some momentum and have the saddle out of the way so you can better maneuver over obstacles and don't smash the pedals in some rock with every other stroke. So too low gears aren't much use, it's better to drop the saddle and power through it in a gear close to 1:1. If the climb is too long to sustain that power, then it's probably a case where pushing or carrying the bike is more efficient than struggling to pedal it out, though I personally also like that challenge – with a fast-engaging hub it's possible to ratchet up very steep and technical climbs in 1st gear, trials-style. Or if it's not too technical, you may also be able to still ride it in the saddle like on a fire road, thanks to full-sus.

On tarmac, there's also not much need for those gears – roads are seldom steep enough to require ratio lower than 0.8, even when riding in the saddle (though this of course also depends on the rider). Traction is not a problem either on tarmac, so you can better get out of the saddle than on gravel. I sometimes use my enduro bikes for longer tours with lots of baggage, and then slow spinning is again helpful, but OTOH I always miss the narrow steps and fast upper gears of a 2× drivetrain. Even my 1×12 \ 10-50t has rather too big steps for road riding, and 1×11 \ 11-51t is even worse. So on tarmac, a 11-42t would be a rather better choice. (Argument also applies for gravel touring.)

Finally, the 11-42t will probably shift smoother and more reliably, which is particularly useful for downhill passages. The smaller cassetter should also a bit lighter, improving rear suspension performance. If you expect to use the bike a lot in bike parks with lift/shuttle, then these are arguments for the 11-42t.

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  • Re traction on roads, those of us who ride year-round in wet countries definitely have traction issues at times. I've spun the back wheel of my tourer/audax bike many times, and repeated wheel spinning until I ran out of momentum is why I've ended up walking up one hill in particular more than once. Trying to get more weight back just meant lifting the front wheel on a heavy bike woth a long wheelbase and only just under 1:1 gearing.
    – Chris H
    Nov 15, 2022 at 6:56
  • @ChrisH surely not while in the saddle. When pedalling out of the saddle in a <1:1 gear perhaps – I always shift to at least 3rd gear when standing up. It's also important to have a smooth pedal stroke; clips helps a lot. — This is assuming knobby tyres and/or clean tarmac (no matter how wet): if you used road tyres on a leaf-covered road then all bets are off of course. Nov 15, 2022 at 7:54
  • I'm very much a sit-and-spin rider and the wheelspin was seated. Lifting the front wasn't because I'd shifted my weight back for better traction. This was on Marathon Mondial tyres (supposedly good for anything; I fit them for winter road rides given the mud I find on the road). I never assume clean tarmac, and this wasn't Streetview in summer looks OK, and on the rare occasions it's dry, it's fine
    – Chris H
    Nov 15, 2022 at 9:36
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Equally efficient, in a practical sense cogs and chain have more or less the same efficiency. There are small differences for high end components.

The 11-51t cassette gives you a slightly lower low ratio of 0.67 while the 11-42 yields 0.8.

That lower ratio is great for grinding up steep hills but maybe you don’t need the extra gear. I personally wouldn’t be without my low 22/36 (0.61) ratio.

The technical issue is that your existing derailleur might not support the 51t cog / 40 tooth difference or the even 42 tooth top cog. Check the specs for the derailleur you have.

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    The disadvantage of the wider gear range is the bigger steps between each gear.
    – Michael
    Nov 9, 2022 at 21:01
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    @Michael I never found this to be an issue on my enduro since I didn't really care how slow or fast I went uphill. It is of course different on road bikes or even XC MTBs.
    – arne
    Nov 10, 2022 at 1:54
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Even with 11 speeds, the gaps between the gears will be pretty big on 11-51, so it really should be based on whether you need such a low gear. If not, other riding will be more pleasant and efficient because you'll be able to ride at a more comfortable cadence more of the time.

The lowest gear you need depends on the terrain as well as your ability to handle the bike at low cadences/high efforts on (hopefully not too common) occasions.

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