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On my new Trek Marlin with a 8 gear cassette, sometimes I try to downshift into the middle of the range of gears and it doesn't take (upshifting works fine). I can hear the gear clicking for a few seconds before the chain finally snaps into the correct position causing the chain tension to jerk while pedaling.

Do cassettes with a large range of gears have more issues with getting the chain to switch to the proper gear? Is this an issue that can be fixed by adjusting the derailleur tension?

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    How new is new? If you're about 4~6 weeks after buying it brand new, then most bike shops offer a tune-tweak up for all those little things. – Criggie Sep 1 '19 at 2:40
  • Also, how's your technique? On a derailleur bike you have to let off the pedal pressure a smidge to allow the rear derailleur's spring some slack to move and lift the chain up onto a bigger cog when going to a lower/easier gear. When changing down (harder gear,smaller cog) the chain just has to fall down and gravity/chain tension helps get it in place. Curiously, an IGH is the other way around. – Criggie Sep 1 '19 at 2:43
  • How long has it been since you cleaned the chain? – Andrew Henle Sep 1 '19 at 12:06
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To shift smoothly, you need 5 components to be working together harmoniously: the cassette, the derailleur, the shifter, the frame, and the chain. Any one of those could be causing your problems.

In the specific case of cassettes, there is a wide range of quality and capability in cassettes. Many models have carefully aligned cogs, with little ramps and pins that assist in shifting, whereas others are little more than stamped plate steel. Those differences in quality will dwarf any difference between 8 and 12 speed.

So in short, a high-quality setup at any cassette size should have clean, crisp shifting.

With this said, a new bike should work reasonably well right away. Check that your deraileur is properly aligned, it may simply be a slight bit off and that is enough to cause your troubles.

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    Precisely the reason quality bike shops ask you to return for a free adjustment and hardware check after a month or so. Things like cables and springs will stretch and seat after initial installation. This can require a small but critical adjustments to optimize operation. – mikes Aug 31 '19 at 20:50
  • "To shift smoothly, you need 5 components to be working together harmoniously..." - Lol, why are bikes so finnicky? Motorcycles don't constantly shift out of alignment like bikes do. – SurpriseDog Sep 1 '19 at 2:22
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    Motorbikes compensate with much heavier-weight components, which they can do because the motor is substantially larger. Consider that a good cyclist can put out ~750 Watts for a few seconds, and most of us can sustain 100-200 watts for an hour or so. That's 1 horsepower and 1/8 to 1/4 of a horsepower respectively. 17cc is roughly a horsepower, so that 49cc stepthrough is 3 HP and a 600cc motor is ~180 HP. That's energy to waste carting around much heavier components. A motorbike bowden cable will weigh a lot more than a normal bicycle one. – Criggie Sep 1 '19 at 2:39
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    @Criggie plus many of those 49cc or similar scooters don't even have transmissions to begin with, often only a centrifugal clutch. Easy to be less efficient when you've got power to spare – whatsisname Sep 1 '19 at 5:16
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    Motorcycle gearboxes are closer to internal geared hubs than derailleurs. And IGHs don't need nearly as much maintenance as derailleurs but are heavier and less efficient. – ojs Sep 1 '19 at 12:02

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