I am new to bikes not ridden one since I was 11 I am now 63! I have a mountain bike and never used gears before they are mind boggling. I went out and rode it no problem but trying gear changes I don't understand at all.

My problem.. chain fell off, I put it back on easily but I dont know if its on the right cog pedal and wheel and if the gear selectors on handle bars are right... Please advise

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    – Weiwen Ng
    Nov 23, 2021 at 15:27
  • 3
    One reason the chain could have fallen off is if it's on a high front gear and a low rear gear. This is known as cross chaining and is bad. While you're bike may have been advertised as 21 speed (3x7) or something similar, there's really far fewer viable combinations. You need to keep the gears similar so the chains not going sideways. You might use the 1st speed on the front with gears 1-3 on the back, 2nd with 3-5, and 3rd with 5-7.
    – yesennes
    Nov 23, 2021 at 17:47
  • If you continue to struggle with the gears, consider getting a bike with an internally geared hub. Those are much easier to use, require less maintenance, but are less efficient and can be more expensive. I'd also argue that a touring/trekking bike (potentially with an internally geared hub) might be more fun, unless you attempt to do actual mountain biking on your mountain bike, which after 50 years of not cycling might not be very advisable. Derailleur gears with 1x gearing (I.e. without front shifter) are a middle-ground considering ease of use, but usually not found on entry-level bikes.
    – Erlkoenig
    Nov 24, 2021 at 8:24
  • Take a picture and add it to your question. Just in case noone ever pointed it out: you need to be pedalling forwards while you use the levers to change gear. Shifters typically have numbers on, and reading both numbers together (so your 21 speed bike might have between 1,1 and 3,7) as if they were a single number (from 11 to 37), the "bigger the number the harder it is to pedal and the faster you go". It's not a perfect rule, but it'll do. Note also that shifter numbers tend to go in the opposite direction; pushing the left shifter makes the number bigger, pushing right makes it smaller
    – Caius Jard
    Nov 24, 2021 at 15:56

4 Answers 4


If the bike is new, it could definitely benefit from a visit to a mechanic.

Bike gears (among other things on a bike) require occasional tuning. Chain dropping frequently, gears not shifting easily, or bike making grinding sounds is a good sign that something needs adjustment. Your local bike shop will help there.


No need for a long answer... Just give the pedals a turn and the chain will find the right "cog" on it's own.

  • 10
    Do this gently by hand, so the chain doesn't jam hard if it's angled weird through the front or rear derailleur. Ideally lift the rear wheel off the ground (e.g. with one hand) while you turn the pedal with the other. Or wheel it forward with the wheels on the ground. You should watch the chain move as you do this, you'll see it straighten out. Nov 24, 2021 at 4:24
  • 1
    Even after getting it back on, work through the gears riding gently in a safe situation, to test them, in case the same thing happens again
    – Chris H
    Nov 24, 2021 at 9:19
  • 1
    I would usually shift the front shifter to the larger ring (to the right/outside) as well. Otherwise this may not work. Nov 24, 2021 at 21:19
  • I wish more StackExchange answers were this way. Short and to the point.
    – Mu3
    Nov 25, 2021 at 16:50

First off: Welcome back the cycling world!

Yup, gears can take some getting used to. This is a common experience for adults getting into cycling after having not ridden since childhood. It will become second nature before you know it.

A quick guide to the confusing world of gears

Your left hand shifter corresponds to the front gears, the ones attached to your pedals. Your right hand shifter corresponds to the rear gears, the ones attached to the rear wheel.

One of the things that can be confusing is that on the left/front gears, a higher number corresponds to a larger chainring. But on the right/rear gears, a higher number corresponds to a smaller chainring (usually called a cog in the rear, don't ask me why the names are different).

It's easier to think of it as lower numbers being closer to the frame and higher numbers being farther away from the frame. That's true on both the front and rear gears.

Now, to answer your question

You don't mention if it fell off of the front or rear gears. Either way, all you need to do is look at the corresponding shifter and see what number it's on. If the number is high, put it back on the outside gears. If it's low, put it on the inside gears.

One thing I find helpful is to pick up the rear wheel and give the pedals a turn or two by hand once you have the chain back on. This will get the chain back in line where it's supposed to be even if you put it on incorrectly.

One last note about why your chain fell off

There are two likely reasons that your chain fell off:

  1. You were shifting under load. Most bikes aren't designed to shift while you're pedaling hard. You'll want to learn to anticipate your need to shift to lower gears and do it a smidge before you actually need it.

  2. Your bike is improperly adjusted. This is incredibly common for bikes purchased from big box stores like WalMart, Target, or even the big all-purpose sporting goods stores. It also wouldn't be surprising to find on a bike that you purchased used.

Unless you got your bike from someone who is a decent bike mechanic themselves and you trust that person to have put the effort in to make sure it's properly adjusted, I'd recommend taking it in to a bike shop to have everything checked and adjusted. This is especially true if you got your bike from a big box store. Those bikes are poorly assembled, sometimes dangerously so.

  • 1
    The selected gear is not always visible on the shifter. Although some do have some indicator, most do not. It is better to look at the derailleur. Nov 23, 2021 at 19:21
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    @VladimirF Even better, just shift to the smallest gear on both first before putting the chain back. Even without numbers, "all the way" is pretty easy to figure out. (If you want to worry about this at all, that is, instead of just shoving it back on and letting it sort itself out.) Nov 23, 2021 at 19:57
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    Putting the chain on both small front ring AND small rear cog makes it much easier to put the rear wheel back in, as there is much less tension on the chain.
    – Carel
    Nov 23, 2021 at 22:18

Have you ever driven a car? If so, they you've used a transmission. Bike transmissions work by the same principles, you have to match the load to the capabilities of the power source, in this case your legs, for the most efficient power transfer.

Most mortal humans can generally produce decent output from about 70 rpm to about 90 rpm on the crank. Below 70 calls for much more muscle strength and above 90 calls for much more speed that most people can manage for long. So the purpose of the gears is to allow you to select the right gear for the conditions. If you are climbing a hill you will want to select the smaller front chainring and the larger rear gear so that you get more cranks per wheel revolution and the pedaling feels easier.

When descending you want to go the other way and choose the larger front chainring and a smaller rear gear. That way you get fewer cranks per wheel revolution.

On the level you want to be somewhere in between and most bikes today have plenty of choices.

The key as a new rider is to develop the skill of shifting smoothly and in anticipation of the conditions so that you don't find yourself in the wrong gear in the wrong time and loose momentum.

In my experience most novice cyclists choose too "tall" a gear for the conditions. By tall I mean you are too large on the front and too small on the rear. This is where a "cadence" sensor can be helpful. Every cyclist is a bit different but I find that a cadence of 80-90 rpm works best for me. I'm now 64 but as a younger rider I used to be comfortable at 70-80 rpm. Experiment and see what works for you but don't be afraid to shift gears and see how different one affect your riding.

  • Thank you for the reply. My question is what of the nine gears on the rear wheel and of the three gears on the pedal do I put the chain that had slipped off, back on too. and how to I match it to the selectors on the handle bar... This is proberly a stupid question but I am brand new to all this Thanks Kev
    – Kev
    Nov 23, 2021 at 12:50
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    As far as the chain back onto the gears, look at the front and rear derailleurs which guide the chain to the proper gear position based on where you have placed them via the shifters. If you put the chain on the wrong gear, which is generally hard to do, it will move to the correct spot once you turn the crank a bit.
    – jwh20
    Nov 23, 2021 at 13:31
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    Standing by the bike, grab the seatpost with one hand, lift the rear wheel and turn the crank. The gears will sort themselves out.
    – Carel
    Nov 23, 2021 at 22:20
  • All sorted now, Thank you to you all for your help I appreciate it
    – Kev
    Nov 24, 2021 at 13:29

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