Singa

Hello people.
My bicycle chain always fall off when theres a little jump... which is very inconvenient to ride this way... so I asked people why it happens (I am not really good with that stuff) and they told me I don't have a front derailleur.
So someone suggested me this one: LINK

The question is... will it fit for my bike? There are 8 cogs on the rear and 2 on the front.

RandomTroll

Some people have only one gear in the front. If you don't care to shift between front gears, to have the larger range of gears that affords, you can go without.

Lacking an FD shouldn't make your chain come off.

Your rear derailleur may be improperly adjusted. You can probably find a manual at the manufacturer's website.

Or the chain and/or gears are so worn they don't mesh correctly; if so you may need to replace some or all of them.

Bicycle frames come in different thicknesses. An FD has to clamp onto the seat tube, so it has to be the same size. Measure the thickness of the seat tube.

Second they have to accommodate the gears. Count the teeth on the chainrings (the gears in front). The FD has to accommodate those tooth-counts.

You can probably make do more happily with a cheaper derailleur. Check out front derailleurs at some random online bike store (choose sort on price low-to-high) for a wide variety of suitable FDs, to give you an idea of what's available. I don't endorse these guys, I just use their website for reference. Lots of online stores sell the same parts.

trailangel

The reason your chain comes off is because it's too long.

demoncyclist

The chain may or may not be too long, but since there are two rings on his crankset, they have shift gates and cut-down teeth to make shifting easier, which can also cause the chain to come off- more so in certain rear gears, since the chainline becomes less ideal. Adding a FD, even if it is just locked in place, will help keep the chain on the one ring that is being used.