Suggestions for upgrading an old F600 mountain bike

[Mapios]

I have this old F600. I converted it to a commuter bike a while ago at a bike shop but I got a knee injury and I stopped riding it. I'm better now, so I don't want to throw it away. I would like to upgrade it, make it rideable again. Can anybody suggest some reasonably-priced upgrades? I remember I was never quite happy with its gears, they would often skip.

 

[black lightning 1987]

Hard to say for sure about the cause of the skipping issue but in most cases it can be cured by cable tension adjustment, cable replacement, or cassette and chain replacement. None of those will be expensive fixes. If you have a bike co-op close by, they can probably put you on the right track.

 

[MEENI]

go for 1 arrow/wide blade in the front
Some slick tyres would make it more usable for the road.
You could go for 2,35/240 wide