8/9/10 speed shifters on a 7 speed cassette?

Hi guys. My mate got one of these a few months ago http://www.decathlon.co.uk/btwin-fitness-3-id_8188895.html but now he wants to change the flat bars into drops and have shifters on the bars not on the downtube. But he can't seem to find any 7 speed triple shifters anywhere and I was wondering whether he could use 8/9/10 speed shifters instead but I wasn't sure if that would work. So I'm here asking for some help on whether this could be done and explain why it can't be done so I can improve my knowledge.

Thanks a bunch, Jackie.

The easiest thing to do would be to put an 8speed cassette/freewheel on the rear wheel, and get some 8speed STI's. Everything else should be compatible.

Without changing the amount of gears on the rear wheel I can only tell you that 9 and 10 speed is extremely unlikely to work, and even using an 8 speed shifter with 7 speed gears will require careful measuring of how much the shifter actuates the cable, and what this translates to in terms of derailleur movement. I'd say take the oppertunity to upgrade to 8 speed as it'll be a cheap transition. Upgrading to 9 or 10 will require new derailleurs.

8/7 have the same sprocket spacing so it works. I've done it. 9 and 10 are not going to be compatible with 7 or 8; some people have done it I believe but it "works" quite poorly.

Obviously set up the derailleur limit screws to avoid overshifting and throwing the chain.

Oh I see thanks guys for the help.

Also, does anyone know where to get cheap 8 speed triple shifters?

Shimano 7 spacing is wider than 8. You can get away with it sometimes though.

Either get NOS rapid-fire shifters or fit an 8-speed block, assuming the freehub/wheel dish suits.