Is it just a case of leaving the stem and changing the bars, shifters and brakes

or

is the geometry and reach etc very different forn drop bar bikes comared to purpose made flat bars ones?

and finally will a 10 speed road mech work with a 9 speed road cassette?

Ta

Dave

Not sure about geometry, can’t be that different.

10sp mech will work fine with 9 speed cassette (as long as you have 9 speed shifters. 9 or 10 speed chain will work, but 9 may a bit better)

Yes, change bars and controls, leaving stem until you’ve tried it. You may want to invert the stem then, or get something longer.
Mech/cassette combo fine if using 9 spd shifters. You may find the front shifting a pain to set up if planning to use road mech, but MTB shifter.

Top tube will usually be shorter on a drop bar bike.

cheers guys, looks like a try it and see exercise then.

I was planning to leave the front mech and rear mech. just get a new 9 speed road cassette and MTB shifters/brake combo.

Ta gents

You may well up up with a much longer stem, I`d reckon on equiv frame sizes teh top tube on a MTB frame could be 4cm longer than on a road bike. However this extra length is then offset to some degree by fact that flat bars will be wider than drop bars (eg 60+cm v 42/44cm), and if you also fit bar ends then riding position may end up pretty clos to that with drop bars. Suggest that before removing drop bars measure a set of distances from saddle nose point as reference to centre bars, top curve of bars, brake hoods top, drop on bars as these can then be used to aid setup with flat bars.
If its any help from my experience riding an MTB commuter with flat bars / bar ends I`m using a similar length stem (up to 2cm shorter) to that on my road bike and achieving similar setup distances to above , therefore I would expect you to end up with a 2cm+ longer stem when swopping over to flat bars.
btw if you`re interested I have in std (not oversize ) clamp stems at 90 / 100 / 120 mm second hand for you to try 🙂