Originally Posted by
jimc101
If you really want to go ahead, you will need to source road compatible flat bar shifter (the M4000 may or may not work, pre-10 speed everything was compatible between road and MTB, now, don't count on it for any speed above 8 with current components), compatible brake levers, and work out the best stem/handlebars solution that make the bike comfortable. Given the age of the bike (as it has 9-speed Ultegra), it's at least 15 years old, you will probably have issues with tire clearance over 25mm as 23mm was the norm back then and anything wider was uncommon for a road bike.
This is not correct. Shimano front derailleurs have always been road/MTB specific. I think MTB pulls more cable so you may be able to get a MTB front shifter to work on a road FD, but you won't have trim positions and setup may be more difficult. For your specific application, I'd recommend microSHIFT R9 R859 shifters, which are Shimano road 9 sp compatible and retail for about $48. You'll need short pull compatible brake levers, which are readily available.
I agree that the bike may not make an ideal flat bar conversion, but in truth in the past a lot of brands high end hybrids were literally their endurance road frames set up with flat bars, and an awful lot of FG/SS riders are on road or track geo frames and flat bars and it works out OK. Also expect to need to change stems to find a good position with a flat bar. It may be financially and mechanically smarter to sell the road bike and buy a mid end hybrid.