I purchased my bike from a LBS few years ago and the frame seems to be small for me. It was my first real bike purchase and I didn't know much about sizing - and it seems neither did the store owner.
I was wondering if I could make the frame bit more comfortable if I replaced my stock 100mm stem with a 150mm one, possibly 10 degree rise or so.
The frame is a 19.5" frame and I'm 6'2". It's not undersized too bad however, i feel like i could use a bit more space.

If you need 5cm more room, I'd try to find a way to buy a larger frame. 150mm is a long stem for a mountain-bike.

FWIW, I've become a convert to the short-stem camp. I don't think I have any of my bikes set up with anything longer than a 70mm stem. And I rock a 50mm stem on the bike I ride the most. (I also run riser bars on all of my bikes now).

One thing I like about the combination of longer top tube and shorter stem is that I'm less likely to endo. Long stems provide more leverage by which to go over the bars.

Here are links to couple of interesting articles on stem length:

https://www.leelikesbikes.com/stem-le...rail-bike.html

https://www.leelikesbikes.com/stems-a...-and-high.html

You could certainly try a 150mm stem though. Buy an inexpensive stem and treat it as an experiment.

why not try a 120mm stem? that is not too long and it might just do the trick.
a set back seat post can help open up a cockpit too.

I wish it helped, I have a 19.5" mtb that I got as a gift 10 years ago, can't bear to sell, but is just plain too small for me anymore. Could turn it into an upright riding high bars town bike I suppose.

Protip

You may be very suprised at how much longer 10 cm is on on a stem. I agree with cbchess. Try the 120. Also, you can slide your seat back a bit (maybe you can...) to make a bit more room. And lasty, you can roll your riser bar and restack your stem spacers to strecth it out.

I have no experience at all with being tall but i do have experience fitting tall riders to bikes that are a bit too small. That long stem works because your comically whippy orangutan arms allow you to still get behind the saddle on a small frame like that, where a 120mm on a 19 would have me doing endos.

...where a 120mm on a 19 would have me doing endos.[/QUOTE]

Correct. Consider the endo factor!

thanks for the tips!
I already have the seat moved back as far as it can go. Maybe I'll stop by a LBS - not the place I got my bike originally - and see if they'd let me try a 120mm stem.
Thanks for the links Jonathan, I will check those out!

Do not adjust your seat fore/aft to achieve desired cockpit length. With the seat in the correct place (relative to the bottom-bracket), if you need a super long stem, then the unfortunate fact is that you need a new frame.

hmm i dont know about leverage. There is no moment for flipping you except your body. I think the phenomenon occurs because the center of mass is shifted forward on a long stem