Mountain Biking - Stem Length

My wife was checking out bikes at an LBS and the guy there mentioned getting a longer stem for more control as she gets more experienced. (We were looking at a Trek 4500 WSD which has shorter stems for women). Is this bull? Most of what I've seen here says stem length is more about fit and feel than something to adjust as you get better.

Building on that, is stem length measured from the center of the bar to the center of the steering axis? If so, does 75 mm sound right for a Mobius stem on a Hardrock Sport? I'm looking at getting a Thomson (local company, so I'm almost obligated...), but they start at 90 mm. My old bike seems to measure 120 mm, which seems to bend me over too much and put too much pressure on my hands. But my newer bike keeps me a tad more upright than needed. Should I split the difference and go with 100 mm?

A longer stem for more control? I would have said a shorter stem would provide more control, thats what I found anyway when i switched to a shorter stem.

Although I wouldn't adjust my stem length for any other reason than comfort (for XC) I can see how more serious riders would to get a more racing fit.

Stem length IS measured center to center.

I found getting the right stem length is just trial and error. I tried 4 different stems before I got the right rise and length.

Sorry couldn't be arsed to use quote function.

Stem length is a personal choice. A longish stem typically gives you more sense of control if you are a new rider. A shorter stem means that the stearing arc is slightly smaller, and steering input is magnified by a short stem and may seem more "skittish" at first. A longer stem means to you need to turn "more" to move the bike around a corner. A short stem has a smaller steering arc and less movement is required to turn.

Regardless, go for what feels best. Remember too, that even if your stem choice is not the ideal length for you, 1 or 2 cm can often be made up by sliding your saddle further forward or back.

Ideally, your LBS would let you try a couple different stem lengths.

Stems are measured center to center (center of headset to centerline of handlebar).

A long stem will make most of your body go into a turn. A shorter stem uses more of just your arms, it will feel like "quicker" steering. Im using a WCS stem, thats 100mm long with a 6 deg rise. I find htis to be very comfortable, a good balance all together. 120 seems long for me, especially on the frame i already have

wow, i run a 40mm stem with 0 degree rise. 100 sounds super long to me :p .

I'm guessing that 40 mm is more of a downhill thing. I ride mostly xc, but considering what everyone has said, I'll probably go with the 90 mm Thomson stem. I definitely like the feel of the shorter 75 mm stem vs the 120 mm. Thanks.

A longer stem is generally more XC oriented which aides in putting the rider in a more forward position. This position helps when climbing and when hammering the flats.

A shorter stem is generally for more aggressive riding. i.e., more Freeride and Downhill applications.

However, it's all a matter of personal choice.

Try several out before you invest.

BTW, Thomson's are very nice stems. I own two myself!