Mountain Biking - Bike stem sizing questions

I am new to mountain biking and I recently bought a used old steel-frame mountain bike for commuting/off road used. I am about 5ft4, the bike frame size is 16 inch, and it fits quite well on me. But the only part I feel uncomfortable is the bike stem, it seems way too long for me, so I am planning to get another stem to replace the current one. So what size of stem should I be getting if I want a better fits? Thanks in advance.

Any LBS worth their weight will have a few laying around for you to try out and see what you like.

Any LBS worth their weight will have a few laying around for you to try out and see what you like.

yes, but I thought perhaps this task is easy enough I could just buy one online, do it myself and save a few extra bucks.

Stem length is a pretty subjective thing. For instance...my Komodo shipped with a 50mm rise bar and a 70mm x 7deg stem on the size Lg. I prefer a 35mm x 10deg stem. My '98 Komodo has the same rise bars, but a slightly shorter top tube, so I go with a 90mm stem. It shipped with a much longer stem and a flat bar.

Times have changed. Riding style is a big factor. Terrain has something to do with it. What works for one guy just frustrates another.

On a mountain bike, altering stem length has a more profound effect on handling as opposed to fit. There are a few different schools of thought on the subject, based on the kind of riding you will be doing. As the stem length increases, the weight distribution moves forward and the amount one can easily move their weight back (useful for steep inclines, challenging terrain, drops, etc.) is decreased. The real world manifestation of this, is that you are more prone to going over the bars when trail riding/tricking on a bike with a longer stem. Typically, riders who aren't planning to do drops or tricks very often, but rather ride longer distances for fitness or a commute tend to prefer stems in the longer side of the range (~100mm and up) as the longer stem stretches them out, which allows them to feel comfortable in the same position for a long time (ie: more like a road bike. When on the trail, and for those who will be on trails most of the time, a shorter stem gives you better control of the bike in the handling varied terrain sense. This is based on the principle that, on the trail a good rider moves around on the bike a lot to alter their position to navigate trail features. This one reason why trail riding short distances can be more tiring than the same distance on a road. Even so, the shorter stem position begins to feel uncomfortable if you aren't moving around on the bike a lot. Any position/stem length is a compromise between comfort and agility. When establishing your position, you are trying to find the compromise that fits your riding style, terrain you ride on and your proportion. Even then, for commuting on paved roads, a mountain bike is necessarily the best tool for the job.

I am new to mountain biking and I recently bought a used old steel-frame mountain bike for commuting/off road used. I am about 5ft4, the bike frame size is 16 inch, and it fits quite well on me. But the only part I feel uncomfortable is the bike stem, it seems way too long for me, so I am planning to get another stem to replace the current one. So what size of stem should I be getting if I want a better fits? Thanks in advance.

Things to do:
measure length of current stem
determine interface - quill or threadless
Determine steerer tube diameter
Get on bike, lean against wall and try to estimate desired bar position
Consult habanero cycles stem chart
Buy stem
Repeat the last 3 as needed.

Posting good pics or sharing make/model/year might get you the answers to 1-3 right here.

like Ed said give your LBS a chance first..worst case you will walk out knowing exactly what you need and can go on-line then.They might even surprise you on price and may even have some take off product they are looking to get rid of.

yes, but I thought perhaps this task is easy enough I could just buy one online, do it myself and save a few extra bucks.

Today, man knows the price of everything and the value of nothing. - Oscar Wilde