Getting a mountain bike to “fit” takes a couple adjustments.  The Mongoose Mountain Bike one of my kids has needs the handle bars adjusted.  I thought I’d explain how to adjust the handle bars on a Walmart Mongoose Mountain Bike.

MTB Handlebars
MTB Handlebars
  1. Figure out the type of stem is on your bike. It will either have a “Quill Stem” which is on most Walmart bikes or a Clamp (sometime called threadless) Stem.
  2. If you have a threadless, you will be very limited on the handle bar height adjustment.
  3. On a Quill stem turn the handle bars and fork to face forward. Make sure the cables aren’t twisted.
  4. With a 6 mm allen wrench turn the stem binder bolt in center of the handle bars in a counter clockwise direction to loosen. Back the bolt up about ½ inch.
  5. With the bolt slightly above the handle bars tap on the head of the bolt to loosen the quill.
  6. The quill stem will “break free” allowing the handle bars to be raised and rotated.
  7. WARNING: the stem will have a MINIMUM INSERTION MARK. Do not raise the stem out of the steering tube beyond this mark.
  8. Loosely tighten the stem bolt to allow adjustment up and down and side to side.
  9. With the handle bars at your desired height, stand in front of the bike facing reward. Holding the front wheel with your legs. Align the bars straight to the frame.
  10. Tighten the stem bolt.
  11. Sit on bike and double check that the handle bars are straight.

Next let’s get into the details of how high the handle bars should be and how to rotate the handle bars to make them a little more comfortable.

Illustrated definitions of the handle bar area of your mountain bike.

Handle bar stem type
Handle bar stem type

So let’s get into the detailed steps for adjusting the seat height.

Type of Handle Bar Stem Quill or Clamp

Quill Stems

Most Walmart bikes and lower price point bikes will have a quill stem.  The quill, is basically a wedge that locks down onto the INSIDE of the steering tube.  This type of system (stem and steering tube) will make it difficult to upgrade the front fork.

The quill is also prone to rusting in place.  Usually a liberal application of penetrating oil from the top and bottom will loosen any rust. 

Because Walmart bikes are not “sized” usually the size is just called out as large, medium and small.  The adjustments with the stem allow some fine tuning to find that comfortable riding position.

The nice thing is that a quill stem is adjustable, but with that adjustability comes a little bit of risk.  Remember my note above you should never raise the stem above the minimum mark.  The reason for this is to allow the quill to wedge into the steering tube without damaging the tube and still hold the handle bars safely.  No one wants the handle bars to come off in the middle of a ride.

A way to align the handle bars is with the tires straight to the frame.  Straddle the font wheel facing the rear of the bike.  Grip the bar ends and turn the bars square to the bike frame. See the picture below demostrating. 

Bike handlebars worth upgrading
Bike handlebars worth upgrading

A Little about Clamp / Threadless Stems

Threadless stems are a stronger and lighter handle bar system.  The stem and steering tube are combined which eliminates the extra joint formed by the quill.  For this reason if you’re looking to upgrade the front shock and fork on a quill stem your selection is going to be very limited.

Truth be told if your reading this with the idea of upgrading your Walmart bike front suspension, I’m really sorry.  I think there is only one after-market fork that is available to buy.  I’m not a heavy guy and this shock easily bottoms out.

My plan with my Walmart Mongoose is to make it into a comfortable cruiser / commuter.

Tools required for adjusting the Handlebars

  • 6mm allen wrench for a quill stem
  • 5mm allen wrench for threadless stem and brake levers.
  • A light weigh hammer and piece of wood
  • 14 mm wrench if you want to slide the seat forward or back.

Maintaining and Replacing Your Handlebar

It goes without saying – steering is important.  Maintaining the handle bars by keeping them clean, having good grips and making sure everything is tight is essential to maintaining CONTROL on the bike. 

Do not try to straighten handle bars by bending them back into position. If you crash and things get bent, the bar or the bar end is exposed, get replacement parts.

Adjusting the Handle Bars Front to Back

You can also adjust the handle bars front to back slightly.  This is done by loosening the bolt and clamp on the front of the stem.  Insert a 6mm allen wrench into the bolt head and turn until the handle bars roll freely.

Essentially you are rotating the handle bars, which in turn moves them slightly closer to the rider.  This “rotation” is only effective to a limited extent.  The geometry of the brake and shifter levers also changes as you roll the handle bars so those will need to be adjusted as well.

Be very careful if you rotate the handle bars.  Being able to squeeze your brakes handles quickly is critical to maintaining control of your bike.  This is a simple adjustment using a 5mm wrench.

Setting the Seat and Handle Bar Height

The seat and handle bar are two of the touch points that form the “comfort triangle” on your mountain bike.  The third touch point is the pedals.  The pedals and bottom bracket don’t adjust, so adjusting the handle bars and seat are usually related back the bottom bracket.

Setting the Seat Height

The correct seat height has your knees almost straight with your leg in the full down position.  If your adjusting the seat height for your young beginning rider, you may want the height somewhat lower to allow the child to touch the ground when stopped.  You can read more about adjusting the seat height in THIS POST. (link to another post)

Do not raise the seat so high that your knees lock straight during the pedal rotation.  This is unsafe.  Read more about seat adjustments in this article – How to adjust seat height.

Another factor in seating position is sliding the seat back and forth relative to the handle bars.  I talk about this in another post, but basically using a 14 mm wrench you can slide the seat back and forth along the seat rails.

Learn more about Pedals, Handlebars and Brakes

Comfort and Arm Angle for Handle Bars

The handle bars should be at a height and easily reachable from the seat while riding.  A baseline position is having your arms slightly bent at the elbow (about 10 degrees) with you bottom on the seat. 

If you feel like your reaching to far or your shoulder and arms a seem to be holding you up, adjust the seat position on the seat rails

Mongoose mountain bikes are not designed for aggressive single track trails.  You should be riding in an upright position.  This allows you to keep your head up, looking clearly at the path ahead.  Don’t push yourself beyond your capabilities particularly on a Mongoose.  The front forks are for comfort and not jumps or steep down hills.  I know for me the front shocks bottom out easily riding over a sidewalk curb.

MTB Tools I Love and Recommend

Bike Hand Repair Stand
Bike Hand Repair Stand
Bike Hand 37 pcs Tool Box
Bike Hand 37 pcs Tool Box
Topeak Smartgauge D2 Air Pressure
Topeak Smartgauge D2 Air Pressure

I own each of these tools and only recommend things I own and use.

  • Bike Hand Bike Repair Stand.  Nice mountain bikes don’t have a kick stand so keeping your MTB safe but conveniently stored is essential.  I keep my bike on my stand whenever I’m not riding it.  This makes it easy to lube the chain, inflate the tires and adjust the derailleur.  Highly recommended – Bike Hand Bike Repair Stand (👈 Link to Amazon to see what thousands of others have said)
  • A basic MTB toolbox for replacing a chain, adjusting brakes and dialing in the fit.  Bike Hand has a 37-piece box that has most of the specialty bike tools to keep your MTB properly maintained.  The Bike Hand brand is value packed for the avid rider.  Check out the competitive prices with this link to Amazon 👉 Bike Hand 37 pcs Bike Repair Tool Kit
  • Get a good air pressure gauge, if you get just a tiny bit serious about MTBing you’re going to start playing with tire pressure.  A couple psi can make your tires sticking or not.  Get a good gauge, I highly recommend the Topeak Smartgauge D2, it’s accurate, flexible and easy to use.  An Amazon best seller, here’s a link 👉 Topeak Smartgauge D2
  • Carry a multitool with you on every ride.  I’m serious, most of the time you can MacGyver something to get back to the trailhead if you have a multitool.  I’ve got the Crank Brothers M19, it’s worn, rubbed and abused – but it still works.   Thousands sold on Amazon – check it out with this link 👉 Crank Brothers M19

David Humphries is the creator of DIY Mountain Bike. For me a relaxing day involves riding my mountain bike to decompress after a long day. When not on my bike I can be found wrenching on it or making YouTube videos at 👉 DIY Mountain Bike Read more about David HERE.

adjust handle bars on mongoose
adjust handle bars on mongoose