Why do you need to change handlebars?
While there are many reasons to change handlebars, the most common is to change the feel of a bike. If you have been riding a mountain bike with riser bars and decide you want flat bars for tighter maneuverability on city streets, then changing your bars will likely fix this problem.
If you plan to begin commuting on your bike or start racing, then chances are that you should invest in new handlebars first and foremost because drop-style road handlebars (drop-style mountain bars) provide an aerodynamic advantage over their flat counterparts.
Handlebar changes are not difficult but do require some time and care to make sure everything is properly lined up.
Types of handlebars
The two main types of handlebars are traditional drop-style bars for road bikes and flat-style mountain bike bars. While there are many variations, you will usually find the following styles: riser mountain flat, risers with sweepback mountain flat, low rise or performance flat (flat with risers near the stem), high rise or cross country flat (doesn't bend around the fork, but straight up) and bullhorns.
Material
Handlebars can be made from aluminum alloy, steel tubing, or carbon fiber tubing. Generally, the more expensive the handlebar is, the lighter it is. Carbon fiber bar construction has become popular in recent years because of its lightweight properties along with its ability to absorb shock without adding too much weight.
How can you choose good handlebars?
There are a lot of options out there and many different styles. The best way is to try them out at a local bike shop for comfort, ease of use, and other factors such as how long the brake cables need to be pulled to reach them properly. Handlebar width depends on your riding style. Flat bars should be around the width from elbow to elbow while drop bars should be a little closer together (around forearms).
Installation process
Time required: 45 minutes (it's more like an hour if you're new at it)
Tools needed: 6mm Allen wrench, 8mm Allen wrench, adjustable wrench, or crescent wrench
First, get the tools out to change the handlebars.
Remove the previous handlebars from the bike and then separate them from their brake levers. A 6mm Allen wrench is required for this.
Remember to align the special washer that keeps the handlebars from rotating with its spot on your stem cap.
Remove both cotter pins holding your brakes and brake levers in place and remove any excess cabling. At this point, you will need an 8mm Allen wrench to work with as well as a way to hold onto both sides of your calipers (a vice grip works great).
Having everything lined up properly is key when replacing handlebars as it keeps all cables tight and brake lines out of harm's way if they should break or be cut during the removal/installation of the new bars. After the previous handlebars and brake levers have been removed, use your adjustable or crescent wrench to remove your old grips and then place them on your new bars.
Get the stem cap and tube ready for insertion into your handlebar. Take a standard tire tube and cut off one of the thin rubber strips inside it (the part with no tread). Slide this over the inside of what will be inserted into your new bars as a nice gasket material to avoid scratching up those lovely alloy surfaces you just polished!
Before inserting everything back onto one side of your bars, make sure that both sides are lined up correctly and that you can still easily turn each brake/shifter lever.
Inserting handlebars back onto the bike is also key to not scratching up your stem, handlebar clamps, and headtube. After both bars are fully inserted (but before you tighten everything down), make sure that the levers on each side easily turn without hitting anything (your tires/tubes) or rotating far enough either way to start braking.
Make sure everything is nice and straight; it should be lined up as if you were looking at a clock where 9:00 would be pointing downwards towards the ground (if you're sitting on the top tube). Once everything is set perfectly straight, tighten down all bolts using an adjustable wrench or crescent wrench first making them "finger tight".
Next, use a torque wrench to tighten every bolt to the appropriate torque amount according to your bike's manual (usually 5-9nm). Make sure that everything is tightened down and double-check all bolts, making sure there aren't any loose parts before you ride it again.
You've successfully changed your handlebars and are now ready to cruise the streets looking like a pro! Have fun and enjoy your new riding style.
In case you want to install flat bars
You will want to buy a new stem and possibly some risers if you haven't already got any for your bike (you're going from drop bars to flat bars). Flat bars come in two flavors: riserless and with risers attached. If you're going to be turning your bike upside down for long periods of time or do something that might scratch up your bars (like parking it on the ground) then get some risers. Otherwise, riserless will not hurt anything and are cheaper than risers so you can put the money towards other things upfront like new grips.
Your old brake levers should fit perfectly onto flat bars with no issue at all though you may need to adjust your brakes slightly (refer to your brake's manual for help, this is usually only needed if the cable isn't pulling far enough). Don't forget that you'll need grips that should go easily onto your bar with little worry about scratching them up.
On flat bars, you will need new shifters if they aren't already attached to your brake levers. A cheap solution is buying little adapters that go on the end of your handlebars and allow you to run twist shifters. Or a more expensive but nicer-looking option is some sort of trigger shifter (referred to as flat bar triggers).
You will also want some type of gear indicators such as an LCD computer or nice hand-made paper one which you can print out and use with no batteries needed! Once everything has been adjusted properly, tighten down all bolts using an adjustable wrench or crescent wrench first making them "finger tight".
Next, use a torque wrench to tighten every bolt to the appropriate torque amount according to your bike's manual (usually 5-9nm).
Make sure that everything is tightened down and double-check all bolts, making sure there aren't any loose parts before you ride it again.
How much does handlebars change cost?
You can buy some flat bars and some new brake levers for as low as 20$. The cheapest you will probably find riserless flat bars is 40$. However, an average price of a nice set would be about 80$ (before shipping).
Grips should be easily under 15$ and I've seen the Shimano twist shifters for around 10$.
Remember that you'll want a gear indicator if your bike doesn't already have one. I bought my digital computer online from Jenson USA for about 60$, but this newer version has SIX modes! There are cheaper options out there or you could even DIY use an Arduino board if you're feeling adventurous.
Any other accessories
You may want to get some new grips if your handlebars are significantly bigger/smaller than you're used to. Grips for bigger bars will have more "surface area" so they feel better for larger hands but don't give as much grip as narrow grips which are better for smaller hands.