There are two main reasons why you want to look into changing your motorcycle handlebars:
Basically motorcycle handlebars (at least on dirt bikes) look something like in that picture.
You get them in shapes from almost flat (at the bottom) to quite high bent (at the top). A lot of tall people choose very bent ones so it is easier to stand. But also little people sometimes choose them so they can mount them tilting back and the grips are closer to the rider (for those short-arms like me).
But what is the effect on the handling? If
the motorcycle handlebars are higher or if they are mounted so the grips
are further back, both will affect your weight distribution on the
bike. It moves the rider’s weight backwards affecting the bikes centre
The higher your motorcycle handlebar the more your weight will be towards the back of the bike. Your position on the bike will be more upright, shifting your weight back.
Constructors design a bike with a specific centre of gravity in mind and every mm that you move your weight upwards and backwards affects this. What then happens is that it becomes more difficult to put pressure on the front wheel, especially in corners. This can cause under steering or bad traction on the front wheel.
As you see on this beautiful demonstration from Grant Langston your weight needs to be almost on top of the handlebar in order to push the front wheel down and get the traction you need. It is the pressure you can put on the upper handlebar that counts. (And the foot peg, but now we are focusing on the handlebars)
When your fork is unweight too much it leads to comfort and performance problems. My husband is 1,86 m tall (6 foot 1”) and stands 90% of the time when I he rides. He never has problems with his handlebars being too low. It is really much more of a riding style issue than an issue of physical characteristics.
If you look at any bike competing in the world champs you will hardly ever see raised handlebars even on the tall riders’ bikes.
In fact many top enduro riders even use lower handlebars to enable them to get as much pressure on the front wheel as possible for maximum traction to make up time in corners!
So obviously you might not want to compete in the world champs and you are just looking for a comfortable ride. But there is another problem to it. You will get used to the lack of traction on the front wheel and the understeer handling. So your riding style will adapt and you will actually get into a bad pattern of cornering.
If you experience regular back pain when standing on your bike for
longer periods then do some core muscle training or visit a physio. You
can also strengthen your legs, because they should really be able to
hold your weight for that time, not your lower back. A really good all round work out for dirt bike riders is the Get fit ride fast regime. It deals not just with fitness but also strength and core strength.
One of the best advices I got from the former Hungarian Enduro Champion was to have only 10gram of your own weight on the handlebar. What he meant was that when you accelerate you don't hold on to your handlebars to support your whole weight but you actually lean forward, so that the main load is on your foot pegs. The same with breaking you shift the whole weight far back. Especially on flowy sections that is very much true. There is almost no weight on the handlebar and that also gives your lower back a break.
As for handlebar raisers, don't even go there. They are really a total waste of time. And if you buy a steering damper make sure it mounts above the handle bar and not below it for the same reasons. (click here to know more about steering dampers and when it is sensible to invest in them).
The Dirt Bike Garage Manual
HOW TO GUIDE for "do it yourself" riders