If your hands get sore and tired on long rides, it might be time to replace the handlebar grips or get auxiliary grips such as Grip Buddies or Super Sharkskins.
Handlebar grips wear out. Have a look at yours and see if there is a wear pattern on them with smooth and grained areas. If they are, then it might be time to replace them. Smooth grips won’t have as much grip, which could be dangerous. If you replace them, you can buy thicker, spongier grips, but you lose some of the throttle feel and effectiveness of the grip warmers, if you have them.
I found Grip Buddies on the web which are pieces of neoprene foam that simply wrap around the current grip with the ends clasping together via velcro. I fitted them to my BMW R 1200 GS and now ride long distances in comfort. The manufacturer says they provide plenty of feel and allow heat from grip warmers to come through. However, I take them off for off-road riding where I need more throttle feel and remove them on really cold days to get the full effect of the bar warmers.
That’s one of the beauties of these auxiliary handlebar grips. I 
can quickly remove them and place them on most of the review bikes I ride. While the manufacturer warns that you should glue them in place, I didn’t it necessary as the neoprene against the existing rubber grip means they don’t slip. Note that the Grip Buddies come in various sizes to suit most models, but a set that fits one bike may not fit other bikes.
I haven’t found anywhere to buy these in Australia, so I ordered them through Californian online company, Adventure Designs. My order arrived 
within a week. They aren’t cheap for what is basically a piece of foam rubber and velcro. They cost $US24.95 and shipping was an extra $US39.95 for a total of $US64.90. But what price do you put on comfort and therefore safety?
You could probably make your own handlebar grips with some old foam stubby holders, but I wouldn’t recommend it. Fit would not be as good and that would make them dangerous if they slip or inhibit the throttle mechanism.