Liquid sunshine brings out the best and worst of all riders. Riding in the wet requires you to be aware of the low friction conditions that exist between the tyres and the road. This can be dangerous but if you are cautious and aware of the hazards, it is no more dangerous than any other normal day. And it is only through riding in the rain that you become aware of your own capabilities and limitations and those of your bike and its tyres in such weather. Tyres have grooves in their tread and their purpose is to remove water from under the contact patch. Obviously, if the tyre is worn smooth with no grooves left, water on the road stays trapped under the tyre and it slips. Tyres in good condition inflated to the recommended pressure go a long way in improving the grip.
Apart from good tyres, the trick to maintaining traction when riding is smoothness. All transitions i.e. acceleration, braking, gear shifting and turning should be accomplished smoothly. Be gentle in braking and acceleration and follow the widest possible arcs during cornering. Remember road grip is already fighting a loosing battle with slippery conditions. Your tire traction is cut by as much as TWO-THIRDS on wet roads. Don't make it worse for the tyres by demanding too much from them and in too short a time. Retaining your traction in the wet is far easier than regaining it. a slide that can be corrected in the dry will almost certainly take you down in the wet.
Brake gently, using more of the rear brake than the front (just the opposite of what you would do in the dry). Keep checking your brakes for effectivity when riding in heavy rain or through deep water. Drum brakes, though difficult to get wet from inside, take time in drying and become effective again. If wet, ride a while with the brake applied partially. The heat generated due to friction between the brake shoes and the drum will soon dry it out. Discs usually work fine though there may be a tiny delay before full effectivity as the pads wipe water from the disc surface.
The roads are at their slipperiest after a light shower. Rubber powder from tyres along with dust and oil, when mixed with water, forms a very slippery concoction. Let consistent heavy rain wash off the roads clean before expecting respectable amounts of traction. Oil droppings from four-wheelers are concentrated around the middle of the road, at stoplights, near petrol stations and toll collection booths. Large trees, whose inviting shade is a great stopping zone for vehicles are also virtual oil reservoirs. Take it easy with the brakes and the throttle when passing through any of these. Painted strips, old metal manhole covers, wet leaves and railroad tracks at crossings are very slippery customers even in the dry and more so when wet. Avoid abrupt changes in direction, braking and accelerating over these.
Hydroplaning is the result of your tires moving fast across a wet surface - so fast that they do not have sufficient time to channel that moisture away from the center of the tire. The result is that the tire is lifted by the water away from the road and all traction is thus lost. Skimming stones across a pond or water skiing are great examples. The tyres on the bike work like skis and the rider has no control over direction. Tread design, tread depth, weight of motorcycle, tire pressure and depth of water all play a part in determining at what speed the tire will begin to hydroplane.
In the event of hydroplaning, do not apply your brakes or try to steer the bike in any direction but the straight-ahead. If you know that you are going to be riding in the rain, add some 3-5 psi of pressure in your tires. Increasing the tire pressure makes its contact patch smaller. In other words, it increases the weight per square inch of the contact patch so that it takes more 'uplift' by water to cause hydroplaning. And just as increasing pressure makes the contact patch smaller, it also tends to spread out the tread grooves which, in turn, makes it easier to squeeze out water away from the contact patch.
Wear a proper rain suit and helmet while riding in the rain. The discomfort of being wet distracts the rider from paying full attention to his riding. Also, raindrops can be very painful when they hit an unprotected face. A good clean visor keeps this unnecessary pain away and you don't have to squint your eyes against the rainy onslaught. Squinting the eyes cuts down the much-needed peripheral vision. Use reflections on a wet road to your advantage. Walls, electric poles, overhead cables and parked vehicles all work as reflecting surfaces that can enable you to see around corners. But avoid all shiny spots on the road like plague. They could mean either a puddle, slippery paint or oil.