Because wet roads mean less traction, you need to adjust your riding accordingly.
However, as long as you do this, it’s not that dangerous (because most modern bike tires are rated for riding in the rain).
The one time you should NOT be riding is the first rain of the season, where all the oil and grime is lifted out of the tar and spun around on top of it. Delay about thirty minutes to an hour, to ensure that the pavement is only wet and not oily slick.
The other dangers of wet rainy roads are:
Gravel washed across the roadway – often in mountainous country, a good ‘gully-washer’ will flood the side of the road and wash sand and gravel up onto the pavement. Bad news to find this the hard way, when leaned over in a turn…
Puddles – water will slow you down, as well as splash everywhere and possibly obscure your vision. So try to avoid, or ride through smoothly and slowly.
Painted road stripes – a lot of these are plastic and VERY slick when wet. Watch where you put your feet as soon you can have a wrong footing if you step on these road strips.
Fog / cooler temperatures / condensation–When you ride through a cold front, in rather humid conditions, where the temperature drop can cause your entire helmet to fog up completely.
Torrential downpours will obscure your vision to what’s ahead. Slow down, or find a place to wait out the storm if you can’t see.
Lightning– if the rainstorm is a thunderstorm, it’s a REALLY bad idea to ride in it, because unlike cars, a motorcyle rider is completely exposed, with wet gear and his head is the highest point of the ensemble.
Wind/crosswinds – similarly to lightning, if the storm is severe or ‘sudden’, it is usually accompanied by a ‘gust front’ that can tear off roofing or pull down a fence. Such a blast of wind can send a bike sideways off the pavement or into oncoming traffic. If you know about it, you can compensate for it (by letting the windward knee ‘flap’ or lean the bike over) but it’s still a scary experience.
Other traffic! If you think drivers are careless/crazy in dry weather, they get downright nuts in the rain.
Once a tremendous motorcyclists said ‘Race the rain, ride the wind and chase the sunset’ and we know no matter what the weather conditions are, we won’t sit back and relax because we know
life is not about waiting for the storms to pass, its about learning to ride in the rain.