It can be difficult to ride right after it starts raining because:

Question

Pavement can be particularly slippery after it has just started to rain. Oil from vehicles will have not yet washed away from the surface of the road, forming a slippery mixture with the water.

Accepted Answer

Pavement will be especially slippery.

Answer

Some other drivers may not react quickly enough to the rain.

Answer

Other drivers do not drive fast enough in wet weather.