Dyfi is set under a darkened sky with the road covered in freshly fallen snow. In fact with the snow still falling, the wise driver will exchange their tyres at the service station for snow tyres. You probably won't have time for any more major car modifications as your mechanics will undoubtedly have to spend the rest of the service time gluing the bumpers back onto your wreck.
Dyfi itself doesn't really throw up any particularly nasty surprises, the worst being the long snow covered sweeping bends that occasionally send the car sliding into the snowdrifts on the road side.