Sweating hoses

Tire compounds are made with a waxy substance in the mix that comes to the surface as the tire heats up in use. This is intended to prevent UV damage and subsequent deterioration of the rubber material. In RVs and trailers, the tire manufacturers recommend the use of skirts on the tires when not in actual use to avoid the UV deterioration as the waxy substance isn't activated/surfaced enough to fully protect the tires.

I suspect that the rubber hoses have a similar compound for similar reasons.