The trouble with snow on the roads, when all is said and done, is that it melts to leave something much worse behind. Grease. Crap. Sludge. Call it what you will, the foul black stuff left by the retreating snow is the work of the devil. Or it does the devil’s work, besmirching anything it touches and making the road surface almost as grip-free as fresh snow itself.

It is not obvious what the stuff is made of. How can two white substances – snow and salt – combine into one ungodly black compound? Clearly, other stuff is involved: tyre rubber, oil, spilt diesel… but surely not enough to pigment the residue of tons of rock salt.

Perhaps some sort of chemical reaction takes place. Water is presumably involved, with grit, sodium chloride and other rock salts joining in unholy alliance with various low-grade hydrocarbons. But, whatever the production process, the outcome is unlovely.

And a bit of a safety hazard to anyone on two wheels. Motorcycling on it is a matter of creeping around even gentle bends and easing away from the line with a steady throttle hand. Cycling is not so bad, the bicycle’s lack of weight and power making for less worrisome progress even around greasy roundabouts. On steel manhole covers, however, it reduces the coefficient of friction to about that of black ice and they are even more dangerous than when wet.

To make the most of what grip there is, I’m riding Vittoria Open Pave rubber until either there’s more snow – forecast for tomorrow in London – or enough rain to wash the stuff away. These tyres have black sidewalls and don’t show the dirt; double bubble!