The test for ‘pneumatic’ is: can the tyre be inflated or deflated so that the tyre wall collapses. Can you see a problem here with some top-selling 50/50 tyres? I can.
I have had a puncture on a Michelin Anakee Wild and ridden my bike home for 15 miles and the tyre certainly did not have a side wall collapse but the tyre is E-marked, and therefore legal and most definitely has a pneumatic chamber. In this case, a punctured one.
Had a police officer pulled me over, as I was riding home at less than 40mph with very gentle braking, he would have had a panoply of powers at his disposal to make my life hard. One of the advantages of the uber tough 50/50 tyres is they can be ridden, cautiously, on sidewall strength alone so long as you modify your riding, but you would be running the risk of a run in with the police.
I run mousses and am prepared to take the chance that Britain’s most officious copper will not only have to stop me, for some suspected road traffic offence (not difficult with a trail bike – flexi plate, number plate or lights or reflectors covered in mud, reports of tosser-on-crossers ragging around on footpaths) but he also has the power to have my tyre pressures checked. If your tyre reads one atmosphere, then it isn’t pneumatic and you have committed a non-endorseable offence.
So, use a bit of common sense. If you are riding in an area where there is a crack-down on illegal riders (or for that matter legal riders) then be super-squeaky clean. If the police want to seize your bike for being dangerously unroadworthy on the basis of a zero tyre pressure, then they can impound the bike or force you to get the machine taken away in a van or on a trailer with a rectification notice. If you are in a crack-down area the police can give your bike a virtual roadside MoT in coordination with VOSA and tyre pressure would be an obvious check to carry out.
I am growing away from mousses as I get better at changing tyres and once my current mousses wear out and disintegrate I will be running super thick innertubes and green slime on my dirt bikes but it is a fairly finely balanced point.
The legality or illegality of mousses is not really an Issue for me. I know they are a C and U breach and I was prepared to take that risk to avoid carting around tyre irons, an innertube and a pump but as I now have short, strong Motion Pro levers, a reliable little battery pump and I have got handier at popping enduro tyres on and off with levers, I choose to have innertubes and slime but I well understand the attraction of mousses.
Your insurer might try to wriggle out of a theft claim on the basis of mousses but, sadly, many will try to wriggle on any basis, real or imagined.
Trail – The members magazine of the Trail Riders Fellowship – Winter 2021