Quite possibly Nick. The tyre shortage was accute for some while following D Day. These old warriors all look like they are awaiting repair, so no doubt wheels were liberated for further service.
Some information gleaned from 'The Road To Victory' by David P. Colley -
1) An interesting statistic on tyres - in early October 1944 the US in Europe were short of 180,236 tyres, yet less than 50,000 were immediately available in the UK and the continent.
2) By November 1944 more than 15,000 broken down trucks in ETO were awaiting repairs. By January 1945 some 33,000 trucks (mainly jimmies no doubt) were out of service, with an estimate that a further 35,000 would be sidelined by March 1945.