Sorry Carnut, my mistake. Genrally I ask for manufactorer and type (Henschel II-6500), but in this case, I forgot it. So, your answer is complete and you have earned the point.
For double tyres: there are two explanations for this.
First: For trolleybusses type II (two axles, up to 90 passengers), tyres in the dimension 12.00-20 where needed, but because of the war preparations not available in sufficient quantity. So, double tyres 9.00-20 were used by Henschel as a substitute. This is a trademark for first generation Henschel-trolleybuses
Second: Through the smaller tyres the entrance height could be lowered, an advantage for the fast flow of passengers.