[Graham]

Graham, Do I read that as:

Class A constructed cars - any chassis on Resin moulded bodies fitted with Class A motors
Class B constructed cars - any chassis on Resin moulded bodies fitted with Class B motors
Class C constructed cars - any chassis on Plastic moulded bodies


It may be a good idea to ditch the U/O sub-classes as there's six different classes in Event 1 and six different classes in Event 2

No, the only thing that’s changed is
Resin body cars with plastic or metal chassis are allowed in class A as long as they use Class A motors
Resin body cars with plastic or metal chassis are allowed in Class B as long as they use Class B motors
Plastic moulded bodies with metal chassis are not allowed in class A or B, they must be in Class C

There dimensional variations in Events1 & 2 are there to enable entrants to make models with the correct to scale wheels fitted. Therefore small cars like Minis or Imps can be entered with smaller wheels and lower track tolerance ( which goes with it). As of course you cannot fit the larger diameter wheels under these Mini cars.

But if you are entering above 2 litre cars you have to comply with the higher diameter wheels (ie you cannot fit tiny wheels on Saloon cars above 2litres) 
Which perhaps entrants would not be doing anyway………or would they, probably yes based on experience