all widths will be in the tractor specifications..... most tractors under 100hp are set at 2.45m wide, and less.
(to be honest no-one cares particully, obviously I'm not saying break the law, I'm just saying that if one was to accidently drive a tractor slightly wider than 2.45, its hard to measure the exact width, and never ever heard of such a thing being a problem)
for example for your widths.... massey 4235 (70 odd hp)- 2.45m, 5435 (80 odd hp)- 2.45m... i think the 5445 and 5455 are also the same tracking, so that takes you up to 100hp on the masseys; thus your alright with anything less than 100 horses.