The law in Queensland suggests (because it’s not totally clear from the website) that you can fit larger wheels, although I couldn’t find a definitive limit to how much bigger you could go. But, the rules also state that the overall diameter of a replacement tyre on a car like the GLC 220d can be no more than 15mm more than the tyres fitted as standard to that car. So, while that suggest you could go up to 22-inch wheels (from the standard 20-inch wheels) the tyres fitted to them would have to be a much lower profile to keep within that 15mm diameter increase requirement.This would have a fairly big impact on the cost of the tyres when you need to replace them, but also on ride quality as you’d be sacrificing a lot of sidewall flex with the lower-profile rubber. And there are other considerations: The replacement tyres can not be more than 1.3 times as wide as the standard tyres, must not protrude from the wheel arch at the straight-ahead and must maintain speedometer accuracy.The best advice is to buy the new wheels and tyres through a proper tyre specialist who will be able to give you the full story on what’s legal, what’s not and what’s advisable. Plenty of car owners have discovered the hard way that the wrong replacement wheels and tyres can ruin the driving experience.