Urban dwellers love the look of huge wheels and low-profile tyres, but their country cousins generally hate them. That’s because those some giant wheel and tyre packages make the car ride more harshly and the tyres themselves are more prone to damage because there’s less sidewall to soak up impacts. Switching to an 18-inch wheel and a tyre with more sidewall would definitely make the car ride better, but it’s not always that simple. For a start, you might run into problems in a legal and insurance sense because you’ve suddenly modified the car. To get around that, you should stick to the smallest wheel and tyre package that the manufacturer specified for that vehicle. In the case of a current model BMW X5 that’s a 19-inch wheel and tyre. That’s going to give a better ride than the 20-inch items you currently have, but it won’t be as big an improvement as an 18-inch package. If, however, yours is not the current model X5, then previous models did, in fact, offer an 18-inch package. Either way, check with your insurance company that you’re not transgressing at some pedantic level and check, too, that the smaller wheels won’t drastically alter the overall gearing and suddenly make your speedometer inaccurate. As for handling and braking, the differences between an 18-inch and 20-inch wheel tyre package would only be felt on a race-track and not in everyday driving conditions. But the improvement to ride quality will be felt every time you drive the vehicle.