There are a few things to mention here. Firstly, while bigger wheels with low profile tyres generally make for a more uncomfortable ride, there's no hard and fast rule that can be applied across the board because no two makes of tyres are the same. The wheel-tyre combo on your XF Sportbrake will also have been designed with the car and its suspension in mind. Finally, fitting smaller wheels may also affect the resale value as some buyers prefer the look of larger alloys with low profile tyres. However, with that said, low profile tyres are more likely to be damaged by potholes and rough road surfaces, as well as proving fairly uncomfortable (especially with a firm suspension setup).

What you could do is look at the manufacturer's recommended wheel sizes (or speak to your local Jaguar dealer) about potentially dropping down to 19 or 18-inch alloys. What you might want to try first, though, is putting the current tyre size into Kwik Fit or Black Circles and seeing what tyre options come back. Black Circles website will show you options that are the same size - along with customer reviews of the tyres, noise, wet grip and fuel economy ratings. Rather than dropping down a wheel size or two, it may be worth trying more comfortable tyres for your 20-inch wheels first. Obviously, if you do this and it's still uncomfortable then you may then be spending even more money to get new wheels so I'd speak to the dealer or a tyre retailer to see what they advise.

Aside from the suspension, you may need to speak to your insurer if you change the wheel size, too — so keep that in mind.