Tyres & wheels?.

Hello guys, please excuse my ignorance but, I need a little advice. As previously mentioned, I've recently bought a 2005 Range Rover 3.0 td6. I have tyres on the front measuring 275/40/20. On the rear 275/45/20. I've been told that different sizes are bad. To put this right I've ordered 4 new tyres 255/50/20. My question is this, will the new tyres fit onto the wheels?. Many thanks for any help. Cheers, Andy

What tyre size does the manual specify, that should be a good guide as to whether 255's are suitable