Been offered a set of hankook 275/45/20 109v tyres, are these ok to fit to my my2010 ? Lower speed rating than the y but better load rating ? Or am I just looking for something that I don’t need to ? As new set for £160 for all four 👍🏻

The hankook's are good tyres, bargain at £160 a set. Don't worry about the Y rating. The only way a 3.0 diesel is ever going to get near that speed, is off a cliff. The hankook's are usually rated within the speed of the diesel RRS MY12 RRS HSE
Gone 4.2 supercharged RRS
Gone 90
Gone s2000

But don't forget you will need to inform your insurance company as you are changing from the original spec.

Might be worth asking them first! 2016 RRS SVR Estoril Blue
2005 4.2L Supercharged Java Black - gone but was my first love.
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If we all point our RR's in the same direction and accelerate at the same time can we turn back time?