Although I do need to in my case.
I assume you use one of the insurers I mentioned, then?
The insurers like to know because they can flag you as pedantic and raise the premium because you are more likely to make a claim for trivial damage.
I put Vredstein Sessantas on my 335d. Great tyres, cheaper than Goodyear etc... Great in Wet and Dry, nice looking tread pattern, and lasted ages (after 16k on them I still had 5.5mm on the front and 5mm on the rears). Would highly recommend them.
For standard 18's they will likely be 225/40/18 on the front and 255/35/18 on the back. My 3SDM's were wider (8.5 fronts and 9.5 rears) and had the same tyre sizes as standard and they were perfect, even with a touch of stretch.
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