On my IS I got the Pirelli Scorpion Snow and Ice on my factory 20" rims. They are 275 40 20 on all four, they actually will fit both width rims. They have worked very well this winter through over a foot of snow. Rarely lose traction.

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Redpoint

2016 xDrive50i

2006 Sapphire Black X5 4.8is
Body color matched Kidneys and hood vents

2005 Alpine White 330cic
Performance Package
Premium Package
Cold Weather Package
Foose 19" Rims

1987 Ducati 750 Paso