winter tyres have a differant compound, below 5c summer tyres harden and as a result become less grippy - its that simple
Winter tyres work best at temperatures below 7 deg C. Indeed, they outperform conventional ‘summer’ tyres for traction, cornering grip and braking in such conditions – regardless of whether there is snow or ice.
Temperature/condition Summer tyres Winter tyres
20 degrees C 65.3m 67m
5 degrees C 70.5m 65.7m
On snow, the gap widens considerably, as the sipes on winter tyres offer grip even when the tread is packed with soft snow. In such conditions, a two-wheel-drive car with winter tyres is invariably safer than 4x4 on summer tyres.
copied off the rac website