The practice of siping, or cutting extra slits into tire treads, is supposed to improve a tire's snow and ice-biting ability. Tire dealerships typically charge around $15 or more to sipe tires.
To see whether siping makes any difference, we tested two performance all-season models, an H-rated Michelin Energy MXV4 Plus and a V-rated Michelin Pilot Exalto A/S, with and without siping.
The siped version of both models showed modest but measurable improvements in snow-traction and ice-braking performance. But braking distances on wet and dry pavement were a few feet longer. Besides costing $60 or so for a set of four, having your tires siped potentially voids any tread-wear warranty. We don't think the modest gains are worth the extra costs.