When it comes to winter driving, it's not just the choice of tire you have to worry about. Once you've installed a set of winter tires, you still need to set the correct tire pressure for winter driving, as this video from the Team O'Neil rally school explains.

Instructor Wyatt Knox demonstrates the difference tire pressure can make in winter conditions using a Subaru Impreza and a snow-covered slalom course. He starts with the factory-recommended tire pressure—33 psi in front, 30 psi in back—and then drops the tire pressure in 5 psi increments.

With the factory-recommended pressure, the all-wheel-drive sedan had enough grip to maintain forward momentum, but the back end stepped out quite a bit. That might be fun on a closed course, but it's not ideal for everyday driving.


Team O'Neil tire pressure for winter driving screenshot

Team O'Neil tire pressure for winter driving screenshot

Lowering front and rear tire pressure by 5 psi didn't make a dramatic difference, and neither did lowering pressure by an additional 5 psi—for 10 psi total. The car was still fairly tail happy, although the lower pressures also allowed the tires to deform more, increasing the size of the contact patch. That's what you want for winter driving, Knox said.

In attempt to lessen oversteer, Knox lowered the rear tire pressure by an additional 5 psi, while leaving the front tires alone. That left pressures at 23 psi in front, and 16 psi in the rear. That seemed to do the trick, making the car more neutral, and also improving straight-line braking feel.

While there are many variables—including weight, tire compound, and whether the vehicles has all-wheel drive—tire pressures can make a big difference in winter drivability, Knox said. He also added that these are not street pressures. Lowering pressure can increase grip on snow, but driving on pavement at higher speeds can cause the tire to overheat. As always, it's also important to set pressures outside, at an ambient temperature close to what you'll be driving in.