"My BMW is equipped from the factory with wider rear tires. Should I stick with this staggered set-up or switch to a square set-up and use the same size on all four wheel positions?"
A staggered set-up simply means that your rear tires are larger than your front tires. A square set-up simply means a vehicle has the same tire size on all four wheels.
Advantages to a square set-up:
- Better winter traction from a narrower rear tire
- Ability to rotate the tires for longer wear
- Simplicity of installation with all four tires being the same
- Generally a lower price in a more common front tire size
Advantages to a staggered set-up:
- Better straight-line dry traction from a wider rear tire
- Improved cosmetic appearance
- More protection to the wheel from curb damage
For example, if you drive a 2007-2011 BMW 3 Series with the staggered 18" wheels, you can use 225/40R18 on both the front 8" wheels and rear 8.5" Original Equipment wheels. This is actually very common, especially when installing a set of winter / snow tires. Eliminating the stagger in this way results in better winter traction by changing the rear 255/35R18 to a narrower 225/40R18.
To learn more about the advantages of using winter tires, read "My Story on Winter Tires."