Wider tires automatically mean more grip, correct? After all a larger the patch, which should translate to more traction, right? In many situations, yes, but could probably guess by my use of rhetorical questions that things aren't quite so simple. In this scientific test video, UK publication Tyre Review .
A BMW 320d is used for this test and fitted with various combinations of Goodyear Eagle F1 Asymmetric tires sized 225/40/R19, 255/35/R19, and 285/30/R19. Tyre Review's Jonathan Benson tests handling and braking in dry and wet conditions, and aquaplaning resistance. The BMW was fit from the factory with staggered tires—225 fronts and 255 rears—so Benson experiments with different staggers, and with 225s and 255s all around.
The results are varied. A combination of 255 fronts and 285 rears performed best on the dry handling circuit and in both dry and wet braking tests, but they gave up a bit elsewhere. In a wet handling lap, this setup was nearly 2.0 seconds slower than 255s at all four corners, and fell short of the OEM 225/255 combination too. And in aquaplaning resistance, the 255 also gives up a bit to the 225.
In the wet, a narrower tire cuts through standing water more easily, giving it the edge over something wider. That's why a lot of people use extra-narrow tires in the winter—the same basic theory applies on snow and ice.
But those are just subjective numbers—all these setups feel subtly different, according to Benson. The OEM fitment produces a bit of understeer, which is ideal for a mass-market car like a 3-Series, while 255s at all four corners provide more oversteer, which is fun. Turn-in was sharpest with stock tire sizes too, but Benson notes that mid-corner balance was best with the 255/285 stagger.
Picking tire sizes—like tires themselves—is all about compromise. Dry performance generally comes at the expense of wet performance, so you need to pick which you want more of. And while wider tires generally provide more grip in the dry on track, their road manners might leave a bit to be desired—fitting ultra-wide tires means a car will follow the camber of the road more easily, which isn't always pleseant.
And, you have to take tire types into consideration as well. A wide all-season might not give you as much grip as a narrower summer tire, with a performance-focused tread design and compound.
With tires, there's a lot to know, which is why videos like this are so helpful. Even if you know a lot, you'll at least be impressed by the rigorous methodology here/