A lot of people have heard about the contact patch, yet at the same time there are a few other considerations that a driver must keep in mind, both when choosing tires, and when driving on them.
We are sure that you heard many times that the contact patch is the size of a human palm. This is a good comparison to give you a general idea, but it is not entirely accurate because there are such tire sizes out there, whose contact patch no human hand will be able to cover.
At the same time, there are popular sizes, such as 205/55/16, whose contact patch is indeed the size of the human palm. Now imagine your car with all your kids, relatives, and baggage, tearing down the highway at a speed of 120 km/h, and realize that its grip on the road depends on mere four little palms…
Quote:Power is nothing without control. © Pirell
It is also important to remember that the contact patch is also an ever-changing thing. See the visual examples in the figures below.
The biggest misconception that is very widespread both online and in tire dealerships is that people tend to confuse the tire width, indicated on the tire sidewall, with the tread width, the latter being responsible for forming the contact patch. I wrote about this recently in this article (click to read)
Effective water traction
Quote:For effective work of the tire, the contact patch must always be dry. ©Tiresvote
I will allow myself to quote my favorite statements) because this is extremely important. You may have the most efficient tire in the world, but there will still be a puddle, in which it will float.
All of these tread pattern tricks; all these grooves and lamellas are made with one thing in mind — to dispel the water from the contact area as quickly and as efficiently as possible.
A vivid example of how the tread depth and the overall negative tread profile handle the water film only 3 mm deep, can be seen in the figure below.
As the figure shows, at a speed of 125 km/h with a tread depth of 4mm, the contact patch shrinks to 11% of its original size. It’s not an «area» or «patch» anymore — it’s a tiny spot… And if you are driving on minimum legal tread depth, you may just as well say that your car is «flying low».
Therefore, I find extremely useful the recommendations from such manufacturers as Pirelli and Continental, who advise changing tires not when they reach the minimum legal tread depth of 1.6mm, but at 3mm, because this tread depth is the borderline of real safety.
We covered this question about the safe remaining tread depth in more detail in this article (click to read).
Tire pressure, one of the key safety factors
Tire pressure is the cornerstone of handling response. People tend to underestimate this component, while the air under pressure is an indispensable part of the wheel in its entirety.
The tire pressure directly affects the size of the contact patch on any kind of pavement. When driving over water, a tire that is underinflated by only 0.5 bar loses up to 20% of contact with an ideal tread depth. Now add to this an average wear, and you will lose 50%.