Tires
Pressure, Stopping Distance and Causality - Part II
By: Patrick Sundby, Accident Investigator
Specializing in Low Speed and Catastrophic Crashes
Mark Studin DC, FASBE(C), DAAPM, DAAMLP
In the previous writing we created the foundation of the importance of tire pressures. Specifically, we demonstrated a third of the vehicles on the road have an underinflated tire and further only a third of those vehicles have a warning light.
We also know a 20% reduction in pressure results in substandard performance, these are the factors we are going to explore.
Underinflated tires have a different profile and contact patch with the road surface.
Where the tire meets the roadway is referred to as the contact patch. Maximizing the contact patch affords the driver the most performance, specifically steering and braking. What happens when we reduce the contact patch? Under inflation does just that.
The contact patch is what connects the vehicle to road, when a tire is properly inflated (all other factors being ignored), the tire can give 100% of the contact patch (and the friction between the tire and the roadway) to steering, braking or a combination of both. If the pressure drops the contact patch is reduced and thus performance is also reduced - but by how much? There are varying schools of thought on this and a ton of research, for our discussion we will say underinflated tires will have a reduction in performance by 15% across all categories.