Wet Traction
Wet traction refers to traction on a wet road surface, such as asphalt or concrete.
Wet traction performance can vary significantly based on a variety of variables, such as the depth of the water on the road surface, the vehicle speed, and more.
When maximising wet traction performance, the goal is to evacuate water from the footprint area as quickly as possible to enable the tread surface to contact the road surface.
This is achieved by increasing the size and frequency of grooves and void areas in the tread.
An extreme example of loss of wet traction is aquaplaning (or hydroplaning), a phenomenon in which a tyre completely loses friction and contact with the road surface.
Once a vehicle begins to aquaplane, its travel path is subject to forces and moments that it had when it lost complete traction.
The depth of the water on the road surface and the speed of vehicle travel play a significant role in the likelihood of aquaplaning.
Testing for Wet Traction
Accurate wet traction testing data requires a defined and maintained testing surface and water depth.
Wet traction testing is often conducted with an instrumented vehicle with tyres in all four positions that can measure stopping distance and deceleration.
This testing can also utilise an instrumented traction trailer, which measures braking force and slip and peak and slide traction.
There are standard protocols for wet traction testing, as well as custom protocols specific to individual tyre or automotive OEMs.
Tread Attributes Benefiting Wet Traction
A tyre engineer seeking to optimise wet traction performance in a tyre may;
- Increase tread depth overall
- Maximise the size and quantity of void areas. Circumferential grooves are made larger, as are lateral grooves in the shoulder and intermediate ribs. All ribs have more, larger sipes.
- Minimise tie bars so as not to constrain the slots and shoulder grooves in a way that might hold up water evacuation.
This information has been reproduced with the kind permission of Smithers
Smithers is an independent, third-party testing and consulting company with a history in the tyre industry starting back in 1925. Their team has many years of experience in the tyre and rubber industries and have created this information as an educational resource on the general science behind tread development.
As an organisation, Smithers do not actively develop tyre treads for commercial use in the market.
Tread design is a complex, highly specialised activity that must take into account each manufacturer’s design and development goals.
© SMITHERS, 2021