Lasting performance: What worn tire tests tell us
Today, tests to check standard compliance are carried out on new tires. We decided to demonstrate that it is just as important to compare worn tires by organizing a grand testing day on May 11, 2017 at our Ladoux technology center. This is what we demonstrated.
Tests on used tires: methodology
Our tests focused on four areas of performance: braking on a dry surface, braking on a wet surface, lateral grip on a wet surface and rolling resistance which influences fuel consumption. We compared the results obtained by the same tire at different wear stages.
We also wanted to compare the most important changes in tire performance when it comes to wear. We tested premium tires and budget tires.
Dry braking: a worn tire shortens the distance
On a dry surface, the more the rubber is in contact with the road, the more efficient the braking. A worn tire with a shallower tread will therefore brake better. The question is all about proportions.
The difference in braking distance is therefore 10% shorter for a worn tire over a new tire. Which explains why racing drivers use slick tires whenever weather conditions allow!
Braking on a wet surface: unequal tires when worn
Wet braking tests with 24 different tires confirmed there is a negative change in wet braking performance when the tire is worn, from the 1st mile, and provided two major learning points:
- certain worn premium tires are capable of braking over the same distances as new budget tires.
- tires are very unequal when it comes to wear. A new tire which brakes better than others can have a much longer than average braking distance once worn. This supports the idea that it is essential to carry out tests on worn tires to enlighten customers about the choices they have.
This confirms that the braking distance on a wet surface depends more on the quality of the tire’s design and manufacture than on its wear level.
Wet braking : testing 5 tires
Lateral wet grip: in line with wet braking performances
A tire does not always drive straight. However, lateral wet grip tests are rarely advertised. This is for a simple reason: it is more difficult to quantify lateral grip than braking distance. Nevertheless, all of the tests carried out have enabled us to confirm one fact: there is a direct link between wet braking performance on a wet surface and lateral wet grip.
In simpler terms, the more efficient a tire is braking on a wet surface, the better it will grip the road in the rain.
Roll resistance: the benefits of wear
As it rolls, the tire squashes a little on the road. This deformation engenders heat loss and therefore energy loss. This is what we call rolling resistance. The higher the resistance, the more energy is required to move forward, which means fuel.
Many factors contribute to rolling resistance - the rigidity of the sides, the quality of the rubber, and even the tire pressure. This resistance also reduces with wear: Less material on the tread means less energy is lost and the tire becomes more efficient.
Our tests demonstrate that a tire sees a linear fall in its rolling resistance throughout its lifetime. At its wear limit, resistance is 20% less than that of a new tire. Bearing in mind that one fifth of fuel consumption is linked to tires, this means that with a worn tire, your total consumption will be reduced by 4 to 5%.
- A worn tire brakes better on a dry surface and consumes less fuel than a new tire;
- A worn premium tire can brake better on a wet surface than a new budget tire;
- In terms of safety and saving money, it is preferable to choose a good quality tire and use it until the wear limit than choose a budget tire and replace it early.
- A new tire’s performance doesn’t necessarily tell its performance once worn. That’s why Michelin advocates to test worn tires
Braking on a dry surface