Engineering Integrity Society

What really happens when the rubber meets the road/runway?

EIS-2135By David Shaw FIMMM
Chief Executive, Tyre Industry Research

We do not know enough about the tire-road interaction. Grip is associated with a number of factors: 

  • Rubber distorting around and engaging with microscopic asperities in the road surface;
  • Weak chemical interactions between the rubber compound and polished surfaces
  • Lubrication from water or ice
  • Lubrication from microscopic particles of rubber

Existing theoretical model do not provide good predictions on the amount of grip available from a given tire-road interaction.

The tire industry does not have real road surface data to build true predictive models. Discussions between Tyre and Road engineers is required. 

Discussion on the interface.

Here’s a few ‘did you know’ questions for starters: 

  • Did you know that the introduction of super-single tires significantly shortened the life of roads in the UK?
  • Did you know that roads have specifications for grip and noise and that rolling resistance is becoming a big deal for them?
  • Did you know that a full description of the surface geometry of a road does not enable you to predict grip? (The type of rock or aggregate has a big effect)
  • Did you know that the available grip on a road can vary from day to day and even hour to hour?
  • Did you know that road makers are seeking to understand the future requirements of tire makers?

 

Here’s another: did you realise that the bitumen used in the top surface of many roads is a visco-elastic material that distorts as tires roll over it? It compresses in a bulk way due to axle loads, but within the asphalt, each particle of rock or aggregate also moves under the lateral and longitudinal loads imposed by tires. All of these things affect grip and the interaction between tires and roads. The movement of particles within the road bitumen will also have an impact on energy consumption and fuel economy.

An understanding of road engineering

As we get a better understanding of tires and their compounds, we are finding that we need to learn more about the road underneath the tire.

I wanted to work with the road industry for a number of reasons.

Significantly, the tire industry has worked very hard on grip and noise, but in my conversations with tire designers, there is a certain amount of frustration. Tire engineers can deliver good results on a standard ISO surface. If they want to deliver good results in the real world, they need more information about real roads.

The need for dialogue between road and tire engineers

There is precious little dialogue with the road industry among tire engineers.

I don’t know if the wide range of roads currently in use around the world makes developing good road-tire combinations impossible, but it seems to me that without that dialogue, we might be missing something.

Just as the tire industry is seeking to develop international standards, so the road industry has a common set of issues. Standardisation might be a good thing.

I suspect we could save a lot of lives, if the tire people worked with the road people to develop good combinations of tread compound and road surface that can improve braking.

Building real-world computer models

Another reason I wanted to understand roads better is for the computer modelling community. We spend a lot of time and effort modelling tires. Part of that effort is to improve wet- and dry-grip. I’ve seen a lot of models of tires, but in most of them, the interface with the road is a smooth, idealised surface.

The road community has a lot of data on the condition of roads around the world. Might we not get a better result if we can use some of the models developed by the road industry to interface with our tire models?

Smart tires help road makers plan for the future

A third reason to engage with the road industry is to plan for the future.

When we look at smart tires, we are expecting those tires to have sensors on board that measure the available grip between tire and road.

Would it surprise you to know that the people responsible for maintaining road networks would find that data incredibly useful?

When I mentioned to the road industry that the tire and vehicle people are working on grip sensors and that the likely model is that the instantaneous levels of grip would be constantly uploaded to the cloud by millions of trucks and cars, their eyes opened wide.

Currently, they spend millions trying to identify areas where the road surface needs to be improved in order to prevent accidents and save lives. That limited information guides decisions about where to direct billions of Euro of annual road maintenance budgets. Budgets that are under severe pressure.

Imagine if they could have a database that identifies levels of grip across the entire road network, generated by sensors on tires from many different manufacturers and correlating that with the air temperature and even the road temperature.

It would enable road authorities to quickly identify area where the grip changes suddenly by location and also areas where the grip changes sharply according to different weather conditions.

Diminishing returns unless we talk to the road community

One of my mentors in this industry – Roger Williams, previously technical director at Dunlop UK – always talked about roads and tried to convince the tire industry to engage more with the roads community.

I find myself doing the same, but for perhaps different reasons.

It seems to me that tire development is suffering from the laws of diminishing returns. As we work every harder to improve grip and noise, we find that our efforts deliver good results on one road surface, but make the situation worse on another surface. Working with the people who design, specify and buy road surfaces might be a way to direct those efforts more efficiently.

A final thought

Did you know that in pre-history, the wheel was invented many times, but it never really took off as a practical device until the Romans built high quality roads. A wheel is not much use on soft ground or a ploughed field.

The development of wheels and tires is intimately connected with the development of good roads. Neither is much use unless the other is equally well engineered.

If anyone in the tire industry wants to learn more about roads, or if you are a road engineer and want to know more about tires, let me know and we will try to make something happen.

To know more about tyres please visit www.tyreindustryresearch.com

 

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