Is it true that eco tires have poorer grip and braking?

Arif · Feb 13, 2021 01:45 PM

Is it true that eco tires have poorer grip and braking? 01

In the quest of reducing fuel consumption, engines have been made to be increasingly efficient, hybrid systems have been introduced, and cars have been designed to be more aerodynamic. Another part that plays a big role is tires. And for that we have low-rolling-resistance, or eco tires.

What are eco tires (low rolling resistance tires)? 

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Low-rolling-resistance/eco tires are tires that need less energy to be turned. As the name implies, there is less of a resisting force when you turn the wheel. Thus it helps you reduce fuel consumption.

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When purchasing tires, you often have the option for eco tires. Some to name are the Continental Eco Contact 6 or the Bridgestone Ecopia. 

The performance (grip and braking) trade-off

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The main concern on eco tires is the performance trade-off.

How good is the grip and how good is the braking? Are they less safe than conventional tires? 
  
Let’s address these concerns

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Continetal Eco Contact 6 and Premium Contact 6

If you look at the design of eco tires, you will see that they have less rubber in contact with the ground.

This is usually achieved by having more negative spaces in the tread pattern and a higher inflation pressure. Another way to reduce rolling resistance is to reduce tread depth.

So, if we take two tires of the same material compound and size, the eco tire will have less contact with the ground, and subsequently less grip and less braking ability. 

However, depending on the situation, eco tires can actually outperform conventional tires. In a video by Bridgestone promoting the Bridgestone Ecopia, it is shown that the fuel-saving tire brakes better in the wet.

A smaller contact area with the ground reduces chances of aquaplaning so eco tires have the upper hand here.

The dry braking performance is not shown in the video, but we’d really like to see that. The truth is, there is a compromise in grip compared to the conventional tire, albeit a small one.

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Perhaps we will have to do our very own WapCar experiment with eco tires to see the dry braking results for ourselves and share it with you.

Can we combine fuel-saving and performance (grip and braking)?

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Eco tires often have stiff belts and streamlined ribs

There is only so much resistance you can reduce with tread design without compromising usability. The ultimate low-rolling-resistance wheels are the steel wheels on steel tracks that you see on trains.

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Low rolling resistance. Photo

To further improve fuel savings from tires, another area that is developed is the material of the tire itself. The main concern is tire hysteresis, which is the energy lost through deformation of the tire (tire gets squished under load).

Tire deformation is not bad and is basically how the tire gains grip in the first place. (basically sidewall flex)

To put it simply,

low hysteresis = small sidewall flex = small energy loss = low grip = low rolling resistance

high hysteresis = big side wall flex = big energy loss = high grip = high rolling resistance

Hysteresis is also a factor that affects ride comfort and there is a slight compromise with eco tires.

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The low frequency deformation caused by rotation of the tire. Here, we want a low hysteresis behaviour for low rolling resistance

Typically, tires are either low hysteresis and low grip at all frequencies (Refer green line graph) or high hysteresis and high grip at all frequencies (refer bright-red line in graph).

What is being used in low resistance tires is a non-Newtonian compound that is low hysteresis at low frequency, but high hysteresis at high frequency (refer maroon line in graph).

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As explained by Engineering Explained

Low frequency does not mean slow driving speeds, but refers to the periodical contact of the tire surface with the ground.

High frequency does not mean high-speed driving, but refers to the high frequency changes in road surface. 

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The high frequency deformation due to changes in road surface. Here, we want a high hysteresis behaviour for high grip. Photo

Thanks to the non-Newtonian compound, you can combine low-rolling-resistance and high grip (and better braking) in one tire.

Although impressive, take not that eco tires are of various makes and models, and hence have differing performances.

Conclusion

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If it is a general answer you’re looking for, yes, eco tires have less grip and poorer braking, but only in the dry.

Besides performance, there is also a small compromise in terms of ride comfort.

In the wet, eco tires tend to have a natural advantage of the smaller contact area (less chance of aquaplanning).

Whether to go with conventional or eco tires depends on your wants and needs. Each tire type offers its own sets of pros and cons.

 

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Arif

Writer

Previously an engineer in an automotive manufacturing company and a highway concessionaire. A part-time research student on biofuels and diesel engines. Obsessed with vehicle electrification and the future of transportation.

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