A PLUGGED IN RIDE tutorial: Understanding why EV-rated tires should be on all EVs.

Tutorial Overview:

Section 1 Not all tires are created equal

Section 2 A selection of EV-rated → Non EV-rated tires

Section 3. How are EV-rated tires different?

Section 4 Key Things to remember

Section 5 Schedule of Interval checks

Section 6 Annual cost comparison EV vs ICE

Learning objectives

Section 1: Not all tires are created equal

Standard passenger tires were designed around internal combustion vehicles. EVs are driven by electric motors, delivering immediate & greater torque than their combustion equivalents. Housing multiple cells, EV batteries are 20-30% heavier than ICE counterparts as well.

Weight: The undeniable factor

The addition of 20–30% more weight and instant torque create higher friction forces during acceleration. What’s more, regenerative braking applies continuous resistance which generates more heat which affects thermal cycling(getting the tires to operating temp and cooling them after) in the actual tire compounds . These factors put greater stresses on EV tires and when all you’ve got are four small contact patches connecting you to the road, you depend on your tires to optimize handling, ride, noise reduction, traction and braking.

Audible improvement: The benefit of foam

Studies of cabin noise, measured at highway speeds (~110 km/h) show conventional, non-EV tires producing 68 dB of interior noise. EVs have numerous benefit from their electric powerplants, one of which being low-to-no engine noise. Manufacturers have answered consumer requests for relative silent driving with the advent of foam-lined EV tires (Bridgestone Turanza EV, Pirelli P Zero Elect (see below), Continental EcoContact 6 Q,…). This tech has reduced cabin noise to 59–61 dB which is noticeable, especially at distance. The increased weight this tech yields is negligible at 0.15–0.2 kg per tire.

Load Rating

Conventional non-EV passenger car tires carry a lower load rating compared to EV-rated tires. This allows the latter to better manage the extra 20-30% weight EVs carry. It’s also important to consider that with weight transfer, especially in aggressive manoeuvres, hard braking and acceleration, EVs, especially heavy ones, can exceed conventional non-EV tire ratings. EV-specific tires sporting higher load ratings demonstrate an increased structural capacity which can prevent sidewall buckling under sustained high loads. The following chart compares the two:

Chart: Load comparing EV-rated and non-EV rated tires

Rolling resistance

EVs are, for the most part, focussed on efficiency and tires are a contributing factor. Rolling resistance, the force which opposes a rolling tire’s motion, is caused by the tire’s deformation and rebounding while in rotation; this generates heat and represents wasted energy as it doesn’t move the car. Manufacturers lower rolling resistance in tires which positively impacts EV range. They employ high-silica formulations, compounds using silica particles in the rubber matrix which slide past each other more easily than traditional carbon black particles. Depending on the EV, this could add an extra 4% of range.

 What about new tech?

With the advent of air-less (puncture resistant) as well as self-healing tires, we still don’t know how these will affect the EV world. It is important to note that regular patching doesn’t seem doable with the latter as the sealant contaminates the puncture area which blocks patch adhesion. It should also be noted that in self-healing tires, the sealant capsules are only in the tread, so sidewall punctures cannot be addressed. Until a manufacturer fits these to their cars or more publically-accessible studies are performed, we remain hopeful. Stay tuned!

We’ve detailed why EVs need proprietary tires, summarized below. The following sections will show you how.

1. Instant high torque
2. Resistance from regenerative braking generates heat
3. Greater thermal cycling
4. Significantly heavier curb weight
5. Unique audible characteristics

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