The need for higher tyre pressures in low-profile tyres is primarily related to sidewall rigidity and the load-bearing capacity of the tyre.
1. Sidewall Rigidity and Stiffness
One of the defining characteristics of low-profile tyres is their shorter sidewalls, which are inherently stiffer than the taller sidewalls of standard tyres. This reduced flexibility of the sidewall means the tyre has a smaller volume of air within it, resulting in higher internal pressure being needed to achieve the same level of load-bearing capacity.
When a tyre is inflated, the air pressure inside pushes against the rubber, which is supported by the tyre’s sidewalls. For a low-profile tyre to support the weight of the vehicle, it needs to be filled with more air pressure to compensate for its lack of flex. If the air pressure is too low, the tyre may deform more than it should, especially when cornering or carrying heavy loads. This could lead to excessive heat buildup, reduced handling performance, and even blowouts.
2. Increased Load Capacity
Low profile tyres are generally fitted to larger wheels (18 inches or more), which means they have a larger footprint. However, the sidewalls of low-profile tyres are much shorter, meaning they don’t flex as much when the vehicle exerts force during braking, acceleration, or cornering. To ensure the tyre can carry the load effectively and distribute it evenly across the tyre’s contact patch, higher air pressure is required.
With higher air pressure, the tyre becomes more rigid, and as a result, the weight is distributed evenly across the surface of the tyre. This makes the tyre more stable under load, improving performance in high-speed situations or aggressive driving. Conversely, if the tyre pressure is too low, the sidewall will flex too much, leading to excessive heat buildup, which can decrease performance and lead to tyre failure.
3. Reduced Air Volume in the Tyre
As mentioned earlier, low-profile tyres typically have a smaller air volume compared to standard tyres. Because the tyre is designed with less air inside it, the internal pressure must be higher to compensate for the smaller air chamber and still provide adequate load-bearing capacity.
Think of it like filling a small balloon with air versus a large balloon. The small balloon needs a higher air pressure to inflate to the same size as the larger balloon, simply because it has less room to expand. The same principle applies to low-profile tyres. To keep the tyre inflated properly and to support the vehicle, more air pressure is needed to ensure the tyre performs as designed.
4. Increased Performance and Handling Requirements
Low profile tyres are often used on performance-oriented vehicles, where handling and cornering abilities are paramount. Higher tyre pressure increases the contact patch of the tyre (the area of the tyre that makes contact with the road). This results in better cornering stability, steering response, and overall vehicle performance, especially at high speeds.
A higher tyre pressure means that the tyre is more responsive to steering inputs, and the vehicle handles more sharply and predictably. However, this comes at a cost: ride comfort. A higher air pressure in the tyre reduces the ability of the tyre to absorb bumps and vibrations from the road, leading to a firmer ride. This is why cars with low-profile tyres often have a harsher ride compared to those fitted with standard tyres, which have more air volume and offer better shock absorption.
Pros and Cons of Higher Tyre Pressure in Low Profile Tyres
Pros:
- Improved Handling: Higher tyre pressure increases the responsiveness of low-profile tyres, improving handling and cornering performance. This is particularly important for performance and sports cars where precision driving is critical.
- Better Stability at High Speeds: Higher tyre pressure helps maintain stability, especially when driving at high speeds. The reduced sidewall flex ensures the tyre maintains its shape and keeps the car stable during acceleration and braking.
- Improved Load-Bearing Capacity: Higher air pressure allows the tyre to better support the weight of the vehicle, improving overall load-bearing capacity.
- Better Tyre Longevity: Properly inflated low-profile tyres reduce the risk of damage due to excessive heat buildup. Higher pressure can also help prevent sidewall bulging or other issues associated with underinflated tyres.
Cons:
- Reduced Comfort: Higher tyre pressure makes the ride firmer and less comfortable. While this is a trade-off for better performance, it’s something that drivers of low-profile tyres often notice on rough or uneven roads.
- Increased Risk of Damage from Road Hazards: With less air volume and a stiffer sidewall, low-profile tyres are more vulnerable to damage from road debris, potholes, or curbs. The high tyre pressure makes it less likely that the tyre will absorb a sharp impact, increasing the risk of tyre damage or blowouts.
- Potential for Overinflation: If tyre pressure is too high, it can lead to overinflation, which can result in reduced traction, premature wear in the centre of the tyre, and a rougher ride. It’s crucial to follow manufacturer recommendations for tyre pressure and regularly check tyre inflation.
Conclusion
Low-profile tyres require higher tyre pressures compared to standard tyres due to the reduced flexibility of their shorter sidewalls, the need for better load-bearing capacity, and the performance demands that they are designed to meet. While higher tyre pressure improves handling, cornering, and overall vehicle performance, it also introduces trade-offs in comfort and potential for damage from road hazards.