Inflating Bicycle Tires: Which Pressure Is Right?

Regardless of whether you are cycling on mountain trails, flat roads, or dirt roads with a gravel bike, it's likely that you've made the most common mistake among cyclists at least once: not inflating your tires correctly. Sometimes, we tend to overinflate them, thinking that higher tire pressure will increase speed, or there is a common misconception that tires are airtight and only lose air due to a puncture. But this is not true.

Having tires as hard as marble does not necessarily mean achieving higher speeds. For safety reasons, it is always important to check that the tires are inflated to the correct pressure, considering the rider's weight, tire width, and other factors. But I don't want to spoil too many topics, so let's start from the basics.

To determine the tire pressure, you will need a pump equipped with a pressure gauge, whether digital or analog. It is even better to use a separate pressure gauge, as many built-in gauges on pumps read the pressure inside the pump itself rather than that of the inner tube.

The two most common units of measurement for tire pressure are PSI and bar. In the past, the atmosphere was often used as a unit of measurement in Italy, but it is now out of use. In this article, we will use PSI but will also provide a table of conversions to facilitate the conversion to bars:

Using this information, you will be able to easily find the equivalent value in bars from PSI.

All tires, as well as many rims, have a recommended pressure range or a maximum value indicated by the manufacturer, which is marked on the sidewall of the tire and/or on the rim profile. This value is expressed in PSI or bar. For safety reasons, these values are often conservative, but it is still advisable to follow them carefully to avoid unpleasant issues.

In the absence of specific information regarding the tire and rim, the recommended pressure levels for a cyclist weighing 70 kg are provided below:

Several factors influence the optimal pressure for bicycle tires, but let's look at the six main ones:

1. Tire Width: If the tire is wider, a lower pressure will be required. This is because pressure is the measure of the force exerted by a weight on a surface. Therefore, with a greater surface area (as in the case of a wider tire), a lower pressure is necessary for the tire to fit correctly into the rim.

2. Tire Carcass: The structure inside the tire, known as the carcass, affects its resistance and deformability. A stiffer carcass will require slightly higher pressure than a more flexible carcass.

3. Tubeless System: In the case of a tubeless system, where the tire adapts to the rim without the use of an inner tube, the optimal pressure may be slightly lower than that of a tube system. However, it is important to follow the manufacturer's guidelines for the best results.

4. Rider Weight and Equipment/Load Distribution: The weight of the cyclist and the load being carried affects tire pressure. A heavier rider may require slightly higher pressure to avoid pinch flats or excessive deformation. Additionally, how the weight is distributed between the front and rear of the bicycle can impact the ideal tire pressure.

5. Terrain: The type of terrain you ride on has an impact on tire pressure. On technical or rough terrain, it may be necessary to reduce the pressure slightly to increase grip and control.

6. Weather Conditions and Temperature: Weather conditions, such as temperature, can affect tire pressure. The air inside your tires tends to expand with heat, so you may need to adjust the pressure based on climatic conditions.

Please remember that these are only general guidelines and that special care may be necessary to experiment with tire pressure to find the one best suited to your personal needs and specific riding conditions. Always follow the manufacturer's instructions for the tire and rim for the best results.

TIRE CASING

Tires are available with different casings, such as cotton or those with a high thread count per inch (TPI). Clinchers with a lightweight carcass and high TPI are more flexible and faster. On the other hand, clinchers with a lower TPI are heavier, stiffer, and more durable, offering greater resistance to punctures. It is logical to think that a clincher with a high TPI has superior performance and greater resistance to punctures when inflated to a higher pressure. Conversely, a lower TPI allows you to reduce pressure to improve grip and vibration absorption without increasing the risk of punctures.

TUBELESS SYSTEM

With tubeless clinchers, it is possible to reduce air pressure to obtain greater grip and comfort without worrying about pinch flats. Furthermore, friction between the inner tube and the tire is avoided, which means that tubeless tires can achieve greater speed than those with an inner tube at the same pressure.

CYCLIST WEIGHT + EQUIPMENT/LOAD AND ITS DISTRIBUTION

The weight of the cyclist and the load carried on the bike are important factors in determining the optimal tire performance. The heavier the cyclist, the greater the necessary pressure. You can consider adding or subtracting approximately 2 PSI for every 5 kg increase or decrease in weight for road bikes, and 1 PSI for MTBs, hybrid bikes, and gravel bikes. Always remember to remain within the maximum and minimum range recommended by the manufacturer.

The position of the cyclist on the bike typically involves a weight distribution of approximately 60-70% on the rear wheel. Therefore, it is advisable to reduce the pressure of the front tire slightly compared to the rear tire. In general, the difference in pressures should be around 2-3 PSI, but this value may vary depending on your location, the cycling discipline, and your pedaling style.

TERRAIN

On smooth and paved roads, it is possible to reach the recommended maximum pressure indicated on the tire (compatible with weight). However, it is rare to find perfectly smooth and uniform roads. To avoid feeling every hole and to improve efficiency and comfort, it is advisable to opt for a pressure between 90 and 100 PSI. In this way, the tire will be faster and offer superior comfort, able to better absorb roughness and vibrations from the ground while providing greater grip when cornering.

For MTBs and gravel bikes, the situation becomes more complicated as the terrain can vary greatly. In this case, it is advisable to conduct some testing. It's best to start with a higher pressure and reduce it later, paying attention to the sensations while riding to find the suitable pressure for different types of terrain. The key is to find a balance between puncture resistance, grip, and comfort without compromising speed.

WEATHER AND TEMPERATURE

It is known that in case of rain, it is advisable to slightly reduce the pressure of the tires, but without exaggerating. Reducing pressure by 2-3 PSI is sufficient for your tires, weight, and the terrain you are tackling. Excessive reduction in tire pressure can compromise stability and reduce grip instead of improving it. Furthermore, it increases the risk of punctures, especially for clinchers with inner tubes.

When dealing with mud, a tread pattern with tall, wide, and well-spaced tread blocks is as important as the tire pressure.

Temperature also plays an important role, especially when there is a significant difference between indoor and outdoor temperatures. The hotter it is, the more the pressure increases, and vice versa. For every variation of 5 °C, the pressure gains or loses 1 PSI. For example, if you inflate your tires at home to 21.1 °C and then are in an environment with an outside temperature of 0 °C, your tires will lose approximately 4 PSI.

Five of these six factors can be considered using SRAM's online calculator to find the optimal tire pressure for performance.

HOW TIRE PRESSURE AFFECTS PERFORMANCE

Incorrect tire pressure, whether too high or too low, can compromise performance in terms of grip, comfort, rolling resistance, and susceptibility to punctures. Since the tires are the only point of contact with the ground, their performance directly affects the bike and the rider.

We have already discussed this throughout the article, but to summarize, here are the advantages and disadvantages of using low or high pressure:

Low Pressure
Advantages:

• Better traction
• Greater adhesion
• Greater comfort
• Less rolling resistance on uneven terrain

Disadvantages:

• Greater probability of pinch punctures with tires and inner tubes
• Increased wear
• Greater rolling resistance on asphalt and smooth terrain

High Pressure
Advantages:

• Less chance of punctures
• Less wear
• Less rolling resistance on asphalt or smooth terrain

Disadvantages:

• Less grip and traction
• Less comfort
• Energy loss on uneven terrain

Every cyclist must find the optimal pressure and try to balance grip, comfort, rolling resistance, and susceptibility to punctures. If you prioritize one aspect, you may lose out on another. Even though tires, rims, and cycling equipment in general are continually evolving, offering performances that were unthinkable just a few years ago, tire pressure remains an important element. Each of us can and should experiment with different pressures in varying circumstances. You learn by trying because air is free.