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"2021 GIANT TCR hookless tubeless tire wheels, what kind of tires can be used?", After the release, judging from the message, many cyclists are not very clear about how much tire pressure they use, and there are not a few who use too high tire pressure. Today I wrote an article to talk about tire pressure. I checked the information and found that the situation is more complicated than we thought. Road tires and wheels are too split. A few years ago, when the mainstream road tires were 21c and 23c, tire pressures exceeding 100 psi was a normal operation, and many people believed that high tire pressures resulted in low rolling resistance and fast cycling. However, it is only on an ideal flat road, the actual road is rugged, and the bouncing caused by high tire pressure will absorb energy, which is equivalent to increasing the rolling resistance. This is why road bike tires are becoming wider and wider. 25c has become the mainstream. As aerodynamic wheels become wider and wider, 28c has a tendency to replace them. At present, the inner width of the rim of road bikes has also developed from 19mm to 21mm. After many 25c tires are installed, the actual expansion width has reached 28mm.

The advantages of wide tires are self-evident, in addition to the use of low tire pressure to improve comfort, the shape of the wide tires and the ground contact is more circular, which considerably reduces the energy loss caused by the deformation of the tires, which is also the rolling resistance of the wide tires. One of the lower reasons. Why can tubeless tires further reduce rolling resistance? That's because there is no energy loss caused by displacement friction between the outer tube and the inner tube. Having said so much, I actually want to show one thing: Too high tire pressure will not become faster. Only proper tire pressure can find a balance between rolling resistance and comfort, and comfort will be faster.

Why is the ideal tire pressure so important? Because it allows the tires to have the correct preload and optimizes road contact. The low tire pressure allows the tire to deform and pass the damaged road more smoothly. In addition to tire pressure, your choice of the tire is also very important. Cotton cords are more easily deformed than nylon cords. At the same time, TPI will also make a difference. A high TPI will make the tire feel smoother and faster. In addition, the puncture-resistant protective layer will increase the rolling resistance, so the fastest tires are often those without puncture protection, and are dedicated to competition. Generally speaking, lower tire pressure provides better control on wet and loose roads, but too low tire pressure will affect the handling, and higher tire pressure provides better puncture protection.

The maximum tire pressure not only depends on the tire markings but also the allowable tire pressure range of the rim. If the tire pressure is close to the maximum value of the rim, the best way is to change to a wider tire. Changing from 23mm to 25mm tires does not seem to have changed much, less than 10%. But considering that the volume is proportional to the square of the radius, the air volume has increased by 18%, which is an obvious change. For example, using 25mm tires requires 90 psi of tire pressure, and changing to 28mm
tires require only 76 psi. Changing wide tires is a solution to many problems, especially for heavy cyclists. And research shows that using 28 or 30mm tires will not slow down, although it can not be faster, you can get greater comfort and better cornering performance from wide tires.

Tire pressure is related to the cyclist's weight, tire width, and inner rim width

Mountain bike tire pressure
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Let's talk about the tire pressure of mountain bikes first. Because this is relatively simple, tubeless tires have been used in mountain bikes more than ten years ago, and they have long been popular now. If you have not used tubeless tires, you can modify them with tubeless tire pads and tubeless air nozzles. The cost is very low, and there is no need to worry about problems because the tire
pressure of mountain bikes is very low. Of course, the premise of our discussion is off-road instead of mountain horses, and mountain bikes on the road can skip this section.

The inner width of the XC wheels introduced in recent years has reached 25mm. In fact, this is not wide. Think about the Zipp road wheelset. Take the XC wheelset with an inner width of 25mm as an example, using 2.1-inch tires, and the corresponding tire pressures for cyclists of different weights are as follows.

Less than 54kg-front wheel 17-20psi, rear-wheel 18-21psi

54-64kg-front wheel 18-21psi, rear wheel 18-22psi

64-73kg-front wheel 18-22psi, rear wheel 19-23psi

73-82kg-front wheel 19-23psi, rear wheel 20-24psi

82-91kg-front wheel 21-25psi, rear wheel 21-26psi

91-100kg-front wheel 22-27psi, rear wheel 23-28psi

Check to see if you are using too high tire pressure. The low pressure of cross-country wide tires is equivalent to entering a whole new world. Now the XC World Cup has begun to use 2.3-inch tires.

Road tire pressure

After talking about simple mountain bikes, let's take a look at road bikes. There is a difference between a clincher + inner tube and a tubeless tire for road bikes, so the tire pressure has to be discussed separately.

If you use 23mm tires and use 116-130psi tire pressure, use 25mm tires can drop about 14psi (1bar), use 28mm tires, and continue to drop 14psi, if you use 30mm tires, the tire pressure will be 72psi.

The road tire pressure gauge on the Specialized's website also confirms this statement. A 60kg cyclist needs a tire pressure of 100psi to use 23mm tires. If you change to a 25mm tire, it will drop to 94psi, and if you change to a 28mm tire, it will drop to 80psi. It weighs 62kg and uses Rapide CLX wheels and 26mm Turbo Cotton tires. Because the actual width of Turbo Cotton reaches 28.6mm, it feels more appropriate to set the tire pressure to 80psi.

The pressure of tubeless tires is a big pit, and there are two types of rims with hook and without a hook.

This picture comes from the Pirelli P Zero Race TLR tubeless tire packaging, so it is the applicable tire pressure for the tubeless tire, and it is the tire pressure used on the hooked rim. It can be seen that it is 14psi (1bar) lower than the clincher. For example, the open tire 60 kg weight cyclist 26mm tire uses 94 psi, while the tubeless tire only needs 80 psi.

Unhooked rims are another situation

Zipp believes that unhooked rims can have 5psi lower tire pressure than hooked rims.

Giant recommended tire pressure (tubeless rim without hook, inner width 19.4mm), 700 x 25c tires:

60kg-76psi

70kg-80psi

80kg-83psi

90kg-86psi

Taking a 60 kg cyclist as an example, the tire pressure has dropped from 80 psi to 76 psi, and the tire pressure used for unhooked rims is lower than that for hooked wheels.

The inner width of the rim also has a great influence on the tire pressure. Take the ENVE 45 with an inner width of 21mm as an example. It is also a 25mm tubeless tire. The tire pressure required for a 60kg cyclist is only 63psi, which is compared with the 19.4mm inner tube of the Giant Cadex wheelset. Reduced by 13psi. Therefore, we are not surprised why Zipp has a maximum tire pressure of 72.5 psi for a 23mm inner width rim.

Basically, it can be concluded that for cyclists of the same weight with the same tire and rim width, a 14psi (1bar) reduction in the tire pressure of the open tire + inner tube is the tire pressure used by the tubeless tire, and further reduction of 5 psi is required for the tubeless tubeless tire. Tire pressure. This rule is valid at least on 25 and 26mm tires.
carbon fiber road bike frameset X16
But we also encountered a problem during the test. If you use a tire pressure below 70psi (recommended tire pressure), you will always feel that the tire will twist when you rock the bike to attack the slope (more than 400 watts of power), and it will basically be above 75 psi. I can't feel it anymore. Therefore, the tire width should be selected according to the purpose and weight, so that the
tire pressure is within a reasonable range.

The tire pressure is not static. The manufacturer gives you the reference value. If the road conditions are good, the tire pressure can be 5psi higher than the high-power output such as cranking, and the tire pressure can be reduced by 5psi in wet and cold weather. You can also reduce tire pressure in poor road conditions.

In fact, the problem has not been fully clarified when I write this. The suggestions given by different brands are not completely the same. Let us leave a message and discuss what tire pressure is the most suitable.

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