What is the best width of road bicycle tires?Reporter Simon tested the 26mm and 30mm outer tires to find the answers.
The choice of tire width has always been one of the most hotly debated topics in the road car movement.Thin tires (23 mm or less) are traditionally used because they are usually lighter and are considered faster.However, recent trends are moving in the opposite direction.Manufacturers are encouraging riders to use wider tires (28 mm or larger), claiming that they can offer lower rolling resistance and more comfortable riding quality.
But what width of tires is best for road cars?The tire width is impossible to go endlessly wide, and to answer this question, the authors designed two tests, both using Pirelli P-Zero Race TLR tires, using two different specifications: 70026mm and 70030mm.The 26mm size was used to represent the standard, narrower tire width, while 30mm was used to represent the road car width considered quite wide.
The first test was conducted on an indoor roller cycling platform, while the second test was conducted on an outdoor track, with a variety of different road conditions for better verification.Indoor testing should give us some reliable data to detect differences in rolling resistance between narrow and wide tires, but it is also critical to assess whether each set of tires is combined in a real-world environment.After all, no matter how the roll resistance will eventually be considered in real road conditions.
And in our experience, when it comes to road car tire width, a balance between comfort, rolling resistance and aerodynamics.For example, wider tires may be more comfortable, but using them may mean sacrificing a small amount of aerodynamic advantage.Of course the balance depends on your car and cycling style, but I will give you some advice to suit your needs.
Indoor roller cycling table test
Since there are multiple variables at work outdoors, such as wind and frequent priming, data testing in the real world may not be optimal.Cycling on an indoor roller cycling platform in such a more controlled environment can better test specific variables.
Indoor roller cycling table test Part 1: tire width
The test is simple.Take the two sets of tires of different width and ride on the roller at a fixed speed within a fixed time interval.The power required to maintain this speed is then recorded.Everything else, such as bikes, wheel sets, riding posture, and more, keeps the same tire pressure each time, with 26 mm and 30 mm inflated up to 90psi.If one widths faster than the other, it should require lower power output to maintain the target speed.We can then infer that this width produces less rolling resistance.
In this test, the target speed was 40 km/h, with an interval of 5 min.Before starting each test interval, the author targeted the average speed km/h for 5 minutes to achieve a consistent operating temperature for all the system elements.Each trial was repeated twice and then averaged to ensure consistency.
It is important to admit that this test does not completely replicate real-world cycling, because the surface of the roller is much smoother than any road.The deformation was also slightly different on the rollers compared to the pavement, as the small diameter roller expanded the deformation.However, it still provides a proven way to control the test variables.
All tests were performed on a vehicle with FFWD F3AD wheel sets and a Jeante TCR Advanced Pro 2 Disc road bike.As previously described, the tires used for testing were Pirelli P-Zero Race TLR with dimensions of 70026mm and 70030mm, respectively.The structure of the outer tire is identical to the rubber, with the only difference being the width of the tire.Although these outer tires are vacuum, this time we have the butyl inner tire for testing to facilitate the replacement of the outer tire.This is a small increase of roll drag than the vacuum tire, but the two direct rounds will not differ.The power was recorded using a set of Favero Assioma Duo power locks and calibrated at the beginning of the test.
conclusion
Using 30 mm tires at a speed of 40 km/h requires 152 watts of average power output, while using 26 mm tires requires an average power output of 166 watts, a difference of 14 watts.Without aerodynamic consideration, the same pressure is applied on the completely smooth surface, and the wide tire is much faster than the narrow tire.
This is because, under the same pressure, the wider outer tire has a higher fetal wall tension and a shorter and wider contact surface.The first factor means that less energy is lost from the outer tire bending deformation, and the second factor reduces the rolling drag because the shorter, wider contact surface reduces the friction loss.
Such a test lacks a key point, and if you ride in reality, the tire pressure needs to work.
Indoor roller cycle table Test Part 2: tire width and tire pressure
When using wider tires in the real world, we usually do not usually inflate them to the same tire pressure as the narrower tires.Doing so results in a higher wider outer tire tension, making it harder and more uncomfortable to ride than the narrower tires.A 30mm outer tire inflated to 90psi, as you can imagine, is very hard.One of the benefits of using wide tires is that they should be more comfortable, but if the tire pressure is too high, then we can’t get that benefit in the real world.
On such a very smooth surface on the drum or on the field, the higher tire pressure and tension reduce the rolling drag, as the deformation loses less energy and the area of the contact blocks decreases.However, in the real world, the road is not as smooth as that, and wide tires need lower tire pressure than narrow tires, because we want the outer tire to absorb the vibration of the road.If we overinflate the tires, the bike crosses these road defects, eventually reducing grip and speed.
Therefore, in the second part of the roller test, we adjust the tire pressure according to the tire size.This means that the inflation pressure is lower and higher for narrower tires.Not only can this reflect real-world use more accurately, but also offset the rolling resistance advantage due to the increased tension on the wider tire.
According to Pirelli advice, weighing about 64kg I should use 26mm at 83psi and 30mm at 65psi, which is the pressure we tested in this part of the test.
conclusion
At the recommended use pressure, 170 watts are required for 30mm tires, and 26mm tires.Now the situation has reversed, on a completely smooth surface without aerodynamic considerations, the 26 mm tire has a 5 watt advantage.
So why does the narrow tire suddenly produce less rolling drag than the wide tire?Again, this is related to deformation tension and tire pressure.A 26 mm outer tire inflated to 83psi was significantly than a 30 mm tire at 65psi, with less shape change and less contact with the roller.It also means that the 30 mm tires compress more under the weight of the bike and my body, increasing the loss of deformation and increasing the size of the contact area.If we precisely adjust the tire pressure for each tire size to give exactly the same deformation tension or stiffness, the rolling resistance may be the same.
Conclusions of drum test
Finally, our roller tests show that wide tires do produce less rolling drag than narrow tires at the same tire pressure.However, this advantage disappears once we adjust to the realistic ride tire pressure.Cycling is important in reality, because this is the way we use the bike, so we still need to carefully consider the best outer tire width.
What about cycling on real roads?
Most people tend to ride outside on the actual road, so it is clear that the roller test doesn’t tell us the whole story.While there may not be much difference on the rollers, experience tells us that wider tires may improve comfort and reduce kinetic energy loss from complex road delays.
Shock absorption and control car
On real roads, road exterior tires need to act as shock absorption, absorbing vibration on the road, rather than rebound.This helps to maintain speed, providing comfort and grip.To achieve this, the tire pressure should be reduced as the road becomes rough.However, on very rough roads, the tires may be too narrow and not large enough to absorb large bumps, and will likely bottom the outer tire with the rim.For example, when hitting a hole, the outer tire will be flattened between the rim and obstacles, which may cause a flat tire and damage the outer tire and rim.
This problem would be more severe for heavier riders and bikes as they exert greater downward pressure on the outer tire.With this in mind, for example, Pirelli recommends that drivers weighing more than 96 kg (or people reaching that total weight) do not use tires of less than 70,025mm.
aerodynamics
On the other hand, on good road surfaces, where the requirements for shock absorption are not very high, narrow tires may provide a smaller aerodynamic advantage with a slightly reduced frontal windward surface.Many modern pneumatic road cars and wheel sets are designed to achieve the minimum wind resistance when carrying 25mm outer tires.As a rule of thumb, you usually want the outer width of the rim slightly wider than the outer tire.Still, this may be just a question worth considering for those who play a time trial or road race on good roads.
Overall, the trick is to find an outer tire that works for yourself and has shock absorption, grip, and aerodynamic balance.If you drive at slower speeds on rugged roads, then shock absorption and grip are priorities, which means choosing a wider tire.On the other hand, if you drive fast on flat roads, the tiny aerodynamic advantage of narrow tires may be worthwhile.
The actual riding impression
While the drum data indicate a difference in rolling resistance between tires in controlled environments, for most people, performance on real roads is the most important.To gather more subjective impressions, we also tested our two types of tires on a 2.7 km loop south of Bristol with a variety of different roads.The loop cleverly combines a newly paved climb, a typical “ordinary” British road and imperfect downhill, and a short, flat almost completely broken road in between.
In this test, the author used the tire pressure recommended by Pirelli. For the author’s weight, the 26mm tire is 83psi, and the 30mm tire is 65psi.While we can try to collect some data by taking the cycling time at the set average power, this test was conducted on open roads, so it is difficult to eliminate the effects of driver and environmental variables.For example, wind speed, passers-by and vehicles, and differences in each brake and line selection, can interfere with the data and lead to considerable errors.
Therefore, the purpose of this test is not to collect data, but to feel how the width of each tire is in the real world.
The conclusion of the actual ride
As expected, the difference in the width of the two tires was minimal on the smooth asphalt surface.On good pavement, with a wider 70030mm than 700 26mm tires, the increase in tire volume has no significant effect on improved comfort, but we know there is a small, aerodynamic negative effect.
When the roads become rough, the benefits of the comfort and grip of the wider outer tire become very obvious.Even in the “normal” British section, the wider tyres were significantly more comfortable.In addition, the wider tires gain more confident grip after the road changes.This is especially true when going downhill, with wider tires giving a stronger sense of stability.
It should be noted that while the narrow outer tire may feel fast on rough roads, the high-frequency vibrations we experience are very uncomfortable.As we discussed in the Tire Pressure Guide, wider tires at lower pressure can help keep the outer tire in contact with the road for more time, thus reducing rolling resistance.
So how to make the roll resistance lower?
It is a complex topic, but the rolling resistance that the tire produces depends largely on its structure and the rubber formula itself.Generally, lighter tires, thinner, soft rubber, are usually faster than heavier, thicker, harder, carrying outer tires such as barbed layers, and you can experience the difference between summer and winter tires.As you might guess, road car tires almost always trade off between speed and durability.The best choice depends on how you ride it.Thin as paper, lightweight tires are suitable for a time trial on the perfect road, but may not be suitable for unplanned excursions or long distance rides on local gravel trails.
How wide of the outer tire should you use?
The roller test showed that at the same pressure, the wider outer tire showed the advantage of rolling resistance.However, once you are in the real world, that advantage disappears.In the real world, ” Are wider tires faster?”The answer to the question is even more subtle.While wider tires produce no less rolling drag than narrower tires, you shouldn’t roll slower once you normalize outer tire tension.Wider tires may also be more comfortable with greater grip.A more comfortable and confident car may also be faster overall, depending on the terrain.
Therefore, we can choose tire width by other criteria, such as shock damping requirements, grip and aerodynamics.Finally, you need to weigh what your bike setup want to achieve.
If your bike has enough clearance, we usually recommend a compromise option, the 28 mm outer tire, as a balancing point for all these features.
If you play a race or time trial on good road, a slightly narrow, 25mm tire may offer a little aerodynamic advantage at high speed.But, if you play on rough roads, being slightly wider may be better.
If you often ride on particularly rough roads, or want to enter some gravel sections, the 30 mm (or larger) outer tire may give you more comfort, grip, and handling, and have no impact on rolling resistance.
From: www.biketo.com
