It’s widely known that rims have been getting wider in recent years. To improve handling and increase tire air volume, no one pairs a 55mm tire with a 17mm or 19mm inner-width rim anymore, as was common a few years ago. Cyclists are curious about how the same tire performs on wide versus narrow rims (e.g., the 17.8mm test rim commonly used in bicycle rolling resistance tests).

To address this, we tested three road tires, three gravel tires, and three mountain tires on 18mm, 22mm, and 26mm rims. Our results cover a rim-width-to-tire-width ratio ranging from 0.32 to 1.04. At the end of the article, we combine all test data to provide recommendations for optimal rim-width-to-tire-width pairings.

We collected a vast amount of data, and since the differences between tires of similar widths within the same category were minimal, we averaged the results for each tire category (road, gravel, and mountain).

Test Setup and Conditions for Carbon Fiber Bicycle Wheelsets

Test Tires
All rolling resistance tests were conducted on a rolling resistance test machine. We used Shimano LX670 hubs with 32 DT Champion 2.0 spokes. The hub bearings were adjusted to be slightly loose. Due to slight variations in rim weight, we adjusted the load to ensure a consistent 42.5kg load across all test wheels.

• 18mm rim
• 22mm rim
• 26mm rim

All tests used tubeless rims and tubeless tires. While wider rims stretch inner tubes more, which can offer advantages with wider tires, we believe using tubeless rims and tires for all tests provides the most accurate data on how rim width affects tire performance. For each of the three rim widths, we tested four different tire pressures to gather more data and better understand how to maximize performance gains.

Rolling Resistance Test Conditions

• All tires used a tubeless system
• Speed: 28.8 km/h
• Wheel load: 42.5 kg
• Temperature: 21.5–22.5 °C
• Diamond-plate drum surface
• Drum diameter: 77cm

Road Tires Paired with 18mm, 22mm, and 26mm Rims
Although 25mm-wide road tires are typically paired with rims around 15–18mm wide, we also tested them on 22mm and 26mm rims to see how they perform. At a tire pressure of 100 psi / 6.9 bars, the tire height and width on different rims are as follows:

It can be seen that for every 1mm increase in rim width, a 25mm-wide road tire mounted on it becomes approximately 0.425mm wider. This means that for every 4mm increase in rim width, it’s equivalent to choosing the next size up in tires (e.g., 26C becomes 28C, 28C becomes 30C). A wider tire also means that, at the same tire pressure, the tire will feel firmer.

Next is the rolling resistance test. The average rolling resistance of three tires is measured across four tire pressure settings and different rim widths. Note that since a wider tire feels firmer at the same pressure, some combinations would likely require adjustments in practice (e.g., 120 psi on a 26C rim would be too hard for most people).

In the test above, we used the same tire pressure for each rim width. It’s clear that wider tires exhibit lower rolling resistance. Although the difference is not significant, the trend is evident. However, directly using these results to guide tire setup may pose some issues, as the tire width increased from 26.4mm on the 18C rim to 29.8mm on the 26C rim. To maintain the same level of comfort, wider tires require lower tire pressure.

In the test below, we adjusted the tire pressure based on equal comfort levels across different rim widths. The tire pressure for the 22C rim remains unchanged, while the pressure for the 18C rim is increased by 6%, and the pressure for the 26C rim is decreased by 6%. The 6% adjustment approximately corresponds to the change in tire width.

After adjusting the tire pressure based on comfort, it is evident that the performance of all setups is nearly identical. The 22C setup seems to perform slightly worse, but the difference is so small that it can be attributed to measurement error.

Conclusion for Road Bikes

We conclude that when the rim width exceeds 72% of the tire width, further widening the rim does not increase rolling resistance. For 25mm-wide road tires, a suitable rim width is approximately 17–18C, which aligns with the standard configuration for most road bikes today. For 28mm-wide tires, the best rim width is 19–20C.

Gravel Tires Paired with 18mm, 22mm, and 26mm Rims

The three gravel tires tested are as follows:

– Panaracer GravelKing TLC 40-622

– Continental Terra Speed TR 35-622

– Michelin Power Gravel 35-622

Here, we examine how rim width affects slightly wider tires and compare the results with those for road bikes. We use the average nominal tire width of the three gravel tires (36.67 mm) to calculate the rim-to-tire nominal width ratio. The nominal rim-to-tire width ratios for the gravel tires in the test are 49% (18C rim), 60% (22C rim), and 71% (26C rim). Most gravel bikes have rims ranging from 19mm to 25mm wide, making this dataset fairly representative of real-world conditions.

Unlike road bike rims, where an increase of 1mm in rim width results in a 25mm road tire becoming approximately 0.425mm wider, for gravel rims, an increase of 1mm in rim width only widens the tire by about 0.3mm. The tire height also shows minimal change with rim width; an 8mm increase in rim width only raises the tire height by 0.3mm.

We began testing with rolling resistance at the same tire pressures, measuring the average rolling resistance of the three tires across four tire pressure settings and different rim widths. Although the changes are less noticeable compared to road bikes, wider rims with the same tire and pressure offer an advantage due to their larger volume.

The trend in changes is clearly similar to that of road bikes: wider rims increase tire volume, reducing the sink and deformation of the tire under the same load, thus giving wider rims an advantage in rolling resistance at the same tire pressure.

We then adjusted the tire pressure to the same comfort level. Since the dimensional changes of gravel tires on rims of different widths are less pronounced, the adjustments to tire pressure are also smaller. Using 22C as the baseline, the tire pressure for 18C rims is increased by 3%, and for 26C rims, it is decreased by 3%.

The trend in changes is clearly similar to that of road bikes: wider rims increase tire volume, reducing the sink and deformation of the tire under the same load, thus giving wider rims an advantage in rolling resistance at the same tire pressure.

We then adjusted the tire pressure to the same comfort level. Since the dimensional changes of gravel tires on rims of different widths are less pronounced, the adjustments to tire pressure are also smaller. Using 22C as the baseline, the tire pressure for 18C rims is increased by 3%, and for 26C rims, it is decreased by 3%.

After equivalent adjustments, we found that gravel tires perform similarly across rims of different widths. Interestingly, gravel tires perform best on wider rims, specifically the 26C, while road tires perform best on narrower rims, specifically the 18C.

Looking at the rim-to-tire nominal width ratio, gravel tires show the best rolling resistance at a ratio of 71%, while road tires perform best at 72%. Although the difference is not significant, we can conclude that a rim-to-tire nominal width ratio of around 0.7 provides the optimal rolling resistance for tires.

Conclusion for Gravel Tires

For gravel tires, we conclude that the performance difference between using 18C, 22C, and 26C rims is very small. Since most gravel bikes come with rim widths between 19 and 25mm, tweaking this aspect seems to offer little improvement.

Mountain Bike Tires Paired with 18mm, 22mm, and 26mm Rims

The three mountain bike tires tested are as follows:

– Continental Race King Protection 55-622 (29×2.2)

– Maxxis Aspen EXO TR 57-622 (29×2.25)

– Vittoria Mezcal TNT G+ 2.0 55-622 (29×2.25)

To save costs and reduce weight, it’s still common to see mountain bikes equipped with relatively narrow rims. While 17mm and 19mm inner-width rims may have become outdated, 21–25mm rims remain quite common. Pairing our selected tires with 18mm, 22mm, and 26mm rims results in rim-to-tire nominal width ratios ranging from 32% to 47%. This test will show us how narrow rims perform with wider tires.

As usual, at a tire pressure of 35 psi / 2.4 bars, the tire height and width on different rims are as follows:

The change in mountain bike tire width with rim width is much smaller than we expected. From an 18mm rim to a 26mm rim, the tire width only increases by 2.2mm (for every 1mm increase in rim width, the tire width increases by just 0.275mm). However, unlike road, CX, and gravel tires, the tire height increases significantly, possibly because on narrow rims with wide tires, the sidewall angle with the ground becomes larger, pushing the tire height upward.

We still measured the rolling resistance at the same tire pressure.

These results are interesting. After adjustment, different tire pressure-rim-tire combinations provide similar comfort levels, but wider rims clearly offer a significant advantage in rolling resistance.

Looking at the rim-to-tire nominal width ratio, switching from a narrow rim with a ratio of 32% to a wide rim with a ratio of 47% can reduce rolling resistance by approximately 3%.

Conclusion for Mountain Bikes

Based on these test results, narrow rims under 25mm on mountain bikes should be phased out. Wider rims not only improve handling but also reduce rolling resistance. (What about the cost and weight concerns you just mentioned?)

Conclusion

The chart above consolidates all test results, serving as a summary of this study.

We found that after adjusting tire pressure for the same comfort level, the impact of different rim widths on rolling resistance is minimal. Tires exhibit optimal low rolling resistance performance when the rim-to-tire nominal width ratio is between 65% and 75%. Within a ratio range of 50% to 80%, tires maintain 99% of their best low rolling resistance performance. Only when the rim-to-tire nominal width ratio falls below 0.5 does the low rolling resistance performance decline noticeably. However, even at a ratio as low as 0.3, tires still retain 95% of their peak low rolling resistance performance.

This raises a question: should we aim to maintain a rim-to-tire nominal width ratio between 0.65 and 0.75? Probably not, as a 1% improvement in rolling resistance is negligible and can easily be gained elsewhere. Additionally, not all tires with tread patterns are wide enough to be suitable for very wide rims. Wider rims flatten the tire profile, and when the bike leans in a turn, using the untreaded areas of the tire can lead to loss of control.

Providing a universal recommendation covering all rim and tire combinations is clearly impractical. We suggest that the rim width be at least 50% of the tire’s nominal width, then consider specific tire characteristics and your own requirements, such as the aggressiveness of your riding style, your weight and bike weight, aerodynamic performance, and more.