The Rim Width Test: Road Bike, CX/Gravel, and MTB Tires on 18, 22, and 26 mm Rims.

As many of you already know, there has been a movement to wider rims going on for the last couple of years. This move to wider rims is driven by the improved handling and increased tire volume that wider rims provide. A couple of years back, we were running 55+ mm wide tires on 17 or 19 mm internal width rims which doesn't make sense anymore.

We get a lot of questions from site visitors that wonder how tires will perform on wider rims when compared to our test results that are always performed with our standard 17.8 mm internal width rim.

To answer these questions and give some more insight into the behavior of different tires on different rims, we've tested three road bike tires, three cx/gravel bike tires, and three MTB tires on three different rims with an internal rim width of 18, 22, and 26 mm.

The internal rim widths of 18, 22, and 26 mm were chosen so the results cover a large range of rim width to tire width ratios (from 32% up to 104%). At the end of this article, we've combined all data of the three categories into a tire width recommendation which we think gives the best performance.

We collected a LOT of data that can be confusing to understand when you're new to our site. To make this an accessible article and the data easy to understand, we averaged the results of the three tires for each tire category (road bike, CX/gravel, MTB). There were no large differences between the individual tires that can change the conclusion.

Pro Members can open the individual tire data and dig into the results further.

Test Set up and Conditions

We've built three wheels that all use the same hub (Shimano LX 670) and a spoke count of 32 (DT Swiss Champion 2.0). The hubs were brand new, and we adjusted the bearing play to slightly loose for all hubs. As the rims we used all have a slightly different weight, we adjusted the load to get to an exact load of 42.5 kg.

• 18 mm rim: DT Swiss R460db
• 22 mm rim: DT Swiss R500db
• 26 mm rim: Ryde Rival 26

Our requirement was a tubeless-ready rim as we tested all tires tubeless. Using an inner tube would be an advantage for the wider rims because the inner tube would be stretched more. We felt running all tests without an inner tube would give the purest data about the performance of different rim widths.

We made a slight adjustment for the 26 mm Ryde Rival rim as its static aerodynamic drag was slightly higher (+0.2 watts).

Per tire category, we tested all tire and rim combinations at the same four different air pressures to get as much data as possible and get a better understanding of where the most can be gained.

Rolling Resistance Test Conditions

• All tires set up tubeless
• Speed of 8 m/s - 28.8 km/h - 18 mph
• Total wheel load of 42.5 kg / 94 lbs
• Temperature between 21.5-22.5 °C / 71-72 °F
• Diamond plate drum surface
• 77 cm drum diameter

Test Results

Road Bike Tires on 18, 22, and 26 mm Rims

The tires we used for the road bike tests were:

• Vittoria Corsa Speed G+ 2.0 TLR 25-622
• Continental Grand Prix 5000 TL 25-622
• Schwalbe Pro One TLE 25-622

Although most road bikes with 25 mm tires come with rims somewhere around 15 to 18 mm wide, we tested these on the 22C and 26C rims to get an idea about what happens when running tires on extremely wide rims.

Let's start with the average width and height of the 3 road bike tires at an air pressure of 100 psi / 6.9 bars.

What we see here is that the width of the road bike tires increases by 0.425 mm per mm increase in rim width while the height of the tires hardly changes. The large increase in width means that you're almost moving up a tire size per 4 mm of rim width increase. A wider tire also means the tire will be stiffer at the same air pressure.

Next on is the rolling resistance measurements at the same 4 air pressures for all rim widths. Please be aware that because the tires are much wider on the wider rims, the air pressures need an adjustment to get to the same comfort level (see next section)

In the first rolling resistance tests where all rim widths use the same air pressures, we see that the widest rim that has a rim to tire width ratio of 104% results in the lowest rolling resistance. The difference is small but there clearly is a difference in how a road bike performs on extremely wide rims.

Because the width of the tires has also increased from 26.4 mm on the 18C rim to 29.8 mm on the 26C rim, these results aren't fully useable in the real world as the same tires on the wider rims would have to be run at lower air pressures to offer the same comfort level.

For the next test, we've adjusted the air pressures to values that will result in roughly the same comfort level. We did that by calculating the expected rolling resistance from the previous tests. We kept the pressures the same for the 22C rim, +6% for the 18C rim, and -6% for the 26C rim. We got to a difference of 6% as that's the change in the width of the tires.

With all tires adjusted to air pressures that result in roughly the same comfort level, we see that all tires now perform nearly the same. The 22C rim sticks out negatively but as the differences are so small we contribute this to small inaccuracies in the measurements.

Road Bike Tires Conclusion

Our conclusion for road bike tires is that there is nothing to gain in rolling resistance when moving to rims wider than 72% of the (specified) tire width.

For 25 mm wide road bike tires that would come down to 17-18C rims which is what most road bikes already come with these days. For 28 mm wide tires, moving up to 19-20C rims would hit the sweet spot.

CX/Gravel Bike Tires on 18, 22, and 26 mm Rims

The tires we used for the CX/Gravel tests were:

• Panaracer GravelKing TLC 40-622
• Continental Terra Speed TR 35-622
• Michelin Power Gravel 35-622

Let's see how the width of the rim affects slightly bigger tires and compare this to the road bike tires. We used the average specified size of the 3 tires (36.67 mm) to calculate the rim width ratio.

The CX/Gravel test results cover a rim to tire width ratio of 49% for the 18C rim, 60% for the 22C rim, and 71% for the 26C rim. These figures are the most realistic as most CX/Gravel bikes use rims with a width of between 19 to 25 mm.

While the width of the road bike tires grew at a very large rate of 0.425 mm per mm increase in rim width, the bigger CX/Gravel tires see a smaller increase of 0.3 mm per mm increase in rim width. The height of the tires also does not change spectacularly as the 8 mm increase in rim width only results in an increased height of 0.3 mm.

Let's again start with the purest rolling resistance measurements which are all rim widths using the same air pressure. Although the CX/Gravel bike tires grow less in width, the same tire mounted on the 26C rim will still have an advantage because of the larger volume.

We see the same pattern here that we've seen with the road bike tires: at the same air pressures, the wider rims have an advantage because of the larger tire volume which results in less tire deflection.

Now let's again look at what happens when we adjust the tires to equal comfort levels. As the CX/Gravel tires didn't grow as much in size as the smaller road bike tires, the adjustments were a bit smaller for these tires. The 22C rim stays at the standard air pressures, +3% for the 18C rim, and -3% for the 26C rim.

At the same comfort levels, we see that the performance of all rim widths again is very close. It's interesting to note that while the road bike tires showed nearly the same gaps between the rims, the CX/Gravel tires perform best on the 26C rim, while the performance of the road bike tires was best on the 18C rim.

When looking at the rim to tire width ratio, we see that the CX/Gravel tires performed best at a rim to tire width ratio of 71% and the road bike tires performed best on a rim to tire width ratio of 72%. Although the differences are small, it looks like a rim to tire width ratio of somewhere around 70% gives the best (rolling resistance) performance.

CX/Gravel Bike Tires Conclusion

For CX/Gravel tires, we conclude that the performance delta between 18C, 22C, and 26C rims is very small. As most modern CX and Gravel bikes already come with rims with a width somewhere between 19 and 25 mm, there is little to be gained.

Mountain Bike Tires on 18, 22, and 26 mm Rims

The tires we used for the mountain bike tests were:

• Continental Race King Protection 55-622 (29x2.2)
• Maxxis Aspen EXO TR 57-622 (29x2.25)
• Vittoria Mezcal TNT G+ 2.0 55-622 (29x2.25)

These days we still see mountain bikes that come with narrow rims to keep the cost and bike weight as low as possible. 17 and 19 mm rims do seem to be a thing of the past, but we still see many bikes that come with 21 - 25 mm wide rims.

Our rim selection of 18, 22, and 26 mm rims results in a rim to tire width ratio of between 32% and 47% and will give us a good idea of what happens when you run wide tires on narrow rims.

Let's start with the average width and height of the 3 mountain bike tires at an air pressure of 35 psi / 2.4 bars.

The increase in width of the mountain bike tires is much less than we expected. When going from a 18 mm rim to a 26 mm rim, width increases by just 2.2 mm (0.275 mm per mm). We do see that, unlike the road bike and CX/Gravel tires, the height of the tires increases quite a bit. This is probably a result of the sidewall angle that is quite extreme on the small rims.

Again, we start the rolling resistance tests with all rim and tire combinations at the same air pressures.

Not surprisingly, we see the same pattern that we've seen with the road bike and cx/gravel tires. The wider rims result in a lower rolling resistance which is partly because of the fact that, at the same air pressure, the wider rim results in less tire deflection.

Let's again see what happens when we adjust all tires to the same comfort level. This time the adjustments were quite small as the width of the tires doesn't change all that much. The 22C rim stays at the standard air pressures, +2% for the 18C rim, and -2% for the 26C rim.

Now we got an interesting result! With the adjusted air pressures so all tire and rim combinations provide roughly the same comfort level, the bigger rims still have a clear advantage in the rolling resistance tests.

When looking at the rim to tire width ratios, we see that changing from a narrow rim with a rim to tire width ratio of 32% up to a wider rim with a rim to tire width ratio of 47% results in roughly a 3% improvement in rolling resistance.

Mountain Bike Tires Conclusion

It looks like rims narrower than 25-26 mm really should be a thing of the past on mountain bikes. Not only will the wider rims result in better handling characteristics, but you'll also gain free speed as the tires roll more efficiently on wider rims.

Conclusion

We've combined all results of our tests into the chart above which provides an excellent summary of all the rim width tests.

What we've found is that there is only a very small difference between the different rim widths when we adjust the air pressure for the increase in tire volume that comes with a wider rim.

Peak rolling resistance performance seems to be reached when the rim width is somewhere between 65% and 75% of the specified width of the tire. Our other conclusion is that a rim width that is within 50 to 80% of the specified tire width results in performance that is within 99% of peak performance.

Only when the rim is narrower than 50% of the specified width of the tire, performance starts to drop-off at a faster rate. The drop-off is small as you'll still get 95% of peak performance when the rim has a width of only 30% of the specified width of the tire.

So should we always try to aim for a rim width of 65% to 75% of the specified width? Probably not as we're only talking about rolling resistance and the 1% peak performance advantage can easily be lost in other areas of the tire and rim's performance.

Also, be aware that not all tires have a wide enough tread for use on very wide rims. Tires will be squared off more on wide rims and you might run out of tread resulting in a loss of grip at high lean angles.

It's impossible to make a general recommendation that covers every rim and tire combination out there. Our recommendation would be to aim for a rim width of at least 50% of the specified tire width and from there look at the specific tire and your own requirements regarding lean angle, weight, aerodynamics, etc.

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