Tech: Why wider rims will improve your ride

Benefits include softer ride, more cornering traction, better climbing

Tech Tires Wheels
Wide mountain rims change the dynamics of a rolling tire in many different ways. Photo courtesy of Art's Cyclery

Wide mountain rims change the dynamics of a rolling tire in many different ways (click to enlarge). Photo courtesy of Art’s Cyclery

Editors Note: Science Behind the Magic is a reoccurring column by Art’s Cyclery web content editor Brett Murphy, who uses his mechanical engineering background to explain the latest industry advances, and breakdown the inner workings of common components. The original article can be found here.

Technology in the mountain biking world is changing quickly these days. In the blink of eye, frame geometries, suspension designs and now wheel profiles change. New wheels are significantly wider than those of the past. Is this just the latest trend in the industry — an attempt to force the consumer to buy new gear — or is there a science behind it that has led to a revolution in wheel construction and bike handling?

The answer is yes — it’s all about the science! Wide mountain rims change the dynamics of a rolling tire in many ways.

Ride Quality

Bigger tires offer more air volume to provide a more supple ride. Tires provide another inch or two of suspension on impact depending on pressure. In the same way an air volume reducer in a shock changes ride characteristics, the same is true with a tire. Comparing the inner width of a Mavic EN 821 Rim and an American Classic Wide Lightning shows 9mm of difference in inner diameter between the rim flanges.

This photo from Ibis shows the differences in the older rims width and the new wider ones.

This photo from Ibis shows the differences in the older rims width and the new wider ones (click to enlarge).

This difference widens the base of the tire and can increase air volume by almost 10% in the tested Continental Trail King 29er or similar tire. The resulting smoother ride makes it possible to add a click of compression damping to your suspension, thereby providing even more control without sacrificing comfort. That increased compression damping means less brake dive and more support when pumping rollers.

Traction

Wider rims create a wider contact patch between the tire and the ground. With the same tire mounted to a wider rim, the cross sectional view of the tire is less rounded and more square. This results in a larger tread area parallel to the ground. Wider rims also put the cornering knobs in more constant contact with the ground. The change in width ends up pushing the cornering knobs up by stretching out the tire.

The Geax Goma 2.4 tires measure in at 2.6 when installed on a 35mm rim.

The Geax Goma 2.4 tires measure in at 2.6 when installed on a 35mm rim (click to enlarge).

The result of pushing the cornering knobs out can have varied effects. It is very noticeable in tires like the Maxxis High Roller 2 or the Geax Goma. Sometimes even while running really low pressure up front, the bike has to be leaned over too far to get the shoulder knobs in contact with the ground. In spite of the pronounced center and cornering knobs, the lack of transition knobs between the two is the major culprit responsible for this handling trait.

When leaning a bike over, a lack of knobbies in the transition zone can leave a rider with a feeling of vagueness. This is where a wide rim can play a significant role in changing tire behavior. Creating a squared off profile and raising the cornering knobs puts them in more constant contact at smaller degrees of lean and thereby increasing handling predictability. A wider rim has the potential to really open up some tire combinations that you would have never considered before.

This graphic illustrates the lateral forces on the tire using different rim widths.

This graphic from Syntace illustrates the lateral forces on the tire using different rim widths (click to enlarge).

Beyond cornering traction, wide rims provide better climbing. With the larger air volumes, lower pressures—about three psi lower than a narrow rim as tested in-house —will result in a noticeably better hook up while climbing.

Continue to page 2 for more of this story and full photo gallery »

About the author: Arts Cyclery

This article was originally published on the Art's Cyclery Blog. Art's Cyclery is dedicated to offering free expert advice, how-to videos, and in-depth product reviews on ArtsCyclery.com to help riders make an educated decision when selecting cycling gear.


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  • Nick Tuttle says:

    Game Changers for sure. Been rocking the Ibis 741 for a season now. Time travel machine back to 2005? These would be the only thing I brought back with me. Throw these on my Bullit witha JR T and donate the 23 mm wide rims to grampapy and granny. Seriously this shit is for realz.

  • tyrebyter says:

    Interesting article. Some of the assumptions are questionable: square profile is better than round? Not where I ride. A square profile will cause a lot of unwanted steering input. Not to mention exposing the sidewall to more potential damage. Better traction when leaned over? Pick a better tread pattern and you won’t have to compensate for poorly designed transition knobs. Wider rims have great potential with the right tire, but you seem to be stretching for many of these supposed advantages.

  • bluegixxer600 says:

    I always have wondered why mtn bike wheels are so narrow compared to the wheels of a 20″ BMX bike….

  • Bob says:

    I want to know what happens to rolling resistance…. a larger contact patch to my logic would indicate more drag when pedalling? They seem to dodge this question, and this is what would turn me off running such wide rims.

    If they are so amazing, why do most enduro racers still run DT EX471 for example, which is *only* 25mm, with the Crossmax being even skinnier?

  • oldmtb says:

    Big minus is increased rolling resistance. Also cornering advantage also depends on the surface. Sometimes a narrower rounder tire will dig into a soft surface better than a flat wide tire which might just skid over the top. i.e. loose gravel on top of hardpack. Too a wide contact patch can float over the gravel like marbles and washout, while a narrower profile can cut through the loam and grip the hard pack underneath. That’s why a lot of DH racers still use 2.35 even when they have 2.5 or 2.7 tire widths available.

  • papally says:

    Fat rims are a favorite of the slow descender club.

  • riderhairder@duh.com says:

    I thought you were half way smart until you said you took the time to measure the tire circumference on two different rims. At first when I read it I thought maybe he is measuring around the tire and rim (going through the spokes), not the circumference of the tire, which would not change for any width under any circumstances. Since you did measure a 2.4 tire at 2.6 width on a wider rim, I gave u benefit of the doubt that you would go one step further and measure around the tire and rim. Wow, I still can’t fathom the lack of realization that you would measure the circumference. Can you explain the reasoning behind that?
    Also, no, you cannot run lower PSI because the larger volume of air is more able to absorb bumps from roots and rocks thereby making it easier to “bang” the rim on something. Higher PSI might need to be run. Think about it like a fork where a wider tire/ bigger air volume has a more linear spring rate, and the old small rims provide a more progressive spring rate, where the spring rate is how quickly the tire’s air pressure ramps up when you hit things on the trail. A linear rate tire will hit things much more than a progressive tire.
    I will not be writing any articles, so this is it.

    • OutSmith says:

      Pretty please write an article. It isn’t your strong suit but it would be entertaining even though your diatribe thus far has been a waste of perfectly good 1s and 0s.

  • Jennifer says:

    Good article.. About time these types of topics are talked about more..

  • derby says:

    Francis, thanks so much for your great rider forum! Derby Rims would never have been possible without your world’s most popular rider review forum.

    When Derby Rims were introduced here on MTBR in a couple forum posts in August 2013, I had no idea these world’s first carbon fiber rims wider than 30mm would ever sell.

    It is a great complement I feel, and validation that so many brands, established and new, have so closely copied my 2012 original design features, including the first for bicycles thick hookless rim walls with tire bead seats having raised angle retention “bead locks”, and wider rim widths improving nearly any tire performance from 38C road and 2.1 mountain and wider tires, introduced publicly on the MTBR forum in 2013.

    I especially want to thank Ibis again for helping when I asked in 2012 for their critique of my wide carbon fiber rim idea and their critique of my original design features, and for promoting wide carbon fiber rims so much more than Derby Rims was able.

    Most of all I wish to thank the customers of Derby Rims. You have promoted the high performance gains in bike handling, stability, and improved confidence, more than any commercial marketing campaign could do, with your experience and passion from riding light-weight, wide, and durable carbon fiber Derby Rims.

    Enjoy!

  • Dennis says:

    Derby! I just got my rims, they built up straight and true, quickly and much easier than previous aluminum rim wheel builds. Thank YOU for putting out a great product and having the vision to do so.

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