I still remember the corner clearly. Dropping off the lift, you pick up the narrow, rocky trail down to the grass. Mud soon replaces rock underfoot and the tyres start biting. The corner itself is just a flat, grassy bend as you traverse from one side of the resort to the other. Leaning into that first corner something unexpected happened. As I started to lay the bike over the tyres held, digging into the dirt and I could push the bar closer and closer to the ground. That's the magic - one of those perfect moments when the bike and the trail seem made for each other, when you feel like a hero, if only for a split second.
That was my first corner on wide rims. Nothing else in my setup changed - same bike, same tyres. My 25mm internal width wheels had been replaced by burly-looking Ibis 741s with a full 35mm internal width that my wife had left over from her race season.
Through the rest of the day, I giggled my way up and down the bike park in Roubion, pushing the bike in a little harder each time, trying to get closer to the limits of grip. For me that was it, I was sold. In fact, since that day in 2015, I have switched all my bikes over to wide profile rims. They felt good, so I haven't built a bike with rims less than 30mm wide since.
There's one problem with this: it was a flawed decision. If I'm honest, that decision was almost entirely based on feelings from that single corner. Over the years since, I have covered a few thousand kilometers on 35mm rims, and I can confidently say that I like them when they are paired to the right tire (I have been running 2.35 Schwalbes pretty religiously). But, if you stopped me and asked why, I couldn't really give you a much better answer than how good they felt in that one corner.Rim Width: Separating Feelings VS Facts
Back in 2015, anything over 30mm was fairly extreme, but today it is generally accepted that wider rims are better. But, if we get down to the fine detail, how exactly does a 30mm or 35mm rim feel better than a 25mm rim? Aside from every manufacturer's press release claiming that their rim offers the perfect balance, what does it actually mean out on the trail? Is it better in every situation? Are there drawbacks? How wide is too wide? Or, did I just get carried away and I've been getting it wrong all along? To be sure, I had to separate my feelings from the facts, and the best method to accomplish that is a side-by-side comparison.
About the Test Bike Choosing the Wheels
To try and break down the benefits and drawbacks of rim width it's not as simple as picking rims based solely on width - after all, comparing a 30mm DH rim to a 25mm XC rim or a 40mm "Plus" trail bike rim, is like trying to compare apples and oranges. The weight of the rim will be vastly different between the two, as will stiffness and strength. The same goes for comparisons between different manufacturers. For this test to work, it would need a single manufacturer that produces a range of widths for a single application.
Enter DT Swiss and their XM1501 wheels
. They produce XM1501 wheelsets in a range of widths that span from 25mm to 40mm, in 5mm increments, something I do not think any other manufacturer offers. They have the same hubs, the same spokes, the same spoke counts and the same intended application. In other words, this is about as close to a neutral test as anybody without their own extrusion facility is likely to get. So, DT shipped me a pair in 25mm, a pair in 30mm and a pair in 35mm. The original plan was to receive a pair in 40mm too, but it was only available as a front wheel, so for the test, I would run it in combination with the 35mm rear wheel.
With the wheels sorted, the next question would be the test bike. Originally I had hoped to use one of my personal bikes as the testing bike. However, what I failed to check is diameters on the DT Swiss website. While they do make the XM1501 in 29, they only offer them in 25mm and 30mm widths, which is not really a big enough range to get usable information from. That meant for the test I would need something with 27.5 wheels, while all my personal bikes (except my DH bike) run on 29.
My criteria for the test bike were fairly strict. I wanted a short travel bike, partly because I like short travel bikes, but mainly because I believe that without the extra suspension, the tyre performance is a much bigger part of the overall feel on the trail. This would mean that I could focus on the wheels much more clearly. After that, I needed something that came off the peg with a fairly sturdy build and had a reach of somewhere between 450 and 475mm (if you're curious as to how I reached those values, check out my piece on how I believe reach should be proportional to body size
). After much hunting, I found the Whyte T-130, which ticked pretty much all the boxes. It has a pretty solid reputation among bike testers as a hell of a lot of fun to spend time on
. Whyte sent the RS build in large with a few small tweaks to the spec - a slightly higher rise bar and shorter stem, plus they stuffed the suspension full of tokens and bands as I like my bike to have quite a lot of ramp-up at the end of the stroke.
Riding Conditions And, the Tires
The final piece of the puzzle was the tyres. This was an easy decision for me as I tend to run one combination of tyres all year round - a Schwalbe Magic Mary
2.35 on the front, paired with a 2.35 Rock Razor
on the rear. I opted for both front and rear in the intermediate Snakeskin casing, as this is what I run on my trail bike, and I know it strikes a good balance between weight and security for me, providing I keep the pressures sensible (I weigh 70kg and run 23psi front, 28psi rear). Also, using a familiar combination meant that there would be no need for an adjustment period for me - I know very well how these tyres should perform in any given situation.
For the first test, I headed to La Mouliere bike park
. My original plan was to shuttle one of my local trails, but who can resist an early season chairlift? While it may be lift-accessed riding, La Mouliere is not a bike park in the style of Whistler - it is more like a collection of fairly natural, rocky trails tied together with the lift. I knew that it would put me close to or past the edge of where I am comfortable riding a short-travel bike, which is exactly what I was looking for to test the tires - trails where I needed every advantage I could get.Width VS Weight
Before I started testing, I wanted to first measure and weigh the wheels. First of all, I weighed each of the front wheels. Each rim was taped for tubeless from the factory, which may account for a small part of the weight discrepancies, but overall the claimed weights are pretty close to the real weights. The only difference between each of the wheels is the rim and each rim is made from the same grade aluminium to provide a uniform level of strength and stiffness. So what should we take from this?
If we take the 25mm wheel as the baseline, the additional weight (50g or so, going up to 30mm) is fairly negligible and you'd have to be a fairly committed weight weeny to care about that too much. Stepping up to 35mm gets to around the 100g mark, which you would feel out on the trail, so there would need to be a real advantage to justify the extra weight. At nearly 150g additional weight, and nearly a 100g step compared to 35mm, 40mm rims would need to be really good to be worth it.
How Rim-Width Affects Tire Profile
Speaking to a product manager at a rim maker, he explained that as the rim gets wider, it is harder and harder to maintain strength as the edge gets farther away from the rim bed. This suggests that, for aluminium, we are somewhere close to the limit for width vs strength vs weight compromises.
This is where carbon starts to make more sense from a material perspective. As Ibis has shown with their 741/941 and 742/942 rims. At 25mm widths, the weight advantage of a strong carbon rim is not that great, but for these wider profiles, they start to make much more sense, creating rims at weights that are not currently possible with today's aluminium technology.
Next up are tire dimensions. The front wheels were mounted with a 2.35" Magic Mary tire and inflated to 30psi, using a Schwalbe digital pressure gauge. One measurement was taken edge-to-edge at the widest point of the tread, the other measurement was of the casing at its widest point.
What is immediately clear, is that the tread-width is more or less constant and any variation within those numbers could be explained by production variances. It is the tread profile and the volume of the casing that changes as the rim's width increases. Inflating the tires in ascending order with a regular pump, it was noticeable how much more air it took to inflate the tire on the wider rims. The most significant measurement here is that the 40mm rim appears to offer little additional volume compared to the 35mm rim, indicating that the 40mm width is either at or past the limit of a 2.35" tire - which is what I expected in this case.
The four widths 25-40mm, clockwise from the top left. It is hard to really show the curvature of the carcass in a photo like this, but hopefully you can start to see the effects of the wider rims.
So, what about the height of the tire? A quick comparison shows that rim width does not significantly affect the overall height of the tire when mounted. I found only a few millimeters difference between the 25mm rim combination and the 40mm rim combination - which could be explained by production variance and it does not appear to be significant enough to have any impact when riding.
The plan for riding was to start by doing two runs on each width, progressing from narrowest to widest. The idea being, to see a gradual progression through the widths. Taking some advice from the lift attendant, I chose the blue run
(imaginatively called "La Bleue") for my testing - it has very little woodwork and no features I wouldn't fancy hitting on a little bike, but offers more challenge than the green runs.
With low clouds hanging over the station most of the day, the trails were in pretty prime condition - a little slippery in the morning from the humidity. For each run, I tried to ride at a consistent pace, not easing off too much, but not pushing too hard either. Partly, because the bike felt very close to the edge and I didn't want to crash and lose a day of testing and partly, so I could see if I could put as much of the difference as possible down to the rim width. Each time I mounted each set of wheels to the bike, I checked the tire pressures with a Schwalbe pressure gauge to ensure the front was always at 23psi and the rear, at 28psi (with a margin of variation of +/-0.3psi). Discounting the 40mm Width
Before we get into the meat of the comparison, we need to get the 40mm rim out of the way. Its inclusion was primarily to provide an example of where rim width went too far and it did just that. The volume of the tire made for a pleasant ride, but it was hard to feel any benefit in comparison to the 35mm rim. The flatter angle of the edging tread was very apparent - providing much less grip, and the tire had no bite when I tried to lean in on it. Factor in that the 40mm rim weighs about 100g more than the 35mm rim and it provides a very clear marker that there comes a point where going wider starts to detract from the performance with a given tire. After a single run, it was very apparent that the 40mm was not worth investigating further.Establishing the Order
For the first two runs of the day, I ran with the 25mm rim, then two runs on the 30mm, then two on 35mm (and one on the 40mm as per above). Once I had finished a full set, I returned to the 25mm to verify if the performance changes of the increased rim widths were due to the track drying slightly and learning the lines. I then alternated between the 30mm and the 35mm rims for the afternoon to try and validate which I preferred and why. 25mm Report:
The 25mm rim made the overall rear tyre profile feel very round - that its footprint did not have a stable connection with the ground beneath. That meant that when it was hunting for grip on rock or roots it always felt a little skittish like it wanted to slip out from under you. Laying the bike on its side the feel was not positive, it found some grip, but was a little indistinct and never felt safe enough to push in on. This feel tallies up with the side profile of the carcass - it has something of a bell shape to the sidewall, which allows for a higher level of deformation at the tyre is compressed, giving a vague feel when you leant on the side of the tyre. 30mm Report:
Moving up to the 30mm rim, the bike immediately felt more stable, more composed. The best way to describe the change is that the contact patch felt much flatter and with a much more positive connection to the ground, there was a definite feeling that it was trying to slide away less often. On the roots and rocks, this translated to a more planted feel that meant you could push a little harder than before. It is not a huge difference, but it is certainly noticeable. The combination of the straighter sidewall profile, that is less prone to deformation, and the sharp, outwards angles of the side tread, meant that when you wanted to dig the side into the dirt, it provided a very definite, positive feel that translated into more confidence to turn the bike hard. On one of the long off-cambers, you could tip the bike onto the side tread and hold a noticeable tighter line than on the 25mm rim. 35mm Report:
The next step was the 35mm rim. The difference in terms of contact patch was less pronounced compared to the jump between 25mm and 30mm, it is a much more subtle difference. It felt a little more stable again and made it easier to push harder still, but it was subtle. You could feel that change, but the profile of the sidewall is still pretty straight, so despite the loss of outright bite there was still a very positive feel to the combination, it offered maybe the best support/contact patch of the test. There was some small trade-off in the side tread, the outer tread profile was less pronounced than the 30mm and on the off-cambers I had to back off slightly compared to the 30mm combination, but less so than on 25mm.The Clock Doesn't Lie
I did not put too much emphasis on the timing. In such a small scope of testing, the numbers are always going to be somewhat unreliable, but a quick scan of the results is interesting:
The most interesting time here is the third run on the 25mm rim. Through the morning the times got faster, so it is easy to discount my first runs on the 25mm rim as getting up to speed, but for the third run, the times show that I had settled into a consistent pace and had slowed noticeably on the narrower rim - 7 seconds faster than my best time on a 3 minute downhill is notable - more so when taken in conjunction with my riding impressions, that the 25mm rim was my least favourite of the lot. The other area worth noting is the consistency of times between the 30mm and 35mm rim - much of the conventional wisdom suggests that a 2.35 tire on a 35mm rim is a less than ideal combination, but in terms of times and feel, it is hard to separate the two - it follows that wisdom in losing some side bite, but the profile of the carcass is better. Disclosures
Just so we are explicit here - this is not a definitive test. To assemble enough data to make clear statements, such as "Xmm is Y seconds slower than Zmm," we would need a much larger, more rigorous test, using multiple riders over a greater number of trial runs. This test was designed to give a little insight and hold the perceived wisdom that "wider rims are better" to some measurable scrutiny.
This test only looks at one tire and rim combination to keep the scope of the comparisons manageable. I have no doubt that throwing another type of tire into the mix would produce different results. For instance, is the fact that 35mm rim felt good because of the extra volume and the change in casing profile, or is it related to one specific Schwalbe tire? I cannot answer that for you. There may also be further performance benefits to be had from exploring tire pressures in conjunction with each rim width combination, but I kept the same pressures in the name of keeping things manageable.The Verdict:
By this point, it should be fairly clear that I feel there is a real advantage in going for a wider rim, and that is based on three factors: carcass profile, tread profile and overall volume. As with most tests, I have come away from this effort with more questions than I started with. I would like to know more about the subtleties between 30mm and 35mm rims. They both felt good, but for slightly different reasons, and I would like to break those reasons down to fully understand the matter. For instance: is there a sweet spot between the two? For 2.35" Schwalbe tires, would changing the width to either 31mm or 33mm produce a measurable benefit?
Then there are the obvious questions about how generally applicable this all is. This is where we, as consumers, need more information from bike manufacturers. Surely every tyre should come with a recommended rim width? In terms of outright performance, it would be interesting to see more wheel/tire systems that are designed in combination to work together perfectly. Also, the 35mm rim makes me want to know if the conventional wisdom that you need a larger tire for a rim that wide is right. If the carcass and overall volume feel good, would it not be possible to re-work a 2.35 tyre's tread to suit?
Maxxis has started down this road with their excellent WT models and Mavic tried to produce systems as far back as 2012, but their combination of poor tyres and a super-skinny rims at the rear were not a winner. With weight as an ever-present concern for wheels, the 35mm rim is a little heavier compared to a 25 or 30mm rim, but the combination is still lighter than anything with a larger 2.5 or 2.6 tire. If we could realistically hope for advances in production technology to reduce even 20 to 30 grams from the rims in the coming years, then we would be looking at a combination that offers useful benefits, compared to what most of us are running now, with increased volume, improved tyre profile and reduced overall weight.
If your question is: "My current rims are narrower, should I upgrade them?" In honesty, I would have to say no. If you are used to riding your current rims, why worry? Unless you have the chance to ride wider rims, you'll never know their benefits. In terms of outright performance, good geometry, suspension, and brakes are always more important. But... would I ever buy a narrower rim for my bikes again? Never. When it is time for me to replace a rim, wheelset, or even a bike, then I will definitely prioritize a 30mm+ rim as one of the things I must have.