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 My 25mm internal width wheels had been replaced by burly-looking Ibis 741s with a full 35mm internal width that my wife had left over from her race season.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.
| DT Swiss XM 1501 wheels 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. |
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.
About the Test Bike 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.
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.
Riding Conditions 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?
Rim Width
25mm
30mm
35mm
40mm
Claimed Weight
736g
786g
840g
890g
Real Weight
743g
799g
830g
914g
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.
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.
How Rim-Width Affects Tire Profile 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.
Pressure
30.3psi
30.2psi
30.3psi
30.3psi
Casing Width
60.4mm
61.5mm
65.2mm
65.5mm
Tread Width
58.9mm
59.0mm
60.5mm
59.1mm
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.
| 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 on a 3 minute downhill is notable... |
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.
| Would I ever buy a narrower rim for my bikes again? Never. |
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.
But I have one concern (professional deformation):
the test would be much more relevant if you did not know the rim width you are on,
we call it a blind test. I know in real world it is difficult to perform, you would need to
erase any information on the rim and someone else would have to set up the bike and
hand it over to you, etc.
But never underestimate the placebo effect. If you like wider rims, and you know you are on
them, chances are you will perform better.
When I got back on my old wheels Easton XC90 (19 internal) it was WHACK.
Shockingly different. For the worse.
Also, for a more accurate compare, in my opinion, you should consider excluding results from the morning as the track consistency was changing and you were becoming familiar with the run, as evident in your afternoon lap on the 25mm. None of these results are statistically significant, but I really appreciate your approach and detailed analysis. Please keep doing these.
I'd say your setup for this was informative, and you were pretty clear about the methodology (and its limitations). Good on ya, and a good read.
Similar bias seems to show up in the analysis of the timed runs. You exclude data points after looking at the results instead of relying on an independent analysis. And cherry pick the largest observed difference to make your point, something a statistician would never do ...
Having said that, great effort!
Instead of timing the whole run, perhaps you should time very specific sections? This reduces the variables and error. For example time an uphill section, downhill, berm, rocky uphill, rocky downhill, etc... Take the same line every time. Record the watts used through the timed section and entrance speed, then calibrate the times on how many watts and your entrance speed. Try to keep the same body position and effort through the timed sections. Consult a statistician for how many trials you will need (it depends on the variability of times).
but the bikerwebs told me wider is better... who the hell are you to challenge the new status quo?
everybody knows you can't have fun, roll with the endurobros, or win races on a "normalish" setup like EX471s (i25) and 2.4s!
#gwinning
But i would agree that if a bike feels more stable or more sure footed it gives you confidence to go faster. thus better times. but hey my stock wheels have crappy spoke nipples that break and frustrate me and bad seals around the bearings. Maybe if i order new ones ill go for something wider. But 35-40mm seems excessive to me.
It's great to read and spot on!
Despite that i think you actualy missed by tring to be as true as possible, and maintaining "lab like" wheel conditions with the same presure.
I would very much rather understand what rim width would be best with your preferred settings for each width.
Conditions that will make rim use for a tester as close to "best" as possible.
After testing in these conditions, a conclusion would be more true and usefull for the masses.
thanks.
But at a larger scale, Pinkbike could encourage its testers to get together and with proper planning these tests would be much more relevant.
Think this does a better job of explaining the ideal relationship between tyre size and rim width.
And as someone else said (in coarse terms and down voted into oblivion), bigger tyres for wider rims.
www.notubes.com/technology/wide-right
Like long top tubes, wide rims are nothing new. Stuff was around in the 90's.
Agreed tyre stiffness is a more dominant effect.
yeah but we want to open that can... time to start drafting up a follow-up article!
thanks for the article!
I’d like to see a new test with different tire widths as well.
But the most used rim in DH and EWS is still the good old EX471...
Have it too .. with WT tires on it.. am I a sinner now?
Here's his race run for reference. Leogang 2014 on the 471
youtu.be/PUoCSzVmhhQ
Looking at your youtube movie... there are no dents to spot in the rim... after the whole DH track... your story is BS...
If you're in the market for a new set of wheels AND you want to experiment with a variety of tire widths, it's hard to go wrong with 30-35mm. You can pretty much run anything from 2.3-2.8" wide (with varying degrees of success, of course).
Cheers!
In verdict it's about 30 & 35. So, you saying your wife need different sizes? )
I'm still on 25.5mm rims and am running various 2.3", 2.4" and 2.5" WT Maxxis tyres. They're all a good shape on that width. The Minion SS 2.3 would definitely be too square on even a 30mm. The DHR2 2.4 WT is surprisingly square on the 25.5 rim and I wonder how it would be on the 35mm it's allegedly designed for? The DHF 2.5 WT and Shorty 2.5 WT would be squarer on a wider rim but they're certainly not too round on the narrower rim.
Now, I'm off for a 50 mile xc loop on my Magic Mary's ;-)
Thx for clarifying your point though!
I think an important point that needs to be made is that even XC racers who run lower pressures still don’t have their (relatively tiny) corner knobs dragging on the straights.
From being at recent DH world cups, an EWS and the Megavalanche I'd have to say that the fast guys are not in line with your findings. Non-scientific observations seems to suggest that the top 10 guys all run rims of +/- around a 27mm average.
And pretty much all run either 2.35 Schwalbe or 2.4/2.5 Maxxis tyres. Absolutely none that I've seen race with 2.6 or bigger
it could so easily have been a blind test with random wheels being used (installed my a separate person)
That'd be nice for this I guess.
Candidly I don't really care...my buddies and I have always ridden and raced what we liked, and when in doubt just followed suit with any top pro who we could relate to style wise. Not scientific, but has worked fine for me.
Never liked wide rims, but I run DH casings on all my bikes, so probably helps a lot with EXO
It’s hard to take any test or review that a journalist does seriously!
Plus-sized tyres are another
But to your point of skill level, this kind of a test (if it yielded sound results) would be great for a website catering to riders of all levels. What tire/rim combination can help the average rider corner better and go faster with fewer flats?
A while ago RC said he knows of nobody who has tried wide rims and gone back and now the same sentiment from MW. Well RC don’t know me but I’ve done just that. I tried it, it sucked. Then I tried 25mm and a 2.5” DH casing and it didn’t suck.
Just a suggestion.
To follow that logic through, every test and review is fallible in that respect. "Am I right?" is maybe not the ideal starting point, but then conversely, if I had been running 25mm rims these past years, would that not also affect the outcome? To have someone test utterly without preconceptions, they would need to have never ridden a mountain bike before (or read Pinkbike), but then obviously they wouldn't understand enough to waffle on about it for 4,000 (hopefully meaningful) words.
There are also a number of practical problems with blind testing - first logistics. You need a support crew to do that, which I don't have normally, this test was me, a pump, a pressure gauge and a boot full of wheels and tyres. That is solvable, but it creates a lot more work and I am a freelancer who has to juggle a bunch of commitments to make my living. Second, how blind is blind? For instance, if we're being ultra-precise here, if I look down at my wheel before the run I should be able to see the profile and figure out the combination, would that invalidate the test? You cannot ride without seeing the overall profile of your front tyre. The only way you could do a truly blind test would be to ride blind(folded?).
That said, I do agree that a blind test would be better and it was something I was originally trying to do, but life, etc got in the way as I was originally hoping DT would come down to me for the test.
I like what you did to be honest, and I see where you are going with logistical aspects. To a certain extent I can see that a rider may be able to look down at their wheel and have an idea what size rim the tire was running, so how to pulling off a proper blind test may prove to be challenging.
Just wanted to put that as a suggestion if in the future you were able to get the resources (crew) and method I would be very interested in the results.
My own confirmation bias is that 25mm rims with 2.35" tires is pretty good (that's what I'm running and why I'm biased) but if someone offered me a free set of 30mm rims to run my tires on, I wouldn't say no
Other interesting thing : Clementz, Vouilloz and Dailly often run narrower rims back to obtain a rounder profile and reduce rolling resistance.
There are a few things to pick apart there. Firstly, I haven't seen Nico or Adrien do it, but I might be wrong. Clementz pushed Mavic in that direction and a lot of the guys around him in Northern France/the Vosges do run that setup, I have seen it less here in the South. I know Barel doesn't go in for it out of choice. Rolling resistance is a non-argument, I know DT have done testing with the Swiss national team and claim to have proven that 30mm is preferable (I haven't seen the data to verify that, but I trust the people I know at DT when they tell me that) - Florian Vogel did much of the testing and now runs 30mm XMC1200s at WC XCO based on that data and I know Nino was part of that test too. As for weight, I personally don't see what 30g will gain you. Maybe some of those guys like the profile, I can't say, but I personally don't like having mismatched feel from front to rear, and I don't like the rounder profile of the 25mm rim.
After that I went ProCore and never looked back. ProCore also provides so much support in a 25mm rim (which is what I run a lot of the time now) with a 2.35" tire that I think it completely negates the stability advantage of wider rims. At that point it just comes down to what tire profile works best for you with the tire you are using.
2,3" rear from MAXXIS or 2,25" from onza on 24mm rim. I switched to 30 mm and almost instantly hat flat's. Ripped the flanges open in no time. My home trails have no single flow trail. Only rock's and deep roots.
Switched to onza 2,4" with same thread and no flat's also instant. Conclusion is simple that there is a balance.
I will install a new minion semi slick today with 2,3" because there is no Enduro version of it with a wider thread. I don't think it will work for long time.
You should compensate in pressure due to the larger volume, as you explained here "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".
But why would you say that tires mounted on wider rims would be "harder" at equal pressure?
The outward "stress" on the casing is what supports the load, which means a larger air chamber (wide rim) at the same pressure as a smaller (narrow rim), will be harder, in fact stressing the rim harder as well. For equal load on rim and surface it has to be compensated by calculating the difference in volume. Basically, you equalize the hoop stress so it's the same for both rim widths, en.wikipedia.org/wiki/Cylinder_stress
Take a tire with, say, 10L of volume at 20psi, and press it against the ground with a force of 100lbs. If you trace the contact patch, it will be 5 square inches (assuming a very soft casing).
Now take a tire with 100L of volume at 20psi, and press it against the ground with a force of 100lbs. You will have the same 5 square inches of contact, even though the volume is ten times as large.
To me, that means they are exactly the same "hardness" -- they compress exactly the same amount.
I don't think anyone can deny that a lower volume tyre feels softer than a higher volume tyre at the same pressure. I've never understood the comments that a higher volume tyre 'allows' you to run lower pressure, as some sort of advantage, I HAVE to run lower pressure to get a higher volume tyre to perform and therefore the advantage of a higher volume tyre has little to do with a lower pressure, n'est-ce pas?
@JohanG: Exactly, this "nullifies" the test pretty much, at least a dummy with different pressure should be used. As mountainbikers, we all SHOULD know that tire pressure is far more important than rim width...
One could argue that the formation of the contact patch actually decreases the internal volume (I'm not sure if or how much that's the case, but it's reasonable), and thereby increases the internal pressure. In that case, it would be safe to assume the lower-volume tire pressure would actually increase MORE for a given load, resulting in a HARDER feel than the large-volume tire at the same initial pressure!
It still seems like you are interested in looking at the hoop stresses, or the "casing tension", as @JohanG notes -- but I maintain that that does not translate into tire "hardness", as hardness is going to a perception of force perpendicular to the hoop stress.
I could see your interpretation if you picture the tire as a sheet of rubber held between two rigid grips: with a low tension, it will feel 'softer' than if it is under high tension. However, in the case of a real tire, the rigid grips aren't there; the casing is able to deform and adjust it's shape in order to minimize the internal pressure of the tire.
Exactly. I'm interested to know what would happen if a 2.8" or 3" tire's tread was put on a 2.5" casing, then mounted on a 40 mm or 50 mm rim. Might be a disaster or it might be the only way to get a wide footprint with a light casing that doesn't suffer lateral collapse.
Giggles) like a moto tyre.
DT Swiss ex 471 is THE best rim for your $€£¥.
2.6 tires -> 35mm rims
Industry trend for 2019: 2.6 tires on 30mm rims
However, since most riders suffer dents on their rear wheel prioritising increased stability over rim width here seems reasonable especially since gains in sidewall stiffness are better felt on the front wheel when cornering hard and most riders run the rear tire at a higher air pressure anyway, further marginalising any theoretical advantages of a wider rim.
Width vs. Stability
A 30mm wide DT EX511 enduro/DH rim has the same weight as a 35mm wide DT XM521 allmountain rim but is far more robust. A narrower rim also makes the tire rounder, reducing rolling resistance and sidewall exposure.
POLE and Mavic seem to prefer not so wide rims (see polebicycles.com/the-tipping-point). On the other hand, the IBIS rims with 36mm inner width get praise and Santa Cruz just brought out a 37mm.
The sidewall is just too far out, and taking too much abuse when under hard cornering.
I'm starting to see the sealant weeping through the fabric around the base of the edge knobs, and around the flat of the sidewall after only 6months use.
(and thats on the Heavy duty "Ebike" Nobby Nic)
However Inconclusive.
Moral of the story:
Run what your bike came with OE.
When buying aftermarket,
buy what suits your Budget,
(ie: what's on sale @ CRC)
Unless you're a Dentist.
How did U guess that?
My favourite 3 items on pizza
Bacon Bacon & Bacon
This is why enduro/DH pros run rims in the 26-27mm range, even with Maxxis WT tires. They are lighter and also less likely to cut a tire/get damaged than rims in the 30-35mm range, yet they ride the same.
Rim width has a significant effect on tire profile (roundness vs. squareness) which influences tire performance massively. It’s why Maxxis came up with Wide Trail (so that for 35mm rims, it’s not too square). Narrower rims make tires roll on center tread more, and thus corner knobs aren’t routinely touching ground on flat trail (i.e. liaisons). This reduces straight line grip (braking, pedaling), but allows the bike to be leaned more to engage corner knobs. This helps for when the tire is too square yet desired lean angle is too far and would overwhelm a square tire profile corner knob. Leaning a square tire into a corner “just a little” gets on the corner knobs, but since the tire circumference at the corner knobs isn’t significantly smaller, the bike doesn’t want to corner so much as a result, and more steering input is required; leaning further actually goes past the knob grip and you slide out. By contrast, a round profile tire wants to turn just by leaning the bike because of the reduced circumference. The key is to match desired lean angle with optimal corner knob placement and angle, which is accomplished with rounder tires (i.e. Magic Mary, Minion). Square tires, by contrast, don’t “want” to corner, and then before you know it, slide out. They do work better for trails where there is less cornering and more grip is desired.
This absence of cornering ability with square tires/wide rims doesn’t get noticed by some riders for a couple reasons:
One, some people don’t really feel comfortable leaning a bike far enough that a round tire profile necessitates, and thus express a preference for squares tires (or WIDE rims) without knowing why, but is because they don’t lean enough (confidence, skill). This can often be felt as a sensation that square tires corner better for such relatively upright riders.
Two, some/many don’t care about the increased straight line speed afforded by a rounded tire rolling on center knobs only. This can also be perceived as having a preference for improved straightline braking. But people putting in miles, and against the clock, notice this advantage.
I certainly can’t speak for pros, but I imagine it’s their commitment to leaning bikes in corners which means they benefit from round profile tires, affording them better straightline speed, rolling efficiency, and of course cornering, all made possible by attaining rounder profile tires via narrower rims (which just so happen to sometimes be lighter, too).
Faster, more grip ..... More positive aspects than imagined.
But: I rode the same track for years and never managed to dent the rim. I am putting a new dent in the AR30 on nearly every second run.
They have to make those rims more durable. I think I will need new rims this summer and going to try the Newmen Rims. They do offer a different geometry and are said to be tougher.
I tend to float between 2.35 when I have to pedal, and 2.5 if I'm shuttling, with stickier rubber. Going faster usually has more to do with me staying off the brakes than anything on my bike!
That set up sees me through bike park days and big days in the hills.
Equally I run a hans dampf on the front at 26 psi.
Would you get more grip from lower presures?
In order to truly leverage a wide rim you need a tire that was designed for it. The author decided to use 2.35 tires which are not optimized for rim widths over 30mm. A 2.6 tires has roughly the same width but a much better shape on a wider rim since it was designed for it.
I also want to know opinions of WC DH folks. I see a whole lot of DT EX471 wheels being run, which have a 25mm internal width, on WC DH tracks. What is drawing those insanely fast riders to the opposite side of the width spectrum? Is it that they run big DH casings and can rely more on that for support in corners?
Great article and experiment, though, I love this kind of content.
I love the article but having been trying all these widths and also these tyres I can see clearly how it comes down to feel, not the clocl. I can easily settle for 30mm it does offer better support in smooth corners, but it is sounter productive in bumpy turns since there is less tyre displacement thus less “sideways suspension”. I talked to two World Cup riders about it, they did prefer 25-30mm range. Feel, let’s leave the clock out of this
I plan on trying out a set of 2.6 Forekasters as my next tire. I think a 35mm internal width rim would be ideal for a 2.6 tire.
Seems like tire size preference is related to the trails we frequently ride. My friends in Minnesota don't run anything larger than 2.3 tires while my friends in Boulder City don't run anything smaller than a 2.5 tire. Most people at Bootleg are running 2.6 and larger.
i25mm rim for 2.3" tire or less.
i30mm rim for 2.3"-2.5" tires.
i35mm rim for 2.5" - 2.8" tires.
Maxxis WT 2.4/2.5" tires are designed for i30-i35mm rims.
Their older tires always measured narrower, but the new Maxxis tire sizes are true to size.
A friend tried the wide rims and noticed a big change to the rolling resistance, not for the better!
Went back to the medium wide rims. Your narrow.
The caveat of different tires creating different results is in part true but if we take the average tyre as being a Schwalbe 2.35 or Maxis 2.4/2.5 wt which are about the same caracas width, then I think the analysis holds true. Run narrow tyres then they will square off on narrower rims obviously.
schwalbe make the widest tyres on the market. to give you an idea.... a 2.35 magic mary is slightly wider profile than a wt 2.5 maxxis minion! i would never try a 2.35 maxxis on a rim that wide but the schwalbe is fine.
i went from 29mm internal to 35mm internal using the same 2.35 magic mary and feel the cornering is just as good but you notice the more volume with the bigger rim. the extra width also helps keep the sidewall in place at hard cornering. my 29mm i could not run any lower than 23psi otherwise the tyres would deform. not so with the 35mm internals.
I agree that upgrading to wider rims just to do so is not necessary but if you find yourself in a position that you need to, you should. And I also agree all my future bikes will have wider stock rims on them. For what it's worth I'm 5' 10" 210 pounds.
Personally, I've settled on 35mm carbon NOX Farlows. Night and day compared to 25mm AL wheels. Apples to oranges, perhaps, but a huge difference in grip and precision. It also allowed me to run 2.5 WT DHR/Agressor combo that is rock solid on 95% of terrain.
How about a control day in your experiment repeating the test in reversed rim order or with one rim next day with hopefully same weather conditions?
You always have to have a control group in an experiment!
Oh yes, i had some fun with the SYNTACE graphic too...
Isn't That Green tire is way bigger than the red one?
What if i put the red tire on the wider rim?
www.pinkbike.com/photo/16105672
oha, doesn't fit? makes things even worth? or is it all just artistic freedom?
I guess what i want to say anyway graphics like that are fun... anyone can draw up whatever story they want to tell/sell... you did a really great test, argued very reasonable and logic.... but that marketing graphic to start out with really set the wrong tone and doesn't do the article justice at all...
tl;dr: I'm impressed if people can objectively assess how far they're tilting their bikes in corners and what their tires are doing exactly. Unless you're already sliding, you probably can't consistently tilt them much further than as shown in the second picture from the top.
The Syntace graphic gives a distorted view. If you have a longer sidewall, you will have to increase internal pressure to prevent side-roll with the wider rim. A fatter tire on a narrower rim at the same pressure wouldn't roll as much, until you reach the bead's breaking-point. You can be too wide of tire for a rim. For a standard 25mm rim, that limit is about 2.4 inches. In halcyon days of 17mm rims, the 2.2 inch tire was pretty much the limit, with 1.95 to 2.1 being the sweet spot.
Wider doesn't make you faster - it just creates "new" standards for the marketing guys.
I am glad you tested the 2.35" Magic Mary's because these are my favorite tires. I have used the Super Gravity's Soft 2.35" on 27.5mm, 30mm and 35mm ID rims without issues. I myself do NOT notice much of a difference at all between the 3 widths, but if I had to nitpick, I am going to say the same as you and say 30mm ID is the best for the 2.35 Magic Mary's. I ride mostly Bootleg Canyon and run all 2.35" MM at 25psi regardless of rim width, because any less than that I will slice the tire on the sidewalls if I go lower than 25psi (The Rocks here are sharp like Coral Reef). FYI: I just Mullted my Furious by using a 2.35" 29er Magic Mary, and this new MM tire only measures 2.28" on a a DT FR560 (30mm) Rim! All my previous 2.35" MM measured 2.35" or more regardless of Rim Size.
* Two points of observation:
1.) A more scientific approach using a time record GPS based device that allows you to do a track overlay or a at least a recorded time vs. top speed, max/min g-forces, acceleration, etc. I am sure the manufactures would likewise loan a unit out for testing in exchange for advertising mention.
2.) The 40mm should be equal in testing iterations, as removing it (regardless of reason) yields a skewed test.
Again, thank you for the time and energy to setup this test. Looking forward to future articles from you.
Awesome! More please. This and your frame geo musings are currently the most interesting reads on PB
www.pinkbike.com/news/26-vs-275-vs-29-Wheels.html
Wider rims are made for WIDER TIRES!
Why would you buy a 35 or 40mm set of hoops to run a 2.35" tire that was designed to run on 10mm narrower rims?
You step up to wider rims so you can run wider tires(2,6-2.8-3.0"), which DO give you more traction.
Is this dude that fricken lost?
And some official manufactures guidelines of tire size / rim width. Probably still online somewhere. However back then nobody run low pressures fat/plus bike style and everything was finalized to racing.
Nowdays such a guideline would be way more complicated because there are way more riding styles, dh, trail, xc, adventure (?) etc...
But overall a balloned tyre is a no-no. 40 internal rim with 2.4 tire same thing, unless you just ride straight.