The new normal: the current thinking behind wide road wheel design
It was only just a handful of years ago that 15mm was considered an optimal width for everyday road wheels, narrow enough to slice through the air, light enough to feel faster on the climbs, and a suitably broad foundation for the 23mm-wide tires commonly used at the time. Today, most modern high-performance road wheels now measure around 20mm — an increase of just 5mm, but a whopping 33%. What's the thinking behind this rapid change? U.S. technical editor James Huang takes a look at the upsides and downsides of this now-common trend.
Why wide?
While the burgeoning dirt, gravel, and adventure riding segments have certainly directed newfound attention to road tire and rim widths, the "wider is better" movement started well before heading off-pavement became popular. I still remember vividly the first time I rode a set HED's original Ardennes aluminum clinchers in 2008, which used a then-revolutionary 17.3mm of space in between the bead hooks (13-15mm was more common). When paired with my usual 23mm-wide Continental Grand Prix clinchers, the actual measured tire width was more like 26mm, with no additional weight as compared to a more conventional 15mm-wide wheelset.
A few millimeters may seem insignificant on paper, but the effect those wider rims had on performance and ride quality was eye opening. Broadening the base of the rim not only effectively widens the tire, but it also changes its profile to one that's shaped more like a "U" than a "C". As a result, you not only get more air volume for the same tire size, but also less casing deformation under load at at a given inflation pressure, and a larger-radius curvature on the tread cap.
These are identical 23mm-wide Bontrager tires, but the one on the right is mounted on a rim with a 15mm internal width, and the other is mounted on a rim with a 20mm width. The one on the right has an actual width of 22.5mm; the other one plumps up to 25mm.
Pacenti's new Brevet rim updates the classic box-section aluminum rim with a wider profile. Note that it's important to draw the distinction between a rim's internal width vs. its external width. Internal width determines the shape of the tire profile when inflated, while external width is more critical when discussing aerodynamics. Photo: Pacenti Cycle Design.
Wider tires aren't just the tools of amateur roadies. Even top professional road racers such as Peter Sagan regularly use 25mm treads, something unheard of just a few years ago.
On the road, that all equates to a faster roll, a more subdued and smoother ride quality, and noticeably improved cornering grip with a more confident feel at the limit as well.
"Our first mockups of the C2 Jets were a 2,200g wheelset made on touring rims," said HED's "Repository of Knowledge," Andy Tetmeyer. "Even on those klunky mockups, we knew after one ride that 19mm [external width] rims were going to fade away. I made those first wheels and rode them before anyone else in the shop, so I can't give unbiased view here, but it is honest to say that skinny rims still have lower frontal area and can be lighter than modern wide wheels. Do those two things add up to any advantage? At less than 2.5-degrees yaw and on a perfect surface, they probably still have an edge to wider wheels. In practical terms that means that riders could stick to 19mm rims and tires for indoor track riding. For any other venue, we don't see a reason to ever ride narrow rims and tires. We don't see any aero difference once the wind comes off zero degrees (and the difference is small even at zero). Rolling resistance is lower with wider tires. Cornering grip is greatly improved. Ride comfort is greatly increased."
HED wasn't first to introduce a road wheelset with a wide tire bed; American Classic beat HED to the punch by a few years with the original Hurricane in 2005. Riders were more willing to accept the idea of a wider wheel when the original Ardennes was launched in 2008, though, so HED is often credited with sparking the movement on a larger scale.
In fairness, HED wasn't the first to bring a wide road wheel to the market — American Classic's original Hurricane beat it to the punch in 2005 with its 18mm-wide rim — but most credit the Ardennes as the first to more widely popularize the concept.
"Wide rims mean riding lighter, smaller performance tires with cushiony, high air volume and firm surface grip," added American Classic president Bill Shook. "Larger width tires offer more air volume, but they are heavy with a sluggish ride quality. The desired combined wheel-and-tire qualities are achieved by stretching out the smaller tire casing on a wide rim and effectively making the tire bigger. Also, smaller tires on wide rims reduce tire roll on the rims. With a narrow rim and a wide tire, the rim floats from side to side on the tire. Using a wider rim with a smaller tire minimizes float for improved handling, confidence and control. The rim is lower weight at the extreme outer edge of the wheel decreasing rolling resistance and boosting speed."
Regardless of which wheel manufacturer was first to market with wider rims, nearly every other brand has since followed suit. HED's newer Ardennes Plus range now features an internal rim width that hovers around 21mm, and that figure is now no longer revolutionary; it's almost the norm. Many newer companies, unburdened by the legacy of decades of existing road wheel designs, have skipped over the old traditional rim widths entirely in favor of the more progressive dimensions.
Although HED is largely credited with spawning the wide-rim movement, American Classic beat HED to the punch by a few years with the original Hurricane, which was shown in 2005 with an 18mm-wide rim. All of American Classic's current range, such as the 420 Aero 3, adhere to the wide-rim philosophy.
"Going wider makes the tire take on a better shape for better handling," according to Boyd Johnson of Boyd Cycling. "It allows you to use a wider tire and not have a lightbulb shape (picture a 28mm tire on a 13mm rim). It also helps with aerodynamics in the higher yaw range, and allows you to use the wheel for multiple purposes. The same wheel you are using in a crit can be used for gravel or cyclocross."
Naturally, it behooves companies that sell complete wheelsets to stay on top of the latest trends, so skeptics could dismiss all of this as merely brands wanting to find new ways to sell more product. Custom wheel builders, on the other hand, merely have to respond to whatever it is that their clients request — and they're also seeing more orders for wider road wheels.
Smaller wheel companies, such as Boyd Cycling, have been quicker to adapt to the trend of wider rim profiles.
"We have seen online sales trending toward 25-28mm for road applications," said Richard Sawiris of Wheelbuilder.com. "The sweet spot on internal width to go between road and CX or gravel-type tires has been around 25mm. What has been popular are the multi-use road/gravel/CX/sometimes XC 29er rims. Carbon XC rims and some of the XC aluminum MTB rims that can handle slightly higher pressures offer a great solution for now, but manufacturers are quickly working on wider section road-specific profiles."
The challenges of going bigger
Few people will argue the notion that a wider tire can offer a better ride quality, more grip — and yes, less rolling resistance — than a narrower one. That old saying still applies, though — you can't get something for nothing. In the case of wider rims and tires, one of the biggest downsides of that extra girth is the extra weight that comes with it.
"Generally, yes, the wider the rim, the more material that is required, and therefore increased weight to contend with," said Mike Bush of Stan's NoTubes. "Weight is one thing that many of us like to obsess over because it's a nice number you can look at. However, the best all-around wheels for a particular rider aren't necessarily the lightest."
Stan's NoTubes went wide straight out of the gate with its first carbon clincher, the Avion Pro.
Alex Applegate, from Bontrager, agreed. "Weight is a really nice stat when you're looking at a product on a website, but there are other factors that are more important to the overall ride experience. Aerodynamics, compliance, and rolling resistance will have a dominant effect on speed and experience over weight — provided that we're talking differences in grams, and not kilos. Add to that the ability of modern design, engineering, and production to make things stronger and lighter while also making them wider and you can see us getting ever closer to the best of all worlds."
Increasingly clever rim and wheel designs are helping to decrease that weight gain, or even eliminate it completely. For example, wider rim profiles can be built with thinner walls while maintaining the same stiffness characteristics as narrower rims.
Bontrager's Aeolus D3 range of aero wheels are all built around 20mm inner widths.
"We believe that weight is still critical to performance," said Specialized global PR manager Sean Estes, in reference to the company's Roval range of wheelsets. "The real challenge is to make wheels and rims that are light, but have the modern technology or features that improve the performance in other areas as well. With carbon rims, even though they have gotten wider, we've been able to maintain or even improve our rim weights through a combination of better materials, engineering design, and improved manufacturing capabilities. A great example of this is our CLX 32, which is about 150 grams per set on average lighter than the CLX 40 it replaces. Even though the rim profile is 8mm shallower, due to the increased width and enhanced overall shaping, the CLX 32 performs better in the wind tunnel than the CLX 40. It also performs better than most 50-60 mm-deep rims on the market."
While weight is seemingly always in the background of every performance-minded rider when it comes to equipment choices, aerodynamic efficiency has become more important in recent years, especially as it's already been shown to have a more significant impact on speed than weight on all but the steepest grades. Even here, though, companies have figured out how to provide wider tire beds while still posting good numbers in the wind tunnel.
Once considered merely a house wheel brand for Specialized, Roval has now rightfully earned a spot among other premium options for road wheels. The aero-profile CLX 64 carbon clinchers use a 20.7mm internal width and 29.9mm external width to match with higher-volume rubber.
"The big tradeoff is tire performance vs. aero performance," said Zipp's PR content manager, Dan Lee. "Our wind-tunnel testing shows that matching tire width to rim width is crucial for optimal aero performance for a given width of rim."
Now more than ever, wheels and tires are engineered as matched pairs, with the former designed with specific sizes of the latter in mind. As tires grow wider, so, too, does the rim cross-section to match.
Case in point is Enve's new SES 4.5AR Disc, which is perhaps the first high-end aero option specifically made with bigger tires in mind. The tubeless clincher version features a gargantuan 25mm inner width to better support tires up to 30mm wide, the tubular version is specifically designed for 30mm sew-ups, and both use 31mm outer widths to maintain a smooth transition between the rim and tire for nearly identical aerodynamic performance to the standard SES 4.5 with 25mm tires.
"If you have 28mm tire on a rim that has an external width of around 23-26mm and a depth of 60mm, the airflow from rim to tire will separate and perform no better than a box-section rim," said Jake Pantone, director of marketing for Enve Composites. "Ultimately the rider using a wide tire on a narrow 40-60mm deep rim would just be carrying extra rim weight around."
Enve's new SES 4.5AR Disc carbon clinchers are on the cutting edge of the wide-wheel trend, with a 25mm internal width, a 31mm external width, and front/rear-specific aerodynamic shapes that have been designed with 28-30mm tires in mind.
Moreover, while the SES 4.5AR Disc rim profile is much bigger than that of the standard SES 4.5, Enve says the rim is actually lighter. Actual weight for a set of SES 4.5AR Disc clinchers that recently arrived for test at CyclingTips is just 1,519g.
"We have specific laminates for disc-brake specific rims," Pantone continued. "These are between 30-70 grams lighter per rim. As an example, the 4.5AR Disc, which has a 25mm internal rim width, weighs less than the 19mm-wide SES 4.5 rim. Both rims are roughly the same depths, so what we are really offering is a weight neutral proposition."
Those bigger wheel dimensions can potentially also wreak havoc in terms of compatibility. Many older frames and forks are built around traditional 23-25mm tires and 19mm-wide (external width) rims, and simply may not have enough room to fit anything larger without creating potentially dangerous clearance issues.
Wider wheels and tires offer plenty of benefits on the road, but you also have to make sure you've got room for them.
"It seems that in the spectrum I operate, people want width, but most of the time I feel like that's because it's what they're being told to get by the industry," said Vermont-based custom builder Zack Macik of ZSpokes. "I get a little worried about some bikes with people running 25c [tires] and wide rims. It seems to get pretty close to the frame/fork."
Also, whereas many modern brake arms are designed with these inflated profiles in mind, most previous-generation brakes aren't so accommodating. Shimano Dura-Ace 9000 brakes, for example, will fit rims up to 28mm-wide in between the pads, but the 7900 version will only handle 23mm-wide ones. Likewise for SRAM and Campagnolo, and even third-party brands such as TRP. Remember, too, that wider tires are oftentimes taller as well, and older calipers may not have sufficient room to clear the tread cap on high-volume setups, either.
These Shimano Dura-Ace brake calipers are just one generation apart, but they're very different in terms of the sizes of tires and rims they'll accommodate.
How wide is too wide?
Most of us are accustomed to looking at things on a linear scale: if some is good, more is usually better, right? But when it comes to road wheels and tires, it probably is possible to have too much of a good thing.
One of the biggest issues currently facing the rapidly evolving conventions with wheel and tire widths is appropriate fitment — in other words, whether certain rim widths should be matched to specific tire widths, and vice versa, in order to maintain a safe and reliable interface between the two.
"Certainly there is a point where the internal cavity of the rim can be too wide," said Mike Bush, president of Stan's NoTubes. "For the Avion, we suggest using at least a 25mm tire which equates to 1.15 times the inner width. Going with a narrower tire can lead to the tire beads rotating inward as the casing height is reduced. Riders rely on a tire profile that allows the bike to be leaned smoothly, with no sudden changes in geometry that could cause a washout or crash. The likelihood of pinch flatting increases as well when casing height is reduced, since we're relying on pressure and tire construction for bump absorption."
Just one peek at the label on the Stan's NoTubes Avion Pro rim provides an indication of the tire sizes the company expects to be used here. See a pressure suggestion for a 700x23mm tire? Nope.
Mavic isn't the only company to offer minimum tire size recommendations with its wider road wheels.
"We don't really think there is such thing as 'too wide' [in reference in road rim width]," said David Allen of Praxis Cycles. "It just depends on the desired tire width, which, in turn, depends on the type of riding being done and the ride quality you require. We tend to find that we prefer the ratio of tire width to rim inner width to be around 1.5 to 2.0, with narrower rims/tires leaning more towards the lower end and wider rims/tires leaning more towards the upper end.
"I don't think width has any bearing on safety. Instead, the rider needs to pick the appropriate tire/rim combination and use the correct tire pressure — in other words, not use too wide of a tire on a narrow rim and vice-versa."
As the name suggests, the new Praxis Cycles RC21 carbon clinchers feature a 21mm internal rim width. External rim width is a healthy 28mm.
Mavic is one of the veterans of the road wheelset world, with one of the deepest wells of knowledge in terms of testing. Perhaps as a result of that, the French company is also quite conservative when it comes to emerging trends, and that trait continues with its attitudes towards wider rims and tires.
"We're supporting the trend for wide rims and tires," said Maxime Brunard, Mavic's category line manager for road, "but within the limit of safety standards established by ETRTO and ISO [the European Tyre and Rim Technical Organization and the International Organization for Standardization, the two main bodies that govern industry standards for tire, rim, and wheel sizes]. They have established, and we have also verified their findings, that in some circumstances using a (too) narrow tire on a (too) wide rim can lead to the tire suddenly coming off the rim. This is especially true if you are using a tubeless system. Out of respect for our customers, we simply will not compromise their safety. This is true even if it is only a small proportion that would recreate the circumstances that result in an unsafe situation.
Mavic is one of few wheel companies that prescribes specific tire sizes depending on rim width.
"We are firm believers in the wheel-tire system approach and building wheels that have the best combination of performance and reliability (including safety)," Brunard continued. "We are currently updating our full range to push to the limit of the norms by offering our 17mm internal width rims with 25mm tires. That is the narrowest tire you should run based on the norms. Then, on a 19mm internal-width wheel, we offer these wheels with a minimum 28mm tire, which is the narrowest tire you can run to maintain the reliability we set as a benchmark for our customers."
Plenty of anecdotal evidence exists to counter Mavic's suggestions that matching tire widths to rim widths more closely can be dangerous, however, and there are dozens of companies out there that openly support more aggressive setups than what Mavic prescribes. That said, it's still anecdotal evidence, not the result of a proper scientific study, and there certainly is a lot of industry discussion going on behind the scenes on what is — and isn't — safe to use.
"Even though the norms might seem silly, they are real," stressed Mavic global brand manager Chad Moore. "The safety concerns are real. The tests are real. The failures are real. It's not bullshit. Being one of, if not the biggest wheel manufacturers in the world, we simply cannot take any chances. I can offer you a lot of math about percentages of failures per hundreds or thousands of wheels based on the ETRTO testing, but I don't think I need to. With the amount of Ksyrium wheel-tire systems that we sell, you can imagine how even just 1-in-1000 failures could impact our customers. We just don't want to take that chance."
How disc brakes are changing the game
The move toward wider road wheels, rims, and tires perhaps wouldn't have come about with the speed and strength that it has were it not for two other trends: traditional roadies' increasing desire to get off-pavement and away from motorized traffic; and the widespread popularity of disc brakes. While the former may be largely driving the trend, it's the latter that is really allowing it to grow wings.
"With rim brakes, the practical limits for rim width were around 27-28mm at the brake track, and the bead walls had to be at least close to parallel," said Jacob McGahey of Industry Nine. "With disc brakes, there is no real limit on rim shaping for a front wheel, and while the rear rim is limited to a small degree by the constraints of drivetrain clearance (assuming traditional chainstay lengths), there is still a lot more theoretical room to work with. In general, optimal tire/rim shapes feature a rim that is wider at its widest point than the tire casing. Within the context of current rim shapes designed around rim brake profiles, a 28mm tire matched to a 28-29mm outer width rim (the widest that are currently on the market) just can't match the performance of a 23 or 25mm tire on the same rim.
Industry Nine's new AR25 Disc All Road wheels fall on the progressive end of the rim width spectrum with a 21.5mm internal width.
Despite the 21.5mm-wide tubeless-compatible aluminum rims, Industry Nine's new AR25 Disc All Road wheelset supposedly tips the scales at just 1,440g, bucking the notion that wider wheels have to be heavier.
"The next generation of disc brake rims will likely start moving north of 30mm," McGahey continued, "which could allow a 28mm tire to be very competitive with a 23mm tire in average wind conditions. This would include a range of yaw angles, as they will be able to maintain air attachment (reducing turbulence and drag) just as well as a narrower rim and tire. All things being equal though, [wider setups] will always have a disadvantages at 0 degrees of yaw due to the increased frontal area. Right now, I consider the new disc-specific rims entering the market to be first-generation, and I, for one, am really excited to see what happens with rim development once we get to the second- and third-generation disc-brake specific rim profiles."
Staying put, and looking forward
As intriguing as the wide rim-and-tire movement is, it's worth noting that many of the major players in the category, such as Campagnolo, Shimano, Zipp, and Mavic, aren't entirely on board with the latest ultra-wide profiles — or at least, haven't had sufficient time to update their ranges.
Campagnolo recently broadened nearly its entire wheel catalog across both the Campagnolo and Fulcrum brand umbrellas, but with the exception of one model — the new 19mm-wide Fulcrum Racing Zero DB disc-specific wheelset — the Italian company is holding back at 17mm internal widths. Shimano's Dura-Ace and Ultegra wheels are standing firm with 15mm and 17mm internal widths, too, and with the notable exceptions of the new 21mm-wide 303 Firecrest Carbon Clincher Tubeless Disc-brake and 30 Course and 30 aluminum models, all of Zipp's clinchers are, at most, 17.25mm-wide.
Zipp has been somewhat slow to move to wider internal rim widths, but new models like the disc-specific 303 Firecrest carbon clincher show the direction the company is headed in with a much more progressive 21mm of space between the tubeless-compatible bead hooks.
Zipp says the new disc-specific version of the 303 Firecrest carbon clincher is ideally shaped for 25-28mm tires.
Disc-specific rims offer more flexibility in terms of shaping than ones designed for rim brakes. In the case of the new Zipp 303 Firecrest carbon clincher, the fatter outer edge makes for a smoother transition to the tire. Note how the dimples also fill in the space where a brake track would normally go, too.
Fulcrum is venturing carefully into the wider-rim waters, with most models growing slightly but still limited to a modest 17mm internal width.
Fulcrum feels that the 17mm internal width used on much of its range offers a better balance of low weight and tire support than wider profiles — at least for now.
One exception is Fulcrum's new disc-specific Racing Zero DB, which uses a more progressive 19mm-wide aluminum rim.
DT Swiss's new OXiC rim treatment is similar to what Mavic has been doing with its Exalith brake tracks. The plasma electrolytic oxidation coating supposedly boosts both wet- and dry-conditions braking performance while also improving long-term durability.
Much like Mavic, DT Swiss has historically been pretty conservative when it comes to rim width. Nevertheless, many of its new road models, like the PR 1400 DiCUT OXiC aluminum clinchers, use somewhat progressive 18mm internal rim widths.
Tubeless compatibility is seemingly coming hand-in-hand with wider rim profiles.
DT Swiss has adopted the more progressive 18mm internal rim width even on aero-profile wheels like the new RRC 65 DiCUT.
Mavic's shift away from traditional 15mm-wide road rims started with the 19mm-wide Ksyrium Pro Allroad Disc, which now has a lower-priced cousin in the Ksyrium Elite Allroad Disc (right).
Mavic has widened much of its range for 2017, but models aimed strictly for pavement use such as the new Cosmic Pro Carbon SL C Disc still stick to a moderate 17mm internal rim width.
Along with the wider rim widths come more blunted aero rim profiles, which should perform better in crosswinds than the aging shapes Mavic used previously.
Like its sister wheel company Fulcrum, Campagnolo has widened most of its wheel range, but only slightly so with 17mm internal widths.
The superb Campagnolo Shamal Mille aluminum clincher road wheelset gets a slight boost in internal rim width from 15mm to 17mm.
Meanwhile, Mavic has revamped a huge portion of its road range for the 2017 model year, finally moving away from the 15mm — and in some cases, 13mm — widths it had been stubbornly sticking to for ages. Nonetheless, with few exceptions, even most of the new models are only modestly wide at 17mm between the bead hooks.
Are those companies right to adhere to these more traditional dimensions, or are they simply lagging behind the competition? Only time will tell, but most agree that we're at least starting to see some stabilization in terms of what people are asking for.
Clement recently expanded into complete wheelsets with the debut of the new Ushuaia. The tubeless-compatible aluminum clinchers have a 23mm internal width that is specifically intended to be matched with high-volume tires.
"Wider tires will proliferate as gravel riding and racing becomes more mainstream," said Lee. "For triathlon, TT, road races, criterium, track (all the usual road applications), 23-25mm will remain the sweet spot. Road widths will probably not change much, but as gravel product lines continue to fill out, we will probably see more offerings tailored to those specific types of riding."
"The emergence of the gravel market really drove rim widths outside of the norm," said Reynolds PR representative Nick Ranno. "Now, we are seeing all sorts of wider options out there. However, in the road market, we are starting to see some stabilization. The current widths are getting ridden by consumers and Grand Tour teams alike, and it seems to be stabilizing somewhat."
Reynolds' move toward wider rims started with the ATR, a model aimed at the gravel scene with its tubeless-compatible, 21mm-wide carbon rim.
Reynolds' revamped aero wheels are all built on wider formats with 19mm of space between the bead hooks.
"I would say that for the near future we are pretty solid with 25 and 28mm tires for the most part," added Campagnolo's global press manager, Joshua Riddle. "We will see what the advent of disc brakes in competition brings about, but that will more than likely persuade those leaning towards 25s to opt for 28s as opposed to those already on 28 to go any wider."
The coming tide
Given all of this, what's a self-respecting roadie to do when it comes to wheel and rim width? In short, there's nothing wrong with what you have now, and given the cost of most higher-end wheelsets these days, there certainly isn't any urgent need to go out and buy something new.
That said, if you are in the market for fresh rolling stock, it's worth checking out some of the more progressive options. The performance benefits they offer are real, not imagined, and all indications point to wider wheels and rims becoming standard fare across the board. Just make sure they'll fit with the rest of your current equipment first, and be prepared to set aside some of your previous assumptions about tire pressure as well. It's a brave new world out there, but one that also has plenty to offer to those that are willing to venture into it.
#aero wheels
#tubeless
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#wide wheels
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