I first rode the Bontrager XXXLite Carbon clincher wheels back at Tour de Georgia – but only for a day on some pretty good roads. So when a set arrived for the ‘long ride’ test – I was keen get to know these wheels on a more personal level. These are nice wheels, but even more impressive is that Bontrager succeeded in building a carbon clincher this good…
Click the thumbnail at top for the BIG view.
What We Have Here Is…
… Full carbon clincher wheels – in case you missed it the first two times. The rims are made from Trek’s famous medium modulous formulation OCLV110 carbon. They’re molded into a one-piece hoop that gets drilled for spokes and completion of construction. The rims are 24mm deep and 21.5mm wide. The hubs are primarily made of carbon, with some aluminum (axles and rear drive-side flange), and the spokes are DT stainless steel flat-bladed, designed to Bontrager specs, the front wheel runs all straight pull spokes while the rear wheel runs straight-pull on the non-drive side and j-bend on the drive side to allow for a more stable dish angle.
Outta the box, the first thing I noticed was (like most guys)… their looks. The second thing was their weight… (we’re so predictable…) First the looks: In a world populated with black and silver wheels – these are colored like no wheel I’ve seen – I’d call it a very very dark green with a hint of ochre… might sound like I’ve been watching too much ‘home design tv’, but they’re different and they look cool.
But I got really excited when I picked ‘em up. 1350 grams (claimed) for the set… that is light. Mine weighed in at 1365g for the set, including rim strips and a 75 gram cassette body. Sure there are tubulars a lot lighter out there, but these are right in the mix of 'light' clinchers'.
The high gloss hubs are darn sexy. Spokes on the drive-side are j-bend, attached to an aluminum flange to allow for a better angle to anchor the rim, while the non-drive side spokes are straight pull (slightly light than the j-bend), anchored in the solid carbon hub body.
Why Carbon?
Good question for sure. There are certainly fewer models of full carbon clinchers offered than there are in aluminum – and not without reason. The manufacturing process for full carbon wheels is still relatively new compared with that for alu wheels, and you need a lot of knowledge and experience working with carbon fibre in addition to knowing of how to build a good wheel. The heat dissipation properties of carbon are a hurdle – since the carbon rims don’t cool off like aluminum, there’s the risk of increased tire pressures from braking, which could lead to flat tires and/ or structural problems with the wheels. Braking is also an issue as the cork compounds required for carbon rims just don’t stop the same way rubber compounds do on aluminum. And then there’s cost – carbon wheels are just more expensive than aluminum, and a lot of consumers aren’t ready to pay the extra price.
But the business of racing is not just about sponsor exposure from the rolling billboard of the pro peloton – it’s also the perfect battle ground to conceive, test and develop new weapons of mass velocity. Like all smart sponsors, the guys at Bontrager Wheelworks know that helping their riders win more races by providing better equipment is a good way to ensure maximum return on their sponsorship investment – and sell a few wheels along the way to keep the business end rolling.
When I asked Bontrager product guru Bill Miller ‘why make a carbon’ rim, he told me the idea came straight from Lance and the boys at Team Discovery Channel. Sometime back in 2004, the word came down that the team wanted wheels that were stronger, more durable, and had better impact resistance, oh and were lighter – than the already tough Bontrager aluminum rims they were riding. (Pros are never satisfied…)
So the guys at Bontrager set about the task of making it so, and their development of carbon tubular wheels led to the development of a full carbon clincher – which is no easy task.
A funky ‘Team’ version is also offered with flashy red spokes for a few dollars more.
Making It Work: Carbon Ain’t Easy
Making wheels out of carbon comes with special challenges. First you lay out the criteria for a great wheel, you gotta make ‘em:
• Strong enough to withstand the toughest ProTour conditions – we’re talking even Roubaix cobbles here.
• Durable - any wheel for the team has to last about 250km of the toughest roads in pro racing, and the rest of us want it to last much much longer. It’s rare that consumers will pay big bucks (or any bucks) for a wheel that lasts half a season. Bearings, spokes, lamination – every part needs staying power.
• Comfortable enough to ride for 7 hours over said conditions.
• Light enough to challenge the UCI weight limits, and not much heavier than your competitor.
Then toss in a bunch more challenges that come from working with carbon. To appreciate how difficult it is to build a wheel that meets all these criteria, consider the many shapes and surfaces of the wheel – it’s circular, it’s hollow, it needs to withstand high spoke tensions pulling the rim into the hub, high tire pressures pushing the rim wall out, and high brake pressures squeezing the rim wall in AND cooking up the heat on said rim… that’s a lot. Then consider the whole rim is molded into a one-piece unit.
Look Ma – No seams! The inside of the rim is the real proof you’re riding a seamless rim – and that makes it stronger. Spoke holes are drilled straight through finished molded carbon.
So how did Bontrager overcome certain problems?
Make Em Strong
First – they set out to design and build a wheel that was stronger than anything they made - specifically focuisng on direct impact resistance. Carbon can be very brittle, so a wheel that’s unable to absorb and deflect the hammering from a tough ride will simply crack, or succumb to something more “catastrophic”. The key to solving this was ensuring the desired ratio of resin to carbon fiber (and proper compaction of both): too much or too little of either ingredient can lead to structural and functional problems, remember that carbon fibers and resin work together like rebar and concrete – the carbon provides the structure, while the resin is the glue that holds it all together and gives it strength.
Bontrager designs, molds and builds these wheels in house in the good ol’ USA. And this is not to say that great quality carbon manufacturing can not be had overseas – because it can and is. But working in house allows ‘em direct and easy access to every step of the process – especially the testing phase. When you own the factory, you can stay up past Letterman (and even Jimmy Kimmel) mixing new resins and pressing wheels until you get what you want. And that’s what they did.
Valve stems are anchored with small rubber washers that eliminate those nerdly ‘ticking’ noises.
Make Em Durable
A major issue affecting durability is heat transfer: carbon rims do not dissipate heat like aluminum rims, so higher rim temps caused by braking can lead to tube punctures and rim wall failures (“Hey buddy – your rim is melting!” is not something you ever want to hear…), not to mention poor braking as the brake pads heat up.
Bontrager solved these problems again with their proprietary resins and brake pad compounds to withstand temperatures in excess of 420 degrees Fahrenheit - much higher than you’d ever experience riding.
It must be noted here that whole 'heat' issue for carbon wheels is still one of contention in some camps. Bontrager is very clear that a certain rim strip be used to prevent flats from braking-heat induced over-inflated tires. And for riders who abuse their brakes on long descents, the possibility of over-inflation is real. Then again, these wheels are intended (and priced) for experienced riders who don't ride their brakes like a jack-ass.
The vertical striping on the sidewall – although nearly impossible to see without good lighting and in extreme close-up - actually aids in braking.
Are They Aero?
Though not designed as an aero-shaped wheel, the design does offer some properties that improve airflow around the tire. The rims are 21.5mm wide, which is only 1.5 mm shy of a 23mm wide tire. And as we all know by now – the less you disturb air flowing over or around an object, the more easily that object passes through the air – thereby becoming more ‘areo-dynamic’. The wider rim allows air to pass over the rim braking surface and onto (over) the tire sidewall with less disturbance than is created by a narrower rim. The wider rim also allows for increased strength in the rim structure, so you win on both counts.
SPOKE LAYUP
Of the infinitesimal minutiae that gives wheel designers, let’s call it ‘high tension’… the spoke pattern is worth noting as well. It’s a clean looking paired layout with 20 on the front and 24 on the rear. When I asked Bill how they chose the pattern, he explained they’re designed to increase wheel life by reducing rim fatigue. Okay – how does that work?
Spokes are stainless steel by DT, and layed up in pairs – 20 spokes in front, 24 in rear.
Now pay attention – the wheel is a weight-bearing hoop that actually flattens out a tiny tiny bit when you sit on (and ride) your bike. The part that flattens out is at the bottom – the part that contacts the road (duh...) At this point, the spokes actually de-tension slightly every time they roll through the bottom of the wheel-turning arc – because they’re under less tension. As the wheel de-tensions at the bottom, the rim can also be pulled to one side - and out of true – depending on spoke lay-up. The paired pattern layup is designed to share the load by maintaining even spoke tension throughout the wheel, even at the de-tensioned section - because there are two spokes pulling in equal and opposite directions from the same point on the rim.
Given that the wheel is designed to perform under uniform tension, you basically don’t want to loosen this tension at any part – this is where you get spoke fatigue and eventually things can start to break.
Swapping hub bodies is the easiest I’ve seen, you don’t even need a wrench. The hub body can be removed with a small flat-blade screw driver and your hand – it pulls straight off. Pretty nice if you’re in that small percentage of riders who have the ‘problem’ of needing to switch wheels between Campy and Shimano.
How’s The Ride?
My main concern was would the ride be too stiff? After all they were designed to be stronger than anything in the Bontrager line. And being a 140lb climber, I put a lot less stress on equipment (I suspect) than most of the guys who’ll be buying these wheels.
I noticed the weight right away – not only do they look light, but they spin up fast and roll along with ease. Of course this is my own unscientific interpretation, but I’ve ridden some heavy wheels and know what it’s like to pedal those up 10km HC climbs… not fun.
And they are stiff laterally – make no bones about it. Rocking the bike in a sprint or climb, I detected no brake-rubbing wheel flex.
Ride Quality? Once I got the tire pressure dialed I was set for several hours of in-the-saddle riding. They were surprisingly comfortable, as I expected a much harsher ride from a tough carbon wheel. But whatever Bontrager has done with their carbon layup it makes for a nice riding wheel.
They’re not designed to be a super stiff wheel (just super strong – more on that later), but they were plenty stiff for me. I ran these between 100-110 psi, and settled in around 100-105 as my optimal pressure. Bontrager recommends you run ‘em around to 95-100psi, even up to a maximum of 120psi. And although they have been tested up to 185psi to meet Bontrager’s specs, like other carbon clinchers they are not made for use above 120 psi.
[A note of awareness on tire pressure. Not enough is written into most wheel reviews about how tire pressure will affect the ride quality, and since ride quality is so subjective, it’s important to understand that wheel properties are very affected by things like rider weight and tire pressure. My point of reference is that of the 140lb man – a light weight built for climbing. It takes a lot more for me to flex a wheel than the guys who weigh 30, 40, 50 pounds more, and whose legs are designed to really stress cranks and bottom brackets. I’m a high cadence guy – a finesse rider if you will.]
I also ran them down my favorite 2km section of dirt road – complete with Roubaix-style bumps and ruts and the wheels felt solid throughout. They ran solid and true and felt even better at some speed (like you should ride the bumps anyway).
Braking? Like all carbon wheels you gotta run special pads - and Bontrager makes their own cork pads from a proprietary compound. And these work just fine and are consistent with how cork-based pads on carbon rims perform – (which is not quite as good as rubber-based pad/alum rims) - but there's a nice solid progression of wheel grab as you apply more pressure to the brake levers. In the wet you need to brake a second or two earlier than normal. They don't 'jab' like some pad/rim combos, and I never had any issues slowing down as fast as I wanted.
About That Strength Issue…
True Tales of Bad Riding
I had the chance to see just how tough these wheels are first hand – thanks to my own navigational shortcomings. I ‘inadvertently’ rode straight over a slotted drain-sewer grate (coulda been avoided but I just made a stupid decision to ride straight over it). The slots were wider than my wheels and running in the same direction as me, so although I popped my front wheel over the grate, my rear wheel sank in and impacted the far edge of the grate. I was going about 20kmh, and I weigh 140 lbs, so you physics whizzes out there can calculate my impact force.
BANG! There goes the tire, and I’m still an hour from home. I changed the tube and inspected for damage. Get this – the wheel stayed round and true, with no flat spots. The only visible damage was on the rim sidewalls at impact point – where a small ‘blistering’ of the carbon was evident. Any damage to the inside of the rims was almost undetectable to my naked eye.
Regardless, broken carbon is not a good thing, so I shipped the wheel back to Bontrager for their own evaluation, and they sent me a new one. Bontrager has a good Carbon Care Program available so consumers can replace damaged carbon Bontrager parts at a fraction of the cost of a new part – they got yer back.
Also remember that damaged or suspect wheels or other parts should NOT BE RIDDEN! My point is that the wheel took a licking and kept on ticking. I got home without problems – spoke tension appeared to not change and the wheel characteristics did not change. If I could not see the damage, I would not have known there was any…
A Connoisseur’s Wheel
The development of carbon wheels is really still in its infancy (certainly compared to aluminum wheels), so consider these ahead of the curve. A full carbon clincher is a rare find among wheel makers today, and this is what makes this wheelset so unique – Bontrager has produced one that’s a very light, very strong, damn-fine riding wheel.
I score these high on most categories: weight, strength, ride quality and looks, with braking consistent with other carbon rims. Sure they’re pricey, but these are not your run-of-the-mill training wheels. I’m not even sure these are racing wheels for most of us. I suspect most folks will buy these as an investment in quality riding. They’re as strong as anything I’ve seen, and stood up to a serious (but admittedly stupid and avoidable) self-inflicted beating. The ride quality is my favorite part and should work for everyone from racers to 7-hour ride guys, and if you’ve got the budget and desire to spoil yourself with some hoops that say “I’m special”, then these are for you.
• Weight: 1350 grams per set
• MSRP: US $1999.00
• More Info: Bontrager.com
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