It would be news to no one that Gravel or All Road riding has exploded in recent years. One of the surest signs of its popularity, is just how broad the range of styles it encompasses. Mention the words “riding gravel” and depending on who you are speaking to, could conjure up images of flannel clad riders aboard fully loaded bikes with camping equipment, to Kanza racers in full spandex kit, with aero bars, and everything in between. True to its racing heritage, Cervelo wades into the gravel segment firmly in the spandex wearing end of the spectrum, the new Aspero is made to go fast. Stopping to smell the roses is decidedly optional.  

The brand new Aspero is a thoroughly modern gravel bike with many of the features racers look for, with generous tire clearance for both 700c (44mm) and 650b (49mm) wheels, dropped chainstays that provides that clearance yet keeps wheelbase short and handling tight, and both 1x or 2x drivetrain compatibility. It makes nods to the rowdier end of the spectrum with dropper post compatibility. But it eschews any suspensions or plethora of mounting options for bags and cargo, the only “extra” mounts in addition to standard 2 bottles set up are top tube bento mount, and a down tube keg mount. 

Speaking with Graham Shrive, Cervelo’s Director of Engineering, one of the key objectives for the new Aspero was to maintain the race focused character that Cervelo have traditionally been known for. “We really want to focus in on racing or fast riding application, like the Dirty Kanza, those kind of events.”

But even focusing on the racier end of the spectrum still presents a pretty diverse set of needs. “The challenge with the gravel scene right now is there are a lot of voices competing to define it. Inside our office I’ve got a couple of guys that are real Grinduro aficionados, where you’d want a minimum 40, 43mm tire. Contrast that with something like the Dirty Kanza, where you are more running a 35 or 38, something like a fat 35 smooth tread. We really wanted to offer something that can do both. And not have your ride experience be tremendously affected by that”

But how to solve the problem that when you run drastically different size tires, handling is affected? Around which size wheels do you optimize for?

A quick geometry lesson

How your bike handles is determined by many factors, things like wheel base, bottom bracket drop, rear center, on and on. But one of the biggest determinants is trail, which is a measure of how easily or not your bike is to turn. Derived from head tube angle, fork rake or offset, and wheel diameter, trail is a key contributor to how nimble your bike feels. The lower the trail, the more twitchy your bike is, the higher the trail number, the more stable it is. 

Wheel diameter are usually defined by intended usage (ie. road bikes will probably have 700c wheels with approx. 25mm tires), so designers will generally play with head tube angle and fork rake, to deliver the desired handling characteristics or feel. But with gravel bikes, both wheel and tire size can vary dramatically, which will throw off trail, potentially radically changing handling from what was originally intended. 

Enter the Trail Mixer

In Shrive’s telling, the optimum wheel and tire size to design around for the Aspero was the subject of intense discussion, “When the opportunity came to make a gravel bike, we had this raging debate at the office, one guy liked 2.2s, I like 35s, someone else wanted something different, everything hit a head. I said ‘here is what we use that flip chip for. We can really offer something applicable and different for the rider.’ That’s how all that came around.” 

That “flip chip” was the precursor to the Trail Mixer, which actually long predates the development of the Aspero. It goes back years to Shrive’s previous work on many of the road bikes in Cervelo’s line up. In working with various teams and sponsor riders, Shrive developed a fork with a flippable insert that altered the rake, to research and validate some of the handling notes from pro riders. There were even discussions of incorporating the flip chip into bikes, but the feature never made it to production, until now. 

With the Trail Mixer, a flippable insert at the fork dropouts positions the wheel for two different rakes, riders are able to adjust the Aspero based on wheel and tire size, retaining proper intended handling. According to Cervelo, in the forward setting, you get less trail for faster steering, recommended for when you are rolling bigger tires with a 700c wheel, to offset the slower steering response of a big tire. Conversely, for a smaller tire, in a more road setting, set the Trail mixer in the rear position, to mellow out the quicker handling small tire. Since 650b, even with a big tire, mimics the diameter of a 700c wheels with a smaller tires, Cervelo recommends treating it the same, with the Trail Mixer in the rear position. A reversible dropout insert is an unusual feature, but by no means unique to Cervelo. Rondo, a newer Polish brand, incorporate a similar feature into their gravel bikes, while Canyon has featured adjustable dropouts on their triathlon bikes.  

Wheel and tire size aren’t the only consideration when positioning the Trail Mixer. “Handling is such a personal preference,” Shrive Adds “The really interesting thing about the Trail Mixer is that… you can use that to influence the personality of the bike. Sarah, who is here at marketing, is not the most confident descender, when she rode it the first time, she said ‘that thing is sketchy.’ But then I flip the chip back which gave quite a bit of trail, and it was night and day difference. She became a more confident descender, more comfortable on the bike, and it’s very much for her. Whereas I am the opposite, I like the minimum possible trail.”

Geometry Refinement

Although the Trail Mixer is the most obvious evidence of the thought that has gone into the geometry of the Aspero, Shrive is careful to emphasize they spent even more time sweating the details of the rest of the geometry.

“The geometry is actually quite similar to the C-series,” the endurance bikes in Cervelo’s line up, but, Shrive explains, “there are three key differences: the head tube angle is a bit steeper, the top tube is about a centimeter longer, and the bottom bracket is a bit lower.” 

A glance at the geometry chart shows that although the Aspero doesn’t have road racing head tube angles, it is steeper than many gravel oriented bikes. And the reach of the frame is long indeed, besting even Cervelo’s R-series racing frames. Shrive explains that is by design, the lengthy reach of the Aspero is meant to be paired with a shorter stem. This is similar to the development of modern mountain bikes, which tends to favor a longer reach to accommodate shorter stems for better control. Although MTBs are usually paired with slacker head tube angles to improve steering stability on steeper technical terrain. 

“The steeper head tube angle is one of the key differentiators of the bike. What we are trying to do is to try to give you a very quick handling experience at extremely low speed.” Given the inbetween nature of Gravel bikes, the steeper head tube angle could prove to be a fitting choice. 

First ride impressions 

I’ve ridden a few gravel bikes lately, from various brands at various price points. But what they had in common were plenty of tire clearance, decidedly slack angles, with tallish headtubes and stack. Which made for very comfortable straightline cruising, perfect for long days in the saddle, but I didn’t love them.  I found the slack angles combine with tall stack, made the front end feel vague when cornering. I could never be quite sure exactly what the front tire is doing, am I about to wash out? 

I am happy to report that the Aspero did not give me this feeling in my first few outings on it. The quicker steering, combined with a short headtube made this roadie feel right at home. The short chainstays and stiff carbon frame also feels a lot like Cervelo’s road offerings, despite the big tires. It’s a lot of fun to launch up a sharp, steep climb, with the big tires taking care of most of the traction duties. When it came time to point it back down, I appreciate the shorter stem letting me tuck low and back on the bike, and let the tires ride out the ruts.

It’s also one of the better looking bikes, gravel or not, I’ve come across lately. An informal poll around the Canadian Cycling Magazine office showed I am not alone, the Aspero looks like a proper race bike, and the Dune colourway on test catches attention without being overly loud.  

Looking at the Trail Mixer feature, admittedly my initial thoughts were “seems a bit of a gimmick”. But as I rode it, it starts to make sense. Many of the gravel rides I do involves significant amount of road riding to get to. For instance, there is a favourite local loop I do to Schomberg, that is about 140km round trip from Toronto, and about 100km of that is on the road, in order to get out of the city, and short road stretches to connect the gravel sections. I usually do that ride on my road bike with 25s (although 28s, which doesn’t fit, would be better). With so much road riding, anything too burly would be overkill. But I also like to partake in more pure gravel events like Paris 2 Ancaster, the Eager Beaver, or the Reggie Rambler this fall, where a more capable bike is necessary. The Aspero lets me pick not just the tire and wheel size, but the preferred handling feel for the terrain and day. Stay tuned for a long term review of the Aspero, after I take it on roads familiar and otherwise, hitting up some gravel events, and experimenting with the setup.    

The Aspero is available in six sizes (48, 51, 54, 56, 58, 61), and three frame colours (Burgundy, Dune and Teal) in the following builds:

Aspero Force eTap AXS 1              $8,000

Aspero GRX                                     $5,300

Aspero Ultegra RX                         $5,300

Aspero Apex1                                   $3,700

Aspero Frameset                             $3,300

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