Innovation and lateral thinking abound on this hot new XC race rig
This new featherweight whippet from little-known brand ARC8 aims to compete with the best XC race bikes on the market. And with progressive sizing, low mass and some clever engineering, it has every chance of hitting the front.
Need to know
- Sub 10kg XC race bike that rides like a trail bike
- With a 1,240g frame weight ARC8 can use burlier components like the 120mm Fox 34 fork
- Frame travel is 110mm stock, but can be reduced to 100mm and paired with a 100mm fork for a more traditional XC ride
- One-piece carbon bar/stem combo looks more enduro than XC race
- Frame available in two sizes: M and L
- Priced at €8,999
When it comes to XC racing, weight is of critical importance. The riders are lean, and the best XC bikes have every ounce of excess fat trimmed back, too. It’s all about optimising the power to weight ratio of rider and machine to increase their chances of success on race day.
But long before the start gun sets heart rates rocketing, rider prep starts in the off season and at the same time bike engineers are looking at ways to minimise frame weight without compromising stiffness. It’s one thing sitting at a computer manipulating layers of carbon, but it’s a very different situation if you live in Taiwan and work directly with the factory. And that’s exactly what Jonas Mueller, the engineer and co-founder of ARC8, does.
And it’s by having a much better understanding of the manufacturing process, that ARC8 is able to make such impressively lightweight frames. At the launch of the Evolve FS in Massa Marittima, Italy, I was blown away by the sub 10kg XTR build with regular, albeit fairly lightweight, high-end components. No custom ultralight kit with questionable durability needed to reach the impressive weights achieved in large part by the 1,240g frame weight.
Take a closer look at the ARC8 Evolve FS and the suspension design lends itself to weight saving too. Instead of having a rotating link to drive the shock, a linear rail takes its place, the shock driven directly by the seat stays. Most XC bikes use short links to save weight but shorter links also generate bigger variations in the leverage rate. By using a rail, ARC8 achieves an infinitely long link, which gives a more consistent and progressive leverage rate across the 110mm of rear travel.
Like most XC bikes, flex in the slender carbon seat stays eliminate the need of the pivot at the rear dropout. And because the more traditional swing link has been replaced by a sliding rail, the seat tube doesn’t need the same degree of reinforcement to support the forces a link typically generates. So again, the frame can be made lighter without compromise.
The reversed main pivot is also a key part in the construction process. With the swingarm going inside the front triangle rather than around it, the bearings can be placed further apart to improve stiffness. The void that the swingarm fills is also a great palace to remove mandrills from the front triangle during the construction process so less filler and resin can be used in the finished product. Which again makes it lighter…There’s a theme here, right?
There are less obvious details that make a difference too; take the aero profile of the down tube. This is much less about aerodynamics and more about weight saving when it comes to wet races, as the thinner end of the tube is facing down, making it harder for mud to stick to. And if you’ve ridden an e-bike with a big flat battery pack forming the underside of the down tube you’ll know exactly what I’m talking about.
It’s not all custom features for the sake of optimisation though, and ARC8 isn’t afraid to toe the party line with proven designs. It’s why the Evolve FS frame has a threaded BSA BB shell and a SRAM universal derailleur hanger.
In terms of sizing the Evolve FS is pretty progressive, at least for an XC bike. I typically ride a size L, but the 465mm reach (when built with a 120mm fork) on the size M ARC8 makes it equivalent to or longer than most other brand’s size L XC race bikes.
And it’s worth pointing out that the bike is designed around a 120mm fork, then you have the option to go down in travel if you want more traditional XC geometry. You get a slack 65º head angle with the 120/110mm build and just over 1º steeper if you bump the travel down to 100/100mm, which also lowers the BB height by 8mm. The bridgeless seat stay design allows for short 430mm stays, but the rear end is not so short as to cause the bike to loop out on the steepest climbs. Something that’s mitigated in large part by the steep 77.1º effective seat angle. So the only limiting factor here, is that ARC8 only offers the frame in two sizes: M and L.
How it rides
As I set off on my first and only ride in the ARC8 I was instantly getting mixed messages. The stubby Faserwerk Baslerstab one-piece bar/stem stem combo is more akin to those found on high-end e-bikes, and the bike pedalled with such ease that you could be forgiven for thinking that there was some hidden assistance inside the frame.
Get out of the saddle to sprint and it was the Fox 34 fork that seemed most active, the rear suspension absolutely steadfast. It was at that moment that a nagging doubt entered my head. If the ARC8 Evolve FS feels so similar to hardtail on the way up, is it going to feel the same on the return leg of my journey?
Thankfully that wasn’t the case. Granted the rear suspension wasn’t super fluid, so you couldn’t really use the rebound of the shock to unweight the bike. Not that I had any issues getting this sub 10kg off the ground. Also on bigger hits the back end took everything in its stride so I had absolute confidence in the suspension capabilities.
I was probably most impressed though, with how solid the bike felt. Diving into switchbacks there was none of the usual waywardness you get with ultralight race bikes. Proof, if it were needed, that ARC8 has got the stiffness to weight ratio of the Evolve FS absolutely spot on. Combine that with the modern geometry and stiffer Fox 34 fork and you have the confidence to charge harder on the descents than the travel and tires should really allow you to on a sub 10kg bike.
When I finished my ride I mentioned to Jonas Mueller that the shock felt a little dead and he was quick to point out that due to supply chain issues they had to use a shock from a higher leverage ratio design to get the bike ready for the media launch, and as such it was a little over-damped for the 110mm travel Evolve FS.
Hopefully I get to ride, or even test a full production version at some point soon, as ARC8 Evolve FS has brought something exciting to the somewhat traditional world of XC racing.