Yeti AS-R Carbon £2199

Yeti's AS-R Carbon frame is lighter, possibly faster, and definitely more expensive than the aluminium version, but is it any better?

BikeRadar score 4.5/5

Yeti's 'standard' alloy AS-R frame would relieve your bank account of a fairly hefty £1349, which is enough to buy a decent complete full-susser these days. So can you justify shedding another £850 on this brave new carbon version which weighs half a pound less? And is there more to it than the low weight?

If you're fretting about such questions, then the answer is to look elsewhere. This is a frame for those who want to treat themselves to the very best, regardless of cost and, to a certain extent, regardless of the sort of logic that usually guides major buying decisions.

The Yeti AS-R Carbon is cutting-edge in every sense, right down to its trim-to-fit seat mast - which comes with its own cutting jig, plus the option of trimming it down to fit a conventional seat clamp and post. That might prove useful if you sell the frame to someone else or feel that occasional seat drops need to be possible. But despite the practical streak in our test rationale, we can't help but find a certain appeal in the 'just for me' custom-fit saddle height.

Speed freaks

Yeti Cycles started way back in the early days of MTB history, and racing has always been the spearhead of its development, with a whole host of legendary riders such as John Tomac, Juli Furtado and Missy Giove adding competitive kudos to the already considerable design expertise. Yeti's speed-freak approach to every bike it creates continues to set precedents for type, performance and durability.

This brings us neatly to the AS-R Carbon. A 'For Racing Only' tag on the top tube is a hint to its design intentions, but don't let that put you off. There's no doubt that the AS-R Carbon would make a superb XC race bike, but it's also a wonderful trail bike. The Yeti's geometry is confidently neutral, to the point of feeling almost casual under pressure. Minimum weight makes it feel nervous from time to time, but the bike's Bambi-like exuberance turns nervous energy into speed surges before any feelings of hesitation have time to grip your ride mood.

Frame: Different material, same design but with that eye-catching seat-post

We tested the original aluminium AS-R frame back in August 2004, and we loved it. In many ways, the song remains the same with this carbon version. The low standover height, generous mud room and top-quality pivot bearings emphasise Yeti's utterly practical approach.

All the frame sections are sculpted to achieve the perfect mix of high strength, lateral rigidity and noticeable absorption of minor vibrations, at the same time as trimming half a pound of heft from the previous alu version. The carbon 'dogbone' bridging the seat stays and the shock across to the top tube is an important part of the design. It inhibits swingarm flex, prevents side load on the shock and controls the system's leverage ratio curve, which helps to dictate the ride feel.

The frame's main pivot sits just above the bottom bracket, between the inner and middle chainrings. Neat alu sections holding the bearings are bonded into a single piece asymmetric carbon chainstay structure. A tough wraparound sheath with an extra deflector plate by the crankset stops chain slap from damaging the right chain stay. Rather than putting an extra pivot at the dropouts, Yeti has shaped the carbon seatstays to give a little vertical flex under pressure. Such detailing flatters the low weight of the full carbon structure, with a medium-sized frame tipping the scales at about 4.25lb, compared with 4.7lb for the alu version.

A Fox Float RP23 shock comes as standard, so you can fettle the ride feel as much as you like. While unwanted shock bob isn't really an issue, there are three ProPedal damping settings and a lockout option.

So what about that seat mast? Aesthetically, it's what draws you to the frame before you've even noticed its carbon build, but is it a good idea? The four-bolt alu clamp on top of the mast weighs about the same as a seat clamp plus a post top, so there's minimal weight saving there compared with a normal carbon post.

Ride: Great frame + great shock = brilliant handling

The AS-Rc frame offers a ride that can be as active or as passive as you want it to be, depending on how you set up the shock. The main pivot position combines well with the dogbone link to offer lots of low-speed comfort through excellent small bump responses. The Fox RP23's ProPedal thresholds allow pedalling stability even with fairly low shock pressures, combined with plenty of medium bump sensitivity. The arc of the dogbone linkage also creates a slightly less progressive shock rate than an in-line setup.

The fact that the ride feels inspired is certainly not all down to the shock, though. This is a frame that would be a pleasure to ride without platform damping. Even on the most demanding rocky singletrack, it's a point-and-pedal bike in the best possible way. The steering angle is a little slacker (read more relaxed) than on some pure race bikes but the steepish seat angle makes you sit right in the middle of the bike and really work the fork. Both the steering and the back end manage to feel tight, animated and remarkably forgiving, all at the same time.

Generous bottom bracket height means you keep pedalling hard through the trails, which is a big bonus on a bike that's built for XC speed. The long top tube offers an efficient stretch for high-speed XC work and climbs, where the 22lb overall weight of our test bike obviously helped considerably too.

Equipment: Frame only or choice of three build-up options

In the UK the AS-Rc is available as a frame-only deal or with a choice of Pro, Enduro or Race builds from importers Bromley Bike. Our test bike was the Pro build, with an XTR drivetrain complemented by Chris King hubs, Magura Marta SL brakes, DT Swiss XR 4.2D rims, Maxxis Crossmark fast-rolling 2.1in tyres, Thomson stem, an Easton Monkeylite SL bar, Lockon grips and a Specialized Toupe road saddle. A Fox RLC 100mm fork felt ideal with the relatively relaxed geometry and just under 4in of travel out back.

Summary

Yeti's AS-R Carbon is a bike built for those seeking maximum XC speed. It's not a pure race bike, but a racer would benefit greatly. The seat mast feature is of dubious benefit, but you can convert it back into a normal post and clamp bike if you don't like the purist touch.

THE DESIGNER SAYS... We asked Yeti AS-R Carbon designer Steve Hoogendoorn to explain a little about the bike. Here's what he said: "We didn't want to make a full carbon AS-R just to make a carbon frame. There needed to be clear advantages. After analysing our current alloy AS-R and talking with our racers, we saw a real opportunity to improve stiffness, decrease energy loss and drop some weight. All of the details we added to the frame were done to improve the following points:

Press-in Shimano BB cups save weight on a complete bike and make the BB shell 19.5mm wider. A wider shell allows a far stiffer construction at the BB to down tube meeting point. Also, the shell can be shaved down to run a 2 by 9 configuration.

The uninterrupted carbon seat pillar saves weight on the complete bike and significantly improves the energy transfer from rider to crank.

The carbon dogbone -- while heavier than the alloy version -- drastically improves the stiffness of the rear assembly. The dogbone itself is over five times stiffer than the alloy version.

The carbon design and construction of the front triangle saves weight from the alu version, but most importantly increases stiffness by 50 per cent.

"These improvements produce more efficient climbing, but we know that racing is not just about going uphill. Races can be won on technical descents, so we improved the frame's descending qualities. To improve stability at speed we decreased our head angle to 69° to make the climbing position and handling spot-on. "The extra stiffness improves tracking and minimises lateral flex in the swingarm and twist at the head tube. With all these improvements I believe Yeti can truly say that the full carbon AS-Rc is a purpose-designed race frame."

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