Jamis Xenith T Time Trial bike

The Xenith T is Jamis' entry level carbon time trial bike, constructed from medium modulus T700 fibres and coming equipped with a surprisingly good component spec. At a suggested retail price of £1730, the Xenith T promises real value for the aspiring time trialist or triathlete looking to up the ante and buy some free speed.

Frame & spec

Despite its entry-level billing, the Xenith T frame includes some pretty impressive features usually reserved for bikes many times the price, most notably, the hidden brakes both front and rear. The front brake is mounted on the rear of the fork and hidden from view by the 'aeroshield' fairings which extend rearwards from the deep section fork. The rear brake is mounted under the bottom bracket where the air is already 'dirty', leaving the seatstays to be shaped and positioned for minimum drag. All cable routing is internal except for the front brake which requires a few cable ties to tidy it up as it tends to hang out there in the wind.

From an aerodynamic point of view, hidden brakes make a lot of sense, but the trade-off comes in terms of braking performance and serviceability. The Tektro linear pull brakes on the Xenith were pretty spongy right from the get go, and things didn't improve with time. The brake design coupled with the convoluted cable routing means that power is much lower that you would expect from a set of dual-pivot road callipers. Having said that, braking performance isn't all that high on the priority list for a time trial bike, especially if it comes at the expense of speed, and I never felt like the Xenith was dangerous during my time with it.

What I did find frustrating though was how difficult the brakes proved to adjust. Being tucked behind the bottom bracket, the rear driveside brake shoe was near impossible to adjust without first removing the chainset. The front brake was easier to adjust due to the two small access ports in the fork (covered over by rubber bungs when riding), but the problem here was the clearance on the pads when fitting wide wheels. It was only by angling the brake pads up at 45 degrees (not recommended) that I was able to fit a Reynolds Aero 58 front wheel that I was testing alongside the bike. This has a similar outside rim width to the Zipp Firecrests and new offerings from HED, Enve and Bontrager, so I'd expect similar issues with those.

Brakes aside, the Xenith T is quite traditional in appearance with a deep aerofoil section downtube and seat tube connected by a slim, horizontal top tube which terminates in a neat integrated seatpost clamp. The steep 78 degree seat tube positions the rider well over the front of the bike and houses a proprietary carbon, teardrop-shaped seatpost. Whilst this aggressive geometry is ideal for triathletes or CTT time trials unencumbered by the UCI rules on bike position, smaller riders wanting to stick to the rules may struggle to achieve the required 5cm of setback because the single-position seat clamp limits fore-aft saddle adjustability. I had to move the saddle nearly all the way backwards on its rails and that's with a saddle height of 80.5cm.

The bottom bracket area is suitably tall and beefed up to house the PF30 bearings, and is paired with a set of FSA Gossamer cranks with 53x39 chainrings. Together with the 11-25 cassette, you've got some proper gears to get you started in time trials.

Moving to the rear of the bike, the Xenith T features horizontal dropouts with adjustable stops to enable you to position the wheel as closely as possible to the seat tube cutout. An additional benefit to this style of dropout is the ability to convert the bike to a fixed gear for velodrome use.

Most top end TT bikes nowadays feature integrated stem and aerobar arrangements but the Xenith makes do with a simple stem and straight 1 1/8in steerer setup.

While you might be giving up a few extra watts in drag, the system is easy to adjust for both height and length by either swapping spacers or changing stem lengths. The short headtube means that most riders will probably end up running a few spacers under the stem, but the option to go very low on the front end is still open to the more flexible.

Similarly, the Profile Design T2 aerobar is perhaps a little overshadowed in a world of sculpted carbon creations, but it features plenty of adjustability and can be set up to suit most arm positions, an important consideration when the majority of a rider's aero drag is down to their position on the bike. With a bit of tinkering, it was possible to get the extensions and pads positioned very narrow (forearms touching each other) for a super-aggressive position that cheaper aerobars can sometimes struggle to produce. All of the adjustment can be done with 5 and 6mm Allen keys so no specialised tools are needed.

The Xenith T's drivetrain is composed of a rather eclectic mix of brands and components, with Shimano derailleurs and cassette, Microshift bar-end shifters and a Sram chain. Despite this, shifting was smooth and reliable throughout the entire testing period. The only real niggle I experienced was a tendency for the rear shifter to release some cable tension (thereby shifting into a harder gear) when hitting any potholes, which admittedly, isn't something that happens too often when riding a TT.

Wheels are often an area of cost-cutting in more budget oriented bikes and that's the case with the Xenith T too. The 30mm deep, aluminium Alex rims are paired to Formula hubs resulting in pretty heavy wheels which are a bit of a struggle to get up to speed. As a set of training wheels, they do all right and have proved reliable over a number of months, but you'll be wanting to upgrade rather soon to a set of deep sections or even a disc wheel for any actual racing.

The ride

Out on the road, the Xenith T proved to be very stable at speed and surprisingly smooth also, inspiring confidence to stay in the aerobars even when heading down fast descents and through flowing corners. For a novice TTer, the Xenith provides a great platform to get used to the more forward position afforded by a time trial bike.

Where the bike does suffer though is when accelerating up to speed. The use of medium modulus fibres in the frame (as opposed to higher modulus fibres on more expensive bikes) results in quite a bit of added weight which makes it feel sluggish and unresponsive in stop-start situations. The stiffness of such fibres is also lower and there is definitely a bit of 'give' in the frame when stomping on the pedals. It's not a noodle by any stretch of the imagination, but compared to a top-end bike, the difference is noticeable. However, time trials are a steady-state effort for the most part and once up to speed, the Xenith's weight becomes insignificant.

Evaluating the aerodynamics of a TT frame is difficult to do outside a controlled setting such as a wind tunnel or velodrome, even with a power meter such as I used. Is the Xenith slower than bikes costing twice the price? Probably a few watts here or there.

However, as an entry-level TT bike, the Xenith T isn't competing against the numerous superbikes out there, but against similarly priced road bikes with a set of clip-on aerobars attached. In this comparison, the Xenith does provide a noticeable speed advantage, mostly due to the specific geometry which enables the rider get to lower at the front without compromising power.

Verdict

Well featured frame and great component spec for the money makes the Xenith T an ideal first time trial bike, only let down a little by its heavy overall weight and fiddly-to-adjust brakes.