WTB Trailblazer tires in Plus format: A game changer that doesn't rewrite all the rules of the game

27.5 Plus fits 29er bikes
The Plus format - a tire with a width of 2.8 or 3 inches - is not a "disruptive" technology for the bike industry: While, as an example, 29er bikes brought a completely new category to the market and it was not possible to convert existing equipment, the Plus format is a different story. In 29er bikes, the 27.5 plus tires often fit without any problems, the smaller rim circumference in combination with the large-volume tires adds up to the 29er dimension.

Bike manufacturer Koba applies this recipe to its portfolio. The 100 millimeter "29 Big Sentiero" and "29 Carbon Sentiero" fullies can be equipped with 27.5 Plus wheels - or semi-fat as Koba calls them - while the "29 Big Racetool" hardtail rounds off the Plus format range. In the Plus version, the abbreviation "29 Big" is replaced by the designation "Semi Fat".

What potential do Plus tires have?
What can plus-size tires do? What are the differences, advantages and disadvantages compared to the familiar, much narrower and less voluminous tires? To get to the bottom of these questions, Ride rode a Koba 100 millimeter Fully: First with 27.5 Plus tires, then with 29er equipment.

The Koba Big Sentiero model is equipped to a high standard from head to toe. Red parts set colorful accents

The basis - the equipment of the test bike
The Koba-Bike Sentiero Carbon can be fitted with 29er and 27.5 Plus wheels thanks to its spacious fork and rear triangle. The bike has a climbing-friendly seat tube angle of 73.5 degrees, the head angle is on the agile side at 70.5 degrees, ideal for tight hairpin bends, but not very smooth on fast sections. At 450 millimetres, the chainstays are on the long side, whereas today 29ers are increasingly rolling onto the trails with 430 millimetre short chainstays to match the ride feel of 26 inch bikes.

The standard version of the frame is anodized in black - and with the à la carte system, it is also available individually powder-coated or anodized

The test bike is equipped to a high standard: a complete 2x10 XT groupset (front 38-24, rear 11-36) ensures fast, precise gear changes, while the XT Trail brakes ensure perfect braking maneuvers. The fork comes from Fox (32 series, Kashima-coated, CTD) and, in combination with the shock (Fox Float CTD, 2016 model), offers 100 millimetres of travel at the front and rear. The rear suspension is extremely bob-free with Horst-Link and does not rock even with a lot of negative suspension travel over 25 percent.

Our own company: Koba also manufactures seat posts, stems, handlebars, headsets, pedals and grips in-house

The in-house Koba parts provide attractive visual accents. The lightweight grips, headset, stem, handlebars and seatpost all come from the company's own portfolio and impress with their low weight.

The ride test with 27.5 Plus wheels

Rolls onto the trails with 12.4 kilos: Koba Sentiero Semi Fat

Koba Semi Fat wheelset
First of all, the wheelset: Koba uses DT Swiss 240s hubs (100 and 142 mm front and rear) in combination with 45 mm wide WTB Scraper rims. A WTB Trailblazer tire in 2.8 inch width is fitted, ridden with a tube. The bike weighs a sensationally light 12.4 kilos for a 27.5 Plus bike with this wheelset in the configuration described above (without pedals, incl. bidon holder). The tires were first inflated to 1.0 bar and then to 0.8 bar for testing. The suspension is set to 25% sag

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Fascinating sight
The 2.8 inch wide Trailblazer rollers from WTB make an impression - and it's not the tire width that makes you look. It's the volume of the tires that fascinates. If you place a 2.5-inch Schwalbe Magic Marry on a wide rim next to the 2.8-inch roller, the difference in width is not very noticeable, but the difference in tire height and therefore volume is very noticeable. In combination with the wide WTB rims, the Plus tire has a much wider footprint. Anyone who has always wanted to balance casually on the bike standing at the red light on the way to the single trail will enjoy this: The wide plus-size tire with low pressure stands there as if nailed down, balancing at a standstill becomes a simple exercise.

Grip, grip, grip...
When riding the bike on trail terrain, the tires provide a lot of confidence: the rollers can be moved perfectly uphill and downhill on loose gravel, and the front wheel can even be braked so hard that it starts to slip. On a thin tire, this causes beads of sweat to form on your forehead; on a plus-size tire, it's a lot of fun. Starting off on steep, slippery terrain is much easier and more effortless with the Plus tire than with tires between 2.1 and 2.35 inches. Where the rear tire used to slip when starting off on steep, slippery terrain, the Plus tire finds its way uphill with a fascinating amount of traction. Yes, these tires are real uphill monsters: the rollers produce incredible grip and uphill passages can be mastered that were previously only possible in pedestrian mode.

Inertia: adjust the gearing
Uphill pedaling power is required with plus-size rollers - traction is good, but the 2.8-inch tires and wide rims add significantly more inertia to the bike. This mass needs to be overcome when starting off, which brings the issue of gear range into focus. A sporty, tight single-chainring drivetrain - designed for a lightweight 29er - quickly reaches its limits on the plus-size bike.

Hands off too much tire pressure
Downhill, the tires act like a buffer and filter out the first bumps before the suspension elements have to do any work. The plus-size tires only become effective with low air pressure. With a rider weight of 75 kilos including equipment, 0.8 bar felt best. The tires take root passages, gravel and stony terrain in their stride and make these obstacles almost disappear. This makes maneuvering and accelerating downhill much easier for inexperienced riders, as there are far fewer bumps on the handlebars and the bike is easy to control.

Semi Fat makes you brave
Thanks to the 45 millimeter wide rim, the roller is perfectly supported and the rubber does not tend to buckle even with very low air pressure, it takes a lot of speed and centrifugal force to get the roller off the track or to slip in the curve. Buckling of the tire is never an issue with a 45 mm rim, and detachment of the tire from the rim sidewall is certainly not an issue. The Koba Sentiero Semi Fat is forgiving and requires less steering precision, making the bike playful and tolerant. Due to the higher system weight of the wheels, tight corners are more difficult to ride, with the rollers you have to be prepared to take wider turns than on thinner tires.

The plus size turns the marathon sprinter or the bike beginner into a stuntman: the tire width makes you brave and encourages small jumps. If the jump or landing is not precise, the rollers ensure good-natured handling with a wide limit range. As the bike encourages an active riding style, a dropper seatpost is highly recommended. The dropper post was missing on the test bike, but thanks to Koba's Custommade system, it can easily be brought on board.

The comparison: Ride test with 29er bikes

Invites a sporty riding style: Koba 29 Big Sentiero

Koba 29er wheelset
2.1 Rocket Ron tires from Schwalbe, Crest rims from Notubes, identical 240s hubs from DT Swiss, the same XT brake rotors and the same XT cassette as on the semi-fat wheelset: this recipe ensures that the wheelset is easy to change and that the brake rotors sit perfectly in the middle between the brake pads at the front and rear without readjustment. After the pit stop, the bike can be ridden carefree immediately without the hassle of grinding brake rotors, making this conversion possible even for inexperienced mechanics. The bike with this wheelset in the configuration described above (without pedals, incl. bidon holder) weighs an attractive, light 10.9 kilos for a marathon fully.

Cross country versus plus feeling
With the wheel change, the change takes place: with the 29er wheels with 2.1 tires, the Koba Big Sentiero looks much more slender, even anorexic compared to the Plus build. At the start of the comparison ride, the Rocket Ron tires are moderately inflated to 1.4 bar, the negative suspension travel is not changed and is generous for a marathon bike at 25 percent. And: The first pebble is already noticeable on the identical test lap.

Gone is the good-natured feeling that the plus rollers convey. On sand, progress feels more strenuous - despite the significantly lower wheel and overall weight - and the tire sinks in, which requires greater riding skills and higher steering forces. Going downhill, you can clearly feel that the steering angle of 71 degrees is on the steep and nervous side and requires a steady hand on the handlebars. The bike needs to be guided as precisely as a scalpel and conveys less confidence than on the Plus model. The rear wheel slips on roots where the 2.8 rollers rolled over them good-naturedly. In contrast to the Plus set-up, the bike is far less likely to pull off into jumps over edges or roots. Presumably, tires with more tread and a width of 2.25 or 2.35 would tickle more stunt character out of the bike.

Spritely, agile, fast
However, the Koba bike in the marathon setup shows other qualities than the plus-size good-naturedness: the bike feels extremely lively and always encourages pedaling and intermediate sprints - pedaling was never an option on the plus-size test ride. The bike hangs on to the throttle willingly and encourages you to go fast uphill. The low system weight makes for effortless climbing and a playful, slightly nervous ride feel. Where the Plus bike climbs fascinatingly steep ramps, the Marathon edition does not necessarily have to stop. However, mastering the steepest climbs requires significantly more physical effort and strength. In order to be able to climb, the rider has to clamp themselves massively into the bike and bend their upper body strongly forwards and down towards the handlebars to prevent the front wheel from rearing up.

The bike masters tight cornering radii and hairpins very well - both uphill and downhill. The rollover behavior of the 29er wheels - albeit with narrow tires - conveys safety and also takes the fear out of high steps.

Conclusion:
The Plus-Bolide from Koba makes it much easier for less experienced riders to tackle difficult terrain. Thanks to the low total weight of 12.4 kg, the semi-fat bike can be ridden uphill without any weight penalty. For experienced riders, the plus-size construction provides a freeride feeling, as the bike encourages a playful riding style with jumps, small drops and explosively fast corners. A dropper seatpost - not fitted in the test, but easy to configure in the Custommade range - would tease even more potential out of the bike.

If you order the bike with two wheelsets, you can switch from one bike world to a completely different one. In the marathon setup, the Koba mutates into a full-throttle machine that cuts a fine figure in competition and invites you to lactate orgies. Extending the range of use of a bike with a second wheelset is nothing new in itself. If you ride the Koba bike with the marathon and semi-fat wheelset option, you have a racing and a freeride light machine at your fingertips in no time at all - and both are really lightweight.

www.koba.ch