You Can Have a 29er Downhill Bike - Trek Introduces the New Session 27.5 and Session 29 17

It’s a big day in mountain bike land with the launch of Trek’s new carbon Session downhill bikes. The most shocking news of the announcement is their commitment to a production 29-inch-wheeled DH machine which you will be able to buy. All you need is $4999.99 for a frame, fork and rear shock and a little patience to get you to October.

Trek’s Session has been a World Cup podium regular for years and the latest generation of the bike features refinements that Trek hopes translates into more speed for racers and more fun for those cranking out park laps.

What's New with Trek Session

While Trek continues to offer alloy versions of the Session, we’re focused on the carbon 27.5 and 29 models. The downhill bikes showcase the design features we’re used to seeing from the brand - OCLV carbon construction with carbon armor, Mino link geometry adjustment, Active Braking Pivot, Control Freak internal cable routing, and an E2 tapered head tube. The major frame design change this time around is the switch from Trek’s Full Floater suspension platform to a fixed lower shock mount arrangement.

Where did Full Floater go? Trek's Dylan Howes explains

The Full Floater was originally designed to provide that last bit of extra progression in the travel. The downside to the design was a compromise in stiffness due to the constraints of the parts in motion. By fixing the lower shock mount to the front triangle, Trek was able to add stiffness to the overall system.

FOX and Trek Suspension Developments

Trek’s Suspension lab also worked with FOX to develop a Session-specific tune on the Factory Float X2 rear shock. The metric-sized shock has a longer stroke, which means a lower leverage ratio and the new internals in the air shock offer more mid-stroke support and that extra bit of end-stroke progression that the Full Floater used to provide. The Float X2 shocks are user-tunable with the addition or subtraction of volume spacers.

FOX and Trek also went deeper on their Float X2 tuning tweaks to remove the initial platform the air shock had built in to it. The platform existed to help with pedaling across a variety of bikes. Trek wanted their Session’s Float X2 to be pure downhill. The internal changes create an X2 which has "better than coil" performance in the initial small-bump stroke of the travel. When Trek Factory Racing ripper, Gee Atherton, was informed of the Float X2's changes, he understood the benefits of the new air shock but preferred the feel of the coil just because he’d been riding them for so long. Had he not been injured at the Fort William BDS race a couple weeks ago, he may have found his way onto the air shock eventually. For those set on coil, don’t fret, 225x75mm metric coil shocks will fit.

Jose Gonzalez on the Session-specific FOX Factory Float X2 Tune

Geometry

The Session Carbon is available in S, M, L and XL sizes. Though this bike obviously “looks like a session,” the bike is longer and more aggressive which is where downhill race machines are headed. Reach measurements have been increased by 20mm and the bike has a lower bottom bracket height thanks to input from the Athertons.

Session 27.5 Geometry (scroll left/right)

Session 29 Geometry (scroll left/right)

The stock head angle on the 27.5 is 63-degrees, but with the combo of Trek’s Mino Link and the included 1-degree off-set headset cups you can tweak your geometry as needed. Head tube angles can go from a super slack 62-degrees or as steep as 64.5-degrees, and bottom bracket height can be tweaked by as much as 8mm. Chainstay length is adjustable between 445mm or 446mm depending on the Mino Link setting.

Trek's Dylan Howes on why the Session 29 head angle is listed as slacker than the 27.5

We were able to use the same main frame for 27.5 and 29 but chainstays, seatstays and rocker links are all different. Using the same main, we set the BB-to-ground height the same, but to meet up with the fork and the bigger diameter wheel, the frame “tips back” about a degree. We correct for this using the angled headset cups to get the 29er back to a 63-degree HT angle. Out of the box, we intend the 27.5 bike to be run with a straight headset and the 29er with a “+1 deg” cup as the standard or nominal setting.

We don’t really expect the rider or racer who has bought into the 29 to want to go steeper than 63-degrees, but we could see some of the more park/jumping-oriented riders who would choose the 27.5 bike for ride quality to possibly want a 64 degree HT angle. The cups are something we include with both bikes to give the rider more set-up and adjustment options.

But bottom line, intended / standard geometry is 63 degree HT angle for both bikes.

Introducing the Trek Session 29 Carbon

Let’s get to the one you’ve all been waiting for, the Session 29 Carbon. That’s right, 29-inch wheeled downhill bikes are here for the masses and Trek could be considered the biggest reason why. There has been experimentation with 29ers in downhill for years, but until now the complete package of forks, tires and wheels hasn’t been available and DH bikes from five to ten years ago were generally a lot more compact than the stretched-out machines we see today. Trek saw the potential for 29ers in DH as far back as 2009 with early but less-than-successful prototyping. With the advent of modern race geometries and component designs, they revisited wheel size a couple years ago and began working closely with FOX to make sure suspension on the front end wasn’t going to hold them back.

Dylan Howes on the genesis of a Trek 29 DH bike

They carefully tested 29-inch DH wheels with modified 180mm-travel 27.5 FOX 40 forks. The data gained from those tests opened the eyes of both Trek and FOX and the 29-inch-specific FOX 40 came to life. While the Santa Cruz Syndicate was the first team to show up at the World Cup in Lourdes with the forks, there’s no doubt it was Trek’s push that excited FOX enough to get the product rolling. Now we’re seeing the snowball effect across World Cup DH teams that have access to the 29er FOX 40.

But 29ers Can't Turn?

The roll-over-anything, haul-ass-downhill wheels are great for World Cuppers going 50mph, but what about tighter handling and cornering? Trek gathered data from over one hundred downhill runs across various riders. They used data acquisition equipment and Lit Pro software to monitor speeds on every section of a variety of test tracks from SoCal to Whistler. The software provided side-by-side analysis of runs on each wheel size. It was no surprise that the 29-inch wheels shined in the rougher, straighter sections, but eyes were opened when the data showed that cornering speeds were also the same or even faster on the big wheels. Trek’s Jose Gonzales noted that he and his testers agreed that the 27.5 just "felt busier" through the turns while the 29er felt more calm. The result was less energy spent by the rider in addition to quicker times.

Dylan Howes discusses cornering

The compiled test runs indicate that the 29er was 4 to 6% faster from top to bottom and there wasn’t a single section in which the 29er was slower. The testers and data report that the big wheels provide more traction, so braking can be done later, corner speeds can be higher and exit momentum greater.

Dylan Howes on fork offset and handling

Additionally, Trek points out that the bottom bracket height of the 27.5 and 29 are the basically the same relative to the ground, but the bottom bracket drop between the two bikes is considerably different because of wheel size and axle height. This means the 29er rider sits lower in the bike and actually has more leverage and input when leaning the bike over in a corner. Combine the stability and traction with the body positioning on the bike and the 29er does it all better on paper and according to those who’ve ridden it.

Jose Gonzalez on Tire Buzz

The Session 29’s wheelbase is less than a centimeter longer than the 27.5’s. This minute change allowed Trek to use the 27.5 carbon front end, only having to develop a 29er-specific rear triangle and swing link, keeping costs manageable for development and the consumer. During development, they took note that the rear wheel position in relation to rider position is in nearly the same place as on the 27.5. The modern bikes are longer and riders aren't hanging off the back like they may have in the past, so their experience with tire buzz is different than what a lot of internet users are speculating as a problem of the wheel size in a downhill application. They did note, however, that in hard-angled cornering, a rider may buzz their upper, inner thighs with the side of the tire because of the bigger wheel.

So who’s the Session 29er customer?

A hardcore racer who embraces the potential of the wheel size is who Trek expects to chomp at the bit for the Session 29. Park riders wanting to flick and whip will want to stick to the 27.5. Trek realizes that wheels and tires are still the weak point in the equation for publicly available 29er DH products and that’s why they’re offering only a frame, fork and rear shock package. Available in September/October of 2017, for a penny under five grand USD, the 29er DH experience can be yours. They believe early adopters of the technology will be serious enough about the bike to fill in any gaps required to get a race machine built and on the track.

Can 29ers be too fast? Jose Gonzalez discusses.

World Cup Racing and the Session 29

Unfortunately Gee Atherton’s injury at the BDS prevents him from racing at the Fort William World Cup in a couple days. We may see Trek World Racing athlete, Graeme Mudd, aboard the 29er, however. For now, Rachel Atherton is sticking to her 27.5 Session, but that may not be for long.

Jose Gonzalez on sharing the 29er DH vision with FOX

Trek Session 9.9 27.5 RSL Highlights and Features

• $7999 complete (September 2017), $3999 frameset (August 2017)
  
• Frame: OCLV Mountain Carbon main frame & stays, ABP, magnesium EVO Link, E2 tapered head tube, Mino Link, integrated frame protection, Control Freak internal routing, Carbon Armor, ISCG mount, 210mm travel
• Fork: Fox Factory 40 FIT RC2, air spring, Kashima Coat, hi/lo speed compression, 20mm thru axle, 203mm travel
• Shock: Fox Factory Float X2, high/low speed rebound adjust, high/low speed compression adjust, tuned by Trek Suspension Lab, 225x75mm
• Front Wheel: DT Swiss FR1950 Gravity Classic, 110x20 front, 157x12 rear
• Rear Wheel: DT Swiss FR1950 Gravity Classic
• Tires Bontrager G4 Team Issue, 27.5x2.35
• Drivetrain: Shimano Saint 10-speed, 36T ring
• Pedals: Wellgo MG-1, magnesium body, Cro-Mo axle, replaceable pins
• Brakes: Shimano Saint M820
• Bars: Bontrager Line Pro, OCLV Carbon, 35mm, 15mm rise, 820mm width
• Headset: FSA Orbit, sealed cartridge bearing, 1-1/8˝ top, 1.5˝ bottom (includes geometry adjust angled cups)
• Saddle: Bontrager Evoke 3, titanium rails
• Post: Bontrager Rhythm Elite, 2-bolt head, 31.6mm, zero offset
• Stem: Bontrager Line Pro Direct Mount, 35mm clamp, 50mm length
• Grips: Bontrager Rhythm, dual lock-on

Trek Session 29 Carbon Highlights

• $4999, frame, shock and fork package (October 2017)
  
• OCLV Mountain Carbon main frame & stays, ABP, magnesium EVO Link, E2 tapered head tube, Mino Link, integrated frame protection, Control Freak internal routing, Carbon Armor, ISCG mount, 190mm travel
• Fox Factory 40 FIT RC2, air spring, Kashima Coat, hi/lo speed compression, 20mm thru axle, 203mm travel
• Fox Factory Float X2, high/low speed rebound adjust, high/low speed compression adjust, tuned by Trek Suspension Lab
• FSA Orbit, sealed cartridge bearing, 1-1/8" top, 1.5" bottom (includes geometry adjust angled cups)

Hit up trekbikes.com for more information on the new Session downhill bikes.

Photos by Trek Bicycles, Sven Martin, Dan Hearn and Shawn Spomer