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Boost 148 moves the rear hub flanges 3mm outboard on each side in order to improve the spoke bracing angle. The spoke bracing angle is the angle formed between the spoke and the vertical plane. By moving the hub flanges outwards, spoke angles increase, creating a more stable base. Larger spoke angles are able to balance a larger component of the lateral forces exerted in the horizontal plane during loading. So, with a wider hub shell comes better bracing angles of the spokes, which results in a stiffer, stronger wheel.
With these minor shifts in flange spacing, the brake rotor mount and the freehub body location have to be taken into consideration and boost bikes compensate with adjustments to the chainring position. In order to get the best shifting performance, with the cassette 3mm outboard, the chainline (the line from the chainring to the center of the cassette) needs to be moved to accommodate that new position. It is necessary to move the chainrings outboard by 3mm and this shift can be accomplished with a redesigned crank arm spider. The crank arm Q factor (the distance between a rider’s feet when they’re on the pedals) and the frame’s bottom bracket shell width remain the same. With the chainline shift outwards, the frame is afforded more tire and chainring clearance and can maintain short chainstays.
A 3” tire, when paired with a 26” or 27.5” rim size, results in an overall outside diameter of the standard version of the next larger mountain bike wheel size. In general, a 27.5 rim with standard 2.2”-2.3” tires results in an overall outside diameter of 27½ inches. 26 Plus is achieving this same overall outside diameter of 27½ inches by downsizing to a 26” rim but pairing it with a 3” tire. Same when looking at 27.5 Plus. A 27.5 rim paired with a 3” tire results in approximately a standard 29er outside diameter.
Larger volume tires on wider rims allow for lower air pressures to be used , especially when set up tubeless, resulting in a larger contact patch with the terrain. Having more knobbies on the ground results in more traction and additionally provides the ability to float easier over rocks and roots. By outfitting our 27.5 and 29er trail hardtails with 3” tires, inexperienced riders benefit from the increased stability, float and traction. At the same time, more traction allows seasoned riders to ride terrain even faster and with greater confidence.
All our frames and forks are tested continually to meet or exceed (in some cases, well exceed) EN standards 14764, 14765, 14766 and 14781 as well as the new ISO 4210 standards. We conduct these tests at our frame manufacturing facilities, but we also use EN accredited testing laboratories such as Intertek and SGS to verify the results of our own tests. If these tests aren’t telling us everything we want to know about our bikes, we increase the loads and cycles, or we determine another way to test. Where current hydraulic testing machines, jigs and hardware aren’t up to the task of emulating some of the forces and impacts our bikes might be subject to, we’ve designed our own.
We relentlessly cycle test for fatigue from pedaling and torsional forces on every single frame size, with deflection tests for stiffness at every point of the frame. Brutal impact tests with massive weights dropped on fixed frames or forks are performed. Then reversed, with weights attached to the frame, the frame hoisted to a given height depending upon product type, then released.
This destructive testing is enormously instructive and important. And it is in continual process. But it’s our ongoing non-destructive testing of frames and forks fresh off the factory floor that’s just as vital.
For our carbon fiber frames, EVERY frame is weighed to make sure it’s neither resin rich nor resin deficient. We also measure the stiffness of each frame in 6 critical areas as a check on lay-up production. Each deflection test must fall within 5% of the standards our machine and field-testing have established. This weighing and stiffness deflection testing guarantees every single frame we produce meets all Jamis manufacturing protocol and will
deliver the ride qualities we defined and demand.
A 27.5x3” tire measures out to a 29” diameter and a 26x3” tire measures out to a 27.5” diameter. Combining them with a 40mm rim, results in the ultimate combination of traction, roll-over and versatility without being too heavy, too bouncy, too tall or feeling lethargic on the trail.
Riding fast with control requires steering precision, which starts with the front of the bike. Stiffening this area results in less wheel deflection, more wheel control. A full 1.5” head tube and steerer would achieve this, but would add unnecessary weight and bulk, and limit stem choices. But a tapered 1 1 /8” to 1 1 /2” head tube serves up a significant increase in rough terrain tracking and stability without much of a weight penalty compared to standard 1 1 /8” systems.
The rear wheel tucks in with short chainstays. With a 12x148 rear hub, you’ve got a stiff and responsive rear end.
A 12x148 rear hub with 3mm offset chainrings minimizes the chance of chain to tire contact with short chainstays and “mid-fat” tires without compromising any pedaling efficiency to a wider q-factor.
Securing the rear wheel to the frame by threading a 12mm axle into the rear drop-outs is not only safer, it’s stiffer. The rear wheel tracks directly in line with the frame, for more precise handling, so you can go faster with more confidence. The increase in stiffness of a 15mm fork axle improves steering & handling significantly. It also puts less stress on the fork’s internals, improving fork durability and performance. The hub drop outs provide a self centering feature for the wheel for fast, easy installation.
A one-piece bottom bracket shell and drive-side chainstay yoke provide a strong and lightweight solution for the potential clearance issues of 3” tires and double chainrings.
Benefits of a tubeless set-up are reduced rotating weight and the ability to use lower inflation pressures for greater traction without the risk of pinch flats. WTB TCS rims feature a tubeless UST “On-Ramp” profile providing a consistent fit between the rim and the tire for easy installation and inflation.
Bigger wheels and tires generate more rotating mass and traction once they are up to speed. So it only makes sense to use larger rotors to help control that larger wheel in the most efficient manner possible. Sure, 160mm rotors will stop the bike. But when you’re riding like every second counts, braking for the shortest time possible while keeping the bike under control is the goal. And a larger 180mm rotor up front let’s you do this.
A 35mm seat tube with 31.6mm seat post assures the stiffest possible pedaling & steering platform, with a sloping top tube for low stand-over.
|Frame||Triple-butted 6061 aluminum, 1.5 - 1 1/8” tapered head tube, post mount disc brakes, 12x148mm thru-axle drop-outs, High Direct Mount (HDM) front derailleur with front-pull internal cable routing, internal dropper post routing, replaceable derailleur hanger, Formula thru-axle|
|Fork||RST Alpha TNL 27.5/26+, coil spring with Turn-n-Lock hydraulic lock out, 32mm stanchions, magnesium lowers, 9x110mm hub spacing,120mm travel|
|Headset||FSA Orbit 1.5 Zero-Stack internal cup, 8mm cone spacer|
|Wheels||WTB Scraper i40 TCS tubeless 26" rims, Formula 9x110 front & 12x148 sealed bearing hubs, stainless spokes|
|Tires||WTB Ranger, 26 x 3.0”|
|Derailleurs||Shimano Deore Shadow Plus rear|
|Shift levers||Shimano Deore, 1x10-speed|
|Chain||KMC X10-1, 10-speed|
|Cassette||Shimano HG500, 10-speed, 11-42T|
|Crankset||SR Suntour Zeron, 32T, 170mm (14”/16"), 175mm (18”)|
|BB Set||SR Suntour External|
|Pedals||MTB alloy platform|
|Brakeset||Tektro M286 hydraulic disc, 180mm front &160mm rear 6-bolt rotors|
|Handlebar||Race Face Ride, 685mm x 25mm rise|
|Stem||Race Face Ride, 60mm (14"), 70mm (16"), 80mm (18")|
|Seat Post||Race Face Ride, 31.6 x 400mm|
|Saddle||WTB Deva Comp|
|Sizes||14”, 16”, 18”|
|SIZE||TOP EFFECTIVE||HEAD ANGLE||SEAT ANGLE||CHAIN STAY||WHEEL BASE||BB DROP||HEAD TUBE||STANDOVER||STACK||REACH|
|14||21.2 / 540||68˚||73˚||16.7 / 425||41.4 / 1051||1.5 / 38||3.7 / 95||28.3 / 718||21.5 / 547||14.2 / 361|
|16||22.1 / 560||68˚||73˚||16.7 / 425||42.2 / 1071||1.5 / 38||3.9 / 100||29.6 / 752||21.7 / 552||15.0 / 380|
|18||22.9 / 580||68˚||73˚||16.7 / 425||42.6 / 1091||1.5 / 38||4.1 / 105||30.7 / 781||21.9 / 556||15.6 / 398|
FIT & SIZING
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Specifications are subject to change without notice.
All bike and frame weights are based off pre-production painted frames. Weights may vary in final production.
Jamis is not responsible for typos or misprints.
Always ride safely and within limitations. Always obey all local traffic, safety and land access laws and always wear a helmet.
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