Trek’s Farley range of fat bikes has always taken a different tack with slightly smaller-than-typical tyres that work reasonably well on snow but are more versatile everywhere else. The new upper-end carbon fibre Farley models take that philosophy even further with larger-diameter 27.5x3.8in tyres that supposedly offer the same benefits that bigger wheels do for trail bikes – but still with plenty of clearance for the fattest 26in wheels and tyres when the snow starts to fall.
Building a frame to handle both of those wheel and formats is relatively easy in one sense, since the overall diameters are so similar. However, accommodating that massive 5in width required a bit of ingenuity.
Aluminum Farleys use 177mm-wide rear dropout spacing and a 100mm-wide threaded bottom bracket – both dimensions being on the narrower end of things as far as fat bikes are concerned – and just barely accommodate 26x4in tyres. The new carbon Farleys, however, can gobble up tyres as wide as 26x5in but still maintain the same pedal stance width and chainstay length.
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It took some doing to build the carbon Farley to accept the biggest 26in tyres on the market but without increasing pedal stance width or chainstay length
As expected, rear hub spacing on the new carbon bikes move to the wider 197mm thru-axle format – essentially the standard for fat bikes running such wide tyres. Instead of widening the bottom bracket shell by 20mm to compensate, though, Trek has moved to a 122mm press-fit format that keeps the bearings and cranks in the same positions as before but still allows the impossibly thin chainstays (just 13mm thick each!) to be pushed further apart for more clearance. To maintain a proper chainline, the direct-mount chainring is flipped from its usual orientation so that it’s offset to the outside.
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