When Yeti discontinued its SB95 last year without a replacement, loyal fans waited anxiously to hear about what the brand had in the works and when they'd get to see it. The new SB4. 5 Carbon X01 Complete Mountain Bike is their answer a moderately slack 4. 5 inch travel 29er designed for stability and speed on the trails with plenty of snappy climbing capability that demonstrates Yeti's faith in the 29er in the midst of the 27. 5's rising popularity. Though it was created to fill the trail niche in Yeti's line, the SB4. 5 has a notable focus on lightness to keep it versatile enough for other disciplines. The carbon fiber frame is stiff and light, with a relaxed 67. 5 degree head tube angle and stability enhancing 17. 2 inch chainstays that don't get in the way on climbs. The FOX 34 Factory fork also provides confidence on descents, with 140mm of plush, forgiving travel that gives you the option to pick a line when you feel like it, and point the bike downhill when you don't. Yeti uses its relatively new Switch Infinity suspension in the SB4. 5, which keeps the pedal stroke consistent and aims to reduce squat using a pivot system that switches direction as you move through the bike's travel. Yeti's inclusion of a 12x148mm Boost rear axle also contributes to the SB4. 5's stiff, efficient pedaling platform, and the departure from the 142mm standard allows for more space between the hubs for better tire clearance especially relevant for 29ers. With a greater hub distance, you also get a smaller, steeper spoke angle, which creates a stiffer wheel and chassis platform. Finally, the hub's bearings themselves will experience less damaging torsional forces with the increase in space, prolonging their lifespan and leading to a more efficient rear triangle as a whole. This stiffness is what makes the SB4. 5 more adept at climbing than you'd expect, aptly demonstrating Yeti's reluctance to allow its bikes to fall too neatly into one category alone.This build kit featu...