This is the new Pivot Mach 4 carbon; it features a full carbon frame, 115mm of rear travel and 650b wheels. If you’re familiar with the Pivot range, you’ll know the company has a Mach 429 carbon 29er in its line-up already, so why launch a 650b version?

Pivot says it wanted to produce a short-travel bike with the handling and acceleration of the old 26in Mach 4, but with some of the benefits of bigger wheels.

Need to know

• 650b, 115mm travel XC/trail bike
• Full carbon-fibre frame
• DW-link suspension design
• Future proofed for Shimano Di2

Using 650b wheels also allowed the company to produce a XS frame size, something that wasn’t possible with the Mach 429. So what are your options?

It’s lively, but does it compare to short travel 29ers?

Like most of the Pivot range, the Mach 4 is available with several build kits — the SRAM X01 option that I rode costs £2,650 on top of the frame cost, or you can choose a Shimano XT build kit for the same price. There’s also a XT/SLX mix for £1,650.

Fancy a more racy set-up? The Mach 4 can be configured for cross-country competition by swapping the stock 120mm fork for a 100mm version and resetting the rear sag using a small guide on the shock.

Basically there are settings for both ‘race’ and ‘trail’, but because our supplied test bike came with a 120mm fork, I stuck with the trail mode exclusively.

Cross-country or race tuned? You decide

In terms of intended use, the Mach 4 is a similar bike to the Saracen Kili Flyer 122 that won our Discount Bikes test in September 2014. It’s also short travel and has 650b wheels, but there’s a key difference in the geometry that makes one of them more fun to ride — the Kili is 20mm longer in the front centre.

The lack of length in the Mach 4 makes it feel twitchy and less stable, especially when riding rough or steep terrain. On the flip side, the carbon frame is incredibly stiff, it weighs practically nothing, has a ton of standover clearance and the DW-Link suspension is very efficient while still offering ample grip and control.

In terms of build quality, there aren’t many bikes that are better made than the Mach 4 — the level of detailing is superb. I particularly like the way the frame is future-proofed for Shimano Di2 and even features a compartment for the battery at the bottom of the down tube.

With 29ers dominating the short-travel market, 650b bikes are a rarity, but they can be fast, fun and flickable. The Mach 4 is certainly lively, but I think its sizing is a bit off. Ultimately, the Mach 4 is not as confidence-inspiring as the Kili Flyer or aggressive short-travel 29ers such as the Specialized Camber Evo or Kona Process 111.