The Mach 4 is the fourth generation of the first bike produced by Pivot and it not only sits on the latest 650b wheel size, it’s also the first bike we’ve ridden that’s fully optimised for Shimano’s upcoming electric XTR Di2.
Frame and equipment: making room for progress
The most obvious aspect is the amount of space needed between seat tube and chain line for the new Side Swing M9000 Di2 front derailleur. That means even with a recessed driveside linkage the back sloped seat tube is shoved all the way over to the left and the off-side linkage mounted on the outside of the tube. Pivot has also found space in the kinked forward offset seat tube to fit the long, thin (think shock pump without a dial) internal Di2 battery and the T base plate bolts into threaded inserts either side of the unavoidable hole in the down tube.
The massively offset seat tube is designed to give clearance for the new Shimano XTR Side Swing derailleur
If you’re not using Di2 (and given there’s still no solid release date almost a year after it was first shown, it’s not surprising that our Pivot wasn’t actually wearing any of Shimano’s new electric kit), that hole is covered by a bolted hatch through the rubberised belly panel. There are also cutouts for the rest of Pivot’s totally comprehensive internal cable, brake and stealth dropper hose and electric wiring routing.
It’s good to see proper bolt-on covers that’ll stay put over time rather than rubber plugs that will inevitably fall out. Somehow Pivot has included all these features and still kept weight low enough to make the Mach 4 the lightest full suspension frame it’s ever made and comparable with the competition at 2.3kg (5.1lb).
All cabling is routed neatly and internally
The chainstays are also extremely short for the fastest possible rear end reaction in both handling and suspension terms. By using printed resin prototypes to double check computer models before committing to carbon (and adding rubber linkage bumpers just in case) the company’s also managed to squeeze in 115mm of travel. Cramming it all in means the chainstays have to be dramatically asymmetric (straight on the offside, dropped on the driveside) so that the chunky bridge joining them is practically vertical. Tyre clearance is unsurprisingly tight and you’ll do well to keep anything much bigger than 2.3in rubber revolving in muddy conditions.
We've recently ridden several excessively offset/asymmetric machines that had all the structural integrity of a balloon animal, but Pivot has managed to keep this bike remarkably stiff. This is down to a combination of several things. The very stiff Hollow Box carbon construction is already proven (the Mach 429 29er is one of the stiffest in its category) and the very short upper and lower linkages also reduce leverage when the bike is being bent sideways.
Ride and handling: a speed demon
Thanks to stout tubes and a tall head tube, the mainframe is also very stiff – again, all the more impressive considering the curved top tube is deliberately designed to give such a low standover height (36-108mm lower than other large sized bikes we tried at Interbike). Indeed, some of our less charitable testers felt it looked like a ladies ‘step thru’ bike. It’s also worth noting that there’s no Mach 4 in XL, because Pivot rightly or wrongly presumes really big riders will want equally big wheels.
There’s masses of standover clearance thanks to the swoopy top tube
Whatever your opinion on its low-slung aesthetics they certainly don’t stop the Mach 4 picking up its skirts and running like hell. The stiff frame and overall weight combine with particularly light and sharply stiff DT Swiss Spline wheels and super-fast rolling Maxxis Ardent Race rubber to take the Pivot supersonic with minimum effort.
A clip-on guide with clearly marked ‘race’ and ‘trail’ sag points also makes setup easy for a firmer or more flowing character and highlights the fact DW Links are designed to work with relatively low pressures. This enhances the already very neutral terrain-following feel, and while it lacks a really direct ‘dig in’ through the pedals the bike stays impressively stable and level as the trail ebbs and flows almost unnoticed under the rear wheel.
A nifty sag indicator simplifies setup of the 115mm rear travel
Given that there’s only 115mm of rear wheel travel you can give it full gas through surprisingly rough and rocky terrain before you’ll start to register it even slightly disturbing the Mach’s composure. The harder we rode it through more hardcore terrain, the more the control and capability gap between it and other shorter travel bikes – even those with 29er wheels – grew.
Thankfully Pivot has equipped it with exactly the geometry it needs to really shine when things get radical. The head angle of 69 degrees with a 120mm fork gives useful self-correction stability without being too slow to snap round uphill turns. The low set frame and generous sag on an already low bottom bracket height mean you can really scythe through high speed turns, and the DW Link rear end isn’t unduly bothered by any braking you have to do.
Lack of suspension feedback doesn’t limit speed, even when the going gets rougher
If you do overstep the traction mark, the super short rear end flares out wide to turn the nose in tighter rather than drifting the front dangerously. Top tubes are long-ish too (603mm on a medium), which works well whether you’re a shaved-leg speed freak looking for extra stretch or a stumpy stem, wide bars fan.
Ultimately, like all DW bikes we ride, the Mach 4 is a bike whose ability and agility is initially undersold by the smooth neutrality of the suspension, rather than a more in your face interactive and dynamic feeling bike that ultimately might have a less consistent and controlled ride.
This article was originally published in What Mountain Bike magazine.