Cannondale has always placed a lot of development emphasis and brand awareness on its racing efforts, and the F-Si is an addictively rapid and distinctive ride.
The head tube is very short but uses a 1.5in diameter bearing top and bottom to cope with the twin-crown design of the Lefty fork. Gear cables and brake lines are kept external for easier servicing and lower weight, due to the lack of outer cable sheath.
The front mech is direct mount, which will leave a stub if you single-ring it, and there’s no routing for side swing front derailleurs. In addition, there’s no direct mount for the rear mech. The direct-fit rear brake has to use an adapter to work with the 160mm rotor, which defeats the object of the simplified, lighter mount.
This does leave the flex-reducing ‘SAVE’ seatstays free from brake loads, though, and their broad stance at the subtly curved seat tube and wide PF BB gives the F-Si massive amounts of mud room.
The skinny 27.2mm seatpost adds flex into the ride but rules out most dropper post options, while the rear dropout is 135x9mm QR only.
The older XT rear mech is only 10-speed and doesn’t have a clutch, which makes it unsuitable for a single-ring conversion Russell Burton
Cannondale F-Si Alloy 1 kit
The big news is that the latest Lefty 2.0 PBR is well worth having. The extra keyhole brake mount means that it isn’t significantly lighter than a conventional fork but, contrary to what you might expect, it’s much stiffer. The Lefty is impressively smooth and consistently controlled too, and the fork-top lockout is easy to reach for climbs and sprints.
What really impresses is how well the F-Si holds its momentum in the rough
Front wheel compatibility is severely restricted by the unique tapered hub that screws onto the Lefty’s conical axle, but the Stan’s rim is a decent, tubeless-ready hoop. The skinny, low-tread Schwalbe tyres were definitely chosen for speed, not comfort or all-weather traction, though.
The remaining spec is OK, if not outstanding, with a last generation, 10-speed Shimano XT rear mech and SLX shifters, driven by 30mm-axle Cannondale cranks with deeply scooped backs. The F-Si is gagging for a single-ring conversion to lose some weight, but that’s hindered by the lack of a clutch mechanism on the clattery rear mech.
The flat bar is slightly narrow at 700mm but the sticky saddle is great for riders who like a stable position from which they can grunt a big gear.
You can really drive the F-Si through rough sections without getting battered off line or out of rhythm Russell Burton
Cannondale F-Si Alloy 1 ride
Even though the bike is on the heavy side with slightly weighty wheels, it’s rare that you’ll have to really strain on the cranks, simply because the ’dale is a naturally rapid and efficient ride. The ‘Smartformed’ alloy frame really pushes the power to the rear wheel and the skinny, low-tread Racing Ralph tyres help maintain speed on smoother trails.
What really impresses is how well the F-Si holds its momentum in the rough. Up front, the Lefty fork’s smoothness compensates for the tyre’s small air chamber. The naturally progressive stroke means that you can bury the F-Si head-first into big rock sections yet still come out mounted and roughly where you wanted, which isn’t always so on a short-travel race bike.
At the rear, the carefully sculpted chain and seatstays plus the under-seat flex of the long, skinny seatpost mean that you can drive the bike through rough sections without getting battered off line or out of rhythm. This level of connection also flatters the tyres’ traction, to the point where we were pushing hard across mixed dry/damp terrain.
When the F-Si did let go, the accurate, agile handling from the custom offset Lefty fork and the relatively steep head angle meant that it was easy to catch and correct. This forgiving ride also helps reduce fatigue, while the generous tyre clearance means you can upsize to much bigger rubber if you really want to float.