We never tested the 2007 Rush, and one of the reasons for that was it had a low, almost too low, bottom bracket. At last year’s press camp we clipped our pedals more often than we changed gear, which didn’t bode well for any future test. For 2008, Cannondale is still running the same geometry on all of the Rush models except for one bike hidden away at the bottom of the range, the Rush Carbon 4.
This bike has a higher bottom bracket and slightly different geometry to the other three bikes in the range. Cannondale hasn’t done anything sophisticated to this frame, it’s simply replaced the 110mm-travel Lefty fork for a longer-travel Fox F-120. This has a taller axle-to-crown height (about 500mm compared to 480mm) and this lifts the bottom bracket enough for the pedals to clear roots and rocks when riding in technical terrain. The increased ride height also slackens the old 69-degree head angle by about a degree and shortens the top tube by a few millimetres. It’s seems Cannondale has hit on this winning formula by chance but we’re not complaining because the bike ticks all our boxes.
light as you like
First off, it’s lightweight. Cannondale has trickled down the carbon frame from last year’s team bike to all the models. Unlike the Taurine, which is co-cured, the Rush is a monocoque, with aluminium inserts for the main pivot, upper shock mount, headset and bottom bracket. The latter starts out as a press-fit SI (system integration) shell, but to accommodate the XT bottom bracket on our bike, Cannondale has bonded in two threaded cups.
Bolted to the main frame is a 6000 series aluminium swingarm with taper-butted seatstays and 3D hydroformed chainstays featuring two kinks designed to increase vertical compliance. Obviously, the elevated stays offer excellent mud and tyre clearance. To save weight, a big hole is machined in the middle of the swingarm and a plate is welded over the hole to create an internal pocket. Cannondale calls this hollow-core construction ‘Hot Box’ and claims it increases stiffness by 30 per cent. There’s also a new bolted-on bridge between the stays on the 2008 bike that ups stiffness a further six per cent.
Speccing the Fox F-120 fork instead of a Lefty has freed up some budget for a better spec than we normal see on ‘Dales at this price. Highlights include a set of pimp-white Avid Juicy 5 disc brakes, a Shimano XT ‘Shadow’ rear derailleur and Crank Bros Candy C pedals. Cannondale claims the Float RPL rear shock is a custom item it developed in conjunction with Fox. Of course we’ve all heard that before, but the difference here is that the RPL gets a lockout, along with fully open and medium ProPedal settings.
We’re not big fans of Cannondale’s colour-coordinated styling, but there’s no doubt the Rush Carbon 4 is a great lightweight trail bike with good geometry, effective suspension and a balanced specification. It’s one bike we’ll definitely be testing next year.