DT Swiss is best known for spokes – that’s the core of its business and what it made its name in. But some cunningly judged acquisitions and developments over the years have seen its range expand into rims, hubs and rear shocks. In some ways shocks looks something of an odd one out in the line-up, but given DT’s location in the heart of the Swiss watchmaking industry and all the fiddly little bits that go into a shock, it starts to make perfect sense.
The SSD air shocks have been around for a while, and have proved to be lightweight and reliable. Now DT has built on that experience and launched the new DT HVR200, which is claimed to be the lightest platform shock available at 192g for a 165mm eye-to-eye unit. Uniquely, the platform damping as adjustable without tools and without stopping, and there’s a host of other neat features too.
But first, some background. Platform damping is a trick nicked from off-road truck racing shocks, specifically those designed by Charles Curnutt. The idea is that as well as the usual piston, there’s a second floating piston at one end of the shock (sometimes in a remote reservoir) with an air chamber behind it. There’s a valve in the main piston, and as the shock compresses the build up of pressure in the damping oil (which occurs because of the main piston pushing on it) tries to open the valve. If there’s not much pressure in the air chamber, the valve opens easily, lets loads of oil through and the shock compresses unimpeded. If there’s lots of pressure in the air chamber, the valve can’t open and the shock won’t compress. This has some very useful effects. First, you can easily tune the shock to remain unmoved by low-amplitude forces that result from pedalling but react to the more sizable ones from hitting bumps, and you can choose where the threshold between not moving and moving is. Second, because the shock will only compress until the pressure on either side of the piston is equal, it’ll only compress as far as it needs to to absorb a bump. Traditional shocks tend to over-travel, leaving the rebound damping circuit to bring things back under control. Platform shocks don’t work the rebound damping as hard and the bike feels more stable. The Curnutt design is found in Progressive 5th Element and Manitou SPV shocks. Fox’s ProPedal is slightly different – it’s essentially a tunable low-speed compression circuit, so it can be set to ignore pedalling forces but doesn’t really do a lot else.
The drawback of the Curnutt/5th/SPV shocks is that you need a shock pump to set them up and it can be hard for riders to get their heads around what they’re doing. This is where DT’s HVR shock comes in. Rather than using air pressure to set the platform, the HVR uses a coil spring with adjustable preload. The preload is adjusted via an additional hydraulic circuit connected to a handy knob on the end of the shock, so you can set your chosen level of platform damping just by twiddling the knob and setting the main spring air pressure is just like on a regular air shock.
The range of platform adjustment available on the HVR is impressive, from locked out (although it’s never actually locked out – if you hit something hard enough it’ll compress) to completely open, which gives you no anti-bob but still offers stability benefits. As well as on-the-fly adjustment, the other advantage of a preloaded spring rather than a pressurised air chamber for platform adjustment is that there’s less to go wrong. If the air leaks out of the platform chamber on a regular platform shock, all the damping goes away. On the HVR, there’s no air to leak – at worst you might lose the oil out of the adjustment circuit, but that’ll just leave you unable to adjust the platform. It’ll still work, though.
The valve and associated ports are cleverly shaped for a progressive transition between closed and open. Get enough force and the valve will partially open, but there’s a pressure threshold at which the valve will quickly become fully open and will tend to stay there – for a given pressure, the force acting on the valve in the open position is three times the force acting on it in the closed position.
What else is clever? The hydraulic nature of the valve adjuster means that it doesn’t take up room at the end of the shock as a mechanical one would, so there’s more air volume available within the constraints of the eye-to-eye length and maximum diameter. That gives the shock desirably linear characteristics. The spring characteristics are further improved by an elastomer-sprung floating wall at the end of the air can, which actually allows the can to get slightly bigger towards the end of the stroke, thus flattening the rate curve just at the end. There’s also an elastomer negative spring in there, chosen over air because it’s simpler and less prone to failure.
The finishing touches are the spherical bearings at the mounting points, isolating the shock from the effects of frame misalignment or twisting. The downside of this is that if you’ll quickly find out if your bike relies on the shock to keep the swingarm in line, but the shock will last longer.
We visited DT’s factory to get the low-down on the new shock, and were impressed by the work that’s gone into it. On paper it all looks good, but we’ve got a test shock to put through its paces – we’ll let you know how it performs in the real world in a few weeks…