Fox DHX RC4 downhill shock £519

Revamped rear bounce

BikeRadar score 4/5

Fox Racing Shox's rivals RockShox and Cane Creek have released rear suspension units with high and low speed adjustments for compression or rebound – or both in Cane Creek’s case – and it was time for Fox to raise their game too.

Luckily, they had the Athertons and a slew of other world class riders on hand to help, along with a team of some of the best suspension designers and manufacturers on the planet.

The new RC4 has been built from the ground up, and it features Fox’s Boost Valve technology, with fully adjustable and independent high and low speed compression adjustment.

This enables you to tailor the beginning of your stroke to high speed small impacts and the end of your stroke to bigger low speed hits. You also get position-sensitive bottom-out control.

A larger diameter piston allows for lower internal pressure and better oil flow throughout the system as a whole. Meanwhile, Fox have left their ProPedal platform damping off the RC4, because they realised it was unnecessary for riders using a high level downhill-specific shock.

We ran the RC4 on both a Yeti 303R and an Evil Revolt this summer in Whistler, clocking up more than a million vertical feet of descending, and it performed superbly.

The setup is more complex than the old DHX5 though. Starting with sag setup, we ran 30 per cent on both the test bikes and found we didn’t bottom out more than once or twice in a ride.

Setting up the high and low speed compression is a matter of personal preference but, as a general rule, you want to run the high speed end pretty soft and your low speed firm to give the shock a smooth ramp-up throughout the stroke.

Riding the shock in Whistler gave us the perfect opportunity to put the RC4 through its paces on some of the best jump trails and roughest downhill tracks in the world. In the rough, the RC4 excelled over fast small bumps and never once got bogged down on big square-edge hits.

We found that initially the shock made a small squeak two-thirds of the way through the travel, but this soon abated once it fully bedded in. On jump trails, the RC4 ramped up perfectly to boost you to the stratosphere or scrub like Bubba.

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