Truck & Driver|March 2020
Tag-axle tractors are considered the best option for tougher applications and are a popular choice for medium/heavy plant and machinery haulage, providing – if used correctly – better traction and manoeuvrability.
Some of the latest versions with steering tag-axles take the concept a stage further, Volvo, Scania and now Daf offering this option in the UK.
Keen to try a rear-steer Daf, we gratefully accepted an XF530 FTN 6x2 rear-steer tag-axle tractor with the low-roof version – called Comfort Cab – of the XF sleeper cab, a familiar option in Europe but rarely seen in the UK.
In keeping with this truck’s specification, we looked to our good friends at Wiltshire-based Bryants Transport, which specialises in shifting agricultural machinery and specialist construction equipment.
Using a variety of step-frame and power-steered low-bed trailers, perfect for the rear-steer Daf, its trucks visit farms, congested construction sites and other difficult-to-reach locations on a regular basis.
Modern farm machinery, such as tractors, combine harvesters and so on, are seriously beefy. Bryants also shifts a lot of big soil-stabilisation machines, often taking outfits into Special Types regulations. Fortunately, Daf was able to uprate this FTN to 50 tonnes gross; we understand that it can operate at slightly higher STGO weights if specified with a higher-capacity drive-axle.
The variety of work included medium- and long-distance routes but also plenty of country lanes, visiting farms, construction sites and dealers’ yards. We had a couple of nights away in the compact cab and the weather was wet and miserable for a fair bit of our week with the Daf.
Ranging from twin-steer lightweight pusher-axles to tag-axles with single/twin tyres and now steering on the rear axle, Daf certainly offers the full range of axle layouts with its three-axle XF tractor units. With a suitable driveline and chassis spec, tag-axles can be plated for up to 80 tonnes, while doubledrives with single or hub reduction, whether on steel or air suspension, can be plated for as much as 150 tonnes.
The rear-steer FTN was introduced a few years ago, with either 3.4 metre or 3.7m wheelbases; the 3.1m version featured, introduced quite recently, is better for mainstream haulage applications. The hydraulic steer axle is the same design fitted to three- and four-axle rigids, where sensors on the front steer-axle detect the amount of lock applied and steer the rear axle accordingly.
Its fully air-suspended bogie has a weight-transfer system to aid traction when loaded and full lift when running empty. Steel front suspension is standard but full air is available. All axles get 315/80 tyres, with other sizes optional, and the single-reduction drive-axle has a diff lock. Our truck had the relatively high 2.53:1 ratio, giving 56mph at 1130rpm; again, other options are available.
The smaller exhaust system introduced with the latest updates frees up space for a hydraulic tank on the right-hand side of the vehicle. Our truck also had a sliding fifth wheel, extended catwalk, work lights, air horns, a beacon bar and optional aluminium wheels.
The base engine is the 450hp version of the MX-11 10.8 litre, useful if weight saving is a priority, but most XF buyers will go for the bigger MX-13 power unit, with outputs of 430, 480 and, as fitted here, 530hp.
Maximum power comes in at 1675rpm, the Euro 6d version of the 12.9-litre motor utilising a variable-geometry turbocharger that helps boost torque at low revs, particularly in top gear, where 2600Nm is produced between 1000 and 1460rpm, dropping back to 2500Nm in the other gears. The Daf engine and exhaust brake system utilises the high-tech turbocharger to boost braking power and torque right down to 1000rpm.
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