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8th December 2011
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MAN tractor units have enjoyed considerable success in CM’s hands over recent years, including victory in our 1,000-Mile Test and delivering the best fuel consumption of Euro-4 road tests at 44 tonnes, so hopes were high for this Euro-5 MAN TGX 26.440

Words: Kevin Swallow Images: Tom Cunningham

Nobody banged the drum louder than MAN when it came to championing exhaust gas recirculation (EGR) as the best way of cutting NOx to meet Euro-4 exhaust emissions limits. Its clever ‘add nothing’ tag line underscored the fact that, unlike the majority of their rivals, MAN trucks need no AdBlue to keep their emissions on the right side of the law.

MAN rammed home its point when its TGA 26.440

tractor unit won our CM 1,000-Mile Test (CM, 28 September 2006) at 44 tonnes. It followed that by delivering the best fuel consumption of all our Euro-4 road tests at 44-tonne GCW (CM, 18 October 2007).

But a clean sweep at Euro-4 is no guarantee of success at Euro-5. It was MAN’s 10.5-litre D20 engine with EGR that performed so strongly at Euro-4 at a nominal 440hp. At Euro-5 MAN capped power ratings of EGR versions of the D20 at 400hp, so customers who wanted to stay at around 430hp-440hp had the choice of either an SCR version of the D20 engine (available at 440hp) or a 12.4-litre D26. The latter also has a nominal 440hp rating but can attain that at Euro-5 with EGR, maintaining MAN’s ‘add nothing’ mantra.

MAN Truck & Bus UK says the majority of its UK customers conclude that EGR is still high on their list of priorities, so the 12.4-litre D26 rated at 440hp is currently the most popular engine choice among UK operators. This is the engine itted in the subject of this week’s road test, a TGX 26.440 three-axle tractor unit. We set out to establish if the 12.4-litre Euro-5 engine could hope to match the proven thriftiness of the 10.5-litre Euro-4 D20.

The truck’s list price, for what it’s worth, is £111,995 (excluding VAT). It has fogand spotlights, costing an extra £365, plus a ixed (instead of sliding) ifth-wheel that takes £500 off the asking price, bringing the as-tested igure to £111,860.

CAP Monitor forecasts its residual price in three years will be £28,825 and £18,125 after ive years.

Technical profile

Although it has a swept volume of 12.4 litres as opposed to 10.5 litres, the D26 engine comes from the same block as the D20, so the ‘bigger’ engine isn’t actually bigger. Surprisingly, the D26 engine is the lighter route to 440hp. Its dry weight is only around 25kg more than the D20’s, rather less than the additional weight of the SCR system and tank of AdBlue needed for Euro-5 440hp D20.

The accurate power rating is 324kW (434hp), developed at an engine speed of 1,900rpm. Maximum torque of 2,100Nm is available from 1,000rpm to 1,400rpm. Both sets of igures are identical to those of the Euro-4 D20, so the D26’s extra couple of litres of swept volume have no impact on the headline speciications. But the D26 is taking life easy at 440hp: this engine is available in nominal ratings as high as 540hp.

Standard transmission in the TGX is ZF’s AS Tronic, rebranded Tipmatic by MAN. This 12-speed automated gearbox has a direct-drive top ratio and the vehicle is paired with a inal drive ratio of 2.85:1. Running with the standard 315/70 R22.5 tyres, this gearing choice means the engine is turning at 1,382rpm, very close to the top of the green sector on the rev-counter, when travelling at 90km/h (56mph) in top gear. Interestingly, MAN has itted 315/80 tyres on this test vehicle, lengthening overall gearing by 6%. That brings engine speed down to a more moderate 1,300rpm at 56mph. CM’s policy is to limit maximum speed to 85km/h (53mph), which brings down the TGX’s engine speed even further to a lazy 1,230rpm in top. For operators who still eschew automated gearboxes, there is the option of a 16-speed ZF manual box.

Braking is a disc set-up with the usual acronyms: EBS (electronic brake actuation) and ABS (anti-lock). An exhaust-valve brake provides secondary braking. The ABS wheel sensors also serve the traction control (ASR) system. The steer axle has steel suspension; there is two-bag air-suspension for the non-steering mid-lift axle and four-bag air on the drive axle.

The test vehicle has the XLX cab, the middle of three sleeper-cab height variants offered on the TGX. It is 40kg heavier than the lowest (XL) but provides 315mm – a foot – of extra headroom, enough to allow most drivers to stand upright on the engine tunnel, which they could not do in the XL. Even at its highest setting, the top of the air-management kit on the XLX comes no higher than 4,011mm according to MAN’s measurements, leaving the cab’s aerodynamics poorly matched to many UK trailers.

On the road

For the driver there is little difference between the D20 Euro-4 and the D26 Euro-5 at 440hp. Their characteristics are similar and their peak output igures identical. Both engines like to lug down to their respective bootstraps, but on severe gradients the D26 seemed to emerge as the stronger, perhaps because we knew it had the greater displacement. Analysis of the two engines’ performance curves suggests that while their torque curves are similar, the Euro-4 D20 offers more power at under 1,600rpm.

To get the best from both engines, MAN has no hesitation in recommending a degree of driver intervention to override the automated transmission. This recognises that although automated shifting usually improves overall leet fuel consumption, good individuals can usually do better thanks to their ability to read the road ahead, making proactive rather than reactive gear shifts. Some other truck manufacturers are adopting the approach that it is best to leave the automated system to its own devices because intervention is more likely to be detrimental than beneicial.

MAN’s trust in the driver is well placed, at least in this instance. From the outset, CM worked to keep the engine speed as low as possible for as long as possible. Running in top gear on lat A-road sections the engine can lug down to 900rpm and still maintain a road speed of 64km/h (40mph) without duress.

On single-carriageway roads with an uphill gradient we found it paid to step in on prolonged ascents, changing down to take engine speed up to 1,250rpm, leaving plenty of margin for loss of speed before the torque falls away steeply below 900rpm.

At 80km/h (50mph) on lat dual-carriageways the truck is in its comfort zone and happy to absorb any short or modest ascents without dropping to 11th gear. But left in auto mode Tipmatic often seems to want to make that downshift, so we learnt to step in and take control. Careful note of our fuel-low meter readings indicated that preventing downshift reduced the volume of fuel consumed by 17% for as long as we could hold off the shift.

MAN opts for a slightly larger steering wheel than most of its rivals. This is designed to offer the driver a truer steering experience, and reduce the number of turns lock-to-lock. Initially, it feels oversized and there is a tendency to under-steer. A safety beneit is that the driver is less likely to cross arms when negotiating tighter turns on roundabouts and corners.

MAN provides a nifty function that allows the driver to cap road speed: if the vehicle is going downhill but still within the speed-limiter’s setting, the driver can tap the brake pedal once and the ECU registers the speed and brings in the exhaust brake to slow the vehicle when it exceeds that temporary speed setting. However, we think MAN should build in some manual adjustment to the operation of its cruise control. Rival manufacturers give some choice about how far the cruise control’s speed setting can be exceeded before braking is triggered. MAN ixes this overrun margin at 3km/h, which can hamper progress on gentle descents immediately ahead of another climb.

Productivity

Let’s cut to the chase. The TGX delivered the best fuel consumption igure at 44 tonnes GCW to date, irrespective of which tier of the Euro exhaust limits we are talking about. Favourable weather was a contributory factor, but the margin of its success indicates that the Euro-5 TGX 26.440 is undoubtedly highly economical, whatever the weather. Its overall igure of 9.27mpg surpasses that of our previous Euro-5 record holder, the Mercedes-Benz Actros 2546, by 1.13mpg (see chart). On our revamped motorway section (see sidebar) the TGX recorded 10.05mpg to the Actros’s 8.74mpg. On a mixed motorway and A-road section (‘Trunking’), the MAN achieved 9.7mpg to the Actros’s 9.35mpg. On severe gradients the TGX managed 6.77mpg to the Actros’s 5.66mpg. The cherry on the TGX’s cake is that it needs no AdBlue. The Actros consumed AdBlue at the rate of 6% of its diesel consumption.

To complete what can only be described as a comprehensive victory, the TGX comes out on top in both average speed and payload.

It completed the test route at an average speed of 74.1km/h, just a tad better than the Actros’s 73.0km/h. The MAN is only a whisker lighter than the Mercedes, weighing in 107kg less as tested: the absence of an SCR system and a tank of Adblue on the MAN and its use of a ixed ifth-wheel instead of a slider accounts for most of that difference.

And, for the record, yes, the Euro-5 D26 in the TGX did drink less fuel than the Euro-4 D20 in the TGA we tested in 2007. The TGX’s 9.27mpg easily usurps the TGA’s 8.46mpg. ■

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