Christmas road test: the world's fastest tractor

You’ll note that its top speed of 43mph, though, is still some way short of 155mph. So to make the WFT that fast while trying to keep it true to its tractorish roots required some extraordinary measures and it’s only when you see the two machines side by side that you really see the lengths JCB’s team has gone to.

The Fastrac looks fairly dynamic for a normal tractor, but with a cab high above your head and tyres that come up to your eyeballs, it’s still a tractor. Next to it, the record-breaking Fastrac Two looks like a computer rendering of a concept.

For one, it’s lower. The Fastrac has two deep chassis rails running from front to rear and the weight of those has been halved. It’s in kind of three sections: there’s a rear section around the suspension, a front section around the engine and a centre section near the cabin. The whole thing has been dropped, with the engine significantly lower and the front drivetrain, which makes the usual Fastrac four-wheel drive, removed. The conventional Fastrac uses a two-ratio CVT transmission, but the WFT doesn’t. Instead, JCB has brought in an old-school ZF six-speed H-pattern manual truck gearbox. Behind the ’box runs a beefier propshaft (albeit one from a tractor), running through to a rear axle that features a tractor crown wheel and pinion, with a spool differential that locks the rear wheel rotation together. In some ways, if you want to go fast in a straight line, you couldn’t ask for a more perfect set-up: a front-mounted, longitudinally positioned, perfectly smooth six-cylinder engine driving through a manual gearbox to a locked rear diff, with four big wheels aligned to point in the same direction.

Those wheels, incidentally, which come up to your shoulders rather than your head, are standard tractor affairs and built by GKN, the usual supplier, although they’re the smallest fitted to a JCB tractor and constructed to a tolerance of less than 1mm, rather than the usual 3mm. They also carry wheel weights, up to 1kg, to balance the tyres, which tractors don’t usually bother with because they don’t go fast enough.

The tyres themselves still carry the ‘A8’ speed rating markings from the mould they’re made in – which is a 25mph-rated standard tractor tyre. However, they carry two internal bands to limit exterior expansion to no more than 2mm at 150mph, they have more natural rubber in the compound and they have had their tread pattern buffed down to 10mm from the standard 27mm. We suppose they could have gone further but this is, after all, still meant to be a tractor.

Aerodynamic body addenda diverts air around a standard-shaped bonnet (it’s aluminium rather than steel) and around a cabin that looks standard at a glance but is anything but. It has been reduced in width by 300mm and height by a further 200mm, so in all, its roof is 400mm lower than a normal Fastrac’s.

Finally, then, to the details of probably the most important bit: the engine. In July, when JCB originally set the record, it had an engine that produced approximately 500bhp. It’s a JCB 672 engine, an inline sixcylinder pushrod four-valve diesel, and its power was good enough for three figures. But to go half as fast again, they wanted twice as much power. Which meant things got very, very serious, very quickly.

The new engine has the biggest turbocharger you’ll find fitted to a tractor. It produces 5.0 bar of boost and, as big turbos do, doesn’t boost big until it has a lot of air going into it. So there is an electrically powered supercharger to keep the turbo spinning at low revs, while during gearshifts on what is a leisurely H-pattern ’box, there is a scuba-dive tank at the rear, which fires air at 100 bar into the exhaust and keeps the turbo spinning while the clutch is in.

So the big turbo is spinning all the time, which is ace. But a 141bhp-per-litre diesel generates lots of heat, which radiates into the intake air, which ideally you want cool. So there is a huge ice-cold water-to-air intercooler between the turbo and the intake manifold. JCB’s engineers load that with 25kg of ice prior to each run, and by the end of a runway, it’s all gone. But in the meantime, it’s taking air from the turbo at 280deg C and cooling it to 10deg C before it comes out of the intercooler.

The air goes into the engine via standard inlet valves, into a cylinder whose compression ratio has been reduced from 18:1 to 11:1, via machining the tops of the standard pistons. They push on forged con-rods but do drive a standard crankshaft. The exhaust valves are the same size as usual, but because of the extreme combustion temperatures, they’re made from a different material, after which gases reach an exhaust manifold that is 3D printed from Inconel because it reaches nearly 1000deg C. It glows red not just when the engine is on a test bed, but even when it’s running at speed in cool air.

So all of that combined gives this machine performance that we’ll come to in a moment but it also means it’s incredibly fragile at those power outputs. After the record runs, JCB discovered some microscopic cracks and saw torque peaks of up to 3300lb ft acting on the propshaft. So the wick was, sadly but inevitably, slightly turned down for our test, leaving us a little over 500bhp to get on with. That’s why the performance figures quoted here are from the record-setting runs, at which point in-gear the Fastrac Two will give a Ford Focus RS a run for its money at higher speeds. In the 500bhp form we ran it, and on a shortened runway, it still did 112mph and left a Ford Ranger Raptor in its wake.

Interior

If the outside looks like a tractor that could have rolled in from the set of a science fiction film, it is pure race car inside. There’s a single Cobra race bucket seat with head bolsters and a five-point harness and, around you in this fairly spartan cabin, there is polycarbonate instead of glass for the surfaces, with two escape hatches, a fire extinguisher and the biggest FIA-approved roll-cage we’ve seen bolted directly to the chassis. Fixed to that are a few screens: a Racelogic speedo hooked up to a GPS data logger, a tyre pressure and temperature sensor, and a big central screen, showing some temperatures and a rev counter.

To your right is the six-speed ’box, with magnetic sensors at the end of each gate because different gears get a different throttle and torque map so as not to destroy the diff or spin up the wheels (a very real possibility, terrifyingly). Behind that is a flat panel with light switches, display switchgear and the most important thing of all: the start switch.

Performance

To start a conventional tractor, you turn a key, there’s some whirring and, after a while, away it goes, because these machines have big batteries and compressors and an alternator on board. The whole thing is self-contained.

The WFT is not so simple because it has gone from being a machine you’d run all day for days on end to one you run briefly not very often. In taking it from nine tonnes to less than five tonnes, JCB opted to delete some equipment, in addition to giving it a lower and lighter chassis and making it slightly smaller. So there is no power take-off, for example, because there is no on-board compressor for hydraulics, or air. And, in fact, no alternator.

So to start the WFT, you have to hook it up to a generator or battery on a truck, which then follows it around in case you stall. Not that there’s as much chance of that as is usual in valuable, rare cars, where a nervous owner will say: please, don’t slip the clutch because it costs a fortune, wears out quickly and nobody makes them any more. It’s different here. JCB designed an eight-plate clutch that runs in a huge bath of oil and is so robust that the way it is tested is to fit it to a tractor, running it at top speed while towing 20 tonnes, selecting reverse gear and slipping the clutch until the set-up is driving backwards.

So it can easily handle the WFT’s five tonnes setting off from rest. JCB’s engineers suggest you select second gear, wind on 2500rpm (max revs are at a 3400rpm hard limiter and 3000rpm is a good change-up point) and slip the clutch almost all the way through second gear while keeping those revs high. This is slightly easier said than done when the clutch pedal is so light and there is no discernible feel through it but, once rolling, it’s that much easier.

Even with less than maximum power, this is still a powertrain with a very narrow operating window. Guy Martin has said you could drive off into a field and plough with the WFT, which sounds great but is not even close to accurate. Running this is like an agricultural-sized F1 car.

Because of the low compression ratio, combustion doesn’t come easily if temperatures are too low so there is a grid heater to pre-warm air at low speeds (yes, that’s reheating air that has just passed through a massive intercooler), but this heater switches out as speeds and revs rise because the thinking is that there’s sufficient heat to keep combustion going nicely. In between those two states, though – once the grid heaters are off but before the tractor is going flat out – it doesn’t run happily. Unfortunately, that’s exactly the sort of low, constant speed that we like to drive at for photos and video. Here, the Fastrac Two is such a smoking, banging, recalcitrant mess that at one point we thought it had exploded. If you want to run at tractory speeds, then, you can’t: it likes to be at idle, or flat out.

And flat out, it’s amazing. A support car like a Ford Ranger Raptor struggles to keep pace with it, even in its 500bhp tune. The performance figures on full power show it reaches 60mph from rest in 9.86sec, but the way this huge, five-tonne machine keeps on pulling is what’s so impressive.

Even on a far shorter runway and with much less power than during the record run at Elvington, we saw 112mph, which would have made us land speed record holders earlier this year and still leaves us the second-fastest tractor drivers in the world (if you don’t count JCB’s in-house testers). Which is quite pleasing.

Once rolling, it’s surprisingly easy to keep the WFT going fast. After gearchanges, the clutch and engine take-up is no more difficult than in a regular car, you’ll never miss a gear on the big-gated manual gearbox and the in-gear flexibility comes without holes or torque gap. It’s a smooth and responsive if noisy engine.

But then there’s the stopping. There are air brakes, massively over-served, and the standard discs are just as up to the job of stopping five tonnes from 150mph a few times on a runway as they are nine tonnes plus whatever it’s towing countless times on the road. But you’ll remember we said there is no on-board compressor: instead, two air canisters on the back must be filled before each outing, because they provide air to the system, and once they’re empty, they’re empty, and you’ll have no braking apart from an ineffectual parachute. The engineers think there are 40 stops in the tanks and they usually recharge well before 20. But still, worth remembering.

Handling and stability

The Fastrac Two runs nitrogen dampers on its three-link suspension, with live axles front and rear, and although the cabin is not suspended, ride comfort is pliant. Granted, we’re only running it on a runway, not in a field.

The steering is hydraulic, with three turns between locks, and there is no direct mechanical link to the front wheels, so you can end up in a situation where the standard JCB steering wheel isn’t showing straight even though the wheels are pointed straight. But the only truly weird thing about the driving experience is remembering that the rear wheels are locked, so the turning circle is a runway’s width. It’ll do tighter turns but I don’t imagine the rear axle will thank you for it.

But whatever crosswinds or headwinds, despite the blocky shape of the machine, this is a straight-line monster. It’s completely stable, with absolutely no drama whatsoever as you run it through the gears. Starting in second and getting through to fifth, it’s huge testament to its engineering that it doesn’t want to do anything other than track totally straight, despite all controls bar the throttle pedal being light. There’s no great brake feel and it’s a bit like a Dallara Stradale in that there’s a lot of movement in the pedal. And you don’t heel and toe: you just knock the stick into neutral and, when going slowly enough, slide it back into gear. It’s an undramatic but deeply, deeply impressive driving experience.

Buying and owning

JCB is disinclined to say just how much it has spent on not just one but two tractors, but it clearly thinks it’s worth it, not only as a marketing exercise but also, given it’s an engineering-led company, as a technical exercise. There has been some help from Williams (aerodynamics) and Ricardo (engine), an existing JCB partner already, but there’s no question this is an expensive machine to make and a complicated one to run. We started setting up the WFT at 8am and it wasn’t ready until midday, having been in a hangar with heaters blowing at its important bits for several hours because the gearbox oil is uninterested below 70deg C.

Verdict

What’s so refreshing and exciting about spending time with Fastrac Two is not just the machine itself, but also meeting the engineers who arrive with it, who designed it, who put it together and who run it. JCB has put a small, talented and young team in charge of the project in a similar fashion to the way Lamborghini put brilliant young engineers, designers and test drivers in charge of developing the Miura. And beyond the headlines and the JCBWFT hashtags and the TV programme and even the record itself, their experience matters most. Because although JCB knows that creating the world’s fastest tractor has benefit to it as a marketing tool, it also has massive merit as a technical exercise, and in the world of agricultural and construction equipment, engineering counts for more than styling, marketing or advertising.

So here’s to a five-star speed record, a five-star machine and its five-star engineers. If you want to do 150mph in a tractor, there’s nobody we’d trust more.