The Big League

Words and pictures by grant spolander. Words and pictures by grant spolander.

I once read a joke that asked, “How do you start an argument on the internet?” The answer was, “Voice your opinion and wait for the replies.” I’ve seen this happen several times in the case of Arctic Trucks; one mention of the name in an open forum, and you’ll see any number of replies – ranging from, “Ooooh, that’s cool!” to “Stupidity comes at a price.” I suppose the reason why some folk are so against the idea of an Arctic Truck conversion is because… well, we don’t live in the Arctic. But, aside from the custommade fender flares (which are simply there to finish off the modification), the sole concept of an Arctic Truck conversion is the fitment of oversized tyres, which, as far as off-road performance goes, is presumably a good thing. However, the subject raises a few questions: are bigger tyres automatically better than smaller ones? And, are the benefits of fitting larger off-road tyres more distinguishable than increasing suspension height?

There’s a theory going around that anything bigger than a 33- inch tyre is a waste of rubber; and, that, beyond 33-inches, the tyre becomes so robustly constructed that it offers poor deflation and restricted flotation. In contrast, many diehard off-road enthusiasts believe that a 33-inch tyre is the bare minimum for serious off-road work, and therefore the starting point of any modified rig. Incidentally, we recently had the opportunity to test-drive two Hilux’s back to back; one was a bog-standard vehicle, and the other was an Arctic Truck fitted with 35” Mickey Thompson tyres. We drove both vehicles on a variety of terrain types; but, before I get started on the results of that test, I’d like to come back to the topic of suspension height versus oversized tyres.

In most cases, it’s possible to increase your 4x4’s suspension height by 40 to 50 mm without incurring side effects. This explains why many suspension kits from Australia offer roughly the same suspension-height increase without going beyond 50 mm. Once you go higher than 50 mm, just about everything that could go wrong, invariably does. The first thing is the prop-shaft angle, which becomes far too acute and causes undue stress on the drivetrain joints. In addition, the vehicle’s suspension geometry is adversely affected, and so, too, is the steering system.

What’s more, with significantly raised suspension, the vehicle’s roll-over risk is amplified; and, to make matters worse – in the case of a solid-axle vehicle – a suspension heightincrease does nothing to improve the vehicle’s actual ground-clearance measurement below the diff. With the exception of portal axles, the only way to effectively increase a vehicle’s ground clearance (under a solid-axle diff or independent suspension strut) is to fit larger tyres.

The idea behind an Arctic Truck conversion is to fit oversized tyres that provide a genuine increase in ground clearance, without affecting the vehicle’s suspension components and steering angles. However, in most cases, the average 4x4 doesn’t have the wheel-arch clearance to accommodate larger tyres – not without excessive tyre rubbing. In this way, the most important part of an Arctic Truck conversion starts with aggressively trimming the vehicle’s fenders to allow for the fitment of oversized tyres. But, of course, doing this comes at a cost − both financially, (big tyres ain’t cheap) and in terms of vehicle performance.

As far as physics is concerned, torque equals force, multiplied by perpendicular distance: T = F x D. What this means is, that at a given torque input (such as the power delivered from your 4x4’s engine), a larger tyre will have less force on its circumference than a smaller one. An easy way to imagine this is to think of two bicycle wheels, one big and one small; naturally, the big wheel is easier to stop with your hand than the smaller one.

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