When big tyres do bad things to good bakkies
Wheels and tyres. They significantly influence – and hopefully, improve – your vehicle’s appearance, but their effect on performance is often misunderstood. That’s one of the reasons that bakkies with oversized (35-inch) tyres have not thrived in our market.
In automotive product development, there is an established tension between what designers want and what engineers recommend. Designers desire the largest possible wheels because they complement vehicles’ profiles. It’s why luxury SUVs can be specced with 23-inch alloys shod with low-profile tyres.
Engineers don’t love oversized wheels that much. When you roll out of a showroom onto real-world roads, the issue with oversized wheels becomes apparent: they communicate surface imperfections such as erosion ridges, potholes, drainage covers, and many others that SA drivers are familiar with.
Real-world roads are imperfect, and engineers know that suspension systems can only absorb so much bump variance – tyres must absorb the rest. That’s why the ideal real-world wheel and tyre solution, for bakkies especially, is a smallish rim diameter and larger volume tyre (with a wider sidewall). This issue is particularly prevalent in South Africa because pothole strikes at speed pose puncture- and crash risks.
If smaller wheels and larger tyres are better for real-world driveability and ride comfort, why aren’t “balloon tyres” more popular on bakkies? Surely a bakkie rolling on 35-inch tyres would have the comfiest possible ride with the safest cruising stability on poorly maintained roads? Well, not quite.
‘Balloon’ bakkie tyres look great
The South African bakkie market is so robust that limited-edition double cabs and extreme bakkie editions always trade at a premium, with demand comfortably outstripping supply. But one bakkie configuration has failed in the local market: a double cab fitted with 35-inch tyres.
Isuzu will now sell you a balloon-tyred bakkie with official warranty and service support, assembled with Arctic Trucks parts on the D-Max line in Struandale. But why would Isuzu attempt something that the market leader, Toyota, doesn’t? And how is it that 35-inch tyred bakkies, which look great, aren’t more popular in South Africa – a market where cost isn’t an issue for committed double-cab buyers?
The reason 35-inch tyred bakkies haven’t been successful – at all – is not about how they look, but what they are like to drive…
The issue with 35-inch bakkie tyres and driveability
If bigger tyres with more air volume are so great at absorbing road texture and allowing drivers to retain control when striking a pothole at speed, what’s the problem with 35-inch tyres?
Any tyre of extreme size is very application-specific. And with 35-inch tyres that application is about low-speed off-road traction, at very low air pressures. At highway cruising speeds and higher inflation pressures, 35-inch tyres aren’t great. They generate a huge amount of noise and have very peculiar self-damping and rebound characteristics, because there’s so much rubber in the sidewall and casing.
Being so much larger, huge tyres also tax a bakkie’s ABS, ESP and driver assistance systems. How “big” is “big” really? The metric width of a 35-inch tyre is about 315 mm.
Think about that for a moment: it’s the width of a hypercar tyre, something you’d find on a Lamborghini Urus, to name but one example. The wider your off-road bakkie tyre is, the more exposed that sidewall becomes to proximity rocks littering a 4×4 trail – just waiting to carve a puncture into your tyre.
Ranger Raptor proves a point
Ford set a benchmark for double-cab bakkies with extreme off-road ability and confident highway cruising comfort when it launched the Ranger Raptor in 2019. The 1st and 2nd-generation Ranger Raptors are excellent high-speed cruising vehicles, especially on the most dangerous road surfaces South Africans encounter – corrugated dirt roads.
The Ranger Raptor has proven that a 17-inch wheel with a 285/70 profile tyre is the best real-world spec for an “oversized” bakkie tyre; it looks great and works even better. And a “285/70” represents notably less tyre than you’d find on Isuzu’s D-Max AT35, which is fitted with 35×12.50 R17s (USC measurement).
What made the 1st-generation Ranger Raptor so impressive upon release was that its larger-volume tyres were complemented by a very trick suspension. And that’s where most balloon bakkies fail, because standard double-cab suspension systems aren’t designed for 35-inch tyres – specifically at the rear. You can upgrade the dampers, but the suspension configuration and load rating genuinely matter.
Isuzu’s AT35 D-Max rolls huge tyres with enhanced dampers, but its load rating and rear-axle kinematics are unchanged – something Ford altered with 1st- and 2nd-generation Ranger Raptor. The AT35 D-Max has the right wheel size at 17 inches, but the 35-inch tyres overwhelm it. It would be a much better all-terrain Isuzu bakkie if fitted with 285/70 tyres, as is (still) the case with the Ranger Raptor.
Why isn’t there a locally built Hilux AT35?
South Africans love bakkies and buy special edition versions without hesitation. But nobody wants to pay R1-million-plus for a bakkie with added visual design drama if it’s worse to drive than its standard sibling.
Toyota is the bakkie benchmark and doesn’t market a factory-built Hilux AT35 in South Africa. The truth is that 35-inch tyre bakkies are too much of a compromise because they generate too much highway speed tyre resonance, tramline too easily and trigger ride quality issues when unladen.
Limited edition double cabs create brand awareness, which is valuable in a highly competitive bakkie market. But the brand-building is pointless when they’re worse to drive. And 35-inch bakkies just aren’t the answer, much like 20- and 21-inch wheels on high-powered double-cabs are also far from ideal.
Isuzu has an entrenched brand legacy in South Africa. The Isuzu D-Max 3.0TD double cab AT35 4×4 is visually dramatic, but it’s not a better bakkie to drive than a standard D-Max V-Cross in all conditions. That’s problematic if you think of what’s on offer in the market for R1-million-plus bakkies, where Ford’s Ranger Raptor is far superior to a D-Max AT35, but costs only R63 480 more (September 2023).
A MU-X rear-axled D-Max?
The issue with Isuzu’s D-Max AT35 is that it retains a traditional bakkie rear-axle load capacity, supported by live-axle rear suspension and leaf springs. Many people forget that Ford’s Ranger Raptor bakkies have a reduced load capacity (only 640 kg) and a rear-axle set-up borrowed from the Everest.
A conventional bakkie rear suspension with a 970-kg load capacity and 35-inch tyres just doesn’t deliver a great all-terrain bakkie driving experience. Even with upgraded dampers at each wheel corner.
Ford has proven that customers in the market for extreme edition bakkies aren’t bothered by reduced load capacity. Who’s going to be stacking a D-Max AT35 with 970 kg worth of construction sand, scrap metal, or cattle feed? Nobody. And D-Max AT35’s 970-kg load rating comes at the cost of ride quality.
An alternative outcome for Isuzu and its South African halo bakkie aspirations? Imagine a special edition D-Max that rolls on 17-inch wheels, shod with 285/70 tyres, has a load capacity that is reduced from 970 kg to 600 kg and features an MU-X rear axle… Now that bakkie would shine on any and all road surfaces.
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