How good are your ute brakes?
Why are old-school drum brakes still fitted to $50,000-plus dual-cab utes?COMMENT
The difference between a collision and a near miss can come down to how good your brakes are, yet the all-new 2020 Isuzu D-MAX, like most one-tonne utes in Australia, will continue with rear drum brakes instead of better-performing discs.
Despite being an all-new model featuring new safety features such as autonomous emergency braking, the new Isuzu D-MAX (on sale from September 1) like most competitors will only be offered with drum rear brakes, a brake design known to offer less efficient stopping power than discs.
While Isuzu Ute Australia has not yet confirmed that the Australian D-MAX will have rear drums, it's a sure bet judging by the D-MAX’s (already published) Thai market brakes specs. While the Thai model has new, larger 320mm diameter front discs, the rear brakes are drums.
The D-MAX however is not the exception with rear drums in the ute segment: not only will its close relative, the new Mazda BT-50 have rear drums when it arrives later this year, but so do all existing volume sellers in the segment. Utes such as the Ford Ranger (except Raptor) Isuzu D-MAX, Toyota HiLux, Mitsubishi Triton and Nissan Navara all feature rear drum brakes.
Overweight utes threaten road safety
Of the other volume-selling utes, only the otherwise old-school Toyota LandCruiser 79 and Volkswagen Amarok use rear discs. Even the much lower volume – and cheaper – players in the market, such as the LDV T60 and SsangYong Musso, run rear disc brakes.
Disc brakes dissipate heat and therefore resist brake fade better than drum brakes. Being exposed to surrounding ambient air, disc brake rotors and pads can more easily shed heat created by braking, whereas drum brakes contain much of the heat created within the drum assembly.
In the opposite situation – when the brakes have been immersed in water, such as an off-road water crossing – drums take much longer to dry out than discs and are far less effective until they have done so. Drums also pick up mud and grit more easily (in off-road or mining applications, for example) and this can damage the internal hardware.
Almost all vehicles from small cars to SUVs are fitted with rear disc brakes. Rear drum brakes only dominate two popular classes in the car industry: micro cars and utes. Such a brake design being popular in a class where vehicles are low-mass city runabouts is one thing, but to have them on vehicles that weigh two tonnes, can carry a further tonne of payload and tow up to 3500kg, is another – even if the drums are much bigger on utes than the micro cars.
In carsales’ own testing of unladen dual cab utes performing an emergency stop at 60km/h, all achieved a similar result – whether drum or disc braked. This data and other reports suggest that for daily family duties in the suburbs, an unladen rear drum-brake ute would not need much if any more real estate in which to make an emergency stop than a disc-braked ute or even a passenger car.
However, as aftermarket suspension firm Pedders has found, braking distance increases considerably when performing an emergency stop at speed in a drum-equipped, laden ute.
While Pedders has a vested interest (with its ute disc brake conversion kits) the independent testing they commissioned showed a 21.4-metre reduction in braking distance with a fully laden Toyota HiLux fitted with their disc-brake kit over a standard, rear drum-brake fully laden HiLux.
Pedders brake director, Steve Altair says rear discs are generally better than drum brakes because of “... their improved heat dissipation, shorter stopping distance, less pedal effort and they’re better for maintenance”.
Manufacturers still fit drum brakes to utes because drum brakes are simpler and cheaper to make. Rear discs brakes are more complex, in that manufacturers have to incorporate a parking brake (either mechanical/electrical activation of the disc brake caliper, drum-in-disc type or a driveline drum brake) and can require an uprated master cylinder/brake booster.
That doesn’t mean that it must be inordinately expensive to build a ute with rear discs – the mechanically near-identical, ute-based wagons such as Ford Everest Isuzu MU-X, Mitsubishi Pajero Sport and Toyota Fortuner are fitted with rear discs – ventilated, no less, for the Isuzu, Mitsubishi and Toyota.
Rear brakes only contribute about 30 per cent to braking in an unladen vehicle, at least; the front brakes (in all utes, ventilated discs) take on most of the work.
Yet 30 per cent is not insignificant; even if it only contributes to a metre or two shorter stopping distance, it could make the difference between a collision or not. Amplify this in a high speed emergency braking scenario with a heavily laden ute, a heavy trailer or simply negotiating a long steep descent, then losing much of that 30 percent because of brake fade could be critical.
Also read:
Tags
Please see our Editorial Guidelines & Code of Ethics (including for more information about sponsored content and paid events). The information published on this website is of a general nature only and doesn’t consider your particular circumstances or needs.
