What exactly are you supposed to do with all the technical info that usually accompanies a road test in a motoring magazine? Is it even worth perusing? In this second part of his discussion, Jake Venter continues to explain why road test data can be very useful. You can read Part 1 here.
The specification sheet that is part of a road test, or a vehicle brochure, contains a lot of information that may not be meaningful to some people. In some cases one might even ask; “why is there a need to know this?”
While it is true that some information is not really necessary, many of the facts are worth knowing, as they can help you to make up your mind about what the vehicle is like, especially if you’ve never driven it.
In this article and the next, I’m going to explain what most of the terms mean and why they’re important. Last month we looked at the engine info, now let’s look at the rest of the vehicle.
Gearbox design is at present in a state of rapid development, so that on the one hand there are still vehicles with manual four-speed gearboxes, while on the other hand you can get anything up to an eight-speed automatic gearbox on some of the luxury cars. Is this complication necessary? Not really. Marketing departments will tell you that a modern automatic saves fuel because it is always in a theoretically correct gear. However, the small amount of money you save on fuel you will certainly spend on repair costs if you keep the car for a long time.
Nevertheless, my personal preference is for a manual gearbox on petrol-engined cars and an automatic on turbo-diesels. Diesel engines are prone to engine and transmission damage if you drive slowly in a high gear while employing a large throttle opening. This is called lugging, and leads to a torsional vibration that causes the crankshaft to shake itself like a wet dog. This cannot happen with an automatic transmission. It will change down to a lower gear and not allow you to drive like that. CVTs (constantly variable transmissions) are able to employ any ratio between fixed low and high gear settings and are therefore even more efficient than an eight-speed automatic, but expert opinions are divided on whether they’re robust enough to actually spend your money on.
Front-wheel drive is the most popular because it leaves more interior space for the occupants and promotes a safe under-steering cornering mode. Rear-wheel drive makes it possible for an expert driver to utilise both under- or over-steer during cornering so it is more common on really fast cars. All-wheel drive is just another name for four-wheel drive, unless there are more than four wheels. Such a layout can be found on off-road vehicles as well as cars that are often driven on icy roads. Its use improves grip between the tyre and the road because each wheel gets only one quarter of the engine’s output
The code on the side of the tyre can best be explained by picking a particular tyre. For example, a 235/45 tyre has a width, measured across the widest part, of 235mm, and a height measured from the ground to the base of the wheel rim, of 45 percent of 235, which is 105,75mm. The figure 45 represents the tyre’s aspect ratio or profile. Percentages above 60 are known as high profile whereas the lower percentages are called low-profile tyres. Some modern tyres have profiles as low as 35, because this increases road grip at the expense of ride comfort. The speed rating and recommended load per tyre is given by codes whose interpretation is given on a chart that may be consulted at tyre dealers.
Disc brakes are now the norm at the front on virtually all passenger vehicles because they fade less when you brake hard and are more controllable than drum brakes. Some of the less expensive cars as well as most commercial vehicles soldier on with drum brakes at the rear. This is certainly not as bad as some journalists would lead you to believe. The harder you brake, the more braking effort is taken over by the front wheels, so that the rear brakes have less to do.
Many modern braking systems include some of the following electronic safety features:
1. ABS: Antiblockier-system prevents wheel locking under braking.
2. EBD: Electronic brake-force distribution distributes the braking effort to each wheel in proportion to the available grip.
3. BAS: Brake assist system monitors the brake pedal speed so that it sanctions maximum brake effort even before you’ve completed any emergency braking action
4. ESP: Electronic stability program brakes one wheel at a time to prevent a car skidding out of control in a corner
5. CBC: Cornering brake control allows you to brake in a corner without the car veering to the outside of the corner.
The quoted fuel tank capacity is usually less than the maximum that the tank can take. Most tanks have an air gap equal to about 13 per cent of the total volume to prevent the tank bursting in an accident, and also prevent spilling due to fuel expanding on a hot day. If a pump attendant keeps tricking more fuel in, after the automatic stop has kicked in, this extra fuel will fill the air gap and make the tank unsafe.