‘If in doubt, blame the computer’ is an office standby. When it comes to car tyres, there are plenty of instances when it would be appropriate to say, ‘Thank the computer’. Several computer-controlled systems optimize car tyre performance these days. Let’s pick our way through the acronyms and look at some such systems.
ABS a.k.a. the Anti-Lock Braking System has its roots in aircraft technology. Gabriel Voisin, a French aeronautical and automotive engineer came up with it as far back as 1929. Forty-two years later, ‘Sure Brake’ appeared on the 1971 Chrysler Imperial. It’s now hard to find a single car tyre whose stopping power isn’t maximised by ABS. Here’s how it works.
Enter the ECU, or Electronic Control Unit, which is what is in charge of ABS. Imagine a car tyre is rotating more slowly than its fellows. A wheel speed sensor detects this, and tells the ECU. The ECU, in turn, opens a hydraulic valve to divert brake fluid pressure away from the locking wheel, until the tyre in question speeds up again. The system can do this at up to 20 times per second. The result? On a wheel that isn’t quite locking, the car tyre is gripping at maximum efficiency. A locked wheel offers virtually no grip, while a wheel nearly at locking point can still offer steering and braking force.
EBD (or EBFD) is a refinement of ABS. This acronym stands for Electronic Brake Force Distribution. On the old, ‘classic’ Mini, for example, there used to be a mechanical inertia valve, which would reduce braking force to stop the rear tyres locking under heavy braking. EBD does the same thing, far faster, far more accurately and in relation to each car tyre simultaneously.
Strange as it may sound, ABS can help a car tyre achieve maximum traction under acceleration. TCS – the Traction Control System – uses the ABS’s wheel speed sensors to detect if a car tyre on a driven wheel is spinning (i.e. not gripping). The TCS applies braking force to the spinning wheel for a few milliseconds. In more sophisticated TCS systems, the throttle can be cut briefly, preventing wheel spin.
Speaking of sophisticated systems, we can now look at ESC (Electronic Stability Control). This again is ABS-related. In ESC (or DSC – Dynamic Stability Control), two further sensors play a role. One detects the angle of the steering wheel, while its gyroscopic stablemate checks this angle against the car’s direction of travel. Should the figures not add up, the system applies braking force to individual wheels. Once again, each car tyre is maintained at its optimum level of efficiency in any given circumstance, by the application of very short pulses of braking pressure, and/or throttle input, as appropriate.
Here’s where further refinement steps in, and where we become awash with acronyms. It’s probably best to think of the refinements under the ACC (Adaptive Chassis Control) banner. Often using a button, with markings such as ‘Comfort’, ‘Sport’ and even ‘Race’, a car driver can dial in all manner of changes to how his car responds. While the stiffness of physical springs can’t be changed electronically, the firmness of the suspension can, by the actuation of electronic tweaks to suspension damper rates. While the car tyres don’t change, that which controls them can. It’s possible for driving force to be distributed according to car tyre grip across an axle and, in some cases, between the front and rear wheels.
The bottom line about these immensely clever, capable systems is that they use car tyre grip as a benchmark. When the car tyres are offering optimum grip, tyre performance – and therefore the performance of the car – is necessarily optimized.