Race Driving Fundamentals: ABS vs Conventional Brake Systems
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ABS vs Conventional Brake Systems
06.45
| 00:00 | - One of the big issues with maximising our braking performance is that we need to be right on the edge of locking up a wheel if we want to get the most grip out of the tyre. |
| 00:09 | This is fine for professional drivers who drive race cars for a living however for most enthusiasts this is a very hard skill to get right consistently on every brake application at every point on the track. |
| 00:21 | Add rain into the mix and this difficulty is multiplied. |
| 00:24 | There are three problems that occur when we lock a wheel. |
| 00:27 | First of all the car won't slow down anywhere near as quickly as it does when we're braking at the grip threshold. |
| 00:34 | Secondly if we've locked up the front wheels, we'll lose the ability to steer the car which isn't ideal when we're about to disappear past the apex and off the track. |
| 00:43 | Lastly even a small lockup will do damage to a tyre which is going to compromise its performance over time. |
| 00:50 | These days you'd struggle to find a production road car that isn't equipped with ABS which is designed to prevent these lock ups. |
| 00:57 | Without diving too deep into the ABS system, it comprises wheel speed sensors that tell the computer when a wheel has locked and a pump that allows the pressure to be reduced at individual corners of the car to unlock the wheel and allow it to rotate again. |
| 01:12 | This is all done 100s of times a second. |
| 01:15 | Because ABS eliminates any chance of a lock up, a novice driver can usually achieve better consistency and in theory a lower average lap time. |
| 01:24 | Compare this to driving without ABS where one lap can be fast and then the next lap we may have a lock up causing us to run wide, not only losing time on that particular corner but often a loss in confidence which is going to result in a loss of time under brakes for the next lap or two. |
| 01:40 | On paper, an ABS system sounds ideal and we do see ABS being employed in many race cars, GT3 just for one example. |
| 01:49 | There is however a big difference between a motorsport ABS system and a conventional road car ABS system. |
| 01:56 | Road car ABS is really designed around the driver being able to retain control of the car rather than maximising the braking performance. |
| 02:04 | By unlocking the front wheels in particular the driver will still be able to steer the car around an obstacle. |
| 02:11 | For a road car, comfort and smoothness for the occupants is also a factor in how the ABS operation is programmed and we'll find the ABS system is overly intrusive, activating early and frequently when we're braking hard. |
| 02:24 | This is vastly different to a motorsport ABS system which is designed purely with the aim of maximising braking performance while allowing the driver to retain control. |
| 02:34 | Smoothness and comfort are usually irrelevant and the driver will also often have the ability to fine tune the ABS operation to suit the track and the available grip levels. |
| 02:44 | The key point to take away from this is that a professional driver with a conventional non ABS brake system who can brake on the grip threshold, will be able to stop the car faster than even a motorsport based ABS system. |
| 02:58 | A road car ABS system on the other hand will generally perform worse again but of course you'll still stop the car faster than you could with all 4 wheels locked up. |
| 03:09 | Many enthusiasts who are new to the track and using their road car tend to treat the brake pedal like a switch and just expect the ABS system to pick up the pieces when the car inevitably locks a wheel. |
| 03:21 | While this will work, in some vehicles you'll actually get better results by trying to stay away from the ABS activation point. |
| 03:27 | When the ABS is operating, you'll know it because the brake pedal will vibrate under your foot, you may also be able to feel the car momentarily locking and unlocking individual wheels as the ABS does its job. |
| 03:40 | The reason that we lose performance with ABS is twofold. |
| 03:45 | First of all the system is reactive not predictive which means it can only reduce the brake pressure one the wheel as locked and that means we've already lost potential braking performance. |
| 03:55 | Usually a road car ABS system will reduce the brake pressure further than necessary to allow the wheel to rotate again so the tyre still won't be generating maximum braking performance. |
| 04:07 | Assuming the driver keeps their foot hard on the brake pedal, the process repeats with the ABS system reinstating brake pressure, the tyre locking and the ABS system again reducing brake pressure. |
| 04:18 | The result is that we're not able to achieve maximum braking force from the tyre and then keep it there so the ABS system will compromise the braking distance. |
| 04:26 | It is hard to make an across the board generalisation though when we're talking about factory ABS and while some systems are terrible and will cost you time, in some cases the ABS calibration is actually excellent. |
| 04:41 | While not strictly related to ABS it's also worth understanding how a brake booster will affect the braking performance. |
| 04:48 | We'll find a brake booster in almost every production road car and it uses engine vacuum to boost or assist the driver's pedal effort. |
| 04:55 | This makes the brake pedal lighter and easier for the driver to press on. |
| 05:00 | That's great on the road but the problem with a brake boost in a racecar is that the level of assistance can vary. |
| 05:08 | This can mean that the brake pedal doesn't feel the same and responds differently each time you apply the brakes. |
| 05:13 | Of course on the racetrack this is the last thing we want and we rely on trusting that the brakes are going to feel the same and respond the same lap after lap, corner after corner. |
| 05:23 | The other problem with brake boosters is that it reduces the amount of feel available to the driver through the brake pedal. |
| 05:31 | This feel is critical to the driver being able to reliably find the threshold of grip and keep it there while braking. |
| 05:37 | For these reasons, a dedicated racecar is unlikely to use a brake booster and instead it will rely purely on the mechanical system where the brake pedal actuates directly on the master cylinders with no external help. |
| 05:49 | The downside is a very firm brake pedal that requires a much higher pedal effort from the driver in order to achieve the required braking force. |
| 05:59 | To summarise, road car ABS is not a bad thing but it's designed to keep a driver safe on the road not to push the limits for lower lap times. |
| 06:08 | A beginner might be able to get more consistent lap times on a track using it however as their confidence and speed grows, they'll quickly find its limitations when the envelope starts to get pushed. |
| 06:19 | Motorsport specific ABS systems do a much better job on the ragged edge, however they may not be legal for every class and they're very expensive. |
| 06:28 | Most racecars forgo both ABS and any type of power assistance as it provides more consistency and a much better brake pedal feel than helps the driver find the maximum braking performance just short of locking up. |
