Field Report: Why Do Pro Racers Remove Brake Boosters?

Speaker 1: 0:00

When it comes to going faster around a racetrack, the more usual approach is to add power. However, actually concentrating on the braking performance of the car can yield much bigger gains. We're here with Ashley from 909 Motorsport to talk about the Bosch Motorsport ABS unit. Welcome to High Performance Academy's tuned in Field Report podcast series. In these special midweek episodes we look back through our archives to find the best conversations we've had through years worth of attending the best automotive events across the globe. We've pulled the audio from these tech-filled interviews with some of the industry's most well-known figures and presented it in podcast format for you to enjoy as a quick hit of insider knowledge. So before we get into the Bosch ABS itself, Ashley, can we talk about some of the shortcomings of factory ABS in a modified car on a racetrack scenario?

Speaker 2: 1:02

Yeah, there's a lot of, I guess, downsides to a factory ABS system. Once you go into a modified car on a racetrack scenario. Yeah, there's a lot of, I guess, downsides to a factory ABS system. Once you go into a modified car, once you change the weight of the vehicle, the centre of gravity, the braking package on the car, then the factory ABS becomes sub-optimal.

Speaker 1: 1:17

So essentially the factory ABS, as you could rightly expect, is going to be calibrated for a stock standard factory car and once you start modifying all of those parameters you just mentioned, then the calibration doesn't work as intended.

Speaker 2: 1:31

Yeah, that's exactly right, and it's important to note too that on a factory car the biggest thing is stability, safety, driver comfort. Those things come very high on the priority list from an engineering perspective. With motorsport ABS, the primary directive is improving the stopping.

Speaker 1: 1:48

All right. Well, let's just dive into that in a little bit more detail. So it's easy to overlook thinking that all ABS systems are created equal. But, as you just mentioned, when an OE manufacturer is designing and calibrating an ABS system, it's really designed around the driver being able to maintain directional control of the vehicle, as opposed to absolutely optimal stopping distances, correct?

Speaker 2: 2:10

Yeah, that's right and I guess they expect in a racing situation. The driver is a high performance driver and they can control the vehicle under racing conditions.

Speaker 1: 2:20

On that note, when something like a Bosch ABS unit is installed and again here the priority here is absolutely optimising stopping distances, maybe at the expense of some of the other parameters like driver comfort etc. You mentioned there that there is an assumption that the driver is a professional or able to control the car better than the average punter, so does that mean it is a little bit more difficult to control the car when the ABS is functioning in a motorsport environment like that?

Speaker 2: 2:48

No, I wouldn't say it's more difficult. It's a more predictable pedal and the stability of the car in the racing conditions is predictable. But it does require if you're on a racetrack. I guess it is assumed that you have a level of ability.

Speaker 1: 3:01

So let's talk about what we may notice with a stock ABS system on the racetrack and where the sub optimal performance can come in. What will the driver actually notice?

Speaker 2: 3:13

The pedal pulsations on the M5 ABS are a lot, lot smoother than most production stuff. You'll find that on some particularly early model ABS units with a big brake package that they can lock tires and everything and they can also actually lock the brake pedal out and not stop the car. So yeah, it's very unpredictable.

Speaker 1: 3:33

That sounds like what a lot of people refer to as ice mode. Am I right there?

Speaker 2: 3:37

Yeah, it's, I think, a factory sort of setup to maintain stability on slippery surfaces such as ice, and if the ABS unit's working outside parameters, you can come across that actual symptom. I guess yeah.

Speaker 1: 3:50

So in that instance you've still got directional control of the vehicle, because obviously the wheels aren't locked, but not a lot of retardation. No, not at all. Alright, so let's talk about a move to something like a Bosch Motorsport ABS system. It sounds like a fairly extensive setup to install. What is actually involved? What do we need?

Speaker 2: 4:09

It's car dependent, but the M5 ABS Club Sport kit is fairly complete. So it comes with a pre-made wiring loom for the car. That's fairly generous, and you install it in the car, give it a power and ground. You have to mount your sensors and things which are all included, and pipe it up. So it's a fairly good start. The wheel speed sensor is a consideration depending model to model, so you've got to have the sensors mounted in the correct location and the correct amount of teeth and that sort of thing. So it is dependent and we like to try and guide people when they set these up.

Speaker 1: 4:42

Alright. So if you've got a car that has an existing ABS system, is there potential for compatibility with the existing wheel speed sensor rings and wheel speed sensors, or do we need to go to a Bosch specific wheel speed sensor?

Speaker 2: 4:56

In most cases you need to use the sensors that are supplied with the kit or the specific sensor type, which is a DF11 type sensor that is required. Some very late model cars have got that sensor from factories, such as an R35 GTR, things like that. You can use the factory sensor. So it is a bit vehicle dependent but certainly old vehicles. You must change a sensor.

Speaker 1: 5:16

The other element we see with most race cars is the move away from a brake booster and a dual style factory master cylinder to what's referred to generically as a pedal box, where we've got a separate circuit for the front and rear brake master cylinders. Is that essential when going to an aftermarket ABS system, or is it just preferable?

Speaker 2: 5:38

I would say it's preferable. I mean, the system of choice would be to have a pedal box and dual master cylinders so that you could set the system up optimally. But we have successfully installed the system into production style braking systems, sometimes with an additional bias valve to allow the drivers some control over the bias, and still got the booster systems in them Again. It's not as good as a pedal box, but in some categories it states that the production braking system rusts remain, so it does still work good.

Speaker 1: 6:08

Are you interested in expanding your automotive knowledge? Start your free lessons with us today at hpacademycom forward slash free. For those who aren't aware, let's talk a little bit about the brake booster, because this is something that generally, as I've mentioned, is removed in a race car. What's that brake booster for in a factory car and where are the potential downsides? In other words, why are they so commonly removed?

Speaker 2: 6:33

I guess it's the driver's variability of assistance that varies with vacuum, and every time they grab the brake it's not exactly the same as what it was last time. So I guess that's where, in a proper racing application, having a pedal box is the ultimate way to go.

Speaker 1: 6:48

You just want that consistency. Every time you hit the brake pedal it's going to feel the same, and that is so important to the confidence of the driver, correct? Yeah, that's right. Yeah, let's just come back to talk about brake bias a little bit, because you mentioned there you can utilise the Bosch Motorsport ABS with the factory style master cylinder, but of course then the bias is not adjustable. So in that instance are we relying on the ABS unit to actually do the biasing? In other words, if you've got too much rearward bias hydraulically, then the ABS unit is going to have to be working overtime, maybe releasing the brake pressure on the rears more than the front.

Speaker 2: 7:25

Yeah, that's exactly right, and that is certainly not the way to set it up, and particularly in something that's a factory four-wheel drive car like an Evo or a WRX, where they have a cross-link brake system. From factory you would get 50-50 hydraulic braking effort front and rear.

Speaker 1: 7:41

Now let's just actually clear that up Cross link what do you refer to by cross link? What's that actually mean?

Speaker 2: 7:47

So that would be the right front and the left rear on the same mass cylinder circuit, and the opposite is true for the other side.

Speaker 1: 7:52

So this is done by OE's to maintain, essentially, if there's a failure, you've got at least one front and one rear wheel that's going to do the braking. Obviously not optimal, but certainly when it comes to a motorsport application, this is as far away from what we want as possible.

Speaker 2: 8:06

Yeah, that's exactly right, and so we change that over when we do the install to a front rear split and then, so that the driver then has a balance of proportioning, and then we fit a valve to the car.

Speaker 1: 8:18

Really all this comes down to, I think, is the fact that a lot of people would assume that you can fit the ABS unit and that's going to do all of the work for you, which, I mean, to a degree is correct. But essentially, if you can get the mechanical braking package correct or as close to the window as possible, then the ABS is going to be able to do a better job.

Speaker 2: 8:37

Absolutely yeah. And what you will find too is if, for example, a car had too much rear bias and you didn't address that, the ABS on the rear will cut in to stop the car from spinning, losing control, locking a rear wheel, and the driver might not push hard enough to optimise the front braking effort. So, yeah, it's certainly something you don't want to happen. You want to have the balance as close to possible as you can and have the ABS as an overlay over the top of that.

Speaker 1: 9:02

Can we talk a little bit about driving style with a proper motorsport ABS system? Is there anything we need to do differently when driving the car? Particularly, I'm talking here about the maximum braking effort areas on the track, not where we're just brushing the brake to bleed a little bit of speed.

Speaker 2: 9:18

Yeah, sure, and it's a big change for a lot of seasoned drivers that haven't been used to using motorsport ABS to retrain your brain. It's rather than driving like you would without ABS, where you might sort of have a sharp application to drop the nose of the vehicle and then bleed the brakes off. You don't do that with the ABS. It's a sharp shot application and hold and maintain through the braking zone.

Speaker 1: 9:43

So essentially you want more pressure than you would typically produce so that the ABS can bleed off that pressure to reduce a lock up. But then it's got that excess of pressure there to reintroduce, to get the braking working again.

Speaker 2: 9:55

Yeah, that's right, and you have to be able to have the wheels locked under all situations so that the ABS can modulate, because it can't generate any pressure, it can only take it away.

Speaker 1: 10:04

And I mean that really also comes back to my previous comment that the basic mechanical package of the braking system has to be right before you add the ABS. In other words, you need something with enough brake torque to actually be able to lock the wheels.

Speaker 2: 10:17

Yeah, that's true and it's also important to remember if you have a marginal braking system that's right at the limit before you put ABS on, you're probably going to be over the limit once the ABS is on because you're going to be working those brakes harder.

Speaker 1: 10:28

So this is going to essentially be introducing more heat into the braking package than you would conventionally yeah for sure. Heat into the braking package than you would conventionally yeah for sure, ok. Last thing I want to talk about is the little adjuster that we see with the Bosch Motorsport system I think a 12 position, if I'm correct there. What is that used for? How should the driver treat that? What sort of control does that give?

Speaker 2: 10:49

Essentially it's a variable slip adjustment, so a wet and a dry setting would be the best way to describe it, and a wet situation. The tyre takes longer to recover, so the algorithms in the ABS allow the tyre longer to recover under those situations when it's modulating the brake.

Speaker 1: 11:07

So this does become a bit of a trial and error sort of adjustment to just see what works best for the driver and the car combination plus the track conditions.

Speaker 2: 11:15

Yeah, that's right, the driver can feel it and we can see it in the data. So we can help people dial that in depending on the situation. But then it's sort of up to the driver as another tunable driver function, not unlike a BIAS or an adjustable anti-roll bar.

Speaker 1: 11:30

Also just in terms of the outputs from the Bosch Motorsport ABS unit. Is there anything there that can be logged by your ECU or any interaction between maybe the Bosch ABS, your ECU or maybe your dash logger?

Speaker 2: 11:45

Yeah, there's a CAN output so that can be fed into a logger or a display and it logs all the wheel speed channels, brake pressure, the 5x accelerometer in the car. So there's a lot of vehicle dynamics stuff that can be taken from that, not just ABS type stuff.

Speaker 1: 12:01

It's been really great to get some more insight into the product. Ashley, if people want to find out more about 909 Motorsport, how are they best to reach out?

Speaker 2: 12:09

You can find us on our website, www.909motorsportcomau.

Speaker 1: 12:13

Great thanks for your time. No worries, thank you. If you enjoyed this podcast, please feel free to leave a review on whatever platform you've chosen to listen to it on. It goes a long way to help us getting the word out there. All these conversations, and much more, are also available in full on our High Performance Academy YouTube channel, so make sure you subscribe. It's a one stop shop when it comes to going faster, stopping quicker and cornering better.