Braking : F1 Vs Low-end Road Car

[GSpeedR]

Don't confuse motorsport derived ABS with what you find on production vehicles. Production vehicle ABS is intended to allow combined steering and braking and thus it (attempts to) controls slip ratio to well below longitudinal maximum. Motorsport ABS is analogous to traction control and can provide maximum braking performance with fidelity that can't be matched by humans. Plus it is often supplemented with compensations from additional chassis sensors. If F1 allowed it they would use it, just like TC.

[jtc127]

I am still wondering how a tankslapper is avoided by these guys.

They avoid a tank slapper because the car is more responsive to corrections? Is it possible to recover a road car that had lost its rear end in a similar way?

Formula cars are going to have a much quicker steering ratio, which makes corrective inputs very quick, whereas a normal production car would take much more turning of the steering wheel. My formula car is less than 270 degrees lock to lock.

Also, the drivers aren't reacting to the cars as a conscious thought. When the back end starts to go you feel it with your body and apply corrective steering input without even thinking about it. At speed you don't have enough time to think about what's going on and think of your response, it has to be completely instinctual.

[raymondu999]

Doesn't ABS/TCS work in a "cure rather than prevent" method? I always thought that TCS cut power back as soon as it detected excessive wheelspin, and ABS cut braking back when the wheels started to lock. A human would be preventing that. No?

While we're talking of locking, I remember last year in Hockenheim Massa was frequently locking even all 4 tyres in his 2nd stint.

[Just_a_fan]

Also, the drivers aren't reacting to the cars as a conscious thought. When the back end starts to go you feel it with your body and apply corrective steering input without even thinking about it. At speed you don't have enough time to think about what's going on and think of your response, it has to be completely instinctual.

And you don't have to be an F1 driver to do this either - a normal guy like me can do it.

I went on a rally day; never done one before so all new to me. Simple track using rally prepared Ford Fiestas. Nothing special if you looked at them as road cars but they were proper rally machines. At one point the track had a little crest/bump at the same point as a surface change from tarmac to loose. There was a slight bend too.

On one lap going through this point, the back end stepped out. I heard the instructor say "ooh, good catch!". Only a moments later did I relaise that I'd whacked in a big arm full of opposite lock, picked it up, got it straight and carried on - all without even thinking. If the instructor hadn't said anything I might not have even realised until later.

Being firmly strapped in to a car makes a big difference to what you feel. And a properly quick steering rack makes a huge difference to what you can react to.

If anyone hasn't yet done so, they should have a go in a kart. It will give you a much better idea of what you can do on reactions alone.

[Just_a_fan]

Doesn't ABS/TCS work in a "cure rather than prevent" method? I always thought that TCS cut power back as soon as it detected excessive wheelspin, and ABS cut braking back when the wheels started to lock. A human would be preventing that. No?

While we're talking of locking, I remember last year in Hockenheim Massa was frequently locking even all 4 tyres in his 2nd stint.

ABS monitors wheel speed. It can be set to intervene at any point between 0% and 100%. If you know the tyres and road surface intimately (as in F1, for example) you could set it up to be as close to perfect as you can get. On each wheel. No human driver can do that. Likewise TCS.

A given road car ABS has to deal with widely varying surface conditions (good dry tarmac, rough tarmac, wet etc.), widely varying tyres (from premium to ditchfinder specials) and even varying brake materials (OEM, fast road, cheap). There's going to be some optimisation headroom available in the system to allow for this variation I would guess.

I would expect an F1 ABS system to be tuned to within an inch of its life...and then have some adjustment available on the steering wheel for the driver to adjust it further if required. Much like the engine maps today.

[Dragonfly]

Don't confuse motorsport derived ABS with what you find on production vehicles. Production vehicle ABS is intended to allow combined steering and braking and thus it (attempts to) controls slip ratio to well below longitudinal maximum. Motorsport ABS is analogous to traction control and can provide maximum braking performance with fidelity that can't be matched by humans. Plus it is often supplemented with compensations from additional chassis sensors. If F1 allowed it they would use it, just like TC.

That's the answer to those who were quick to jump on me. Road cars, unless they are high end, have ABS systems with binary action. On input it's wheel spinning or locked, at the output it's apply pressure or not. The frequency depends on the actual friction level between tyre and road.
I haven't looked in detail how the combined ABS/ESP/ASR systems work. Maybe they have proportioning ability.

[Just_a_fan]

Don't confuse motorsport derived ABS with what you find on production vehicles. Production vehicle ABS is intended to allow combined steering and braking and thus it (attempts to) controls slip ratio to well below longitudinal maximum. Motorsport ABS is analogous to traction control and can provide maximum braking performance with fidelity that can't be matched by humans. Plus it is often supplemented with compensations from additional chassis sensors. If F1 allowed it they would use it, just like TC.

That's the answer to those who were quick to jump on me. Road cars, unless they are high end, have ABS systems with binary action. On input it's wheel spinning or locked, at the output it's apply pressure or not. The frequency depends on the actual friction level between tyre and road.
I haven't looked in detail how the combined ABS/ESP/ASR systems work. Maybe they have proportioning ability.

Sure, but the key thing is that they can do that to each wheel separately. A human can only affect overall system pressure - if one wheel locks and is released then all wheels are running at less than optimum braking because reducing brake pressure to the locked wheel reduces brake pressure to all wheels. ABS can keep the overall system closer to locking than a human can.

[GSpeedR]

That is certainly true, but to my knowledge production car ABS (meaning found on a Toyota Corolla) will not be tuned for maximum longitudinal force, but to a slip ratio significantly below it. A serious race system should have to ability to measure or calculate slip angle demand and can adjust ABS thresholds according to the combined input.

[Edis]

I would be very surprised when a modern ABS system is not able to brake better than a skilled human and be able to find out exatcly the perfect point.

Some car magazine, can't remember which, tested this with a racecar driver and the ABS system won every time when this was done on tarmac. A good driver simply can't keep the tires near their optimum slip during braking as well as the ABS system can. The only way for the driver to beat the ABS system is on loose surfaces like gravel, where locking the wheels give you a shorter stopping distance.

That's the answer to those who were quick to jump on me. Road cars, unless they are high end, have ABS systems with binary action. On input it's wheel spinning or locked, at the output it's apply pressure or not. The frequency depends on the actual friction level between tyre and road.
I haven't looked in detail how the combined ABS/ESP/ASR systems work. Maybe they have proportioning ability.

ABS systems are not "binary".

The most common ABS system on cars these days is the four channel system with one pump and two servovalves per channel. One inlet valve which is normally open and one outlet valve which is normally closed. This allows oil to flow from the master cylinder to the brake cylinder.

Before a wheel is about to lock up there will be a sharp rise in wheel deceleration. The ABS system monitors wheel speed and calculate wheel deceleration for each wheel. When the wheel deceleration falls below a threshold value (-a) the ABS system will close the inlet valve and further build up of pressure inside the brake cylinder is prevented. The ABS system also calculate what is called the slip switching threshold and if the wheel speed drops below this value the outlet valve is opened and brake fluid is pumped back to the master cylinder using the pump. This reduce the pressure in the brake cylinder, and this will continue as long there is an (-a) signal. So the system is capable to actually adjust the pressure inside the brake cylinder using certain threshold values.

ABS systems found in racing cars work using the same principles (and often using the same hardware), but have software which allow the these parameters to be adjusted for maximum performance.

[ubrben]

1 - All fast race car drivers trail brake to a degree. The smart one don't trail brake all the way to throttle application, because they know that slip angle drag is still slowing the car

2 - Even top level pro drivers will be faster with ABS - if it's set up right

3 - I've worked on the same car with ABS and without ABS, once the pedal kick back was acceptable on the ABS no-one wanted to run without it, secondly when they went back to the non-ABS car they tended to spend a morning flatspotting fronts until they weaned themselves off it

4 - A good ABS system makes a pretty good stability control system that can operate way in excess of the bandwidth of a human driver

Edit - Audi run ABS on the R8 GT3 and were dominant in the wet during Spa 24 hours practice this year.

Ben