Here’s why you can’t out-brake ABS

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Kyle Smith

One of the interesting commonalities among driving enthusiasts is that we all think we are the second coming of Senna and thus believe we have both legendary reaction times and fine motor skills. After all, how many folks have you heard over the years talk of pulling ABS fuses or disabling the system because they claim they can stop a car faster if ABS is not “interfering,” and they can truly threshold brake? Those people are wrong, and Jason Fenske of Engineering Explained just did the math to prove it.

There’s one thing to get out of the way right off the hop here: This is a discussion of modern ABS systems. First- and even second-generation systems likely were quite cumbersome and slow reacting. However, computer technology has come a very long ways in the last 40 years, and any judgements previously made against ABS should be re-evaluated against a current system.

I say that because Fenske does a good job of putting that into hard numbers. The first to know is slip, which is pretty self-explanatory when you think on it. Slip is the speed differential between tire and the vehicle. This is what determines if you have traction or not: 0 percent slip is traction, 100 percent slip is sliding.

The next important data point is processing speed and inputs. A modern ABS system is picking up wheel speed and slip from each individual tire and can modulate at each tire. You only get the joined feedback at the brake pedal, along with your internal accelerometer. The ABS system can cycle and analyze data between 15 and 100 times per second. Your human brain has a whole lot of processing power, but the average human has a reaction time of 120ms, meaning that by the time you even understand you’re sliding, the ABS system has cycled at least twice.

That’s in ideal conditions, too. Add in changes in surface that affect coefficient of friction. A small patch of dirt or sand, or maybe a little oil or water, and suddenly you need to react to that and you won’t be able to predict that change in braking capacity—neither can the ABS, to be fair—but your reaction will likely require some amount of give and take fluctuation before you zero back in on perfect threshold, and by that time the surface could change again. A human simply cannot act fast enough to keep brake pressure in the sweet spot. We can do really well in some situations, but considering the depth and breadth of variables when driving on public roads, there’s no way even the best can beat ABS consistently. It’s statistically impossible.

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Comments

    Actually, ABS can be a hinderance in a few, albeit uncommon instances.
    1) sand/loose gravel – it is better to pile it up.
    2) two-foot driving when stuck, the wheel-spin required to engage the ABS traction systems is dangerous if on an incline.
    3) snow and ice. Ice = good, sliding tires melts a thin layer of ice adding water to the surface reducing the coefficient of friction. Snow = less good. Snow easily shifts giving false readings. But locking em up like most folks do is perfect for straight line delivery of the vehicle.

    Albeit rare, it isn’t perfect. Like everything. I still have it, but I’m not going to retrofit it.

    I’ve worked in chassis control systems for a bit and I had some interesting insights from my time in the industry I wanted to share.

    You are 100% correct on the sand/loose gravel point. So correct in fact that some modern ABS systems have added a function called “rough road detection”. By looking at the wheel accelerations during standard driving the system is able to determine if the vehicle is on gravel, sand, or loose dirt. In this case the slip targets are dramatically increased in order to create a wedge in front of the wheels during ABS stops. This is also the case in snow.

    Snow is definitely tricky. I never realized how many different “types” of snow there were until I did winter testing calibration work. The goal of ABS in snow is to balance control-ability and stability of the vehicle with stopping distance performance. Fully locked wheels allow for 0% control-ability in case a driver wants to do something other than a pure straight line stop. In addition fully locked wheels can quickly cause a vehicle to lose stability and go into an uncontrollable spin.

    I got to agree with your conclusion. My family hauler has ABS and that’s great. My toy does not have it and I’m not about to put in the work to retrofit it.

    Good video. I personally have not seen a scenario where ABS was an issue, more like traction control using the ABS was the issue preventing movement that was otherwise possible.

    ABS in Ice Racing, no thanks. I am a die hard pass on owning it. However the baseline programming on a Ferrari, Porsche, or BMW is on another level from a Mazda. Since I can only afford Mazda level cars I find the ones without it attractive. Of course I hate Stability Enhacement and slushboxes to. My version of hell is driving a current CRV.

    Stability control is certainly one of the best car-related inventions that modern electronics have made possible – right up there with current ABS systems.

    My sister-in-law’s husband is a car enthusiast, and he likes driving their 2015 Honda CRV, even if he is not passionate about it. I don’t know if something has happened since then, to make them bad?

    Car magazines have put ABS to the test against the human factor before. In general, the average person cannot outbrake an ABS system but some individuals were able to outperform ABS consistently. These were folks who spend a lot of time behind the wheel; e.g. race car driver, professional trucker, etc.

    I also agree with BMD4800 that there are times when ABS is detrimental.

    The question I have is; I took my 09 fusion in for a ABS recall they could not do the recall work because the abs pump motor was froze up Makes sense since brake fluid is so corrosive and since I never made panic stops that sitting there so long and not being used. Question is how many how many others out there are like mine. They won’t know until they need them!

    That is food for thought about the stuck motor. As someone who has activated ABS just once since exposed to it in 1993, I think I may have to go find a dirt road or something to make sure it works on my 15 Mustang. I live in Phoenix, so there is no snow to try, and, while rain is rare, the Michelins grip so well that I don’t want to put extra wear on the tires by braking hard in the wet.

    Ok, if you are trying to be scientific about this lets keep our units consistent, 120 mSec equates to 8 times a second for the human brain.

    So you mentioned that ABS does not work on snow or gravel. I would also like to add ice and slush.

    I live in the north where snow, slush and ice are common for almost half of the year.

    Panic stopping on dry pavement which accounts for about 90% of the situations during the warm months. In this situation I can stop almost as quickly as ABS.

    During winter months panic stopping or just stopping in general involves snow, ice, or slush at which ABS sucks at. I have been in numerous situations where I have had virtually no brakes due to ABS and had to resort to the emergency brake to get the car to slow down and stop. The first couple of times I experienced this it caught me by off guard and I missed stopping at an intersection and went right through it.

    To rectify this I disable ABS during the winter months to allow me to have a fighting chance of stopping my vehicle.

    In my opinion ABS is not worth having as I have no control during the majority of driving where ABS comes to play.

    I live in Minnesota. Snow, slush and ice are common from roughly December 1 to March 15 to April 1. I don’t know what kind of driver you are but I seldom if ever have a situation where I am wishing I didn’t have ABS.

    I agree in a few cases that is not true. I have seen people in gravel driveways go though a garage door as if the brakes had locked it would have dug the car in.

    I had an accident a few years back. I tried to avoid a left turn of a texting driver. I locked down into the anti locks and ended up in gravel. The tires did not dig in and the car failed to make the corner. If they had locked I could have slid the car around and make the turn.

    While I know anti locks are best as a whole for most drivers I would never say they are good 100% of the time. there is 2% out there that things can be different.

    Nothing is ever 100% no matter what you are looking at.

    Lots of interesting comments here on this.

    A point, relative to low friction condition, worth repeating: ABS can’t create friction (traction) that isn’t there, it just helps you manage what you’ve got (ie, you can’t violate the laws of physics).

    All our 4 wheeled vehicles have ABS (Porsche, VW, GM) of varying generations and absolutely makes a difference, pretty much 100% in low friction conditions. We live in what passes for mountains in northwest NJ, and definitively have our share of all the rain, snow, ice, slush that folks here seem to think are issues.

    If you are driving in the winter and have traction problems, and don’t run winter tires on all four corners, please re-read my note above.

    I think trying to compare ABS and non-ABS in test conditions is missing the point. For the average driver who is suddenly faced with an obstacle or situation they weren’t expecting most, myself included, will panic and slam on the brakes. In my case a truck suddenly turned into my lane back in the 90s when I was driving my 89 Probe GT. I don’t have time to do anything but slam on the brakes and hope for the best. The ABS worked and I avoided the truck by a few feet. Without ABS I would have sheared off my fact pop up headlights.

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