ABS and Brake Upgrades

[twilightprotege]

Hey,

I was just flicking through the service manual and I had an idea.

As we all know or might know, upgrading the brakes on a car is forking great, but when your car has abs you cant take full advantage of the brakes. the reason is that the stock abs system thinks that the car can only stop at a rate of 1G (i have no idea what the real values are). when you upgrade the brakes, your car can now stop at 2G, but since your abs system is still thinking your car cant stop any quicker than 1G, you will only stop at 1G...no matter how good your brakes are.

i am under the impression that recalibrating the computer to allow the car to stop at a rate of 1.5G is not possible....

anyway, each wheel has a cog and sensor for the abs - allows the abs to monitor at what rate each wheel is stopping under braking.

my idea is to reduce the diameter of that cog so the abs thinks you're driving along at 30mph but you're really doing 60mph. this would then allow in theory twice the stopping power because the abs system is thinking you're slowing down at 1G, but in reality you're stopping at 2G.

i know that's a very simple explaination and i certainly wouldnt recommend playing around with your abs unless you've done extensive testing and know what the hell you're doing....but it seams like a great way to get around big brakes and keeping your abs.

does anyone know if this has been done before - or even can it be done?????

 

[njaremka]

no offense, but i think your reasoning is way off. the abs system on the protege (and all mazda's, i belive) monitors that your wheels keep spinning, and that all wheels are slowing the vehicle at the same rate. so if the front needs more stopping power, more power will go to the front. if the abs system would only allow you to slow down at the rate of 1G under all conditions, you would have no way to modulate your brakes. you can upgrade to a bigger brake set-up, but for abs i have heard not to upgrade to ss lines. (but, i could be wrong)

 

[twilightprotege]

no offense taken, but my reasoning is right on the mark - maybe i just said explained it incorrectly.

please note, when i talk about abs, it's only when abs is active - ie full braking force going to the rotors

the evil scientists at mazda have formulated that our cars have a maximum stop at a rate of xxx feet per millisecond in perfect stopping conditions. this is where it gets a little tricky. because our abs knows this, it will not allow a wheel to slow down quicker than that (ie the wheel starts to lock up). this is when the abs kicks in and for a millisecond allows a slight lift off of brake force on that wheel to allow it go get back to the same deceleration value of the other wheels.

this is where i come into explaining about a new brake system. our abs will not allow any wheel under full braking force to slow down faster than a rate of xxx feet per millisecond. that's how all abs's work....but now that we have a new brake system that can handle more than xxx feet per millisecond, we cant slow down quicker than what the abs thinks is the fastest the car can slow down in ideal conditions.

does that explain it a little better?

anyway, i've been thinking more about the cog and how we could go about fooling the abs into allowing the car to stop quicker (with upgraded brakes etc). the cog cant be made with a smaller diameter, but, if say your car and your new brake system can slow down (with a lot of testing to make sure of this) 20% quicker, we could increase the distance between each rise in the cog...

does anyone else have any insight or ideas about what i'm saying/trying to say???

 

[ZiO]

I think i understand the reasoning, but if you are putting bigger brakes on which also mean bigger pads etc, then there is less force needed to stop the same...??? getting confused.....

 

[njaremka]

I was always under the impression that ABS only monitors that a wheel is either spinning or not spinning; not the rate at which it is spinning. I looked at it as the ABS will allow the maximum force on the brakes to the point of lock-up. And when it senses that a wheel has locked-up (ie stopped or slowed in it's rotational force) it will release brake force on that braking circuit. Follow? So, if it takes 2G's of braking load to to make your car start to skid on a good sticky surface, it will let it do so. But if it takes 0.5G's to make you car start to skid on a not so sticky surface, that's all it will allow.

I think you need to look at ABS as allowing maximum braking force (whatever that force might be equal to) for a given situation. On a slick surface, such as ice, it will only allow a very small braking force since the wheels will be sliding easier. On a sticky surface, the ABS will allow a greater force on the brakes since the tires have better traction.

 

[Familia323]

or you could just take the ABS fuse out of the fuse box.

 

[BSN_mt]

question for twilight, does the abs monitor both deceleration speed and wheel lock. You deceleration speed would be far less on ice than on dry pavement, and when you braking on a slick surface, you need less force to cause the wheels to lock up than on a non slick surface. How does the abs handle these situations.

 

[thewrench]

As far as I've been able to tell, the ABS monitors, or at least mainly monitors whether a wheel locks up, and then fires the corner that does. I've upgraded my brakes and tires and just hit the ABS the first time since then last night. Not every corner fired the ABS, only the wheels that broke traction. And I can definitely say the brakes haul the car down much faster. It was a VERY hard stop to get the ABS to fire. BTW, the ABS has definitely saved my ass more than once in the wet. Also, twilight, I don't see how you could change the sensors, you'd have to do major work to relocate the sensor on the backplate, and even more work to change the gearing on the hub.

James T

 

[twilightprotege]

zio - sort of....the same amount of force is needed to stop the car. this doesnt matter what brakes you upgrade or downgrade to. all that bigger brakes allow is more force to be applied to brakes.

njaremka - abs is much much more complicated than that....if the abs only monitored locked up or not, imagine how much time (i know, milliseconds) a wheel going from 100mph takes to lock up before abs would kick in. this is the reason it measures speed. it can realise that a wheel is starting to lock up and stop it from locking up way before it ever does

BSN_mt - abs monitors deceleration speed of each wheel....see above

all - i've had a look on the net - check this site out - it explains it better than what i could - http://auto.howstuffworks.com/anti-lock-brake2.htm

now that site says "The ABS controller knows that such a rapid deceleration is impossible" - this is what i'm getting at. this figure is entered into the abs from mazda's factory. it knows how fast in absolutely perfect conditions the car will stop....so any faster than that..."is impossible"...this is why i'd like to trick the abs into thinking that the car is decelarating slow than what it really is.

thewrench - if you have a look on page 04-13-9 in the bottom right corner, that is what the abs sensor and set up looks like. from what i can work out, if you increase the gap inbetween the peeks of the cog like thingie, the abs will think you're travelling slower than what you're really doing, and therefore allow a greater deceleration value than original.

i am a big fan of abs. it's a fantastic system.....but when you start upgrading to insane brakes that have the ability of massive stopping force....it wont allow full benefit of it

 

[twilightprotege]

BSN_mt....forgot to add...chances are every corner did activate abs...you just didnt realise it. you normally dont notice abs on rear wheels because only 15% of the braking is done by them

 

[njaremka]

If ABS works the way you think it does, then my buddy's Z-28 with ABS and upgraded big brakes was a waste of money. However, according to him it wasn't. He can stop much quicker with his upgraded brakes than he could before. But, if the ABS was limiting his deceleration rate, his upgraded brakes and tires wouldn't have done anything.

I still think you have a mis-guided view of ABS brakes.

 

[mazdadan]

Yeah, there are some misguided views of ABS brakes. Since the protege has 4 wheel ABS it constantly monitors all wheels. So if you upgrade the brakes, the computer will realize that the car has upgraded braking power. This is because the sensors work relative to what the other sensors are saying. The sensor will sense an abnormal braking condition and compensate based on the other sensors.

There is no reason that you would have to adjust the cogs, sensors, etc. If this were the case, anybody using larger or smaller rim/tire combinations would run into all kinds of issues. Think about all the trucks that put on lift kits and much larger tires. If ABS was an issue, these modifications wouldn't be so popular. Not to mention it would be a real pain for an auto manufacturer to have to make a unique computer for each model/trim level of a vehicle.

 

[BSN_mt]

Well, I went and read the page that you listed and this is what I see. The ABS measure not whether the wheel locks up or the deceleration of the wheel, but the change in the rate of deceleration of the wheel. Buy monitoring the rate of change, the computer can detect when a lock up in eminent (sp?). That is why regardless of how fast you are going, or what type of surface you are on, if the system detects a lockup about to occur, it releases force on the brake. This makes it possible to put the most force on the brakes as possible without causeing a lockup.

Example:
Wheel is spinning at 100 rpm.
Apply brakes and wheel begins to slowdown at a rate of 5 rpm per sec. (Within acceptable range)
Wheel suddenlty change to a rate of 25 rpm/sec. (outside of acceptable range)
ABS reduces force on brake to bring rate back to 5rpm per sec. (Pumping action on brake)


This is why larger wheels don't effect the system. The ABS will still only allow the wheel to change the rate of deceleration so fast. Same with better tires. The tire can get more grip to slow down faster, but the system wont let the tire stop spinning.

I realy don't see how larger brakes will cause a problem if is measure what it says. And the only thing that larger brakes do is help disapater heat fast for less fade and provide more leverage so you can use the same force but get better stopping power. The only reason this would cause a problem was if you had a large enough brake that when ever you tried to stop, it wanted to lock up the tires, in which case, you are just burning up tires and actualy reducing the distance your car can stop in.

I know for more complicated systems it will need a lot more discription, but for a basic system, this seems to be what is being said.

Please correct me it I'm wrong.

 

[twilightprotege]

njaremka - the upgrade was worth it....remember what howstuffworks said. there is an acceptable decelaration rate built into the abs.....it just that if those brakes were so kick ass that the car can now stop quicker than the acceptable deceleration rate...that's what i'm trying to point out...

mazdadan - rim/wheel/tyre size has nothing to do with abs - they do not alter the rate at which the abs thinks the wheel is spinning. maybe i should refer to wheel speed as what BSN_mt says - rpm.

BSN_mt - you're starting to think along the lines of what i'm trying to say...the abs will only allow a certain rpm deceleration of the wheel. if the new brake system, suspension, tyres etc...if all those combined now allow the car to stop quicker than what the abs knows is safe - you're loosing some of the potential of a new brake system.
by the way - larger brakes allow more force to be applied to the wheel. think of it this way. at 5" from the centre of the wheel the rotor is traveling at say 20mph....but at 6" it's traveling at 35mph...the further away from the centre of any circle, the faster it spins relative closer to the centre of the circle. think of a bicycle with 3 cogs on the pedals...the largest one allows you to ride faster than the smallest one....and in the same instance, the larger one requires more effort

 

[njaremka]

Dude, you're thinking way too hard about this. Just upgrade your brakes and get it over with!

 

[mp5]

1st. Relocating the cog and sensor on your abs system will have no effect on abs. The easiest way to explain this is by thinking of a single spoke on a bicycle. Everywhere along the length of that spoke will pass true vertical at the exact same time. The fact that the outer edge near the rim travels at a faster speed then the inner edge near the hub has no bearing on a sensor monitoring its rotation. That sensor will detect that single spoke at the same rate no matter where the sensor is located along the length of the spoke. In addition, changing the distances between cogs will have no effect either. The abs system monitors a change in rate of rotation, not the actual speed of rotation. So even though you can effectively fool the abs into thinking your are traveling a different speed then you are, it doesnt really care. When you step on the brakes it only moinitors the rate at which the speed of the wheel is changing.

2nd. Abs actually works better with ss brake lines. The abs system rapidly releases and applies pressure to keep a wheel at its threshold of traction. The expansion when pressure is applied that occurs in standard flexible brake lines actually slows the transmission of abs pulses to the brakes. In addition, typically the calipers that come in brake kits are stronger and flex less then stock calipers. This will also transmit the abss pulses quicker and therefore allow abs to work better. Sport Compact Car had a good article about this when the tested the brake upgrades available for the Toyota Matrix last year.

3rd. No braking system can handle braking more the xxx feet per millisecond. Just about all well maintained braking systems are strong enough to lock up your wheels whenever you feel like. Abs allows you to keep a wheel at the threshold of traction and traction is an interaction between your tires and the road surface. What typically allows the upgrade kits to shave a few feet off stopping distances was discussed in item 2 above. The major advantage to brake kits is their ability to resist fading when you are braking hard for long periods of time.

 

[mazdadan]

mazdadan - rim/wheel/tyre size has nothing to do with abs - they do not alter the rate at which the abs thinks the wheel is spinning. maybe i should refer to wheel speed as what BSN_mt says - rpm.

That was the whole point of my post. The rotational diameter of anything (rotors, rims, tires) has no effect on the ABS system.

Same holds true with upgraded calipers. The system will compensate for braking force. I have personally never seen a brake upgrade have any issues with the ABS system. If it's that big of a deal, you could always disable it. Even when I had my RX7, I switched out the braking components with no ill effects on the ABS system.

 

[ahb11m]

ABS stops lock up, or trys to prevent it, based on a certain braking force... should a wheel lock it will release the braking force just before lock, and then brake again, with the same force... ABS CAN be felt... thats the pulsing you feel through the peddle (not to mention the car), and the crazy sounds when abs comes on... ABS is not a gentle thing....
the ABS will actually increase your braking distance due to the whole pulsing thing... but it will allow you control under braking, which is the trade off

sooo changing the studdy things won't change stuff... it'll probably just stuff ya cars abs

 

[BSN_mt]

"(ABS) brakes keeping the tires very near the point at which they will start to lock up" This line from the howthingswork article explains why the tires/wheels/brakes/etc would have no effect on an ABS system. If bigger brakes let you lock up the tires easier, then the ABS will kick in sooner. If better tires allow better connection with road and reduce lockups, then that ABS will apply more force.

Regardless of what you do, the ABS is there to keep the wheel from locking up by monitoring and reacting to extreme changes in the rpm/sec (I can't think of the proper units for that measurement for the life of me). The best think you can do to help you braking distance on a cold system is tires. That is what connects you to the road. Bigger brakes will only allow for the system to have to work less or fade less (Slotted / drilled roter, etc.) That is why the brakes on a big truck are big. Small brakes wouldn't be able to handle the heat and would burn up.

 

[Natey]

Abs actually works better with ss brake lines. The abs system rapidly releases and applies pressure to keep a wheel at its threshold of traction. The expansion when pressure is applied that occurs in standard flexible brake lines actually slows the transmission of abs pulses to the brakes. In addition, typically the calipers that come in brake kits are stronger and flex less then stock calipers. This will also transmit the abss pulses quicker and therefore allow abs to work better. Sport Compact Car had a good article about this when the tested the brake upgrades available for the Toyota Matrix last year.

Thanks! I've been pondering buying some SS brake lines(calipers and rotors will be later), and now I'll definately go for it!

Also, when installing a big-brake kit, is it necessary/a good idea to upgrade the master cylinder too?