View Poll Results: When you fit big brakes do you -
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Big Brakes and ABS?????
#1
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Big Brakes and ABS?????
Since a lot of people have fitted big brakes on their cars now I was wondering what people do about the abs.
Overall I don't like the ABS on fords as IMO it lets the car run on in emergency stop situations.
On my car I found with the Tarox 6pots 330mm discs they were too bitey to have the ABS off as it locked up the brakes too easily and deformed tyre carcuses on oh shit moments.
Now with AP's I feel the pedal pressure is a lot better and if I have the ABS connected it tends to come in when its not necesary so I have unplugged it.
What do you do on your cars??
Cheers
Daniel
Overall I don't like the ABS on fords as IMO it lets the car run on in emergency stop situations.
On my car I found with the Tarox 6pots 330mm discs they were too bitey to have the ABS off as it locked up the brakes too easily and deformed tyre carcuses on oh shit moments.
Now with AP's I feel the pedal pressure is a lot better and if I have the ABS connected it tends to come in when its not necesary so I have unplugged it.
What do you do on your cars??
Cheers
Daniel
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so it seems ABS is a good thing then, Hmmmm
I'll have to try a few stopping tests to see how it feels. It seems that the ABS trys to work too often because the brakes work better than the standard ones.
maybe the ABS is playing up in my car
I'll have to try a few stopping tests to see how it feels. It seems that the ABS trys to work too often because the brakes work better than the standard ones.
maybe the ABS is playing up in my car
#7
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I have 378mm / AP six pots on my Escort and have not managed to get the ABS to come in yet. The brakes have so much feel that you can detect the second that it is going to lock the wheels and back off the pedal pressure to compensate BEFORE the ABS has time to get it's knickers in a twist . On the Sapphire at slow speeds from 7mph to 0, the pedal used to pulse, hence why I installed a switch as it was disconcerting (but not as disconcerting as forgetting to turn it back on when you most need ABS ). Don't get any pulsing with the Escort...
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#8
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Originally Posted by Mike Rainbird
I have 378mm / AP six pots on my Escort and have not managed to get the ABS to come in yet. The brakes have so much feel that you can detect the second that it is going to lock the wheels and back off the pedal pressure to compensate BEFORE the ABS has time to get it's knickers in a twist . On the Sapphire at slow speeds from 7mph to 0, the pedal used to pulse, hence why I installed a switch as it was disconcerting (but not as disconcerting as forgetting to turn it back on when you most need ABS ). Don't get any pulsing with the Escort...
have no ABS on escort,m so should be interesting
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IF find at low speed when braking quite hard the ABS loves to come in and grab the front wheels! does my head in. But never had a problem when braking hard from high speeds
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I'm gonna take it out later and switch the ABS back on and see how it feels.
suppose its better than big flat spots on the tyres
Cheers
suppose its better than big flat spots on the tyres
Cheers
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I also got the pulsing and also sometimes the car would just DIE and you would have NO brakes!!!!
Fitted a cutout switch like mike and its all been pretty good, but there is a big lack of feel and I often have HUGE lock up moments so I am going to put in a proper pedal box.
The Escort has a much more complex and better ABS I believe and so i would leave that alone. Mikes brakes are staggeringly good
Fitted a cutout switch like mike and its all been pretty good, but there is a big lack of feel and I often have HUGE lock up moments so I am going to put in a proper pedal box.
The Escort has a much more complex and better ABS I believe and so i would leave that alone. Mikes brakes are staggeringly good
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cheers for the replies - thinking about it I haven't had the same problem on the Escort because I disconnected after the problems on the saff.
didn't get a chance to take the car out tonight I will try it tomorrow.
didn't get a chance to take the car out tonight I will try it tomorrow.
#20
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not sure if this is relevant as i don't know how Nissan ABS compares to Ford's.
i got 315mm discs with 4 pots and 225/45/17 Eagle F1's. i found that the ABS would kick in quite often under heavy braking. i started to think that it was actually cutting in before it should.
as it happens, its kicked the bucket and doesn't work now.
the car has become leathal without ABS, my stopping distances have increased alot. it locks up so easily, its scary. i got cut up doing 70 on a dual carriage way, i jumped on the brakes and locked up.
its not down to me being a shit driver either, as all my other cars haven't had ABS and i never really had problems with locking up. its just that i've learnt to live with the ABS, and the difference is big.
Nissan ABS is nothing special either i'd say - designed late 80's for my car. it must cut in alot more than i realised and i can't feel it through the pedal much, so i suppose i don't notice it too often.
i got 315mm discs with 4 pots and 225/45/17 Eagle F1's. i found that the ABS would kick in quite often under heavy braking. i started to think that it was actually cutting in before it should.
as it happens, its kicked the bucket and doesn't work now.
the car has become leathal without ABS, my stopping distances have increased alot. it locks up so easily, its scary. i got cut up doing 70 on a dual carriage way, i jumped on the brakes and locked up.
its not down to me being a shit driver either, as all my other cars haven't had ABS and i never really had problems with locking up. its just that i've learnt to live with the ABS, and the difference is big.
Nissan ABS is nothing special either i'd say - designed late 80's for my car. it must cut in alot more than i realised and i can't feel it through the pedal much, so i suppose i don't notice it too often.
#21
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on the track its a bloody nightmare ... the abs didnt like me heavy braking before corners .. the ap's were sayin stop ..abs was sayin foookright off
it was like havin brake fade just ask sean bicknall as i came careering up behind him at combe brakes .. what brakes
also the choice of pads makes a difference
on the road the abs is on .... kinda scary when end up with a possible rainbird moment
it was like havin brake fade just ask sean bicknall as i came careering up behind him at combe brakes .. what brakes
also the choice of pads makes a difference
on the road the abs is on .... kinda scary when end up with a possible rainbird moment
#22
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i don't see how having big brakes can make a difference to abs. bigger rolling radius from bigger wheels, maybe.
my abs also pulses at low speed without putting on the failure lamp which is horrible. have tried cleaning the sensors, and will try replacing them next.
my abs also pulses at low speed without putting on the failure lamp which is horrible. have tried cleaning the sensors, and will try replacing them next.
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I have lost count of the times my ABS has saved me from an unfortunate incident.
IMO it is madness for a road car NOT to have it.
I have a set of 4 pot AP's on my escort cossie and the ABS works perfectly still.
I also do track the car quite a bit and find then the ABS does like to work alot more
than normal but then that may be just because I am braking harder and later because
of the increased braking performance and confidence it gives.
IMO it is madness for a road car NOT to have it.
I have a set of 4 pot AP's on my escort cossie and the ABS works perfectly still.
I also do track the car quite a bit and find then the ABS does like to work alot more
than normal but then that may be just because I am braking harder and later because
of the increased braking performance and confidence it gives.
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the problem i find with ABS is when I'm driving in those moments where you NEED to stop as you have no where to steer you have no option ABS kicks in and the car runs on
I switched the ABS on this morning took the car out as I braked at the end of the carpark fooking ABS pulsing. Set off driving normally, slowing on to roundabouts just at the last second brake pedal pulses
I'm gonna leave the ABS on for a while and try a few more tests when it dries up.
I switched the ABS on this morning took the car out as I braked at the end of the carpark fooking ABS pulsing. Set off driving normally, slowing on to roundabouts just at the last second brake pedal pulses
I'm gonna leave the ABS on for a while and try a few more tests when it dries up.
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#27
Testing the future
Jamz, interesting, but is it really true, or just a made up sales pitch?
Dan@Rapid-Ford, the 'run on' that you are describing is a symptom of the pedal pulsing which is caused by a fault in the system. if you press your pedal harder during that final 'run on' phase, you will come to a stop in the same time. but the best thing is to sort the problem that's causing it.
Dan@Rapid-Ford, the 'run on' that you are describing is a symptom of the pedal pulsing which is caused by a fault in the system. if you press your pedal harder during that final 'run on' phase, you will come to a stop in the same time. but the best thing is to sort the problem that's causing it.
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Thats quite interesting and it kinda explains what is happening.
heres what I thought the most interesting bit was.
Taken from the above link.
Anybody say anything about the above??
heres what I thought the most interesting bit was.
Taken from the above link.
ABS Control In Super-Slow-Mo
In order to best explain how the ABS "depends" on the base braking system, let's have a look at a typical ABS event at the micro level - from the processing algorithm's perspective.
Say you are driving down the highway at 75 MPH (the posted speed limit, of course) when all of a sudden the truck in front of you spills its load of natural spring water across all three lanes of traffic. Now, this alone would not be so bad, except the water is still sealed in 55-gallon drums - one of which would certainly make a mess of your car's front fascia. Time to take evasive action.
Being the trained high-speed individual that you are, you immediately lift off the gas, push in the clutch (you are driving a manual transmission, right?), and simultaneously nail the brake pedal...but in the heat of the moment you hit it a little too hard.
Meanwhile, the ABS is hanging back watching the world go by, seeing a constant stream of 75 MPH signals from its four wheel speed sensors. Let's call this "observation mode." Upon your application of the brake, however, the ABS snaps to attention, its antenna up, ready for action. You have just hit the brake pedal after all, and who know what's coming next.
After 50 milliseconds (it's actually much faster than that - 7 to 10 milliseconds is typical - but it makes the math easier) the ABS takes another snapshot of the wheel speed information in an attempt to figure out what's going on. This time the wheel speed sensors are all reporting a speed of 74 MPH. Doing a quick calculation, the ABS determines that in order to have slowed 1 MPH in a 50ms period the wheels must be decelerating at a rate of 0.91g's. Because you are driving a sports car, the engineer who calibrated the system 'taught' the ABS that your car is capable of decelerating at this rate, so the ABS continues to hang back and watch the event from the spectator's booth. No problem so far.
The next 50ms, however, are a little more interesting. This time around, the wheels are reporting 72.5 MPH. Now, it may not seem like a big jump, but to slow 1.5 MPH in a 50ms window equates to a deceleration of 1.36g's. Not alarming, but the ABS 'knows' that based on this deceleration level, the wheels are probably beginning to slip a little more than they should - after all, your car is probably not decelerating at quite 1.36g's..and any error between the two indicates slip.
ABS is now in "ready mode." It's probably too soon to jump in, as the wheels might spin back up on their own in the next 50ms loop, but things are definitely looking bad!
As the first barrels of spring water bounce left and right, missing your car by inches, you stay on the brake pedal but push even harder. This time around, the left front wheel speed sensor is registering 68 MPH - a 4.5 MPH drop in the last 50ms, or a deceleration level of 4.1g's. Doing the math faster than you can (after all, you are busy dodging barrels of spring water), the ABS quickly comes to the conclusion that, unlike the left front wheel at this moment, the car cannot possibly be decelerating at 4.1g's. Best case is that the car was decelerating at 1.0g (or thereabouts) over the last 50ms, so the 'real' vehicle speed is still somewhere around 71.5 MPH, even though the left front wheel speed is reading 68 MPH - a 3.5 MPH error.
So, based on a wheel deceleration of 4.1g's, a slip level of 5% (3.5 MPH 71.5 MPH), and a couple other factors not listed here, the ABS jumps in and enters "isolation mode." (Note that the wheels are nowhere even near "wheel lock" - the 100% slip point.) The first thing the ABS does is shut off the hydraulic line from the master cylinder to the left front caliper, isolating the driver from applying more pressure - after all, it was the driver that got us into this mess in the first place.
Next, the ABS starts work in "decrease mode," releasing the excess pressure from the left front caliper in order to allow the left front wheel to reaccelerate back up to the vehicle's actual speed - 71.5 MPH in this case. Since the ABS knows how quickly the wheel is decelerating (4.1g), how fast the car is actually going (71.5 MPH), and the pressure-torque characteristics of the left front caliper/pad/rotor assembly (we'll come back to this one in just a second), it can precisely calculate how long to open its release valve to vent that extra pressure, leaving just enough pressure in the caliper to maintain 1.0g of deceleration (or thereabouts).
Let's say that calculated time turned out to be 10 milliseconds (this again makes the math easier later on). Bang! Valve opens, pressure is released, and 10ms later it closes, leaving just the right amount of pressure in the caliper so that the wheel spins back up to exactly 71.5 MPH, but continues to decelerate at 1.0g. Everything is going as planned.
Time to close the loop and enter "increase mode." Once the ABS sees that the left front wheel has returned to near the 'real' vehicle speed, it slowly reapplies pressure from the master cylinder to make sure that maximum sustainable brake force is being utilized. To this end, the ABS calculates precisely how long to pulse open the isolation valve, slowly building pressure at the left front caliper until once again the left front wheel begins to slip. It performs this calculation based on - you guessed it - how quickly the wheel is re-accelerating, how fast the car is actually going, and the pressure-torque characteristics of the caliper/pad/rotor assembly.
In our hypothetical little world, the ABS calculated that four pulses of 5ms each were necessary to build the wheel pressure back up to the point that the wheel began to slip again, returning to "isolation mode."
The cycle is repeated on all four wheels simultaneously until either the driver gets out of the brake pedal, or until the car has come to a stop. Hopefully, this did not include punting a spring water barrel or two along the way as the ABS kept all four wheels slips in the 5%-10% range, allowing you to turn and swerve to your heart's content as the drums bounced out of your path. Happy car, happy driver.
The Potential Impacts Of "Big Brakes"
Let's now take the exact same scenario, but add a twist: you are returning home from having that long-sought-after big brake kit installed. You know, the one that required new 18" wheels to clear the 8-piston calipers and 16" rotors. Driving around the parking lot you couldn't believe the improvement in pedal feel and initial bite they displayed. These things must really throw a boat anchor behind the car at high speeds, right?
Well, let's see.
Resisting the temptation to run in the fast lane at triple-digit speeds, you once again find yourself behind the spring water truck at 75 MPH. Barrels fly and you again lay on the brakes, but with the increased confidence of your new hardware to slow you down in time. Plus, you now know how the ABS works, so you lay into the pedal, confident that you will have both deceleration and steerability. It couldn't get any better.
Like scenario 1, after the initial 50, 100, and 150 milliseconds the ABS takes snapshots of the wheel speed information and registers 0.91g's, 1.36g's, and 4.1g's on the left front wheel. Again the ABS quickly comes to the conclusion that, unlike the left front wheel at this moment, the car cannot possibly be decelerating at 4.1g's. Best case is that the car was decelerating at 1.0g (or thereabouts) over the last 50ms, so the 'real' vehicle speed is still somewhere around 71.5 MPH, even though the left front wheel speed is reading 68 MPH - a 3.5 MPH error. So far, so good - just like last time.
Here's where things start to get interesting, though. ABS enters "isolation mode" and shuts off the hydraulic line from the master cylinder to the left front caliper, isolating the driver from applying more pressure. Next, the ABS starts work in "decrease mode," and once again calculates that 10ms are required to the excess pressure from the left front caliper in order to allow the left front wheel to reaccelerate back up to the vehicle's actual speed - 71.5 MPH in this case. Unfortunately, this calculation was based on the standard vehicle's pressure-torque characteristics of the left front caliper/pad/rotor assembly. Let's talk about this briefly while the barrels roll in closer.
Pressure-Torque And Pressure-Volume Relationships
When a braking system is designed and installed, the components are chosen to provide a certain deceleration level for a certain amount of force applied by the driver to the brake pedal. While the overall relationship is critical, there are many ways to achieve the same end but fundamentally the parts are chosen to work together as a system.
One of the most important relationships for the ABS engineer is the pressure-torque (P-T) relationship of the caliper/pad/rotor assembly. In so many words, for a given brake fluid pressure, X, the caliper/pad/rotor assembly will build up a certain amount of torque, Y. For the sake of argument, let's assume that adding 100 PSI of brake pressure to the stock caliper in our example vehicle generates 100 ft-lb. of torque.
Another important relationship is the pressure-volume (P-V) characteristic of the system. This relationship defines the swelling or expansion of the brake system for a given increase in pressure. Let's also say that our stock vehicle brake system 'swells' 1cc for every 100 PSI.
Unfortunately, there are several big-brake systems available today which pay no regard to the original P-T or P-V relationships of the original vehicle and in fact many make it a point to affect drastic changes in these relationships in order to give the consumer that feeling of 'increased bite.' While the upside is certainly a firmer pedal and higher partial-braking deceleration for the same pedal force, the trade-off can be ABS confusion.
Back To The Barrels
So, back to our example - the ABS has just calculated that a 10ms pressure reduction pulse was necessary to vent that extra pressure, leaving just enough pressure in the caliper to maintain 1.0g of deceleration (or thereabouts) but the new system with its decreased P-V characteristics (increased stiffness!) releases twice as much pressure as the stock system in the same 10ms window (the equivalent of a 20ms pulse with the stock system)! Of course, the increased P-T characteristics (bigger rotor! bigger pistons!) don't help either, as now three to four times as much torque has been removed from the wheel as with the stock system, leaving only enough torque to decelerate the wheel at, say, 0.3g. In ABS land this is known as a 'decel hole' and feels just like you momentarily took your foot off the brake pedal.
Now, given that huge pressure decrease, the ABS quickly enters "increase mode," trying to correct and build the pressure back up near the vehicle's maximum sustainable brake force. This takes time and time equals lost stopping distance.
The ABS calculates precisely how long to pulse open the isolation valve and determines that four pulses of 5ms each are necessary, just like before. Because of the new P-T and P-V characteristics however, after only two pulses the wheel is again being forced into slip, leaving the ABS scratching its head and wondering what's going on. Not expecting wheel slip so soon, the ABS quickly releases pressure in an attempt to recover, but the damage has already been done.
The cycle is repeated on all four wheels simultaneously until either the driver gets out of the brake pedal, or until the car has come to a stop but this time the ABS is always one step behind. In some cases the ABS is robust to modest changes in the base brake system, but in extreme cases there can be a significant negative impact to the vehicle's steerability (increased front wheel slip due to poor control) and a measurable increase in stopping distance (multiple 'make up' decrease pulses).
So, your chances of stopping in time or swerving to avoid one of the bouncing barrels have been decreased. In this game, inches count and you sure need every one.
TCS/ESP/EBD Impacts
The analogy above translates directly to the TCS/ESP/EBD subsystems without exception. Like the ABS, these three technologies rely heavily on the P-T and P-V characteristics of the OEM system, and any changes can manifest themselves under braking, accelerating, or dynamic maneuvers.
Are You Telling Me That Big Brakes Are A Bad Idea?
So, will all big brake upgrades wreak havoc on the chassis control systems found on your favorite ride? Not necessarily. In fact, if designed and chosen properly, these upgrades can make the most of these control technologies while providing all of the cooling and thermal robustness advantages these kits have to offer.
The "secret" to brake system compatibility is that there is no secret - it just requires fundamental engineering expertise and design know-how.
As mentioned earlier, far too many of the big brake upgrade kits on the market today pay no attention to the P-T or P-V characteristics that the car originally possessed. In fact, there are kits available today which have P-T characteristics which more than double the output (P==>2T) of the stock systems they replace - "200% More Stopping Power" must be better than stock, right?
In most cases, these vendors procure large quantities of big rotors and red calipers, fabricate an adapter bracket to mount them to a variety of different suspensions, and market the kit as a 'one-size-fits-all' without first determining if the system will be compatible with the remaining foundation braking system, let alone the electronic chassis controls. Sure, it's quick, cost-effective, and looks like a million bucks through your 18" wheels, but what about ultimate performance?
In order to best explain how the ABS "depends" on the base braking system, let's have a look at a typical ABS event at the micro level - from the processing algorithm's perspective.
Say you are driving down the highway at 75 MPH (the posted speed limit, of course) when all of a sudden the truck in front of you spills its load of natural spring water across all three lanes of traffic. Now, this alone would not be so bad, except the water is still sealed in 55-gallon drums - one of which would certainly make a mess of your car's front fascia. Time to take evasive action.
Being the trained high-speed individual that you are, you immediately lift off the gas, push in the clutch (you are driving a manual transmission, right?), and simultaneously nail the brake pedal...but in the heat of the moment you hit it a little too hard.
Meanwhile, the ABS is hanging back watching the world go by, seeing a constant stream of 75 MPH signals from its four wheel speed sensors. Let's call this "observation mode." Upon your application of the brake, however, the ABS snaps to attention, its antenna up, ready for action. You have just hit the brake pedal after all, and who know what's coming next.
After 50 milliseconds (it's actually much faster than that - 7 to 10 milliseconds is typical - but it makes the math easier) the ABS takes another snapshot of the wheel speed information in an attempt to figure out what's going on. This time the wheel speed sensors are all reporting a speed of 74 MPH. Doing a quick calculation, the ABS determines that in order to have slowed 1 MPH in a 50ms period the wheels must be decelerating at a rate of 0.91g's. Because you are driving a sports car, the engineer who calibrated the system 'taught' the ABS that your car is capable of decelerating at this rate, so the ABS continues to hang back and watch the event from the spectator's booth. No problem so far.
The next 50ms, however, are a little more interesting. This time around, the wheels are reporting 72.5 MPH. Now, it may not seem like a big jump, but to slow 1.5 MPH in a 50ms window equates to a deceleration of 1.36g's. Not alarming, but the ABS 'knows' that based on this deceleration level, the wheels are probably beginning to slip a little more than they should - after all, your car is probably not decelerating at quite 1.36g's..and any error between the two indicates slip.
ABS is now in "ready mode." It's probably too soon to jump in, as the wheels might spin back up on their own in the next 50ms loop, but things are definitely looking bad!
As the first barrels of spring water bounce left and right, missing your car by inches, you stay on the brake pedal but push even harder. This time around, the left front wheel speed sensor is registering 68 MPH - a 4.5 MPH drop in the last 50ms, or a deceleration level of 4.1g's. Doing the math faster than you can (after all, you are busy dodging barrels of spring water), the ABS quickly comes to the conclusion that, unlike the left front wheel at this moment, the car cannot possibly be decelerating at 4.1g's. Best case is that the car was decelerating at 1.0g (or thereabouts) over the last 50ms, so the 'real' vehicle speed is still somewhere around 71.5 MPH, even though the left front wheel speed is reading 68 MPH - a 3.5 MPH error.
So, based on a wheel deceleration of 4.1g's, a slip level of 5% (3.5 MPH 71.5 MPH), and a couple other factors not listed here, the ABS jumps in and enters "isolation mode." (Note that the wheels are nowhere even near "wheel lock" - the 100% slip point.) The first thing the ABS does is shut off the hydraulic line from the master cylinder to the left front caliper, isolating the driver from applying more pressure - after all, it was the driver that got us into this mess in the first place.
Next, the ABS starts work in "decrease mode," releasing the excess pressure from the left front caliper in order to allow the left front wheel to reaccelerate back up to the vehicle's actual speed - 71.5 MPH in this case. Since the ABS knows how quickly the wheel is decelerating (4.1g), how fast the car is actually going (71.5 MPH), and the pressure-torque characteristics of the left front caliper/pad/rotor assembly (we'll come back to this one in just a second), it can precisely calculate how long to open its release valve to vent that extra pressure, leaving just enough pressure in the caliper to maintain 1.0g of deceleration (or thereabouts).
Let's say that calculated time turned out to be 10 milliseconds (this again makes the math easier later on). Bang! Valve opens, pressure is released, and 10ms later it closes, leaving just the right amount of pressure in the caliper so that the wheel spins back up to exactly 71.5 MPH, but continues to decelerate at 1.0g. Everything is going as planned.
Time to close the loop and enter "increase mode." Once the ABS sees that the left front wheel has returned to near the 'real' vehicle speed, it slowly reapplies pressure from the master cylinder to make sure that maximum sustainable brake force is being utilized. To this end, the ABS calculates precisely how long to pulse open the isolation valve, slowly building pressure at the left front caliper until once again the left front wheel begins to slip. It performs this calculation based on - you guessed it - how quickly the wheel is re-accelerating, how fast the car is actually going, and the pressure-torque characteristics of the caliper/pad/rotor assembly.
In our hypothetical little world, the ABS calculated that four pulses of 5ms each were necessary to build the wheel pressure back up to the point that the wheel began to slip again, returning to "isolation mode."
The cycle is repeated on all four wheels simultaneously until either the driver gets out of the brake pedal, or until the car has come to a stop. Hopefully, this did not include punting a spring water barrel or two along the way as the ABS kept all four wheels slips in the 5%-10% range, allowing you to turn and swerve to your heart's content as the drums bounced out of your path. Happy car, happy driver.
The Potential Impacts Of "Big Brakes"
Let's now take the exact same scenario, but add a twist: you are returning home from having that long-sought-after big brake kit installed. You know, the one that required new 18" wheels to clear the 8-piston calipers and 16" rotors. Driving around the parking lot you couldn't believe the improvement in pedal feel and initial bite they displayed. These things must really throw a boat anchor behind the car at high speeds, right?
Well, let's see.
Resisting the temptation to run in the fast lane at triple-digit speeds, you once again find yourself behind the spring water truck at 75 MPH. Barrels fly and you again lay on the brakes, but with the increased confidence of your new hardware to slow you down in time. Plus, you now know how the ABS works, so you lay into the pedal, confident that you will have both deceleration and steerability. It couldn't get any better.
Like scenario 1, after the initial 50, 100, and 150 milliseconds the ABS takes snapshots of the wheel speed information and registers 0.91g's, 1.36g's, and 4.1g's on the left front wheel. Again the ABS quickly comes to the conclusion that, unlike the left front wheel at this moment, the car cannot possibly be decelerating at 4.1g's. Best case is that the car was decelerating at 1.0g (or thereabouts) over the last 50ms, so the 'real' vehicle speed is still somewhere around 71.5 MPH, even though the left front wheel speed is reading 68 MPH - a 3.5 MPH error. So far, so good - just like last time.
Here's where things start to get interesting, though. ABS enters "isolation mode" and shuts off the hydraulic line from the master cylinder to the left front caliper, isolating the driver from applying more pressure. Next, the ABS starts work in "decrease mode," and once again calculates that 10ms are required to the excess pressure from the left front caliper in order to allow the left front wheel to reaccelerate back up to the vehicle's actual speed - 71.5 MPH in this case. Unfortunately, this calculation was based on the standard vehicle's pressure-torque characteristics of the left front caliper/pad/rotor assembly. Let's talk about this briefly while the barrels roll in closer.
Pressure-Torque And Pressure-Volume Relationships
When a braking system is designed and installed, the components are chosen to provide a certain deceleration level for a certain amount of force applied by the driver to the brake pedal. While the overall relationship is critical, there are many ways to achieve the same end but fundamentally the parts are chosen to work together as a system.
One of the most important relationships for the ABS engineer is the pressure-torque (P-T) relationship of the caliper/pad/rotor assembly. In so many words, for a given brake fluid pressure, X, the caliper/pad/rotor assembly will build up a certain amount of torque, Y. For the sake of argument, let's assume that adding 100 PSI of brake pressure to the stock caliper in our example vehicle generates 100 ft-lb. of torque.
Another important relationship is the pressure-volume (P-V) characteristic of the system. This relationship defines the swelling or expansion of the brake system for a given increase in pressure. Let's also say that our stock vehicle brake system 'swells' 1cc for every 100 PSI.
Unfortunately, there are several big-brake systems available today which pay no regard to the original P-T or P-V relationships of the original vehicle and in fact many make it a point to affect drastic changes in these relationships in order to give the consumer that feeling of 'increased bite.' While the upside is certainly a firmer pedal and higher partial-braking deceleration for the same pedal force, the trade-off can be ABS confusion.
Back To The Barrels
So, back to our example - the ABS has just calculated that a 10ms pressure reduction pulse was necessary to vent that extra pressure, leaving just enough pressure in the caliper to maintain 1.0g of deceleration (or thereabouts) but the new system with its decreased P-V characteristics (increased stiffness!) releases twice as much pressure as the stock system in the same 10ms window (the equivalent of a 20ms pulse with the stock system)! Of course, the increased P-T characteristics (bigger rotor! bigger pistons!) don't help either, as now three to four times as much torque has been removed from the wheel as with the stock system, leaving only enough torque to decelerate the wheel at, say, 0.3g. In ABS land this is known as a 'decel hole' and feels just like you momentarily took your foot off the brake pedal.
Now, given that huge pressure decrease, the ABS quickly enters "increase mode," trying to correct and build the pressure back up near the vehicle's maximum sustainable brake force. This takes time and time equals lost stopping distance.
The ABS calculates precisely how long to pulse open the isolation valve and determines that four pulses of 5ms each are necessary, just like before. Because of the new P-T and P-V characteristics however, after only two pulses the wheel is again being forced into slip, leaving the ABS scratching its head and wondering what's going on. Not expecting wheel slip so soon, the ABS quickly releases pressure in an attempt to recover, but the damage has already been done.
The cycle is repeated on all four wheels simultaneously until either the driver gets out of the brake pedal, or until the car has come to a stop but this time the ABS is always one step behind. In some cases the ABS is robust to modest changes in the base brake system, but in extreme cases there can be a significant negative impact to the vehicle's steerability (increased front wheel slip due to poor control) and a measurable increase in stopping distance (multiple 'make up' decrease pulses).
So, your chances of stopping in time or swerving to avoid one of the bouncing barrels have been decreased. In this game, inches count and you sure need every one.
TCS/ESP/EBD Impacts
The analogy above translates directly to the TCS/ESP/EBD subsystems without exception. Like the ABS, these three technologies rely heavily on the P-T and P-V characteristics of the OEM system, and any changes can manifest themselves under braking, accelerating, or dynamic maneuvers.
Are You Telling Me That Big Brakes Are A Bad Idea?
So, will all big brake upgrades wreak havoc on the chassis control systems found on your favorite ride? Not necessarily. In fact, if designed and chosen properly, these upgrades can make the most of these control technologies while providing all of the cooling and thermal robustness advantages these kits have to offer.
The "secret" to brake system compatibility is that there is no secret - it just requires fundamental engineering expertise and design know-how.
As mentioned earlier, far too many of the big brake upgrade kits on the market today pay no attention to the P-T or P-V characteristics that the car originally possessed. In fact, there are kits available today which have P-T characteristics which more than double the output (P==>2T) of the stock systems they replace - "200% More Stopping Power" must be better than stock, right?
In most cases, these vendors procure large quantities of big rotors and red calipers, fabricate an adapter bracket to mount them to a variety of different suspensions, and market the kit as a 'one-size-fits-all' without first determining if the system will be compatible with the remaining foundation braking system, let alone the electronic chassis controls. Sure, it's quick, cost-effective, and looks like a million bucks through your 18" wheels, but what about ultimate performance?
Anybody say anything about the above??
#29
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Originally Posted by foreigneRS
Jamz, interesting, but is it really true, or just a made up sales pitch?
Dan@Rapid-Ford, the 'run on' that you are describing is a symptom of the pedal pulsing which is caused by a fault in the system. if you press your pedal harder during that final 'run on' phase, you will come to a stop in the same time. but the best thing is to sort the problem that's causing it.
Dan@Rapid-Ford, the 'run on' that you are describing is a symptom of the pedal pulsing which is caused by a fault in the system. if you press your pedal harder during that final 'run on' phase, you will come to a stop in the same time. but the best thing is to sort the problem that's causing it.
and if jamming the pedel down to beat the ABS is the solution not really the best fix
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Another quote from the site
I'll fit some smaller brakes
The Solution
Unlike the "if it works on brand P, it must work on your car" approach, at STOPTECH all brake upgrade kits are designed with the characteristics of the original braking system taken into account to minimize these differences. This is the reason that when you order a STOPTECH big rotor upgrade kit the new caliper bores may actually be smaller than the units you are replacing to "balance the equation." This is just one way in which our engineers attempt to retain the original system's P-T and P-V integrity. Sure, it's not one-size-fits-all, but neither is your car or your driving style. Why should you expect any less from your brake upgrade?
Unlike the "if it works on brand P, it must work on your car" approach, at STOPTECH all brake upgrade kits are designed with the characteristics of the original braking system taken into account to minimize these differences. This is the reason that when you order a STOPTECH big rotor upgrade kit the new caliper bores may actually be smaller than the units you are replacing to "balance the equation." This is just one way in which our engineers attempt to retain the original system's P-T and P-V integrity. Sure, it's not one-size-fits-all, but neither is your car or your driving style. Why should you expect any less from your brake upgrade?
#31
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So how do you tell if the brake setup you intend fitting will be suitable ?
Say you fit 4pot AP's and 330mm discs to a 4x4 Sapph, are there other things you can do to make the baking more efficient - changing the master cylinder etc ? (other than using the correct pads & fluid etc)
Say you fit 4pot AP's and 330mm discs to a 4x4 Sapph, are there other things you can do to make the baking more efficient - changing the master cylinder etc ? (other than using the correct pads & fluid etc)
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I have lots and lots and lots of respect for people here and their experience but I will keep with this - if you say it's impossible to drive safely without ABS either there is something wrong with your brakes or you just can't drive properly. There always comes time when electronic gods (ABS, EBD, VDC, ESP, EBV, and many others) are not enough to replace skill and imagination :-/
#33
DEYTUKURJERBS
I removed the ABS on my 3dr when the big brakes went on, and i didnt like it, far far too easy to lock the fucker up
I hope the ABS works well on the GTR when its done, as i dont wanna be locking that up for some rainbird roundabout jumping...
I hope the ABS works well on the GTR when its done, as i dont wanna be locking that up for some rainbird roundabout jumping...
#34
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Originally Posted by foreigneRS
i don't see how having big brakes can make a difference to abs. bigger rolling radius from bigger wheels, maybe.
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the harder you try and clamp the disc the more it reduces the force allowed...
#35
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i have proven on tarmac rallies that teh car will stop alot faster without it than with it , teh cossie system is so antiquated and is a very slow sampling system that its only any good for the non driver to stop and steer as he would normally have kept the brake on hard and crashed , but if were talking competiton use then ditch it your only increasing your stopping distances
im all for all the electronic gizmos all singing and dancing ESP systems are fantanstic - but i will be leaving them on the wifes car where they belong
im all for all the electronic gizmos all singing and dancing ESP systems are fantanstic - but i will be leaving them on the wifes car where they belong
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Originally Posted by Itsmeagain
I removed the ABS on my 3dr when the big brakes went on, and i didnt like it, far far too easy to lock the fucker up
It's more a problem of driving skill and low feel on the pedal then problem of it being impossible to brake, just have to get used to/learn to use it. People used to race really bad handling cars, and they still do around the world.. and nobody has got ABS, and they live with it.
Sometimes one can get imporession reading thechnical threads over here that it is impossible to drive fast without bling bling stuff for hundreds of $$$$$$$$$$$$$. It is not so.
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Originally Posted by markk
im all for all the electronic gizmos all singing and dancing ESP systems are fantanstic - but i will be leaving them on the wifes car where they belong
#38
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I was wondering the same since I'm going to be getting nice big AP's.
Ok so when the light (on the 3dr) comes on, the abs is acting up right?
spiky how did you clean your sensors?? with a wool pad?? ok, maybe I need to clean mine then.
Ok so when the light (on the 3dr) comes on, the abs is acting up right?
spiky how did you clean your sensors?? with a wool pad?? ok, maybe I need to clean mine then.
#40
Testing the future
but just because the light doesn't come on, doesn't mean that abs is working properly (the bulb could be blown, or the car has sensor issues that cause this bloody annoying pedal pulse at low speed that a few of us are talking about).