Keep the ABS brakes on the 818R?

[MurrayT]

A few years ago I got into weekend track racing and have been discussing building my 818R with other drivers. I get mixed feedback on ABS brakes on a track car. I planned on transferring the very good Brembo ABS brakes from my 2006 WRX STi to my 818R. I love the ABS braking I get on my STi and thought it would be great on my 818R track car. Anyone have experience with this? Should I plan on removing ABS systems when I do the donor transplant? Should I transfer the ABS braking system to the 818R?

Please advise.
MurrayT

[metalmaker12]

The 818r has no abs, but if you want it than go for it. You will have to transfer the abs module and make lines to that unit back to the brake lines.FFR will only be supplying brake lines from the master to the caliper extension lines. You will also have to keep the abs in the wiring, as they deleting it in the 818r. Also keep in mind a 2006 sti hubs will not match up to the kit.The 6pd will also not match up exactly and you will need to get your own center diff delete gear kit and plate. FFR will only be supplying this for the 5spd. You will be able to use the brembos with the 5x100 wrx hubs but you will need 04 sti 5x100 sized rotors and a set of rear spacers for the calipers. The other option for the hubs is LIC motorsports that makes custom Subaru hubs, check them out too. If you got questions, i am here to help

[longislandwrx]

Also the abs computer's calibration is for a stock weight car. No sure what reprogramming would be needed to increase performance and reduce lockups.

[Xusia]

Is that a factor (honest question)? I always thought it was wheel speed, and potentially other sensors...

[RM1SepEx]

I don't think weight is a problem, but it could be...

[VD2021]

Is that a factor (honest question)? I always thought it was wheel speed, and potentially other sensors...

I don't think weight is a problem, but it could be...

Exactly. The design specifications for these basic production type systems were written with operating windows. The system's work load will be decreased in the lighter 818 and it should perform as expected.

[RM1SepEx]

Exactly. The design specifications for these basic production type systems were written with operating windows. The system's work load will be decreased in the lighter 818 and it should perform as expected.

yes but we will be well out of the design parameters with a road weight of 2000-2200 lbs vs 3400-4000 lbs...

with less weight won't the system actually have MORE to do since I expect that the tires will be more responsive to the pulsing effect of ABS, meaning the system needs to act faster?

Personally I HATE ABS and like to practice threshold braking in all of my vehicles... more fun that way. Part of building and driving this car is the connection with the road and driving dynamics... everything will happen faster with less weight, lower polar moment of inertia and a better power to weight ratio!

[VD2021]

yes but we will be well out of the design parameters with a road weight of 2000-2200 lbs vs 3400-4000 lbs...

with less weight won't the system actually have MORE to do since I expect that the tires will be more responsive to the pulsing effect of ABS, meaning the system needs to act faster?

Personally I HATE ABS and like to practice threshold braking in all of my vehicles... more fun that way. Part of building and driving this car is the connection with the road and driving dynamics... everything will happen faster with less weight, lower polar moment of inertia and a better power to weight ratio!

No, I would expect not. Have you been able to review the design specification? I've reviewed a few ABS design specifications and vehicle weight is usually not mentioned unless the system is for a huge gross weight vehicle.

A lighter gross weight vehicle will have less moving mass and yield less work for the system as the valves, that allow pressure to be decreased or increased to the wheel's calipers, function.

In the end, actual road test will determine how well the system performs in its new environment.

If you(OP) decide to add the system, you can also add a disable swt.

[AZPete]

VD2010, I think you are right that ABS should work on the lighter 818. I built an FFR roadster with the ABS controller, ECU and wiring from a Mustang GT donor and then used Mustang front brakes and T-Bird rear brakes (for the IRS). The ABS system worked perfectly even on the much lighter car with different front-rear brakes, though both had OE ABS. Actually, it saved my butt when a Prius stumbled out of a hidden driveway! I'm no expert on how they work but it seems the ABS system reacts to variances in wheel speed.
Pete

[Matty_STi]

There is some misinformation in this thread. Though the ABS was "calibrated" with the production car it was actually designed on the prodrive wrc cars and the same system is used on ALL subies (in other words they test it on production cars make sure it works, tweak the algorithms a bit based upon abs aggressiveness and intended vehicle use and that's it.). The abs system also integrates with the stability control system. The abs controller can get inputs from the wheels speed sensors and with the dsc system in place also include accelerometers, a gyro, throttle position sensor and steering position sensor.

The abs and dsc systems were developed with the help of prodrive and brembo with probably some assistance from cosworth and a few others.

The subaru abs system and dsc systems are top tier and in fact short of some of the most recent ultra high end bosch stuff really is just tied with other top tier products like the gtr, and what has come out of VAG's upper echelon makers (porsche, audi, lambo). It really is a work of art.

And with that all said. The abs system doesn't car about the weight of the car. It determines piston cycling based upon the wheel speed sensors and accelerometers nothing more. That's why the abs dynamics won't change when you have say 1/8 tank of gas with a lightened car and a 140lb driver versus 4 200lb men a full tank of gas and camping gear. Abs engagement will vary but that still depends on sensor input. If it was based on arbitrary weight tables then things would get overly complex really really quickly. No to mention changes in sprung and unsprung mass would cause vastly different effects that would be nearly impossible to calculate for. Also variance in rotational inertia would total mess up that calibration if you say had super light wheels and tires but where also much bigger causing increases in rotational inertia despite being lighter. I'll save the physics but it just doesn't work that way and there are far more efficient and better ways of doing that.

Also you will never be able to out brake a modern abs system, except in some very very specific circumstances, and those would be where you want the tires to lock up AND dig in because of lock up. Of course threshold braking won't beat abs in this case and the lock up, though more efficient at braking faster, still removes steering control. In other words, abs is always the better option. It's why it was banned in motorsports for so long - it can control the brakes better than any living human.

I will transplant the abs and look at the dsc as well.

-Matt

[Matty_STi]

yes but we will be well out of the design parameters with a road weight of 2000-2200 lbs vs 3400-4000 lbs...

with less weight won't the system actually have MORE to do since I expect that the tires will be more responsive to the pulsing effect of ABS, meaning the system needs to act faster?everything will happen faster with less weight, lower polar moment of inertia and a better power to weight ratio!

nope. counter intuitive but the heavier car will create situations where inertia causes lock up far more easily. Yes ground pressure is higher but that doesn't linearly translate into more grip. You get a regressive curve as more and more weight causes more and more inertia at the expense of increased grip.

Also the abs cycles based upon the wheel slipping and then gripping. weight would have no effect on the rate of the cycling and the efficiency of that. the abs system will only cycle as fast as it needs to and will vary that accordingly.

And like you said lighter weight means lower moment of inertia that also means the car will stop faster in a high brake pressure event and in fact the abs system will have to work LESS.

An abs system pulses much faster than you would think greater than 10 times a second, some possibly closer to 20. Also abs can apply itself to an individual slipping wheel, you can't do that with one brake pedal.

There's lots of other stuff too related to the subie brake system like the automated brake booster in emergency stops (i.e. you slam on the brakes) the brake position sensor determines that you have attempted to slam on the brakes so it will actually use electronic goodieness to apply the brakes faster than you are able to fully push the pedal engaging the brakes faster than humanly possible further decreasing stopping distance. Also EBD (electronic brake force distribution), automatic front-back brake force biasing, absolutely amazing on the track especially for those not nearly experienced even to change their brake bias and it can do it much much faster.

Be in """control""" all you want, I will rather stop before you. Safer on the road, faster on the track, also having that edge means more fun for me. I'll keep my ABS thank ya.

-Matt

[Matty_STi]

I should add I am talking about the 08+ rex/sti's but something similar is on the 05+ rex's as well. though not as advanced.

I am going to use an 08+ abs setup.

(also it's 4 channel 4 sensor abs)...

-Matt

[metalmaker12]

+1 Matty, but you must have too much time on your hands to write and think it out so much, lol. What you have mentioned is true about the speed sensor and I concur. I will not be using the abs though, even though it is an advantage.

[Xusia]

Good info Matty! The only thing I would add to your excellent points is that it is possible (just not likely) for a human to stop in a shorter distance than ABS - I've seen it done in tests. Test conditions are more favorable than real world conditions, however, and even with that advantage it took experts multiple tries to beat ABS. Even then they couldn't do it repeatedly. After multiple runs, the number of times they were able to stop in a shorter distance without ABS was a very small fraction of the number of attempts.

If experts can only beat ABS a fraction of the time under controlled conditions, how likely is the average person - or even a highly skilled, but not expert person - to beat ABS in a real world panic stop? I'd say not very frickin' likely. Like you, I'll take ABS when I can get it!

[Evan78]

I'm glad Matt has "too much" time on his hands. You could say that about anyone posting here, thankfully there's people willing to contribute for the benefit of others. Brakes are an area worthy of thinking things through.

[VD2021]

There is some misinformation in this thread. Though the ABS was "calibrated" with the production car it was actually designed on the prodrive wrc cars and the same system is used on ALL subies (in other words they test it on production cars make sure it works, tweak the algorithms a bit based upon abs aggressiveness and intended vehicle use and that's it.). The abs system also integrates with the stability control system. The abs controller can get inputs from the wheels speed sensors and with the dsc system in place also include accelerometers, a gyro, throttle position sensor and steering position sensor.

The abs and dsc systems were developed with the help of prodrive and brembo with probably some assistance from cosworth and a few others.

The subaru abs system and dsc systems are top tier and in fact short of some of the most recent ultra high end bosch stuff really is just tied with other top tier products like the gtr, and what has come out of VAG's upper echelon makers (porsche, audi, lambo). It really is a work of art.

And with that all said. The abs system doesn't car about the weight of the car. It determines piston cycling based upon the wheel speed sensors and accelerometers nothing more. That's why the abs dynamics won't change when you have say 1/8 tank of gas with a lightened car and a 140lb driver versus 4 200lb men a full tank of gas and camping gear. Abs engagement will vary but that still depends on sensor input. If it was based on arbitrary weight tables then things would get overly complex really really quickly. No to mention changes in sprung and unsprung mass would cause vastly different effects that would be nearly impossible to calculate for. Also variance in rotational inertia would total mess up that calibration if you say had super light wheels and tires but where also much bigger causing increases in rotational inertia despite being lighter. I'll save the physics but it just doesn't work that way and there are far more efficient and better ways of doing that.

Also you will never be able to out brake a modern abs system, except in some very very specific circumstances, and those would be where you want the tires to lock up AND dig in because of lock up. Of course threshold braking won't beat abs in this case and the lock up, though more efficient at braking faster, still removes steering control. In other words, abs is always the better option. It's why it was banned in motorsports for so long - it can control the brakes better than any living human.

I will transplant the abs and look at the dsc as well.

-Matt

nope. counter intuitive but the heavier car will create situations where inertia causes lock up far more easily. Yes ground pressure is higher but that doesn't linearly translate into more grip. You get a regressive curve as more and more weight causes more and more inertia at the expense of increased grip.

Also the abs cycles based upon the wheel slipping and then gripping. weight would have no effect on the rate of the cycling and the efficiency of that. the abs system will only cycle as fast as it needs to and will vary that accordingly.

And like you said lighter weight means lower moment of inertia that also means the car will stop faster in a high brake pressure event and in fact the abs system will have to work LESS.

An abs system pulses much faster than you would think greater than 10 times a second, some possibly closer to 20. Also abs can apply itself to an individual slipping wheel, you can't do that with one brake pedal.

There's lots of other stuff too related to the subie brake system like the automated brake booster in emergency stops (i.e. you slam on the brakes) the brake position sensor determines that you have attempted to slam on the brakes so it will actually use electronic goodieness to apply the brakes faster than you are able to fully push the pedal engaging the brakes faster than humanly possible further decreasing stopping distance. Also EBD (electronic brake force distribution), automatic front-back brake force biasing, absolutely amazing on the track especially for those not nearly experienced even to change their brake bias and it can do it much much faster.

Be in """control""" all you want, I will rather stop before you. Safer on the road, faster on the track, also having that edge means more fun for me. I'll keep my ABS thank ya.

-Matt

I should add I am talking about the 08+ rex/sti's but something similar is on the 05+ rex's as well. though not as advanced.

I am going to use an 08+ abs setup.

(also it's 4 channel 4 sensor abs)...

-Matt

Matt,

Great specific info. Not being a Subaru owner or having vehicle/system specific specifications to review, I have to keep it in general engineering terms. This info really brings it all together.

[VD2021]

Remember also that it is all about retaining steering control to keep the vehicle moving in the direction in which the wheels are directed, instead of skidding in the direction of the car's forward momentum.

[Matty_STi]

LOL! Thanks guys. I am just unable to stop writing once the the brain juices start flowing. And I was just taking a brake (HA!!) from auditing some code for a project I am working on and couldn't help myself form jumping in.

And yes it IS possible to beat an ABS system. But now I doubt you could except in snow with ice layer underneath and someone with a decade of rally experience and the knowledge of how to get tires to dig in versus just slide. ABS will still give you the ability to point the nose of the car. But combining the straight subie abs with all it's other goodies is just too great a performance advantage for me to pass up.

I am not saying everyone would need or want abs, we all have our reasons for doing stuff. In my case the benefits outweigh any possible negatives of weight, complexity, costs or installation headaches. Can't be said that someone else will come to the same conclusions with different parameters of requirement...

tl;dr - abs good 4 me. hahaha


also ignore grammar and spelling mistakes, lots of this is stream of consciousness writing.

[VD2021]

LOL! Thanks guys. I am just unable to stop writing once the the brain juices start flowing. And I was just taking a brake (HA!!) from auditing some code for a project I am working on and couldn't help myself form jumping in.

And yes it IS possible to beat an ABS system. But now I doubt you could except in snow with ice layer underneath and someone with a decade of rally experience and the knowledge of how to get tires to dig in versus just slid. ABS will still give you the ability to point the nose of the car. But combining the straight subie abs with all it's other goodies is just too great a performance advantage for me to pass up.

I am not saying everyone would need or want abs, we all have our reasons for doing stuff. In my case the benefits outweigh any possible negatives of weight, complexity, costs or installation headaches. Can't be said that someone else will come to the same conclusions with different parameters of requirement...

tl;dr - abs good 4 me. hahaha

Almost my exact thoughts when I decided to add the full C5 Active Handling system to my GTM build.

[RM1SepEx]

I don't think misinformation was provided, many just indicated that there would be some issues or questions with the ABS application on the 818... No detailed analysis was attempted

There is no assurance that the ABS will work "as designed" in an 818 vs the original car, the weight is very different
That doesn't mean that it won't work, I expect that it will
I also expect that with traction control and ABS you could do better lap times and have a car that is easier to drive fast. As I mentioned earlier many of us want a more basic car to enhance our "connection" to the driving experience.

These systems will not react as intended by the design engineers as the application is far different that what was originally designed

In braking all that matters is weight and the torque that can be applied to stop the rotation through clamping and the traction with the ground. (this is directly affected by the normal force F=uN) ... N is the mass of the car.) Let us assume that we use the same tires (perhaps the most important braking variable!)

As the car gets heavier it has more traction to road, more mass to decelerate, and requires a higher brake torque to stop the rotation. It will either take longer or take more force to stop the wheel from rotating and more force to slow the car (Force=Mass * Acceleration) The std WRX brake system will be very twitchy or grabby in a 818 and it will be very easy to lock the wheels. (I'm even considering no power brakes) Bias will also be way out of whack... The rears will need more brake bias. Add more weight, increase braking distance.

The 818 will lock much easier and faster than the WRX/STI so the ABS will need to react differently for optimum performance.

We have a similar thread somewhere on airbags and safety... God only knows what is "optimum" for a low volume, design phase, kit car vs the production vehicle that its parts came from. The is no way that Factory Five can be expected to test, design, or determine such factors.

It is highly likely that alternative ABS programming would yield better performance in an 818 vs a WRX as it will weigh almost 50% less than a WRX

[Evan78]

VD2010, I think you are right that ABS should work on the lighter 818. I built an FFR roadster with the ABS controller, ECU and wiring from a Mustang GT donor and then used Mustang front brakes and T-Bird rear brakes (for the IRS). The ABS system worked perfectly even on the much lighter car with different front-rear brakes, though both had OE ABS. Actually, it saved my butt when a Prius stumbled out of a hidden driveway! I'm no expert on how they work but it seems the ABS system reacts to variances in wheel speed.
Pete

Is there a lot of users like yourself that have experience with this on the roadster? I haven't bothered to go looking for the information outside the 818 bubble, but I always assumed there's probably a good number of people that have experience in a similar situation using Ford components.

[Matty_STi]

The abs used on a wrx is the same used amongst all subaru's... there is some serious weight differences and yet the controller works without flaw. Individual wheel speed and accelerometer measurements are all that are used. Nothing else. If the things you mentioned were true than there would massive massive massive massive massive issues THROUGHOUT the entire automotive industry as common parts are used through out. ABS is a common part. Audi doesn't use a different ABS controller for their cars, just small tweaks based on how aggressive to match the intended performance envelope. You think the GTR has it's own unique ABS? nope, every nissan is the exact same. Porsche? yep. Ferrari, sure thing. Ford? of course. And you'll even see cross platform use on different brands. I honestly think the audi, lambo, porsche abs systems are all based on the same controller with some minor software tweaks.. Part numbers will be different of course, and product lines are always changing but i bet if you compared the hardware and software of a production year with similar design years they would all be the same.. That's saying something. If what you say is true than every single car would get it's own unique abs controller. But that's not the case. The physics don't agree with what you are saying, the mechanics of ABS design don't either. The only places you'll see differences is in large heavy duty pick up trucks and commercial vehicles. And that is related to issues that don't really belong in this discussion.

Yes weight effects grip but not in a linear fashion and not in the same way that you understand it. Also tire lock up has more to do with tire compound and brake torque than weight. A stock wrx can lock it's wheels up. A stock sti can too. Hell a stock ford focus can lock it's wheels up. All on dry pavement. Weight and grip are not linear. Grip is a function of tire compound, contact patch size and the amount of time that contact patch is on the ground. Contact pressure is also important but grip from the previously mentioned is more important. Why is it that F1 strives to have thousands of pounds of extra downforce and changes of 40-50lbs of down force result in fractions of second per lap differences? yet very minute changes in suspension setup can result in upwards of a second per lap? that is due to the non-linear nature ground contact pressure. Contact patch size which increases with ground contact pressure gives you more benefit than just the ground pressure in fact if you compared the friction increase in a larger contact patch to just a weight increase that would result in a similar sized contact patch increase then the difference in friction and thus grip would be about an order of magnitude different (more grip going to the large contact patch).

Yes F=MA and your point about increased brake torque to slow down a car with more mass. But the increase in grip is not twice as much with a twice as heavy car. Friction does not equal grip. Grip is a very complicated set of forces in varying vectors, friction is vectorless and is either kinetic or static. Grip consists of friction in 6 degrees of freedom plus static friction plus the variable of temperature. The dynamic nature of this means that though you can double static friction with a doubling of mass and thus force, you don't double grip and thus the linear nature of the equation in which an ABS system would be able to determine wheel lock up based upon that varying nature would become one hell of a stupid algorithm to develop. I don't know how much you know about code development, algorithm development, mechanical physics and associated but trying to run an ABS system as with that as your calculation point would be stupid. And of course when looking at the nature of that non-linear relation we can conclude that the changes this would impose on an ABS though they look daunting are in fact trivial at best. If they weren't then the system used on a 2400lb sports car wouldn't also be used on a 5000lb suv. The differences in performance envelope and system design parameters would be too vast to overcome and the financial investment would be of a nature so daunting that few companies could afford to develop ABS systems let alone actually deploy them to any vehicles anyone could afford. That isn't the case, obviously.

Yes you could fiddle around with the abs programming but to say it is highly likely that you will get better performance from said reprogramming or implementing a different systems is wrong

As for the brake bias thing. well that's actually fairly easy to deal with, again because the software is so great and the algorithms so amazing.


That all being said, ABS may not be the easiest thing to implement and that could the be the biggest and likely most relevant issue at play. I have no qualms dealing with overtly technical projects that are daunting, others may see the complexity involved and just walk away (and likely for the best). A poorly installed abs unit could be dangerous and troubleshooting could be very very time consuming. Who knows until one of us tries.

-Matt

[Slatt]

I've had my 03 WRX for 10+ years and I think I know it's brakes pretty well. There is no doubt in my mind it's ABS is flawed. Specifically, once the ABS reduces braking force to reduce lockup it does not attempt to increase or restore braking force.

Here's what that means. If traction is lost momentarilly while under braking (perhaps due to a bump, pothole, or surface crack) the ABS kicks in. Even if traction is immediately restored the ABS keeps braking force reduced, causing your stopping distance to become VERY interesting. Of course you can get out of this 'ice mode' by quickly releasing then restoring brake pedal pressure. Um, that means you must 'threshold brake' the ABS.

I hope 'modern' ABS systems are better, but there is no doubt that I can outbrake my car's ABS on an irregular surface.

[Matty_STi]

I've had my 03 WRX for 10+ years and I think I know it's brakes pretty well. There is no doubt in my mind it's ABS is flawed. Specifically, once the ABS reduces braking force to reduce lockup it does not attempt to increase or restore braking force.

Here's what that means. If traction is lost momentarilly while under braking (perhaps due to a bump, pothole, or surface crack) the ABS kicks in. Even if traction is immediately restored the ABS keeps braking force reduced, causing your stopping distance to become VERY interesting. Of course you can get out of this 'ice mode' by quickly releasing then restoring brake pedal pressure. Um, that means you must 'threshold brake' the ABS.

I hope 'modern' ABS systems are better, but there is no doubt that I can outbrake my car's ABS on an irregular surface.

that was a pretty common complaint about most older abs systems (regardless of manufacturer, subies tend to get beat around in the mud and rough terrain more than a corolla or S4 though).
A few reasons for that (in no particular order): 1) they tended to use fewer channels and wheel speed sensors (it was more complex and required more computational horsepower)
2) If the wheel left the ground due to dumps then the brakes would immediately stop the wheel and then have to release by which time the wheel was back on the surface and no real braking has thus occurred. - This is still one of the biggest issues that ABS systems face and really can only be solved by better suspension design and components that keep the wheel planted on the ground.
3) Gravel and ice covered with snow are both very hard surfaces to brake with ABS on. the reason is that as you brake harder then a layer of material builds up in front of the wheel digging it in and thus actually making the wheel lock up usually this creates a slippery surface underneath that further promotes wheel lock up. The wheel speed sensors of course will detect this and the system will understand that the wheels stopped faster than any vehicle physically could and thus release the brakes, and start pulsing like mad but without any real braking being done. The slipperiest part of the road during winter is right in front of the lights, that is from everyone locking up their wheels and polishing the surface. Only way around this is to integrate other sensor information to determine what the vehicle is doing, subaru just uses dozens of sensors, where as mitsubishi in their evo's has settings from gravel, tarmac, snow, etc. My ex had an evo x mr, and we compared the differences between my sti and her evo all the time and we constantly were swapping cars. Both work well each has it's quirks.

As things like dcs have been implemented into the control scheme of newer abs systems there is much more sensor information that allows the brakes to more accurately adjust to the various conditions. Rough surface and ice/gravel are still not as good as they can be and im sure there will be improvements in future systems but they will be incremental from here on out. Especially with integrating DCS, EBD and tcs and having these things also connect to the ecu and differential control schema like dccd or what the GTR uses. I am sure suspension travel/acceleration sensors and wheel acceleration sensors will be the next thing to hit sports cars, they are common amongst formula 1, wrc, lower formula series, le mans/wec, indy cars, and others. Probably also see more integration with active aero stuff as well into all this.

-Matt

[RM1SepEx]

Matt, physics applies, period.

The brakes as removed with power brakes from a 02 -07 WRX will be too boosted for the car... too easy to lock them up... pedal effort will be very light. Again physics applies, pedal force is directly proportional to clamping force. All can be directly calculated based on piston diameters, pedal leverage, etc... We will somehow be adjusting the brake bias, again, we have to due to weight bias. I did discuss this at Factory 5 after SEMA with Dave and one of the engineers. They did note that the brakes were indeed overboosted and that they would be further investigating bias and perhaps running them w/o vacuum boost. Much more development has been done, who knows where it will end up.

Most of us will not be using abs, F5 doesn't in the prototypes, you can see that in photos, I've seen it in the flesh. I expect that it will be relatively easy to implement ABS, just a matter of running more brake lines and finding a location for the components. We will be compensating for dramatic design changes and weight bias that will change brake dynamics.

As noted I expect ABS will work just fine. The abs looks at each wheel independently, and modulates pressure on and off, faster than we can imagine to avoid lock up. We can "feel" this happening through our seats and the rest of our body. It will be working overtime on an 818 since required pedal pressure will be so low. Some of us don't "like" that ABS feeling, others just want to use whatever they can for ultimately faster lap times. ABS removes the control from the driver and puts it in the computer's hands. ABS can also be used to stand for Allows Braking and Steering. That can allow a novice to ask for too much of one over the other because again it moves the control from the driver to the computer. ABS and DCS ultimately slow down a driver's skill development process. Many modern cars are so easy to drive that our overall level of driving skills is poor in the US.

I'm an autocrosser, not a track rat. Most faster drivers disable ABS to autocross. They want the tactile feel of the tires finding and losing traction and the ability to "feel" the tire's grip through the friction circle... It allows us to learn where the right balance is in braking points, cornering lines, surface imperfections, etc. I know many track rats, they do the same to improve their learning of driving skills.

ABS, traction control etc... are driver's aids that make it easier to drive faster but the separate the driver from ultimate control. They slow down the rate that a driver learns to drive. That's why the best drivers in the world sharpen their skills on very fast, raw shifter karts.

Subaru uses the same ABS on everything... OK, but they don't make a mid engined 2000 lb beastie... The WRX is actually on the low end of their braking parameter requirements with the Impreza being their smallest car and their SUVs are not that much bigger. I'm willing to bet that Subaru has more hours than we can imagine figuring out the braking for each and every model. We get to do that "testing" on our own, one on one. Our donors used that same "older" ABS that Slatt mentioned above. The design of those systems most likely happened in the early to mid 90's. I'm not aware of traction control systems on 02-07 WRX donors. Most traction control systems apply brakes to maintain control, that isn't "faster" in all cases.

Again you are absolutely correct that the absolute best performance capabilities can be obtained with advanced ABS and traction control as used in high end racing. However we don't have anywhere near the information or experience to categorically state that the ABS from our donors will work as well as possible on the 818.

Dan

[longislandwrx]

Saying the wrx brakes will be twitchy and grabby well, dunno if you watched the videos of the car driving around, doesn't look twitchy or grabby to me. Ever driven any modern lotus or other super lightweight PRODUCTION (not kit car) with modern high performance super grabby track brakes. Well, they really aren't twitchy. Get your tires right for what you intend to do, have the aero you need, have the suspension setup you need and the brakes will be the last of your worries. Yes they are bigger brakes with some serious grip, but you are making way more out of their stopping power than you really understand.
-Matt

The twitchy comment came from FFR themselves, not from speculation. I tried to find that post, but it was a long time ago.

You don't know how these systems are developed or the underlying physics or technology that created them. Nor do you understand the speed and precision of the systems that exist. You also don't know how these are implemented and what changes result in variances in performance of said systems. So yes there is misinformation here, I am correcting that.

No need to make it a personal attack, this is just a discussion. With all due respect, that came across very pompous.

[Matty_STi]

The twitchy comment came from FFR themselves, not from speculation. I tried to find that post, but it was a long time ago.




No need to make it a personal attack, this is just a discussion. With all due respect, that came across very pompous.

youre right on both counts, edited.

not my intended goal an no insult meant but yeah that wasn't the best way of saying that. my bad and apologies. sorry rm1sepex.

-Matt

[Matty_STi]

Matt, physics applies, period.

The brakes as removed with power brakes from a 02 -07 WRX will be too boosted for the car... too easy to lock them up... pedal effort will be very light. Again physics applies, pedal force is directly proportional to clamping force. All can be directly calculated based on piston diameters, pedal leverage, etc... We will somehow be adjusting the brake bias, again, we have to due to weight bias. I did discuss this at Factory 5 after SEMA with Dave and one of the engineers. They did note that the brakes were indeed overboosted and that they would be further investigating bias and perhaps running them w/o vacuum boost. Much more development has been done, who knows where it will end up.

Most of us will not be using abs, F5 doesn't in the prototypes, you can see that in photos, I've seen it in the flesh. I expect that it will be relatively easy to implement ABS, just a matter of running more brake lines and finding a location for the components. We will be compensating for dramatic design changes and weight bias that will change brake dynamics.

As noted I expect ABS will work just fine. The abs looks at each wheel independently, and modulates pressure on and off, faster than we can imagine to avoid lock up. We can "feel" this happening through our seats and the rest of our body. It will be working overtime on an 818 since required pedal pressure will be so low. Some of us don't "like" that ABS feeling, others just want to use whatever they can for ultimately faster lap times. ABS removes the control from the driver and puts it in the computer's hands. ABS can also be used to stand for Allows Braking and Steering. That can allow a novice to ask for too much of one over the other because again it moves the control from the driver to the computer. ABS and DCS ultimately slow down a driver's skill development process. Many modern cars are so easy to drive that our overall level of driving skills is poor in the US.

I'm an autocrosser, not a track rat. Most faster drivers disable ABS to autocross. They want the tactile feel of the tires finding and losing traction and the ability to "feel" the tire's grip through the friction circle... It allows us to learn where the right balance is in braking points, cornering lines, surface imperfections, etc. I know many track rats, they do the same to improve their learning of driving skills.

ABS, traction control etc... are driver's aids that make it easier to drive faster but the separate the driver from ultimate control. They slow down the rate that a driver learns to drive. That's why the best drivers in the world sharpen their skills on very fast, raw shifter karts.

Subaru uses the same ABS on everything... OK, but they don't make a mid engined 2000 lb beastie... The WRX is actually on the low end of their braking parameter requirements with the Impreza being their smallest car and their SUVs are not that much bigger. I'm willing to bet that Subaru has more hours than we can imagine figuring out the braking for each and every model. We get to do that "testing" on our own, one on one. Our donors used that same "older" ABS that Slatt mentioned above. The design of those systems most likely happened in the early to mid 90's. I'm not aware of traction control systems on 02-07 WRX donors. Most traction control systems apply brakes to maintain control, that isn't "faster" in all cases.

Again you are absolutely correct that the absolute best performance capabilities can be obtained with advanced ABS and traction control as used in high end racing. However we don't have anywhere near the information or experience to categorically state that the ABS from our donors will work as well as possible on the 818.

Dan

ill give you most of these points. And I agree the brakes form the wrx aren't designed with an 818 in mind. That we can and do both agree on. I am just debating the merits of the abs controller.

I also agree that tcs and dcs are limiting factors to driver development, abs less so but I can't argue the point you are making.

If you want to debate the merits of using the wrx brakes in this application you will likely find that I agree with just about everything you say. bias will need to be adjusted and boost level will too and the brakes as designed were not done so with a light mid engine rwd car but a nose heavy understeer prone awd sedan.

I will still contend you aren't correct about the abs.

-----

A point I should make is that traction control systems tend to use the ecu to limit revs and power output to prevent wheels spin, where as stability control systems use the abs controller to apply the brakes. Not necessarily always the case but in the large majority that is what happens. (can't think of a tcs using brakes example off the top of my head, but I do know they exist).

-Matt

[AZPete]

Is there a lot of users like yourself that have experience with this on the roadster? I haven't bothered to go looking for the information outside the 818 bubble, but I always assumed there's probably a good number of people that have experience in a similar situation using Ford components.

Evan, there are not many roadsters with ABS. Mine was a 4.6L build so was EFI with an ECU from a 2000 Mustang GT and most roadsters are built with push rod engines (90%?). I hooked up the ABS not knowing if it would work, or even how it works, but it did. Some other 4.6 builders have also done it, but not a lot. It was an old system so I'm sure many advancements have been made in the last 13 years by all manufacturers so I'm fascinated to read these posts by guys with bigger brains. I'll try to install the ABS on my 818S.
Pete

[Evan78]

Thanks Pete. I'll have to do some searching to see what I can find on the roadster, coupe and hot rod.

[Evan78]

I've had my 03 WRX for 10+ years and I think I know it's brakes pretty well. There is no doubt in my mind it's ABS is flawed. Specifically, once the ABS reduces braking force to reduce lockup it does not attempt to increase or restore braking force.

Here's what that means. If traction is lost momentarilly while under braking (perhaps due to a bump, pothole, or surface crack) the ABS kicks in. Even if traction is immediately restored the ABS keeps braking force reduced, causing your stopping distance to become VERY interesting. Of course you can get out of this 'ice mode' by quickly releasing then restoring brake pedal pressure. Um, that means you must 'threshold brake' the ABS.

I hope 'modern' ABS systems are better, but there is no doubt that I can outbrake my car's ABS on an irregular surface.

Did you have your ABS controller replaced under the technical service bulletin (TSB) for 2002 and 2003 WRX's? This was a common complaint that Subaru attempted to address, although I don't know how much difference it made since I never had the service performed on my car. I put 130k on my 02 WRX and I experienced this issue several times.

[Evan78]

RM1SepEx - can we try to keep the conversation technical in nature and stay on the topic? Every time ABS comes up, you spend as much time speaking about driver development and why people shouldn't use ABS. That's a fine conversation to have, but I don't think we need to have it every time someone asks about making ABS work in the 818. Not many people here are budding professional race car drivers, and if they are, they probably already know what conditions they want to train under. Perhaps you should create a thread that contains your thoughts on why someone should elect to not use ABS and just post a link to that thread in the future.

ABS should not be looked at as an either/or proposition. You can simply pull the ABS fuse or wire in a switch to disable it whenever you want. Of course you will still be carrying around the additional weight and there may be other penalties associated with having it there, but it is possible to have the best of both worlds to some extent.

[RM1SepEx]

you need to re-read my posts, I think I've been as technical as anyone here. I originally just stated that it should work and it was a choice. It is a unsupported technical crap shoot when you use donor parts in a vehicle that dramatically differs in concept and execution. Why do you think the 818R was observed with a balance bar, two cylinder pedal assembly, perhaps they were looking to improve braking performance?

I beg to differ re ABS not being an either/or proposition, just pull a fuse. Significant work will need to be done to install ABS (Based on F5's previous offerings) as the base kit will not include ABS support.

If you have a problem hearing why I choose not to use ABS... please ignore that part of the posts. Unlike many here I have never attacked some one or belittled their opinions. I try to simplify the technical issues so those who are not technically inclined can understand the issue. I feel that it is as important to understand why people make decisions as the decision itself.

[RM1SepEx]

youre right on both counts, edited.

not my intended goal an no insult meant but yeah that wasn't the best way of saying that. my bad and apologies. sorry rm1sepex.

-Matt

no problem, no offense taken, just made me restate/reword/explain position... :-) Such discussions are healthy to flesh out subjects.

[Evan78]

I'm not trying to attack you or belittle your opinion, that's why I suggested creating a thread dedicated to why to use or not use ABS. I think it deserves it's own conversation so that it is not mixed in with conversations of how to implement it. You're right, your posts are primarily technical. I just know that you have a strong opinion on the matter, that driver development is a high priority to you, and I sensed that you were going to take the conversation that way, but you're right, you only spent a couple paragraphs on it. Fair enough.

You missed the point of my post on ABS being an either/or question. A car could be built that satisfies your desire for driver development while maintaining the option of enabling ABS when desired. The fact that it takes additional work over a car without ABS is obvious and does not negate the fact that it is entirely possible.

[Erik W. Treves]

We have also put ABS system on the FFR Roadsters, also a rear biased car and it works just fine, actually it appears to "correct" the under rear braking issues with the roadster. Some like me just installed larger rear brakes, others play with brake pad compound. GregM over on the other forum has a very detailed thread on how he applied ABS to his FFR. His report is that it works better than OK. I can see no down side to attempting it other than somebody's time spent. Theory and math only go so far until you actually put it to test and see. The OP asked what appeared to be a simple question and all that I think that got resolved is that the forum is as equally divided about the issue as the folks were at the track. Bottom line...these are kit cars and a blank canvas (as far as I am concerned).. build them to FFR specs or build outside the box..then share and compare good ideas and performance aspects of what was done. I would not look at either of the 2 first cars 818S or 818R and draw any conclusions of what was done and why. The balance bar on the R is a take off from the "upgrades" made to the FFR assy line.."could be" simply off the self and available...maybe..maybe not. I will say two last things....

1. Don't know if it will work, work great, or like crap.
2. My car will have ABS from the donor for a start point.

[Evan78]

It is a unsupported technical crap shoot when you use donor parts in a vehicle that dramatically differs in concept and execution. Why do you think the 818R was observed with a balance bar, two cylinder pedal assembly, perhaps they were looking to improve braking performance?

Adjusting bias is done to improve performance and suit driver preference. It's no surprise that they allowed for bias adjustment and it would be foolish not to on a development car, regardless of whether the car has ABS or not.

What factors does ABS take into account? It seems to me that changes in wheel speed are all that matter. I imagine that the system looks for a wheel that changes to 0 MPH while the others are still moving. Does wheel behavior look that much different on a 1800 pound car than a 3200 pound one when you're approaching the limit of traction and sampling wheel speed many times per second?

Where's an ABS engineer when you need one?

Thanks Erik, I'll have to include FFCars in my search for prior implementations.

[Xusia]

Unlike many here I have never attacked some one or belittled their opinions.

I've felt attacked by you in the past (for the benefit of everyone else, it's all worked out - no lingering negative feelings, and I do believe it was not intentional). I mention it here because I think it's important for everyone to understand that while they may not intend to attack (or belittle, or whatever), others may interpret your words differently.

Written language does not have the benefit of facial expressions, tone, vocal inflections, etc. Word choice is very important, and responses constructed quickly can be misconstrued easily even when intentions are good. Therefore, it's even more important in a forum like this to choose your words carefully. Personally, I like to add statements of intent to help clarify where I'm coming from, why I'm responding, etc.

What factors does ABS take into account? It seems to me that changes in wheel speed are all that matter. I imagine that the system looks for a wheel that changes to 0 MPH while the others are still moving. Does wheel behavior look that much different on a 1800 pound car than a 3200 pound one when you're approaching the limit of traction and sampling wheel speed many times per second?

Individual wheel speed plays a very significant role, to be sure, but that's mostly in regard to when to activate. When it comes to how a system will actually perform (that is, how well it actually stops the car), I think there is a bit more to it than that. ABS doesn't just reduce braking force when active, it cycles it as well. The amount of force applied to the brakes during cycling, the frequency of sampling/cycling, as well as how it reacts (and how quickly it reacts) when when wheels regain traction, are probably factors as well. The previous post regarding the 2003 WRX is a good example of what I'm talking about.

[MurrayT]

I am glad so many have taken interest in my ABS question. Let me rephrase my original question.

Since alot of F5 guys drive their cars on the track, my question is directed at them. If you do not have ABS on your track car, do you want it? If you have ABS on your track car, do you like it?

Some of the local track guys tell me that ABS on a track car is something to break or malfunction. They say keep the car simple and uncomplicated. Other track guys, usually guys driving high dollar street sports cars, love having ABS on their cars.

I am only going to drive the car about 1 or 2 hours a month on the track. I do not want to be a professional driver. I want to have fun, excitement, and be safe.

After talking with Jim Schenck at SEMA, I am confident I can transfer the ABS system over to the 818R. The question is should I?

[metalmaker12]

I am not, an I am build the 818s/r