GT4 and Brakes

[wfooshee]

Something else that has been repeatedly misunderstood besides ABS, which I addressed yesterday, is why big brakes don't stop faster. As Scaff has repeatedly stated, the tire patch is THE FACTOR in stopping distances. Big brakes/little brakes is nearly irrelevant. Brakes generate friction, converting kinetic energy to heat. The more heat they throw out, the less kinetic energy the car is left with. It's the tires that interact with the roadway to slow the car. If you remove kinetic energy faster than the tires can deal with it, you get lockup. Here's the important part, without formulas and math that to most folks is evidently gibberish:

Big brakes exist to dissipate more heat.

They don't generate better stopping power, they generate stopping power for longer than small brakes. I mentioned previously that I was an autocrosser. My car was a Probe GT, a great handling and fairly strong (for '95) coupe. The brake rotors were smaller than a Miata's, on a car that weighed what, 1000 lbs more? Yet with 245-width tires, I could outbrake the Miata from a comparable speed (because neither vehicle weight nor brake size is a factor) -- at least until the brakes got too hot to work (not dissipating enough heat.) I could make one hard stop from 80 mph, then I would have to park for a while. I could not make a single hard stop from 100; the brakes were fading before the car stopped (the higher kinetic energy overloaded the brakes' heat capacity). Lucky for me, autocrossing rarely gets to even 60 or 70 mph. (Ford/Mazda made the brakes small to reduce unsprung weight, I would guess, but that's a whole 'nuther discussion, and probably totally irelevant to GT4.)

As for carbon vs cast iron rotors, the difference is that carbon brakes convert kinetic energy to heat faster then iron. (Or probably more correctly: they have a high enough heat capacity to convert kinetic energy to heat faster than iron.) As anybody who watches Formula One can see, the stopping power of carbon brakes is phenomenal, but without those tires, there would be no point having them. Why do you think front tires have gotten so large the last 15 years or so? Look at Formula One cars from the 70s, and look how small the front tires are. No weight in the front of the chassis, and with metal brakes, nowhere near as much weight transfer during braking.

It's the TIRES doing the stopping ! ! ! !

 

[KaiZen]

OK. So I'm a little confused..

Which is the best way to apply the brakes? Because I'm hearing/reading different things.

85% initially, then 100% then trail off?
85% initially, then 100% then completely off?

100% initially, then 85% then trail off?
100% initially, then 85% then completely off?

Is there another technique I can try?
Does the difference in corner and apex mean a different technique or can I generally apply the same technique for most corners?

Has someone done a write up on braking techniques for different apex's? Like early, mid corner, late apex's? Tight to opening, closing to tight, hairpin corners? Double hairpin or slow chicanes?..

point me in the right direction please!



I did a "Drive to Survive" course at the John Bowe Institute of Driving (aussies will know who that is!) a few months back and the course was mainly focused on braking (and especially, experiencing ABS), assessing condititions ahead and avoiding accidents.
Brake Exercise 1:
We started the day by braking in a straight line on a wet road to a complete stop. Starting at about 55km/h then increasing by 5k's each run till about 75 or 80. We were taught to apply max braking untill ABS kicked in, then lift off slightly untill we couldn't feel it anymore. So 100% then 85%. This was the general technique we were to use in all the braking scenario's.

Brake Exercise 2:
Next, the scenario given was that we had to brake hard to avoid an accident straight ahead, again on a wet road. But, if we were to keep going straight we'd end up hitting the car in front so we needed to change lanes to avoid the accident. We can't change to the right lane because of on-coming traffic so we must go left but, there's a parked bus about 3 or 4 metres down. The extra 3 or 4 metres gives us enough room to come to a complete stop without hitting the other vehicle.

Brake Exercise 3:
For the last brake test we were given two scenarios. We are driving on a single lane two-way road (dry) and either (a) a driver is reversing out of their driveway on the the road in front of you, or (b) a meteorite falls out of the sky on the the road in front of you. I like option (b) my self . It's more intense And the objective was obviously to avoid scenario a or b, to play chicken with on coming traffic and then avoid on-coming traffic by returning to your lane. No complete stop. Brake hard, change lanes, change back.

That was fun! I got my speed up to about 85-90km/h around that chicane of witches hats in my big azz 4 door RAV4, while the rest were doing a max of 70 in their sedans! The instructor took us for a run in an XR8 04 with three passengers. He only did about 80. He kept asking me to slow down. I think he was too happy about me showing him up!

To me, I didn't see scenario a or b. I saw a chicane. All I wanted to do was go through it as fast as I could without hitting any hats, and I did!

Slalom:
The last test was a slalom test at about 70km/h. That was cool. It really brought me back to the licences of GT. The knowledge acquired doing the licence test in GT really helped with that exercise. It was good fun!




So anyways, back to my initial questions, which is the best technique for braking on a race track that will allow me to drive through corners at the fastest speeds?

I can understand that what I learnt may mainly apply to "real world accident situations" where the rule is to instantly panic (slam the brakes 110%) then with proper training, take control (bring back to 85%)..

One more thing. Can someone explain to me the different terminologies, too?
I've heard Thresholding and Cadence. What do these mean??


Thanks in advance people

 

[Scaff]

OK. So I'm a little confused..

Which is the best way to apply the brakes? Because I'm hearing/reading different things.

85% initially, then 100% then trail off?
85% initially, then 100% then completely off?

100% initially, then 85% then trail off?
100% initially, then 85% then completely off?

Is there another technique I can try?
Does the difference in corner and apex mean a different technique or can I generally apply the same technique for most corners?

Has someone done a write up on braking techniques for different apex's? Like early, mid corner, late apex's? Tight to opening, closing to tight, hairpin corners? Double hairpin or slow chicanes?..

point me in the right direction please!



I did a "Drive to Survive" course at the John Bowe Institute of Driving (aussies will know who that is!) a few months back and the course was mainly focused on braking (and especially, experiencing ABS), assessing condititions ahead and avoiding accidents.
Brake Exercise 1:
We started the day by braking in a straight line on a wet road to a complete stop. Starting at about 55km/h then increasing by 5k's each run till about 75 or 80. We were taught to apply max braking untill ABS kicked in, then lift off slightly untill we couldn't feel it anymore. So 100% then 85%. This was the general technique we were to use in all the braking scenario's.

Brake Exercise 2:
Next, the scenario given was that we had to brake hard to avoid an accident straight ahead, again on a wet road. But, if we were to keep going straight we'd end up hitting the car in front so we needed to change lanes to avoid the accident. We can't change to the right lane because of on-coming traffic so we must go left but, there's a parked bus about 3 or 4 metres down. The extra 3 or 4 metres gives us enough room to come to a complete stop without hitting the other vehicle.

Brake Exercise 3:
For the last brake test we were given two scenarios. We are driving on a single lane two-way road (dry) and either (a) a driver is reversing out of their driveway on the the road in front of you, or (b) a meteorite falls out of the sky on the the road in front of you. I like option (b) my self . It's more intense And the objective was obviously to avoid scenario a or b, to play chicken with on coming traffic and then avoid on-coming traffic by returning to your lane. No complete stop. Brake hard, change lanes, change back.

That was fun! I got my speed up to about 85-90km/h around that chicane of witches hats in my big azz 4 door RAV4, while the rest were doing a max of 70 in their sedans! The instructor took us for a run in an XR8 04 with three passengers. He only did about 80. He kept asking me to slow down. I think he was too happy about me showing him up!

To me, I didn't see scenario a or b. I saw a chicane. All I wanted to do was go through it as fast as I could without hitting any hats, and I did!

Slalom:
The last test was a slalom test at about 70km/h. That was cool. It really brought me back to the licences of GT. The knowledge acquired doing the licence test in GT really helped with that exercise. It was good fun!




So anyways, back to my initial questions, which is the best technique for braking on a race track that will allow me to drive through corners at the fastest speeds?

I can understand that what I learnt may mainly apply to "real world accident situations" where the rule is to instantly panic (slam the brakes 110%) then with proper training, take control (bring back to 85%)..

One more thing. Can someone explain to me the different terminologies, too?
I've heard Thresholding and Cadence. What do these mean??


Thanks in advance people

OK, some good questions here, first ones what are Cadence braking and threshold braking.

Threshold Braking
To understand Threshold braking you need to understand how a car brakes, as I'm sure you know when you press on the brake pedal this forces the brake pads on the discs (or shoes onto the drums) this then slows the rotation of the wheels.

As the wheels slow they are moving at a different rate to the car, this is known as the slip percentage. A cars tyres can only accept a certain slip percentage before they lose grip and you lose traction. It is this slip rate that princiapaly determines how quickly a car slows down.

Now the braking system of a car is capable of applying braking force at a very high level, and if you just stamp on the brake pedal, the braking force will force the tyre to exceed its slip percentage and the wheel(s) will lock.

Threshold braking is maintaining the braking force at a level that ensure you are at the maximum deceleration offered by the tyre, without exceeding its slip percentage.

Gradually releasing braking force as you start to enter a turn is know as trail braking and allows you to overlap the braking and throttle phase of a turn.


Cadence Braking
A road driving technique used when you have exceeded the grip level of a tyre and it has locked; by 'pumping' the brake pedal you can unlock the tyre and get grip back, this will allow you to regain some control of the braking and possiable allow you to steer around an obtacle.

In its simplest form this is all that ABS systems do, the apply and release the brakes many thousands of times a second.

While cadence braking is useful in an emergancy situation on the road (in a non-ABS exquiped car), it is of no value on the track. The sudden release and aplication of the brakes causes weight to be constantly shifted from the rear to the front and back again, causing massive problems with the stability of the car.

Route_66 carried out a Cadence vs threshold braking test, here are the results.

In answer to your first question, how should I brake?

Well that depends on the car, the corner and your driving style.

The simplest way to begin is to understand that in GT4 few cars need true threshold braking (generally only the very fast stuff), get a feel for the car and try braking from different speeds, if you find the tyres are locking simply don't apply as much braking force the next time.

The idea is to maximise your braking potential, by applying as much braking force as the tyres can take without losing grip, this ammount of pressure will not remain constant as you brake and you may need to 'modulate' the brakes. In other words, if you find you are applying to much braking force, then you back off the brakes and if you find you are not applying enough braking force then you need to increase the braking force. However, you need to be smooth and subtle with the brakes, they are not an on/off switch.

At first you should concentrate on getting all your braking done in a straight line, before you turn in (and with some cars you will need to stick with this), this helps you to get used to how much you need to brake and what braking force will slow you to the corect corner entry speed in the shortest distance possiable.

Once this is soimething you are comfortable with, you can then try 'trail braking' which is where you gradually reduce braking as you enter faster corners and can help maintain stability and reduce understeer. This, however needs practice.

The image below is taklen from the Ross Bentley book 'Speed Secrets' and should help illustrate what I have tried to explain.



I would also recomend that you get one of the first two books listed under recomended reading in the first post, both as written by race driving instructors and will help you to understand how the brake/constant throttle/acceleration phases of a turn are managed. Well worth the money.

Other than that, have a good read of this thread, a lot of people have contributed information that will help you.

 

[KaiZen]

Thanks for the prompt reply Scaff!.. 👍


Let's look at some numbers here..

So, I'm driving down the long straight coming to a hard braking, slow or mid speed corner at Tokyo (or maybe Midfield or any track that has a long straight to slow corner braking situation). I don't really like to trail-brake much so I do most of my braking in a straight line.

Because of the speed of the straight, braking time will be approximately 2 seconds. Reading Route_66's post he states that applying "85% brake power then 100% before turn-in" was the technique he used that gained the most time, but, during the 2 seconds of braking roughly how long was he applying 85%, 100%, and trailing or completely off braking?

Was it more likely that he was braking at 85% for, let's say, 1.5secs then half a second before turn-in he applied 100% pressure?

Or was it more likely that he applied 85% initially, then gradually increased to 100% about half a second later?


So, on a time/pressure graph, what would the numbers look like regarding a track with a long straight and hard braking zone that lasts over 2 seconds? 💡

Without asking about my own driving technique, how would you (or anyone else), attack a corner like Midfield or Tokyo R246's or Fuji's or Infineon's (yes, there's more long straight to slow corner tracks) heavy braking first corner? Disregarding straights like Grand Valley or La Sarthe because they have a left or right kink that upsets balance.

 

[Scaff]

Thanks for the prompt reply Scaff!.. 👍


Let's look at some numbers here..

So, I'm driving down the long straight coming to a hard braking, slow or mid speed corner at Tokyo (or maybe Midfield or any track that has a long straight to slow corner braking situation). I don't really like to trail-brake much so I do most of my braking in a straight line.

Because of the speed of the straight, braking time will be approximately 2 seconds. Reading Route_66's post he states that applying "85% brake power then 100% before turn-in" was the technique he used that gained the most time, but, during the 2 seconds of braking roughly how long was he applying 85%, 100%, and trailing or completely off braking?

Was it more likely that he was braking at 85% for, let's say, 1.5secs then half a second before turn-in he applied 100% pressure?

Or was it more likely that he applied 85% initially, then gradually increased to 100% about half a second later?


So, on a time/pressure graph, what would the numbers look like regarding a track with a long straight and hard braking zone that lasts over 2 seconds? 💡

Without asking about my own driving technique, how would you (or anyone else), attack a corner like Midfield or Tokyo R246's or Fuji's or Infineon's (yes, there's more long straight to slow corner tracks) heavy braking first corner? Disregarding straights like Grand Valley or La Sarthe because they have a left or right kink that upsets balance.

KaiZen, you are getting to fixated on the 85%/100% braking force from Route_66's post, with a lot of the cars in GT4 (and if you have the brake balance set to the default of 3/3) you may find that the tyres threshold can be 100% of the braking force. Only decrease your braking force if you need to, depending on the car, tyres and set-up. Its a case of practice and more practice.

Now, with regard to using Tokyo's first corner as an example, its a good choice because in all but the very slowest cars you will be braking from 100mph+.

Now to find the ideal braking point for this corner will require a little trial and error (as it will depend on the car, tyres and speed), the gear indicator will help to begin with as it will show you the required gear for the corner and start flashing when it thinks you should be braking.

On your first try, pick a braking point, start with the 200 and 150 metre boards, as the braking point for a lot of cars is between these. For this example we will say we are using the 200 metre board, apply the brakes smoothly upto 100% brake force, if you hear the brakes chatter (if you have ASM switched on) or 'feel' a loss of traction (with ASM off) you have locked a tyre of engaged the ABS. You need to back of the brake slightly (not fully) until grip returns. This is threshold braking with modulation.

As you slow to a speed that you believe you can take the corner at, you should smoothly transfer from the brakes to the throttle, but do not accelerate, keep a constant speed by balancing the throttle. Turn into the corner and steer towards the apex, once you clip the corner apex and start to unwind the steering you can slowly feed in the acceration out of the corner.

If you find that the car will not turn into the corner, the chances are that you are going to fast, try slowing down more before turning in (if you do not have room then move you're braking point back.

If you find that you are too slow into the corner, and are not using all of the road, then you are not cornering as fast as you could. Try moving the braking point forward next time and carrying more speed into the corner.


You will find that GT4 is much more sensitive to tyre loads, particularly when cornering under brakes or throttle, and if you exceed the tyres grip limit you will understeer.

It does take practice to get high-speed corners thi sthese right, and you are better to be slow on a corner to begin with and then build up to an ideal cornering speed.

Always remember 'Slow-in and Fast-out'. keep your steering, brakes and throttle inputs smooth.

Hope this helps, if I get time later I will try and put some rough figures to the above.

 

[RedWolfRacer]

Personally, I would go 100% pressure on braking (not necessarily using 100% of my tires for braking, but you get the idea), and ease off as I head into the corner. I typically use cars with stiff springs and low ride-heights though. It works for me and it works well for such corners.

On a side note: why is that at these forums, people seem to forget very basic things?? I.e. pressing in your brakes 100% of the way does NOT necessarily use 100% of your tire. I think something needs to be done about this, and, assuming I have time tonight, I think I will rectify this with a FAQ thread or other. A driving-style thread may follow it as well. I shall be busy.

 

[Scaff]

Personally, I would go 100% pressure on braking (not necessarily using 100% of my tires for braking, but you get the idea), and ease off as I head into the corner. I typically use cars with stiff springs and low ride-heights though. It works for me and it works well for such corners.

On a side note: why is that at these forums, people seem to forget very basic things?? I.e. pressing in your brakes 100% of the way does NOT necessarily use 100% of your tire. I think something needs to be done about this, and, assuming I have time tonight, I think I will rectify this with a FAQ thread or other. A driving-style thread may follow it as well. I shall be busy.

RedWolfRacer, a very good point and one I hoped to make (but it may not have been clear) in my last post.

The subject has been covered within this particular forum before, but you are quite right it is a common misconception. If you do put something together on the subject and post it in here I would be more than happy to add it to the index that has now been included in the first post.

I just feel that it would be more helpful to people to keep all of the braking issues together.

And a driving style thread, now thats something I (and a few others I know) would enjoy, looking forward to that.

 

[Scaff]

Excellent, the thread has been made a sticky, my thanks to who every was involved.

Regards

Scaff

 

[RedWolfRacer]

Sorry, folks but the driving styles thread will have to be post-poned until later. Didn't finish it last night and I have to work today so I won't have it up by tomorrow. Looking like it'll be up Thursday or Friday at the latest. I hope it sheds(sp?) some light on how you brake and how you should theoretically brake depending on your overall style.

 

[///M-Spec]

Excellent, the thread has been made a sticky, my thanks to who every was involved.

You're welcome. It was long overdue.


M

 

[KSaiyu]

Ah this thread is still going, it seems it wasn't just me that found that threshold braking is beneficial in some instances in GT4.

Why didn't PD take the simple route and model the cars without ABS

 

[route_66]

Ah this thread is still going, it seems it wasn't just me that found that threshold braking is beneficial in some instances in GT4.

Why didn't PD take the simple route and model the cars without ABS

This was really the point to my test, aside from showing that cadence braking < threshold braking in most cases, it is most efective in faster cars, notably the Ford GT - complaints about that car induced Scaff to start this post IIRC.

However with regardeds to how much braking (85%, 100%, whatever), It will vary according to driving style and car, there's not going to be a hard and fast "brake x% and then y% and you'll always stop faster." It will vary and threshold braking isn't going to have as massive an effect as it did in my test. It does make a difference to car control, but really getting it to work requires gettting a good feel for the car and lots of practice.

Just out of interest, has anybody tried setting the ABS controller to 0, 0? Does it turn the ABS off, meaning you can lock up under braking whenever you want (or don't want)? Would be interesting to turn it off in older cars that wouldn't really have ABS.

 

[KSaiyu]

There is no ABS controller, only a brake balance controller which distributes the brake torque

 

[route_66]

There is no ABS controller, only a brake balance controller which distributes the brake torque

Yes, the brake balance controller adjusts brake torque if you set front/rear at different values, however if you push both values up, then the ABS will kick in earlier - you can hear it, turn it up to about 12/12 on the Ford GT and you will hear the Wheels Lock and unlock very quickly as the ABS kicks on (makes a horrible chittering noise), gradually turn it down and the ABS calms down and the car brakes much more smoothly. Turn it right down and you will lock the wheels instantly if you apply 100% braking (You can see it in the reply, Controller set high - wheels keep spinning, controller set low - wheels lock up). That's why i was wondering if 0/0 will give the effect of no ABS.

 

[Scaff]

There is no ABS controller, only a brake balance controller which distributes the brake torque

KSaiyu if you have a look at the adjustments screen for the Brake Balance controller it says that it controls the strength of the ABS system. So this would imply that it certainly does have any effect on the ABS system of the car.

This did get me thinking as to if setting the ASM (both) controls to zero would disable the ABS.

The results of my test can be found here ABS Test. The results are not conclusive and I do want to do some more testing in this area, but it does seem that the ASM setting does effect the activation of ABS (from these early test results) and that if ABS is enabled then the brake balance controller will effect when the ABS cuts in, as it controls braking force, which can result in losing grip from the braked wheels at a faster rate.

Have a look and let me know what you think; as I say I hope to test this some more (14 hour days at work are making that a bit difficult - should have some spare time next week).

Regards

Scaff

 

[slammer]

👍 Thanks for a great topic Scaff 👍

Read every page and those links were great 👍

One thing that helps me at the track is to remember to squeeze the brakes on (to 100%) rather than JUMP on them, and roll off the brakes prior to turn in to keep the car settled

 

[KSaiyu]

Yes, the brake balance controller adjusts brake torque if you set front/rear at different values, however if you push both values up, then the ABS will kick in earlier - you can hear it, turn it up to about 12/12 on the Ford GT and you will hear the Wheels Lock and unlock very quickly as the ABS kicks on (makes a horrible chittering noise), gradually turn it down and the ABS calms down and the car brakes much more smoothly. Turn it right down and you will lock the wheels instantly if you apply 100% braking (You can see it in the reply, Controller set high - wheels keep spinning, controller set low - wheels lock up). That's why i was wondering if 0/0 will give the effect of no ABS.

That's because you're overwhelming the tyres grip by putting that much brake force on the wheels - it's not affecting the ABS setting itself.

KSaiyu if you have a look at the adjustments screen for the Brake Balance controller it says that it controls the strength of the ABS system. So this would imply that it certainly does have any effect on the ABS system of the car.

This did get me thinking as to if setting the ASM (both) controls to zero would disable the ABS.

The results of my test can be found here ABS Test. The results are not conclusive and I do want to do some more testing in this area, but it does seem that the ASM setting does effect the activation of ABS (from these early test results) and that if ABS is enabled then the brake balance controller will effect when the ABS cuts in, as it controls braking force, which can result in losing grip from the braked wheels at a faster rate.

That's a problem I noticed when I saw ABS was mentioned in the Japanese manual (it's not even related to brake balance in that manual, it actually says there is an ABS controller, although there are quite a few discepencies in how GT4 represents the real world). However, I doubt you can turn ABS off in GT4 since the fact that you can slam on the brakes whatever the setting of the ASM/Brake Balance controller and still stop reasonably close (possibly shorter than) compared to when you threshold brake is proof in itself. As you probably know you lose around 25-30% (can't remember right amount) of a tyres traction when you lock the brakes up, so you're bound to have a more noticibly longer braking section.

This topic has driven me mad ever since GT2

 

[Scaff]

That's a problem I noticed when I saw ABS was mentioned in the Japanese manual (it's not even related to brake balance in that manual, it actually says there is an ABS controller, although there are quite a few discepencies in how GT4 represents the real world). However, I doubt you can turn ABS off in GT4 since the fact that you can slam on the brakes whatever the setting of the ASM/Brake Balance controller and still stop reasonably close (possibly shorter than) compared to when you threshold brake is proof in itself. As you probably know you lose around 25-30% (can't remember right amount) of a tyres traction when you lock the brakes up, so you're bound to have a more noticibly longer braking section.

This topic has driven me mad ever since GT2

The test I carried out on the Brake Balance and ASM setting did not support you statement.

I do agree that the differences in GT4 are smaller than would be expected in the real world, but the first test did show that braking distances are greater with ASM set to zero (both) than with it engaged. These tests were at 100% braking force with a Ford GT on comfort tyres.

With ASM disengaged the braking distance was longer than with it engaged, threshold braking was shorter than both. Now while I quite clearly state in the test that these results are not conclusive and that I will be carrying out further tests, the results do suggest that the ASM setting is effecting the stoping distance of the car.

The only logical conclusion that I can draw from this is that the ASM setting does have some effect on the ABS system of the cars in GT4, if it turns it off completly is not something that can be 100% verified, but as I have only ever seen tyres lock up when this has been set to zero (both) that is the conculsion I have (for now) drawn.

The test was not to see if threshold braking is better, thats not a debatable point threshold braking (if done correctly) will alway be faster that hard braking when the ABS is activated. In the real world ABS assisted 'panic' braking will almost always stop you quicker than unassisted 'panic' braking when the tyres lock up.

The tests I carried out gave results that supported this, as a result I have (as I say for the moment) drawn the conclusion that ASM does have an effect on the ABS.

I quite agree that this has never been true for previous versions of GT, but then again GT4 is the first game in the series were the brake balance controler actually allows you to set the level of braking force, previously it has just controlled the ratio between the front and rear.

I am going to repeat my last test in an environment that should hopefully give a larger difference. Tskuba wet in a Ford GT with comfort tyres should make for some interesting results, if I have the time I will also run the dry track to allow for a direct comparison between wet and dry braking.

 

[KSaiyu]

The problem I had was that set 4 was faster than set 1, which defies all logic and put some doubt in my mind as to how long these MI's were. That's not to say the ASM doesn't affect ABS, although I still believe it can't turn the ABS off.

 

[Scaff]

The problem I had was that set 4 was faster than set 1, which defies all logic and put some doubt in my mind as to how long these MI's were. That's not to say the ASM doesn't affect ABS, although I still believe it can't turn the ABS off.

I quite agree that the stopping distance being shorter for set 4 than set 1 is an issue, and as I said in the post, this is something that I do want to look into in the future.

The difference is however very small and I can't discount that it was down to me as the driver. Its one of the reasons why I want to run these tests again on a wet track as the differences should be more visiable.

The question of ASM switching off the ABS is a difficult one; as i've said its a very difficult one to be 100% certain about, I have however only experienced true lock tyres with both ASM settings at zero. Hopefully the wet tests will shed some more light on this.

What you say about the MI's is a real pain, its very hard to say exactly what an MI is.

 

[v BONES v]

Wow...this is a mighty read!

I just discovered the site a couple of days ago and have been slowly working my way through this thread ever since! I think I have gleaned most of the information but since I have been thinking about little other than braking physics for the last 72 hours now I have a coupe of questions.

It took a while but I got my head around the whole "weight doesn't affect braking distance" concept. Obviously weight transfer affects how a car will react to braking - I imagined a very tall heavy car with a high COG, it would lock as soon as you tap the brakes because the weight transfer would increase the load on the front tyres very quickkly and therefore increase braking power beyond the traction available at the road surface. Conversely a car with little weight transfer would be much easier to control under braking - perhaps this is why people have difficulty believing that weight doesn't affect braking distance - its not the distance so much as the lack of control when there is a big weight shift which affects braking power? This means heavier cars frequently lock up more easily.

Anyway, this got me thinking. As weight shifts toward the front of the car, the extra weight on the tyre creates more brake power, presumably this means that the rear tyres unload and therefore have less brake power? But surely unloaded tyres have a tendancy to lock as well (see an F1 car going into a corner too hot and it is the inside, unloaded tyre which loses grip first). So there is a double whammy here, too much load increases brake power to induce a lock - but unoading the tyre and therefore reducing brake power also induces a lock.

Somewhere in the thread it is stated that CoF is constant and not affected by surface area, but in the unloaded example above, isn't the deciding factor the size of the contact patch?

Sorry if this has been covered, but I've been here 2 days and I didn't come across it yet!

 

[FIDO69]

Welcome to the thread vBonesv,

Since Scaff is off experimenting on Enthusia (and I'd love to hear what he finds out regarding braking. hint, hint), I'll give your questions a go.

First, a little pet peeve of mine. Weight reduction DOES reduce stopping distance, but not as much as most would assume (10% weight reduction might give you 3% reduction in stopping distance).

See this post in this thread:
https://www.gtplanet.net/forum/showpost.php?p=1550861&postcount=171

Second, yes, the transfer of weight to the front of the car causes the back tires to unload and this makes the rear tires lock faster if the brake caliper force is distributed equally front and rear. In standard street automobiles, the manufacturer balances the brake bias so that more caliper force is applied to the front wheels and this causes understeer (fronts lock sooner than rears). This avoids panic stopping 360 spins.

In a race car, normally the driver will have a brake bias control knob that he can adjust mid race to control his braking balance.

COF is NOT constant. There is no such thing as a constant COF. See:
https://www.gtplanet.net/forum/showpost.php?p=1552879&postcount=176

The contact patch matters because it affects the load on the tire in pounds/in^2. The COF decreases as the load increases. If the size of the contact patch goes down, then the load goes up (even with the same amount of weight!), and the tire will brake away sooner.

 

[Scaff]

Scaff messed up big time

Last night I was looking at the wet braking tests and printed out my ABS test post, as I was looking at it something caused me to stop and pause. After reviewing my original notes for this test, I can not believe that I did something this stupid. So here we go (and I'm surprised no one spotted this), the stopping distances for set 3 and set 4 were wrong. I put the result from set 3 against set 4 and the result from set 4 against set 3.

So this:

Set 3
BB 20/20
ASM 20 (both)
Stopping distance 22.7 mi


Set 4
BB 20/20
ASM 0 (both)
Stopping distance 21.2

Should be this

Set 3
BB 20/20
ASM 20 (both)
Stopping distance 21.2 mi


Set 4
BB 20/20
ASM 0 (both)
Stopping distance 22.7

I still can't believe that i got them mixed up in the first place, and then failed to notice it at all. I even edited the post to point out that.

What is also interesting is that Set 4 stops slightly shorter than set Set 1, which is not what I would normally expect (the higher brake force should cause the tyres to lock sooner and the car then take longer to stop), however we are looking at a difference of 0.3 mi. Again this could be down to the driver, need to look at this more closely in the future.

Now I have corrected the figures, this is not true, so I guess that explains why it was unexpected.

I have edited the original ABS test post to reflect the correct figures and would like to apologise for any confusion this caused. The edited figures (above and on the original post) are correct, the mistake was mine when writing the post.

On a side note I now have the results of the Wet ABS test and will be posting them up later on today.

BTW Fido69, I will be putting together a piece on my impressions on GT4 vs. Enthusia braking as soon as I can. I have put together some general thoughts on Enthusia and these can be seen over in the Enthusia thread.

 

[Scaff]

This is the second ABS test that I have carried out, the first was high speed stops at the test track. However, it was suggested that using the Tsukuba wet circuit would perhaps be more effective.

The conditions and expected results are the same as with the high speed ABS test, but for clarity are detailed again here.

First off, you should be aware than the results if this test are subjective and based purely on what I would expect to find in real life when comparing the braking distances between ABS and non ABS equiped cars when exceeding the tyres grip level under wet straight line braking.

Now what I expected to find was than a car fitted with ABS should stop quicker than a car without ABS, if the tyres lock under hard braking. Please be aware that threshold braking will be quicker than either of these, but thats another subject.

The reason behind this is that the ABS system is able to release and apply the brake many thousands of times a second when it detects that the tyres has exceeded its slip percentage. Without ABS you are simply waiting for the tyre to regain grip, if and when it does .

The question is, does setting the cars ASM to zero disable the ABS.

The car I used was a Ford GT fitted with Comfort tyres (to ensure I was looking at a low grip level), a brake balance controller was fitted, but no sports brakes. The brakes were applied from 100 mph, I use the DFP and just floored the brake pedal, straight to 100% braking force.

The braking area was the final back straight at Tsukuba, and it was fun just getting around the circuit in the wet with these tyres fitted. I would have liked to have braked from a higher speed, to allow direct conparison with the high speed ABS test, but given the circuit conditionas and tyres this was just not possiable.

The first run was with the brakes set at 3 front and rear, stoping from 100 mph. This was done with ASM set to 0 and then 20, the average of each set of three runs was used. With the brakes set low I would expect to see a small difference, if any. I then repeated this with the brakes set at 24 front and rear, with this much higher setting (which should make locking the brakes easier) I would expect the differences to be greater.

Results

Set 1
BB 3/3
ASM 20 (both)
Stopping distance 7.4 mi (no idea what an mi is)


Set 2
BB 3/3
ASM 0 (both)
Stopping Distance 7.7 mi

The difference was 0.3 mi, now while the difference is small, this was from an average of three runs, and given the lower speed (against the high speed test) this does re-enforce what we have seen before.


Set 3
BB 24/24
ASM 20 (both)
Stopping distance 7.6 mi


Set 4
BB 24/24
ASM 0 (both)
Stopping distance 7.9

Thats a difference of 0.3 mi with the brake balance set to max front and rear, now while this is identical to the lower brake force test, it is consistent with the high speed results.

It is also interesting to see that Set 3 stops quicker than step 2, even with a much higher Brake Balance setting the car stopped quicker when ASM was used. The difference is small, but again it was consistent over three runs. Additionally it is consistent with the high speed ABS test results.


Conclusion

Well the test results again seem to back up what I would expect to see in a real car, and with these results I think we can say that the ASM setting does at the very least have an effect on the stopping distances. If it did not effect stopping distances we would not expect to see any significant difference between Set 1 and Set 2 or between Set 3 and Set 4. However both this and the high speed test have shown clear and consistent differences

I am however still not ready to say that an ASM setting of 0 (for both) disables the ABS, as nothing I have seen completely confirms this. ASM definately has an effect and may lower the point at which ABS activates to such a minimal level that we rarely feel it.

Any and all constructive feedback on the above would be appreciated.

 

[FIDO69]

I tried a little quick testing last night. Very unscientific, but it makes me think there are screwy things going on...

I took the Plymouth Cuda, no ASM/no TCS, out onto the test oval. Installed the brake controller and tried to threshold brake.

I started from 100mph, and either slammed 100% brake force or 80-90% brake force (not well controlled, just tried to avoid excessive tire squealing). I did this with both 1/1 and 24/24 settings on the brake controller.

Results:

In a straight line, there was no difference in stopping distance between 100% and 80%, nor between 1/1 and 24/24 brake settings.

However, when braking and turning at the 24/24 setting, the car spun out and was not controllable. The car behaved well while braking and turning at the 1/1 setting for both 80% and 100% braking.

This reinforces my initial impressions of braking in GT4: 100% is always acceptable, because the computer automatically threshold brakes for you.

Second, the "ABS" chirping does NOT do what it is supposed to do in real life. i.e., it does not cause your car to be steerable while braking.

These are, of course, preliminary conclusions.

 

[Uncle Harry]

In real life any ASM system would be useless without an ABS braking system.
However PD's application to the game possibly has some shortcuts.
Scaff, can I ask you a question. Did you notice the ASM indicator flashing as you braked when you had ASM active?

 

[Scaff]

In real life any ASM system would be useless without an ABS braking system.
However PD's application to the game possibly has some shortcuts.
Scaff, can I ask you a question. Did you notice the ASM indicator flashing as you braked when you had ASM active?

Good question, and yes I have looked. With the ASM set,the light will only flash when turning under braking, not under straight line braking.

Being honest I was not expecting it to flash under hard braking, my theory is just that the ASM setting has an influence on the ABS system, not that ABS activates the ASM.

 

[Epinionator89]

Stopping distance 7.4 mi (no idea what an mi is)
Stopping Distance 7.7 mi...
...The difference was 0.3 mi, now while the difference is small, this was from an average of three runs, and given the lower speed (against the high speed test) this does re-enforce what we have seen before...
...Well the test results again seem to back up what I would expect to see in a real car, and with these results I think we can say that the ASM setting does at the very least have an effect on the stopping distances. If it did not effect stopping distances we would not expect to see any significant difference between Set 1 and Set 2 or between Set 3 and Set 4. However both this and the high speed test have shown clear and consistent differences

How were you able to measure braking distance?

 

[Scaff]

How were you able to measure braking distance?

Run a complete lap of your required track in Free Run, after you exit back to the options screen, gop to the data logger. Here you can compare the lap time, with throttle and brake levels and speed.

If you save a ghost from a Free Run lap, you can also load this into the data logger and compare two laps side by side.

Its a very useful tool, but all distance mesurments are in MI's and no-one seems to have a clue what they are.

 

[RedWolfRacer]

Its a very useful tool, but all distance mesurments are in MI's and no-one seems to have a clue what they are.

I could be completely wrong, but my guess would be that "MI's" are miles. I haven't looked at the screen you refer to, however, but this is, again, just a guess and, again, I could be completely wrong.

EDIT: I noticed the 7.x breaking distance, but I am not discounting the possiblity of "mi" being miles, though the decimal in the wrong place. A VERY wrong place. Of course, this is all speculation. Curse the PD folks' ideas of using very odd measurements without at least explaining them! That and not telling anyone quite how the suspension or much of anything works in the first place.