GT4 and Brakes

[Rob the Fiend]

I guess the key is that the diameter of a motorcycle wheel changes due to the lean of the bike changes by that 3-6% - hence the change in measured speed. I would hope that there would not be a significant change in a car tyres' diameter as this would indicate a weak sidewall - there are obvious exceptions (eg a drag car's rear tyres).

Just look at any normal car. The tyres sometimes look as if there isn't enough preassure in them.

I cannot look it up atm, but a couple of years ago a swedish car magazine had a table with many standard, and some non standard, tyres in it. Including a column that read "rolling diameter". Dont remember how much it differed, compared to ordinary diameter as told by Scaff's formula, but it was aprox 3-6%.

 

[Ezz777]

there may well be a difference in rolling diameters of different tires, but i can't imagine the difference would be that significant for a single set of tires over a reasonable speed range (again there will be exceptions - but hopefully not on a road car)

 

[Scaff]

Yeah, imagine the formula that takes into account all factors that you wrote.
Probably look like something out of a comic book.

And i agree with you, keep all formulas simple.

Any way, one thing that mph@1000rpm is good for is how to tune your gearbox.
So that you hit a good rpm after each shift, much to win in that.
Both in games and RL.

Gearbox tuning is exactly what I use them for in GT4, in the real world I use the formula to illustrate the effect of changing tyre/wheel sizes have on vehicle performance.

I have a question for Scaff, would it be possible to test if there is any difference in tyre wear (sp?) from fitting race brakes or running standard, by doing a endurance race in B-spec mode and see if there is any difference in number of laps between pit stops? I mean let the tyres wear down so much that the car do a stop by itself.

Thats just given me something new to do, as you may have read from previous tests Fido69 and myself have yet to find any measurable proof that Racing Brakes do anything at all in GT4 (have a look at the tests linked from the first post). I will look at this and put something together.

there may well be a difference in rolling diameters of different tires, but i can't imagine the difference would be that significant for a single set of tires over a reasonable speed range (again there will be exceptions - but hopefully not on a road car)

I think the point that Rob is making is that even small changes can have an effect, particularly when looking at the higher gears (i.e. sixth), I've thrown together a few quick calculations to illustrate this. One with tyre diameter reduced by 1% and another with tyre diameter increased by 3%; under or over inflation of tyres and extremes of temperature could account for changes of this order, particulalrly when you consider (as Rob has correctly said) that the tyre is never perfectly round.

I've used the Celica example above for easy avaliablility of figures.

Tyre diameter 24.26"

-1% = 24.01"
+3 % = 24.99"

1st Gear MPH per 1,000rpm
Standard = 5
-1% TD = 4.97
+3% TD = 5.18

6th Gear MPH per 1,000rpm
Standard = 19.44
-1% TD = 19.24
+3% TD = 20.02

As you can see the greater effect is visable in the higher gear, if we now imagine our car is running at 6,000rpm in sixth and look at the relative speeds (be aware that these are just possiable speeds from the gearing, as rolling resistance, aero drag, etc is not accounted for)

Speed @ 6,000rpm in 6th gear
Standard = 116.64
-1% TD = 115.44
+3% TD = 120.12

The change is clearly visiable, it also helps to illustrate the problem in gearing of top speed vs acceleration.

If you consider the tyre diameter to be part of the gearing (which arguably it is - just the final part), then the larger the wheel the greater the top speed (as it travels further per revolution = more MPH per 1,000rpm), but as it is now larger it will take longer to travel this distance, the Reverse is also true.

Regards

Scaff

 

[Scaff]

New link to a thread on the data logger unit of measurement (the ml) added to the first post, this also includes a quick Ford GT 70-0mph braking distance test.

How long is an ml & Ford GT 70-0mph test

Regards

Scaff

 

[Ezz777]

i'm cool with the effect of a different tyre diameter on final speeds, however my point (which maybe wasn't clear enough) was that there shouldn't be that much change in rolling diameter of a single set of tires over a given speed range. Rob had said - and maybe i missed the point earlier - when you were trying measure the speed per 1000 rpm in a gear that the rolling diameter would change making the measurements inaccurate. Sure this may be true for a different sets of tires - but for the same set, i cannot imagine that the rolling diameter would change that significantly within the speed range of a given gear. Ie that the rolling diameter for one set of tires say at 90km/h (or whatever the start of your 3rd gear is) as compared with the rolling D at 130km/h (or whatever the top of your 3rd gear is) would not be significantly different - hence the measurement of you were making would be perfectly valid.

 

[Rob the Fiend]

Sorry Ezz777.

I wasn't clear enough, the rolling diameter doesn't change much at speed, its neglible. (unless we are talking about Bonneville speeds)

It was the difference in diameter measured on a tyre when its not mounted, compared to when its on a car and being loaded down by its weight.

Easiest way to measure that on a real car, is to mark the tyre with a chalk(at the bottom,center), roll the car forward until the mark is in the same position, and measure the distance rolled. That is the rolling diameter, and one of the only times you use that, is when you check how much the speedo is wrong.

For example: Your friend says that his car does 125mph, but when you check, it was the speedo that said 125. Use rolling diameter, rpm and Scaff's fomula, the correct speed is easy to calculate.

 

[Scaff]

Sorry Ezz777.

I wasn't clear enough, the rolling diameter doesn't change much at speed, its neglible. (unless we are talking about Bonneville speeds)

It was the difference in diameter measured on a tyre when its not mounted, compared to when its on a car and being loaded down by its weight.

Easiest way to measure that on a real car, is to mark the tyre with a chalk(at the bottom,center), roll the car forward until the mark is in the same position, and measure the distance rolled. That is the rolling diameter, and one of the only times you use that, is when you check how much the speedo is wrong.

For example: Your friend says that his car does 125mph, but when you check, it was the speedo that said 125. Use rolling diameter, rpm and Scaff's fomula, the correct speed is easy to calculate.

I (being quite lazy) use my GPS system and the innacuracy can be quite telling.

My Celica T-sports speedo will show an indicated 80mph (not on a public road of course ), but the true speed is actually around 77mph.

In Europe a speedo can legally under read by up to 10%, so you speedo could read 80mph but your true speed actually be as low as 72mph.

In the US its still 10% but it can under or overread, so strictly speaking youre speedo could read 80mph but your actual road speed could be as high as 88mph (to be 100% acurate for the US the actual legislation reads as +/- 5mph per 50mph - but thats 10% in my book).

Regards

Scaff

 

[~Sp33~]

thats realy.. disconcerting to know scaff.. thanks..i think..lol.

So when the Police pick you up for speeding, you can sue the car manufacture for not having an accurate reading?

 

[Scaff]

thats realy.. disconcerting to know scaff.. thanks..i think..lol.

So when the Police pick you up for speeding, you can sue the car manufacture for not having an accurate reading?

Worrying in the States as the speedo can legally over-read, in Europe its not a problem as legally they can't over-read (only under-read by 10%).

I must confess I have no idea was the Australian regs are, but given the nature of some traffic cops I have heard of in parts of Australia I would hope they are more like the European ones.

Regards

Scaff

 

[Ezz777]

i think our speedos (in oz) are the same as the european ones (ie must be less than 10% over at 80kmh).

sp33 - i don't like your chances with that one. if you are lucky they may drop you one speed range (ie if you are doing 20 over they may drop you to 15 or less under) which is quite significant over here.

 

[~Sp33~]

It realy does depend on where you are in oz im pretty sure. Victoria cops are apparently VERY strict. My dad has been booked many times there ( he lives there). At one stage he got caught doing 102kph in a hundred zone. He got fined with points deducted, but other parts of oz such as NSW, where i live, theyre much more ... i was going to say leaniant (sp?)... but more oblivious almost. Outback Oz is very forgiving, give or take 20kph.

Speed camera are absolutely an ass in NSW, where more then the majority of cameras are placed at the bottom of steep inclines and blind spots. Nothing but revenue raisers in my opinion, they should be banned.

 

[militantmandy]

I mentioned this to a collegue of mine. He's big on his physics..this is what he had to say about the notion that weight has little effect on a cars ability to stop.

"See, this is correct:

"Stopping distances are principally dictated by the total area of the contact patch offered by your tyres and the tyre compound."

So is this:

"...your maximum deceleration is limited every time by the tire to road interface."

The 'contact patch' is the area of the tyre that is in contact with the road. That area is directly affected by 2 things; tyre pressure and vehicle weight (weight distribution will also come into play if you have the ability to move the CoG of the vehicle, but only because it alters the contact area of the tyre on the ground by shifting the weight).

The 'tyre to road interface' is similar, in that the 'contact patch' is clearly an important part of that interface, but in this case we can also consider friction. The amount of friction energy required is inextricably linked to mass and speed. Check this:

>>
In physics, a force is defined as the time derivative of momentum:

F = dp/dt = d(mv)/dt
If mass m is constant, then second Newton's law mathematically follows from this definition:

F = d(mv)/dt = m(dv/dt) = m · a

If the mass m is measured in kilograms, and the acceleration a is measured in metres per second squared, then the unit of force is kilogram x meter/second squared. This unit is called Newton: 1 N = 1 kg x 1 m/s^2

A prevailing misconception is that force is a fundamental quantity in physics. There are, however, more fundamental quantities, such as momentum. (Energy, however, is less fundamental than force and momentum, because it is defined as a work, and a work is defined via force). Two most fundamental theories of nature - quantum electrodynamics and general relativity - do not contain concept of force at all.
<<

The equation for work energy is Ew=fs, where f=force and s=distance (don't ask). If the brakes exert maximum energy every time, and the 'force' effectively = 'veh mass' then the only variable is the stopping distance.

However, to apply the same energy you need to avoid any losses in the system, and a heavier veh will require a stronger brake system in order to transfer the energy to the contact patch.

Consider a half-ton car travelling at 60mph. The manufacturer must ensure that the vehicle can stop within a certain distance (regulations). Given the mass of the vehicle the manufacturer knows what energy will be required (Ew=fs, remember). So the manufacturer puts a braking system (callipers blah blah) that can deliver the required energy, and therefore the veh will stop in the distance specified. Remember also that the manufacturer will specify the tyre pressures that are required to do so!

If you take the brake system from that car, exactly as is, and put it into a 1.5-ton car, there is no way that the brakes can transfer sufficient energy to stop the vehicle in the same distance (even if the tyre pressures are increased so that the contact patch is the same size as the one for the half-ton car, and the tyre are the same compound. The brakes will not be able to apply themselves as efficiently.

Energy in the bigger car will be lost; heat and sound will be generated. If energy is lost through heat and sound then it is not being passed to the 'tyre to road interface'.

The manufacturer of the bigger car will know this, and will have fitted a braking system capable of stopping the larger mass in the same distance.

Therefore a more massive vehicle needs a better brake system in order to stop in a given distance.

Something like that anyway :-)"

Not supposed to be an argument starter\ender etc, I just thought some people might find it interesting!

 

[Ezz777]

Not supposed to be an argument starter\ender etc, I just thought some people might find it interesting!

I get the feeling its an agreement more than anything else. basically it states the limiting factor is the tire grip.

the braking system won't be the limiter for any production vehicle. if it is then the manufacturer has some serious issues...

 

[militantmandy]

But he does dispute that the weight of the vehicle would make liitle difference to the stopping distance.

 

[Ezz777]

But he does dispute that the weight of the vehicle would make liitle difference to the stopping distance.

Well yes, but this would be the case with the same braking system and the same tires on a car that in one instance weighs 0.5 tons and the next weighing 1.5. Sure putting some bicycle brakes on a bus isn't going to stop the thing very quickly, but putting bus brakes on a bicycle will make little or no difference in stopping distance.

This point is fairly obvious. However, one of the points of the thread generally is that car manufacturers will tend to supply braking systems and tire combinations that will stop cars within safe guidelines (read about the same distance). Hence, the weight of a vehicle does NOT play a very significant role in the stopping distance.

 

[Scaff]

But he does dispute that the weight of the vehicle would make liitle difference to the stopping distance.

Hi militantmandy

I've been on holiday for the last week and as such have only just seen your posts on the subject of weight and stopping distances.

It's an interesting subject, which has been covered in this thread a number of times. but given the size finding it can be a bit of a problem, so I will try and cover the main bits for you.

Your friend is quite right that weight is a major factor in determining the requirments of the braking system of a car, and therefore ensuring that it is sufficent to the requirments of its weight and speed. It is also true that all manufacturers will ensure that the brakes are 'fit for purpose' and capable of the demands placed upon them.

However brakes do not stop a car, the tyres do. A car's braking system is designed to slow the rotation of the wheels, the maximum amount they can be slowed is determined by the slip percentage of the tyres (the % difference between wheel speed and vehicle speed), if this is exceeded then grip will be greatly reduced and braking distances increased significantly.

As long as the braking system is fit for its purpose (which is a caviat I have put in all my posts on the subject) then weight will only have a minor effect on stopping distances; weight transfer and tyre compound having a much more significant effect. FIDO69 put together a post which looked at the effect of a 10% weight loss in a car on stopping distances, now taking into account that 10% is a major weight loss on a car, the maximum reduction in stopping distances was just over 3%, a lot less that would be gained through better rubber.

Don't get me wrong, you get a lot of benefits in racing through weight loss (better transient cornering ability, better PTW ratio, etc) but big gains in stoppin distances is not one of them.

One of the best pieces on this subject is

Braking systems in Plain english

Its written by James Walker, Jr. of scR motorsports and was originally published in Grassroots Motorsports. Its an excellent discussion on what and how a car is stopped.

You may also find the Physics of racing series of interest, however they are a lot heavier on the physics side of things.

Regards

Scaff

 

[Scaff]

The following has been supplied by Alfaholic and is an extract from a book on Colin Chapman regarding the subject of Engine Braking. Its is supplied purely as another example of why Engine Braking is not a general track method of slowing the car.

The book is called "Theme Lotus" subtitle "21 years of Grand Prix and Indianapolis cars from Lotus 12 to John Player Special Mark IV"

Author: Doug Nye
First puplished by Motor Racing Publications Ltd in 1978.

From Chapter "Lotus 79", pg 168, Nye writes of the redeveloped "queerbox":

"Since its gear engagement involved neither dogs nor meshing there was no need to declutch. Now the driver could merely back-off the throttle when changing-up"... "A free-wheel mechanism could be applied which would allow the same clutchless trick for downchanges.."

Nye then quotes Colin Chapman directly:

"We learned at Indy the only quick way was to honk into corners on the power and the brakes at the same time to minimize pitch-change, then come off the brake and leave the corner smoothly under power. On faster road circuits you sometimes have to just dab the brakes to check the car, and that unsettles it. If our drivers could left-foot brake with the power still on they could damp-out pitch, and then by rolling off the brakes away they'd go. Two pedal control simply offers a quicker way of driving. Then, with a freewheel installed, there's no engine braking, and that can help because engine braking varies dependent on what gear you're in and what revs you're using, and that means you can't be precise when balancing the brakes. Remove engine braking and you can brake more accurately. Having this freewheel under development is the reason for the 77s, 78s and 79s being basically over-braked."

It's an excellent read. Picked it up in an antiques shop in Barkham.

Many thanks to Alfaholic and a book I hope to pick up ASAP.


Regards

Scaff

 

[ozanzac]

Scaff, I wish to thank you for all the effort you've put into this thread... Reading just the first post made me want to spend the time necessary to read the entire discussion. A good couple of hours reading, but worth it in every sense. Mostly in disproving the common misconceptions.

For Ezz777 and ~Sp33~ regarding Speedometers in Australia.

i think our speedos (in oz) are the same as the european ones (ie must be less than 10% over at 80kmh).

That's not the case, or at least it wasn't the last time I checked. Australian Design Rule 18 (which governs instrumentation in vehicles, notably speedometers) calls for all indicated speeds above 40km/h to be accurate to plus or minus 10 per cent.

(edit) Apparently, this has changed quite recently to upgrade to UNECE harmonisation was to be signed by Anderson, who was the Commonwealth Transport Minister and Deputy PM. This according to DOTARS would make the speedometer accurate @ 100km/h, but within 'plus 10%', AND +/- 4km/h over that.

The Australian Design Rules set out design standards for vehicle safety and emissions. It is the Australian Government which legislates these standards via the 'Department Of Transport And Regional Services' (DOTARS), and should in most circumstances, reign supreme over the rulings of the individual states.

What this means is, if you or your father were booked for speeding for going less than 10% over the limit. Take it to court, and the charge will most likely be dropped.

Why draconian states such as Victoria book people for tolerances less than 3 km/h over beats me.... If everyone fought the fines, (as they should) it would clog the court system, and probably serve notice to the states that they can't pick from the pockets of motorists and claim to be doing it for our safety.

Edit: I've yet to be caught speeding, so have never had to personally challenge a fine, but it's a handy card to have up the sleeve, as it's worked for others.

 

[~Sp33~]

Very true. Its strange how the victorian police tolerate so diferently to the rest of Australia. They believe that the speed limit is meerly the maximum speed in which you should be travelling, therefore ANYTHING over this and youve pushed your luck too far.

 

[G-T-4-Fan]

OMG, I have the feeling like my parents dont really believe it's such a good race simulator, I should let him read this sht man I have GT4, but didn't know this worked in it!!

Some things seem pretty obvious: I have no driving experience, am 15, and already figured out that 85% braking IN REAL LIFE decreases stop distance, and I already thought that just because of racing programms, that just showed you (not on purpose) some cars braking and letting the fron tyres slip.

It's obvious that it just looses grip and that you could just as well put icecream under your tyres IMMEDIATLY lol, cause it's like riding on ice I guess.... It's still cool that my thoughts got confirmed though, cause previously it were just guesses, not anything more. Now I know there's proof.

Scaff, lol I came across this in your sig, when I quoted you in some gallery from ViXeN lolz. But this little curiousity click in you sig seems WELL WORTH the curiousity lolz

GREAT GREAT THREAD:tup: Especially the first post, otherwise I would've skipped all this "I-would-think-it-was CRAP" stuff. So thanks for such a clear first post with all the links:tup:

👍

 

[Scaff]

OMG, I have the feeling like my parents dont really believe it's such a good race simulator, I should let him read this sht man I have GT4, but didn't know this worked in it!!

Some things seem pretty obvious: I have no driving experience, am 15, and already figured out that 85% braking IN REAL LIFE decreases stop distance, and I already thought that just because of racing programms, that just showed you (not on purpose) some cars braking and letting the fron tyres slip.

It's obvious that it just looses grip and that you could just as well put icecream under your tyres IMMEDIATLY lol, cause it's like riding on ice I guess.... It's still cool that my thoughts got confirmed though, cause previously it were just guesses, not anything more. Now I know there's proof.

Scaff, lol I came across this in your sig, when I quoted you in some gallery from ViXeN lolz. But this little curiousity click in you sig seems WELL WORTH the curiousity lolz

GREAT GREAT THREAD:tup: Especially the first post, otherwise I would've skipped all this "I-would-think-it-was CRAP" stuff. So thanks for such a clear first post with all the links:tup:

👍

Thanks for the feedback, and yes the first post is needed to ensure members can find there way around the whole thread. It was one of those that just gained a life of its own, as you can tell I'm quite into all of this, but then it is my job (I'm a training consultant in the motor industry).

If you like this one you may like to take a look at the following as well (it my latest work).

Gran Turismo – A comparison across the series.

Regards

Scaff

BTW Its nice to hear that members do actually use the 'clicky' in my sig.

 

[FastEddie12]

I know the general opinion here is that "racing" brakes are useless on GT4, but do they make a difference if you use the stickiest of sticky tyres? You know the ones that are stickier than a stick of stickers in a sticky situation?

Just thought I'd ask. Maybe it's just KY's idea of a joke to catch us out....

I keep thinking of all the money I've spent on brakes over the last 7 years...

 

[Scaff]

I know the general opinion here is that "racing" brakes are useless on GT4, but do they make a difference if you use the stickiest of sticky tyres? You know the ones that are stickier than a stick of stickers in a sticky situation?

Just thought I'd ask. Maybe it's just KY's idea of a joke to catch us out....

I keep thinking of all the money I've spent on brakes over the last 7 years...

I must admit that I have not tried them with and without using the 'stickiest of sticky tyres'.

I have just finished the testing on the next part of the GT series comparison (4WD and MR), so once I have writen that up and posted it I will have a look at this.

Regards

Scaff

 

[~Sp33~]

i would much prefer on gt4, like games such as v8 supercars 2, where if you come into a corner way to hot, and you cram the brakes on, then the tires should lock up... but its so dam hard to lock the brakes in gt4. Although they do lock when your drifting across grass, but on track it never locks so severly that you loose control. I think that would put a nice edge on the game

 

[WaterBoy]

i would much prefer on gt4, like games such as v8 supercars 2, where if you come into a corner way to hot, and you cram the brakes on, then the tires should lock up... but its so dam hard to lock the brakes in gt4. Although they do lock when your drifting across grass, but on track it never locks so severly that you loose control. I think that would put a nice edge on the game

I agree!

In a real car if you jump on the brakes the wheels lock up

Yet in GT4, even in their stock condition, wheels rarely lock up on heavy braking.

 

[Scaff]

I agree!

In a real car if you jump on the brakes the wheels lock up

Yet in GT4, even in their stock condition, wheels rarely lock up on heavy braking.

You are quite right that in the real world vs GT4 wheel locking is out, this thread has seen a lot of debate on if you can turn off the GT4 ABS or if GT4 automatically threshold brakes for you.

To have a look at some tests on these subjects (and otehrs) have a look at the first post in this thread, I have organised it so that all the good stuuf from the 20+ pages are listed and linked to.

I would suggest looking at the GT4 ABS tests to start with on that one.

Regards

Scaff

 

[~Sp33~]

Thanks dude, much easier then reading through 20 pages of threads.

 

[qwejibo]

OFF TOPIC - but regarding speeding in Australia, strictly legally if they think you were doing 1km/h over the limit they can book you - but of course no-one has instruments that accurate so it would get thrown out in court.

So the police allow you +3km/h to account for their instruments(radar, road sensors, specially certified speedometers in police vehicles*), and also give you 10% for your speedometer(as per the ADR's).

Problem is, the politicians in Victoria decided that they wanted a "zero tolerance" policy - so you don't deserve that 10% and the police there operate on a +3km/h limit! Thusly they can claim the higher revenue and produce lots of tickets to satisfy their bosses!

* - these speedos have caused problems, many speeding fines became void because of faulty or uncalibrated units, also the WRX speedo was unable to be certified accurate because of the AWD system iirc.

 

[Scaff]

Setting Brake Bias

The purpose of this post is to explain how brake bias can be set to optimise braking distances in GT4. It is how I set brake bias for my driving style and any reader should be aware that as with a tuning, 'right' is very subjective. What works for me, may not suit your driving style and may not work for you. If however you are new to brake tuning or just interested please read on.

Before reading this I would recomend having a look at the following white paper by StopTech, which discusses real world brake bias settings and is the basis of what is explained below.

Brake Bias & Performance

It should also be remembered that adjusting brake bias allows you to maximise the grip of your tyres for deceleration, you can not shorten braking distance below that which the tyre can offer. However, get Brake Bias wrong and you can increase them dramatically.


The purpose of brake bias settings is to ensure that all four tyres are doing an equal share of the work when braking, any time this is not happening, you are going to increase your braking distances. Also important is which end of the car will 'lock' first when braking exceeds the tyres limit, ideally this should be the front (but not always - see later), as if the rears lock first the car will become unstable at the rear and a loss of control may occur. Remember normally you don't want either end to lock as it will increase your braking distance, but if it does happen you want to remain in as much control as you can.

This second benifit of brake bias is to ensure that the car is stable while braking, this is particularly important when braking from very high speeds and/or in a car in which a lot of weight is going to transfer from the rear to the front.




Starting Out - Static Weight Distribution.

If the aim of this is to ensure that all four tyres share the braking load equally the first place to start is the static weight distribution of the car.

If Car A has 50% : 50% static weight distribution then to begin with we would look at the same F/R ratio for the brakes, say 3/3

If Car B has 60% / 40% static weight distribution then to begin with we would look at the same F/R ratio for the brakes, say 3.6/2.4

Now don't worry about the decimal points at the moment as this is just on paper, but it does illustrate an issue I have with GT4's Brake Balance settings, as it does not allow as much fine tuning as I would like.

Now we have a base set of value we need to look at the issue of weight distribution under braking.


Weight distribution under braking - Adjusting the Brake Balance

As the static weight distribution is only correct when the car is experiencing no accerative forces (either accelertaion or deceleration) we have to try an take this into account.

The amount of weight transfered from the rear to the front is not mesurable in GT4, but is determined by the following:

Static Weight Distribution - Provides the base starting point

CG Height - the higher the more weight will be transfered to the front under braking.

Wheelbase - the shorter the wheel base the more weight is transfered to the front under braking.

You have to estimate how much is being transfered in order to set the brake balance correctly.

If our two cars from above both weight 1,000 kilos and transfered 250 kilos front to rear under optimum braking then the following is happening.

Car A

Weight Distribution Static = 50% : 50% = 500kg : 500kg

Under Braking = 750kg : 250kg = 75% : 25%

So the brake bias would go from our static setting of 3/3 to a setting of 4.5 / 1.5


Car B

Weight Distribution Static = 60% : 40% = 600kg : 400kg

Under Braking = 850kg : 150kg = 85% : 15 %

So the brake bias would go from our static setting of 3.6 / 2.4 to a setting of 5.1 / 0.9


Damn Decimal Points

Once again we have decimal points getting in the way of things, only trial and error will show which way around to 'round the values to. With car A above I would try both 4/1 (80%:20%) and 5/2 (71%:29%) to see which one worked best.

With Car B I would try 5 / 1 (83.3% : 16.7%) and 6 / 1 (85.7% : 14.3%)

So why not just increase the values until you get a ratio that is right? For example Car A could run with a brake balance of 9 / 3, which would give 75% : 25%, however this may or may not work, depending on the tyres and the driver.

As has been discussed before the brake balance controller (unlike in GT3) does not just control the ratio, but also the level of force applied. Set it too high and the ABS will kick in and you will end up increasing you braking distances. You may be able to control this through good brake modulation (use the brake force indicator in the HUD as a guide).

Once again trail and error is one of the best ways of determining what the setting should be, for example our car B may have the following setting dependent on tyre.

N's = 6 / 1 (85.7% : 14.3%)

S's = 11 / 2 (84.6% : 15.4%)

R's = 17 / 3 (85% : 15%)




The importance of Testing

Now the above is just the theory and advice to give you some basic settings to start with, but as with all things in tuning, the only way you will know what works is to play around with the car and the settings.

Remember that the above is a guide only and the most difficult thing to judge is going to be the amount of weight transfered, keep in mind that the only adjustments in GT4 that will effect the amount of weight transfered are the following:

Weight Reduction 1 - 3
Ride height adjustment
Balast

Keep brake balance in mind if you change any of the above.

For testing I would recomend using the data-logger to check on braking distances on a variety of circuits, I tend to use the Test Course a lot as it allows around 5 - 6 stops from 100mph to be analysied in a single lap.



What the Brake Balance controller is not for.

With a few exceptions I would never recomend using the brake balance controller to trim understeer or oversteer (despite what the GT4 screens say). Use of the brake balance controller to do this can and does have a serious effect on braking distances.

You have plenty of other tools to manage under and over steer in the spring rates, ride height, damper and roll-bar settings. These give you more then enough to do what you need, leave the brake balance to maximise your braking performance and ensure stability under braking.

The only exception to this would be in setting a car up to drift, here outright lap-times are rarely an issue and a high rear bias will cause the rears to lock first making it easier to initiate a drift. Once again, however, car needs to be taken with the settings.

Hope that the above helps.

Regards

Scaff

 

[G-T-4-Fan]

Setting Brake Bias

The purpose of this post is to explain how.....*snap*

Thats quite....difficult... I'm jealous that you know this much about tuning
It's so complicated, I think I have to read it again tomorow to really let it sink in...💡 It's very fun to read though:tup:

But I still see it as an offence to.....