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can someexplain to me what the wheel rim size has got to do with things. As long as the circumference of the Tyre is the same, does it matter

Yes it really does. I understand where you are coming from, but think about it a second, if it was only about the circumference and the current road speed being shown correctly on the instrument pack etc, why do sports cars have bigger rims with thinner profile tyres on them and why are different rim sizes available for the Disco and folks want to fit bigger rims beyond them looking better

Although it's a bit geeky of me, along with the CAN bus, i happen to have a bit of a penchant for the technology involved in the braking system and stability control technology of the Disco 3 which is also now the standard in most vehicles.

Once upon a time the best available was servo assisted brakes, then someone came up with a system to compare wheel speeds from all four wheel speeds with sensors to determine if one wheel had stopped rotating in comparison to the others. feed this info into an ECU, put some valves in line that the ECU could operate to relieve pressure being applied to each corner and voila, you have ABS.

Adding in a the brake switch state, valves to allow addition of pressure from a reserve with a pump and later a control line to make the EMS back off the power produced an additional capability for the ABS to also provide a traction control ability

With these sensors and valves in place and a tilt sense input, it only takes just a few lines of code to the ABS software for it to also have HDC capability.

Even with these sub function capabilities, the ABS system and it's primary function is now such a household name, it's hard to imagine it and it's main functionality being replaced and surpassed.

But that is in fact exactly what happened, and what everyone now typically thinks of as being an ABS ECU in their vehicle, with it's a primary role of stopping the brakes from locking and the anti lock functionality will no doubt be surprised to learn that ABS has now become just sub role of the modern ECU, which is now more correctly known as a Dynamic Stability Control Module, or DSC as you prefer.

I won't go into the depths i know about this advent, but trust me, it is as revolutionary and significant to vehicle safety as the Jet engine is to Air travel.

The DSC system, does not just measure road speeds from all four wheels with immense nanosecond precision, it also knows what you are doing with the accelerator pedal, the engines power output, brake pedal, steering wheel with the steering angle sensor, what the EAS has the vehicles height set at, what gear the Autobox has and even knows which seats are occupied from the Airbag ECU and in some markets the weight of the occupants. But mostly there is a very sensitive Piezio electric sensor mounted very exactly to the floor of the vehicle in as close to dead center as you can get that tells it precisely to the nanosecond what G forces are being applied to the vehicle. Naturally it also brings into play what wheels and tyres are fitted and calculates the rolling mass of each wheel and un-sprung weights from these.

It's ultimate aim is to do whatever it can, by controlling anything and everything possible to maintain vehicle stability within is programmed envelope of acceptability, no matter what the driver does and for sure to work as it should and provide its best, it really needs to know what brakes you have fitted.

So it's really quite obvious that Bodsy should figure that if you uprate the brakes, you really want to let the vehicle know you did, and i guess the same follows if you upgrade the rim size, albeit maintaining the same circumference with lower profile tyres.

Bodsy, thanks for the clarification

As the value is indeed different on the respective vehicles, i can only imagine that the instrument pack objects because it is a Diesel. It would be good to see if a V8 owner can apply the higher spec brake option without problem.

BBS SPY wrote:

it really needs to know what brakes you have fitted.

Without trying to appear difficult Colin I'd like to see some hard evidence of why? There are several site users out there who have made this conversion... some a long time ago and there have been no reported issues so when they are now being enlightened to a potential issue then it is important that they can have a full understanding of the level of importance being attributed.

You have mentioned the monitored systems but can the system really take into account all of the variables such as:

Weight - does it know that I have 500kg in the boot or 150kg on the roof or that I am towing a trailer of 500kg 2000kg, 3500kg ??

Conditions - does it know when its wet or dry, hot or cold, ...that I've been coming down a mountain and my brakes are red hot and fading fast.

Mechanicals - what are the known differences between the brake types in terms of stopping distance at a known speed....is it 10 20 40 100 ft ? Is it that great as to make a difference to the reactions of the monitoring modules...are they going to say "oh he's stopping faster...so I need to apply this now instead of in another 20ft?"

I still think that the DSC is doing nothing other than reacting to the monitored systems including braking force whatever that may be at that particular nanosecond irrespective of brake type.....as I said earlier... surely as far as it's concerned, stopping is just stopping.

I know I'm being a bit of a devil ....and no doubt there's a bit of huffin' and puffin' going on in the Cypriot air but you have to convince my scrambled egg a little bit more I'm afraid.

Hiya DG

You are certainly not appearing difficult and your thoughts and input are most appreciated and welcome, so no huffin and puffin here at all, just chilling into the evening with nice bottle or two and techno babbling away as per usual.

I did say i have a bit of a geeky penchant for this stability control stuff, and it's fairly obvious i have some deep admiration for such vehicular technology, just as well really given my profession

I apologize therefore if my comment

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to work as it should and provide its best, it really needs to know what brakes you have fitted.

DG wrote:

I still think that the DSC is doing nothing other than reacting to the monitored systems including braking force whatever that may be at that particular nanosecond irrespective of brake type.....as I said earlier... surely as far as it's concerned, stopping is just stopping.

Everyone who has posted so far has been correct in one way or another. I quoted DG to highlight an important point about traction control and ABS that may be pertinent to the disc diameter debate (and it is a debate - we won't know the answer until someone from Land Rover tells us, or else we do something more extreme like find the ECU RAM address of the parameter and scan the software code for read instructions from that address).

What DG says is correct to an extent, as many of the control algorithms in a vehicle are closed loop and by definition reactionary. What many of the current advanced algorithms do though is predictive control. Predictive control has been around for a long time, but we now have more advanced plant modeling systems and more powerful CPUs to devote to creating and calculating the algorithms.

A good advanced control system will use a 'model' (the plant) to use as a basis for deciding on what to do next. The model is itself an algorithm plus a collection of numerical tables/maps that take as inputs the current values of all the relevant ECU inputs (at that particular microsecond). The model uses these inputs to spit out the desired control values for whatever it is controlling such as a throttle, solenoid, fuel pump or, in this case, braking force. When using this sort of arrangement for predictive control, the model incorporates the current state (and 'n' previous states) to make a very educated guess about what the physical system is about to do and what should be done to control it to a desired state. The plant model is a mathematical representation of the physical system, however simplified.

An easy example of a model to understand is a valve - the model will be an algorithm that represents the physical properties of the valve and what is going through it. A bunch of things including as temperatures, speeds etc. will be used to feed into the calculations that will know how long the valve will take to open/close given the current temperatures and engine speeds (allowing the algorithm to calculate viscosity if it's oil etc.) The ECU will then apply the appropriate current to its output to control the valve as accurately as possible.

This is particularly relevant for ABS and traction control which is all about predictive control i.e. an ideal traction control system will know when traction is about to be lost and try and prevent it rather than react to it.

What does this have to do with the brake disc size in the CCF? It's possible that it's one of the parameters of the vehicle model used by the traction control system i.e. it uses the calculated potential braking force in the model to predict how much effort to apply for HDC for example.

Now, DG has a great point about things like vehicle contents - how does the system know you have 500KG of Chateau de Chasselas in the back? It doesn't. The model will quite likely have been developed using design of experiments methods to be accurate for the possible range of vehicle weights from unladen to recommended maximum.

Or it might not. It could be just left there from a redundant bit of prototype code and is completely unused. It's been a long day.

Whatever the outcome, I suspect that changing the brakes and not changing the CCF parameter will not have a great effect on anything.

I just changed my brakes from the standard V8 discs and calipers to EBC Dimpled discs and Green Stuff pads and the braking performance had changed dramatically. I'll be finding out first hand whether this has made a significant difference to the traction control when it snows soon here. My guess is that it wont have, but you never know.

BrewMonkey wrote:

Now, DG has a great point about things like vehicle contents - how does the system know you have 500KG of Chateau de Chasselas in the back? It doesn't. The model will quite likely have been developed using design of experiments methods to be accurate for the possible range of vehicle weights from unladen to recommended maximum.

Bodsy wrote:

LT, IMHO you should at least have the same brakes all round. It will I'm sure affect the brake balance with only doing the front to V8 size.

Will be doing that in the near future, as my rear discs are looking tired. I'll report back.

I've previously fitted larger discs and 4 pot calipers to the front of an Abbott Racing Saab (much better than it sounds ) whilst leaving the rear discs and calipers as standard. Obviously that was a technically "simpler" vehicle to the D3, no HDC etc.. but it caused no issues at all. It was regularly thrashed on the track & road and braking was superb.

Bodsy wrote:

MPG drop is coz you is stimping on the brakes more and having to re-accelerate