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[mark3]

I would assume it works by seeing a difference in the speed signal from the front and rear ABS sensors and as the front wheels turn faster the the rears when cornering can i also assume it only works if it see's the rears going faster than the fronts as opposed to just a difference?

[Kevin Wood]

The algorithms involved can be quite complex but the ECU can build up a picture of the car's actual speed based on all 4 wheel sensor outputs. It will trim each wheel sensor speed to account for differences in tyre diameter and take an average. If a driven wheel exceeds that average it's an indication that it's slipping. Likewise, if a braked wheel drops below the average it might be approaching lockup. The rate of change of speed at each wheel is also part of the equation.

[2woody]

they're very complicated software routines - mainly because they have to be failsafe - indeed, there's three sets of everything in the ECU & they all have to agree before intervention. The software looks mainly for change, rather than a constant speed, to make up for muppets putting the wrong size wheels and/or tyres on.

Also, they need to differentiate between different types of surface ( snow, ice, rain, mud, etc ) so the ABS/TC knows how to intervene.

Generally there's a threshold set for intervention of either ABS or TC for each type of surface.

I do have some Bosch information if you have a more specific question.......

[TheBoy]

In addition to above, the post 1998 ones (the unreliable ones ), will monitor each rear wheel seperately, and initially try to brake the spinning wheel, before asking engine to reduce power.

Pre 1998 will monitor each wheel, but cannot actuate the rear brakes individually, so will go straight to asking engine to reduce power.

[Brikhead]

In addition to above, the post 1998 ones (the unreliable ones ), will monitor each rear wheel seperately, and initially try to brake the spinning wheel, before asking engine to reduce power.

Pre 1998 will monitor each wheel, but cannot actuate the rear brakes individually, so will go straight to asking engine to reduce power.

In addition to the above addition! I'd like to add that on the later cars tc operation is much less intrusive (therefore safer) than the earlier systems.

I find the t.c. light off putting as for me default setting is always off, as long as I've remembered to press the button when starting out...

[2woody]

yes, the early Omega TC is truly nasty of the first order....

[mark3]

Right, i was wondering how it worked as i have a set of 4 very good 205/55/15 tyres down my garden and i need new tyres on the omega but there 205/65/15 so about 20mm less in diameter.

As i don't mind the front of the car being a tad lower i got them fitted and balanced at only £5 each (result) and the results are good, very good, its a win win x 2 situation

1st win, they cost me nothing

2nd win, only a tenner to fit and balance both

3rd win, steering is much improved being a lot more direct (less side wall flex)

4th win, brakes are noticeably better due to the discs now being larger in comparison to the rolling diameter.

Its made a huge difference and all for a tenner, lol.

[TheBoy]

Right, i was wondering how it worked as i have a set of 4 very good 205/55/15 tyres down my garden and i need new tyres on the omega but there 205/65/15 so about 20mm less in diameter.

As i don't mind the front of the car being a tad lower i got them fitted and balanced at only £5 each (result) and the results are good, very good, its a win win x 2 situation

1st win, they cost me nothing

2nd win, only a tenner to fit and balance both

3rd win, steering is much improved being a lot more direct (less side wall flex)

4th win, brakes are noticeably better due to the discs now being larger in comparison to the rolling diameter.

Its made a huge difference and all for a tenner, lol.

That one will need explaining to me I'm afraid

[mark3]

Smaller overall diameter wheels/tyres but same size brakes mean improved braking efficiency, its the same equation as it would be if you fitted larger diameter discs to same size wheels/tyres.

Basically the closer to tyre tread you move the pads the better the braking will be.

[Entwood]

Smaller overall diameter wheels/tyres but same size brakes mean improved braking efficiency, its the same equation as it would be if you fitted larger diameter discs to same size wheels/tyres.

sorry .. not in my book ... larger diameter discs/pads give a greater friction surface and so increased braking. The ratio of disc size to wheel size has absolutely nothing to do with braking power. All that counts is friction area (given no change to friction material of course   which will make a major difference.)

Your comment about pads being nearer to tyres is also wrong IMHO .. what matters here is pad to axle distance .. as the pads are effectively levers .. and the longer the lever the better the force applied .. so large wheels+ large discs = very good brakes...

Just changing ratios (wheel size) makes no difference at all.... as the discs and pads remain.

[mark3]

Smaller overall diameter wheels/tyres but same size brakes mean improved braking efficiency, its the same equation as it would be if you fitted larger diameter discs to same size wheels/tyres.

sorry .. not in my book ... larger diameter discs/pads give a greater friction surface and so increased braking. The ratio of disc size to wheel size has absolutely nothing to do with braking power. All that counts is friction area (given no change to friction material of course   which will make a major difference.)

Your comment about pads being nearer to tyres is also wrong IMHO .. what matters here is pad to axle distance .. as the pads are effectively levers .. and the longer the lever the better the force applied .. so large wheels+ large discs = very good brakes...

Just changing ratios (wheel size) makes no difference at all.... as the discs and pads remain.

Sorry mate but you have all your basic laws of physics ass about face, either that or you need to throw your book away as its no good at all.

Pad friction area of course counts BUT if the pads was right out as far as the tyre tread on massive discs you would go through the screen with the slightest of pressure on the brake pedal. and distance from axle to pads is only relative if your not changing the rolling diameter of the wheels/tyres!

The lager the diameter of the disc friction area (closer to the tyre tread) the less force per same friction area needed to slow the vehicle, as you say its all to do with leverage and the larger diameter the disc the greater the leverage! basic law of pysicis is the longer the lever the easier it is.

Also as i first said since the change my brakes ARE noticeably better.

[Entwood]

Smaller overall diameter wheels/tyres but same size brakes mean improved braking efficiency, its the same equation as it would be if you fitted larger diameter discs to same size wheels/tyres.

sorry .. not in my book ... larger diameter discs/pads give a greater friction surface and so increased braking. The ratio of disc size to wheel size has absolutely nothing to do with braking power. All that counts is friction area (given no change to friction material of course   which will make a major difference.)

Your comment about pads being nearer to tyres is also wrong IMHO .. what matters here is pad to axle distance .. as the pads are effectively levers .. and the longer the lever the better the force applied .. so large wheels+ large discs = very good brakes...

Just changing ratios (wheel size) makes no difference at all.... as the discs and pads remain.

Sorry mate but you have all your basic laws of physics ass about face, either that or you need to throw your book away as its no good at all.

Pad friction area of course counts BUT if the pads was right out as far as the tyre tread on massive discs you would go through the screen with the slightest of pressure on the brake pedal. and distance from axle to pads is only relative if your not changing the rolling diameter of the wheels/tyres!

The lager the diameter of the disc friction area (closer to the tyre tread) the less force per same friction area needed to slow the vehicle, as you say its all to do with leverage and the larger diameter the disc the greater the leverage! basic law of pysicis is the longer the lever the easier it is.

Also as i first said since the change my brakes ARE noticeably better.

The power of wishful thinking ...    

[mark3]

I know my car and how the brakes was before and after, its not wish full thinking.

The most basic laws of physics apply here and i cant believe you don't see it? it really is so so simple, move the friction area nearer to the tyre tread and you will need much less pressure to brake as well as you did before so using the same pressure you will notice an improvement in braking efficiency.

[Entwood]

I know my car and how the brakes was before and after, its not wish full thinking.

The most basic laws of physics apply here and i cant believe you don't see it? it really is so so simple, move the friction area nearer to the tyre tread and you will need much less pressure to brake as well as you did before so using the same pressure you will notice an improvement in braking efficiency.

You are NOT moving the friction area .. you are moving the tyre .. the friction area/axle distance, the friction pad area, the caliper size/pressure have all remained EXACTLY the same ... therefore the braking power exerted on the disc remains exactly the same.

If the friction area moved you would have the basis of an argument ..

Your braking "may" feel different because you are going slower for the same engine RPM, you therefore have less inertia, and the same brake force "could" have a slightly greater effect.

[mark3]

Oh god!

Yes im moving the tread nearer to the brakes friction area, its the same thing and if you cant see it? well i guess there's no point me keeping on.

one last thing, bear this in mind, if you say fitting smaller wheels has no effect on braking efficiency what would happen if you fitted much bigger wheels instead?