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Alex, you seem to know you stuff. I have a few questions based on your post. How does the calibration change ( or car know) how many passengers there are? It seems that weight and weight location have a large effect. Of course it would. Also, it would appear that if you change from all-weather tires to say, high performance summer tires (or vice versa) that would also throw the system for a loop. I'm trying to put this into various compartments in my brain and they aren't fitting. Heck, I don't even know how many compartments I need .

Thanks.

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Most OEM systems just watch yaw and steering wheel angle; they don't care about tires or weight distribution. Those are handled by the ABS system, which is the primary stability control output, though some drive-by-wire systems use throttle as well.

At the ABS end, the thresholds are simply turned down to where tires and weight distribution aren't all that important. 20 years ago the engineers sweated odd suspension harmonics, tire carcass stiffness, and all sorts of stuff that turned out to not really matter much in the end. Not to say you couldn't get into trouble somehow, but any problems show up easily at road testing.

For practical purposes, stability control is just an enhanced ABS system.

There is a 'window' of error allowed around the target yaw rate. This window accommodates day to day changes like passengers or very similar replacement parts. As another interesting aside, this window requires a 2 week long trip to various special roads around the country to validate that the window is calibrated correctly.

If you want the black and white answer on high performance parts it's this: you are expected to replace your tires with OEM tires, anything you choose to do beyond that is up to you to determine if it's worth the performance compromise. For instance, many people who complain of 'ice mode' on race tracks or autocross courses have replaced their tires with something stronger or replaced brake pads with aftermarket. This is directly related to the changes they made. So, yes, you do throw the system for a loop. However, most of the time the extra grip of the new tires or the extra temperature tolerance of the new brake pads more than makes up for the reduction in ABS performance on the race track but there is no free lunch, you do pay a penalty in the effectiveness of your calibration. Most people shut ESC off on the track anyway so it is less critical but similarly affected.

Alex

Alex

There is a very fundamental difference, ABS cannot apply brakes on it's own. ESC systems have entirely different hardware to allow pressure to be created at any wheel independent of the driver.

ABS is a very small supporting actor in an ESC system and really only critical when the driver is both panic stopping and creating oversteer or understeer with the steering wheel. At that point ESC will request changes in the way ABS operates but if the driver isn't braking there isn't much ABS interaction.

Alex