Suspension strain gauge loads vs. time

[Jersey Tom]

...and so it goes. All of those are measurable.

That they are, and part of my position is that objective measurement of understeer is fundamentally no different than oversteer. Just different ends of the scale. Though if you're trying to come up with these measures from track data it is not as straightforward as mini maneuvers on a skidpad. In any event, to date I don't think I've had difficulty in measuring understeer.

Still a question of which objective metrics (and ranges of) are most relevant to different platforms and different drivers. Do driver inputs impact these things? Absolutely. Car X may be neutral on entry to Driver A and U/S on entry to Driver B - but the reasons for which are generally fairly apparent.

[Greg Locock]

if teammates have different routes to the same laptime, there must be a better route than either has found ?

Not necessarily. It is possible, but not likely, for two different setups to be their local optimum, and to have the same peak value. Also, the teammates skill is one of the variables, and as we often see, a car set up for one driver may be slower for another that has set their own car up.

[speedsense]

...and so it goes. All of those are measurable.

That they are, and part of my position is that objective measurement of understeer is fundamentally no different than oversteer. Just different ends of the scale. Though if you're trying to come up with these measures from track data it is not as straightforward as mini maneuvers on a skidpad. In any event, to date I don't think I've had difficulty in measuring understeer.

Still a question of which objective metrics (and ranges of) are most relevant to different platforms and different drivers. Do driver inputs impact these things? Absolutely. Car X may be neutral on entry to Driver A and U/S on entry to Driver B - but the reasons for which are generally fairly apparent.

Tom,
I don't disagree with you at all. Except maybe the last statement "but the reasons for which are generally fairly apparent". iMHO,They aren't always apparent.
Let's create a scenario and talk pavement and road racing, so we narrow the framework. Let's say we are dealing with a 800hp Trans Am car, wings and air dam (modest aero-1300 lbs DF @ 150). Front independent/rear live axle, 3 link. We can light the rear wheels, in any gear, with little throttle input (especially mid/slow speed)..... (the description isn't so much for you, but everyone else, pretty sure your familiar with the car).
The car can be put into over steer with very little input of throttle. Let's say the car has slight-light understeer on entry to slow corners, slight on mid speed corners, and in high speed stuff very slight understeer. If the driver pushes the speed into the apex, the U/S will amplify. This is on purpose, to counter the ease at which O/S can be induced. The setup direction is what a Trans Am car does best, accelerate out of a corner. The Driver is a multi champion in Trans Am, and very experienced the car.
The driver will have options in technique with this, on the slow or mid speed corners, lets say he uses one of these two A) brake into the apex, effectively weighting the front and kill any of the U/S. and may even rotate the car into a slight O/S. B) He may roll in, no brake, but use the throttle to get rotation, effectively killing U/S again. Now, to clarify, he's putting the car barely just over neutral, into O/S, just outside of the slip angle, so that he's neutral-o/s-neutral-O/s on his way to the apex. His exit speed and handling shows the edges of O/S again, with no U/S visible, physically or in data.
Let's move on to the high speed corner, we have very slight u/s at turn in, the driver is leaning on the car attempting to flat a corner (he has confidence that the car will U/S if he leans too hard, he turns in knowing the U/S is there, and gives it a slight rotation and neutrals the car.
The car comes back after the run, and the front tires have no graining, except slight graining on insides (due to camber heat, straights?) The rears have a little more graining and have 15 deg. over all higher heat.
There's nothing here to indicate understeer, the driver has effectively covered up and neutralized the understeer. The car has U/S, is not neutral, but is being driven and brought to neutral or even had O/S as the limits are pushed. The driver likes the car, doesn't want it touched.
Not an obvious analysis and if one didn't know what was going on, they would think the car was neutral or even over steer. IMHO

[Jersey Tom]

Not an obvious analysis and if one didn't know what was going on, they would think the car was neutral or even over steer. IMHO

And they would be correct. Understeer and oversteer are system responses, and the response of a system is a function of both its physical structure (the car setup) and the inputs to that system (the driver's hands and feet). Ultimately that's the argument you're making, but I would say that to assign a binary or otherwise objective attribute of oversteer/understeer to a vehicle by itself is what is misleading.

Now, to clarify, he's putting the car barely just over neutral, into O/S, just outside of the slip angle

This phrase doesn't make sense to me. I've heard it used before though, maybe even on F1T. It sounds like it's implying that there's some yaw or sideslip angle which defines the limit envelope of the car, and that's what the slip angle is. This is not the case. [Side]slip angle of a car or tire or whatever is just a state variable, same as velocity or lateral, longitudinal acceleration, etc. I (the driver) choose what slip angle the tires or car are at for any point in time. I can make 0 degrees slip angle (straight ahead driving for the most part) happen just as much as 90 degrees (throw the car into some wild purely sideways slide).

[speedsense]

Not an obvious analysis and if one didn't know what was going on, they would think the car was neutral or even over steer. IMHO

And they would be correct. Understeer and oversteer are system responses, and the response of a system is a function of both its physical structure (the car setup) and the inputs to that system (the driver's hands and feet). Ultimately that's the argument you're making, but I would say that to assign a binary or otherwise objective attribute of oversteer/understeer to a vehicle by itself is what is misleading.

The vehicle itself? Sorry, but i've never won a race without a driver. I would contend that in data measurement, O/S, U/S are subjective and are in fact trends that are being analyzed. There are no absolute numbers for these. Milken, Dixon, Rowley do well to explain, but fail to apply absolute to it.
To add, the driver himself (another non absolute), is analyzing (while driving) a trend of either, and changing how he drives in response and according to his experience as a driver. The driver as you say, is an input but at the same time is an output, because he can change the outcome of the engineering, based on his definition and comfort level of U/S and O/S , and yes, neutral according to him.
A driver has several options/tools to get his car to "his" neutral, if it has U/S (with improved lap time) than with O/S where he has far fewer options to bring the car to neutral. Due to the "cures" that a driver has with U/S, makes it more subjective as being an ill to the same amount Of O/S IMHO

Now, to clarify, he's putting the car barely just over neutral, into O/S, just outside of the slip angle

This phrase doesn't make sense to me. I've heard it used before though, maybe even on F1T. It sounds like it's implying that there's some yaw or sideslip angle which defines the limit envelope of the car, and that's what the slip angle is. This is not the case. [Side]slip angle of a car or tire or whatever is just a state variable, same as velocity or lateral, longitudinal acceleration, etc. I (the driver) choose what slip angle the tires or car are at for any point in time. I can make 0 degrees slip angle (straight ahead driving for the most part) happen just as much as 90 degrees (throw the car into some wild purely sideways slide).

"slip angle of a car or tire or whatever is just a state variable, same as velocity or lateral, longitudinal acceleration, etc." Sorry, but I have to strongly disagree with this statement.... it's the "cause" of lateral, Long G, not a variable of, or "same as" but "the" variable, the state, the only opposing force that counters the car centrifugal, longitudinal forces and the resulting slip angle (due to elasticity of the tire) that is preventing the car from being flung into the horizon or achieving max acceleration, like a drag boat....

[Jersey Tom]

"slip angle of a car or tire or whatever is just a state variable, same as velocity or lateral, longitudinal acceleration, etc." Sorry, but I have to strongly disagree with this statement.... it's the "cause" of lateral, Long G, not a variable of, or "same as" but "the" variable, the state, the only opposing force that counters the car centrifugal, longitudinal forces and the resulting slip angle (due to elasticity of the tire) that is preventing the car from being flung into the horizon or achieving max acceleration, like a drag boat....

Having a hard time following your thought process here. Are slip angles coupled with forces and moments? Sure, of course. What I'm holding in contention is:

he's putting the car barely just over neutral, into O/S, just outside of the slip angle

This phrase has no meaning to me. I'll borrow a graphic from OptimumG to help me out here. The way that phrase comes across is as if you're saying the point I've indicated with a black arrow is "the slip angle" of the tire (or car). This is not the case.



Slip angle is a continuous state variable. Same applies at the total car level

[speedsense]

"slip angle of a car or tire or whatever is just a state variable, same as velocity or lateral, longitudinal acceleration, etc." Sorry, but I have to strongly disagree with this statement.... it's the "cause" of lateral, Long G, not a variable of, or "same as" but "the" variable, the state, the only opposing force that counters the car centrifugal, longitudinal forces and the resulting slip angle (due to elasticity of the tire) that is preventing the car from being flung into the horizon or achieving max acceleration, like a drag boat....

Having a hard time following your thought process here. Are slip angles coupled with forces and moments? Sure, of course. What I'm holding in contention is:

he's putting the car barely just over neutral, into O/S, just outside of the slip angle

This phrase has no meaning to me. I'll borrow a graphic from OptimumG to help me out here. The way that phrase comes across is as if you're saying the point I've indicated with a black arrow is "the slip angle" of the tire (or car). This is not the case.



Slip angle is a continuous state variable. Same applies at the total car level

"Just outside of the slip angle MAX" .. Better?... in other words to the left of your arrow.... even a sliding road race car, "sprint car style" has a slip angle on the rear tires.... not as I said outside the slip angle, which is misleading... can't have lateral G without the resistance of a slip angle to create an opposing force.

[Jersey Tom]

Better.. but I still think not quite 100%

All tires have the same max slip angle - 90 degrees, a geometric limitation of how slip angle is defined. I'd call that point on the graph "saturation" or "peak lateral." Whether you're left or right of that point though doesn't define whether you're under-, neutral-, or over-steer. Can have any of those conditions all well below saturation.

For that matter you can have lateral forces / accelerations at slip angle = zero. Non-trivial forces, due to camber thrust and ply-steer. In fact, passenger tires are deliberately built this way to track straight ahead on cambered roads.

[riff_raff]

Even if you have detailed, high-frequency data acquisition from strain gauges, triaxial accelerometers, and displacement sensors at each suspension component, it would still be difficult to correlate specific driver inputs with chassis responses.

The dynamic response of the chassis system (tires, composite suspension and chassis structures, dampeners, etc.) is complex and mostly non-linear. While discerning general trends vs. gross changes would be possible, it would also not be possible to quantify the exact effects of specific suspension adjustments.

[speedsense]

Even if you have detailed, high-frequency data acquisition from strain gauges, triaxial accelerometers, and displacement sensors at each suspension component, it would still be difficult to correlate specific driver inputs with chassis responses.
The dynamic response of the chassis system (tires, composite suspension and chassis structures, dampeners, etc.) is complex and mostly non-linear. While discerning general trends vs. gross changes would be possible, it would also not be possible to quantify the exact effects of specific suspension adjustments.

Such as?

[Greg Locock]

Sorry, riff raff that is just plain wrong. I drive my ADAMS models with the exact SWA and speed trace froma real car, and then compare its behaviour to the real car. I then switch to a synthetic controller for a similar maneuver, and modify my model, and rerun it. When we have a tune that works it goes into the real car and gets signed off. That sort of model is sensitive to static toe setting for example, which is, when push comes to shove, one of the more subtle change you can make to the car.

Just because a given racing series doesn't operate at that level does not mean it can't be done.

[Andrewsmith112]

Nah, doesn't work well enough. Trust me if we could get away with accelerometers instead of strain gauges, load cells and wheel force transducers we would. Sometimes some manager says we can use accelerometers to scale measured forces from one car to those on a different car. That's one less guy we pay attention to.

Well your thoughts was good can you share some more info about it to clear the concepts. use of load cells will be a better option for you in your project.