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well, at least that "sounds" more scientific!

MJones

Tire slip angle (°) and PSM Slip angle (%) are totaly different....

a selected wheel or several selected wheels are braked in a controlled manner in order to counteract a rise of the deviation of the actual yaw velocity detected by way of a yaw velocity sensor from a desired yaw velocity estimated from the steering angle and the vehicle speed. The system intervenes when the deviation is greater than a certain control value.

Deviation = % PSM Slip Angle

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not according to jack miller
psm basically determines the slip angle of the front and rear
tires, or more simply, when the car is not going where the steering wheel
is pointed.
psm allows approximately seven percent slip angle before intervening.

the angular difference between the direction the contact is pointing and that
of the wheel itself is called its slip angle.
the slip plane lies horizontal and extends perpendicular to the normal plane (90 degrees)

jeff
chief of rocket science

B-Line

Unless things have changed at Skip, which I do not belive they have. In the Intro to Racing, 3 day school, you drive a Formula Dodge (not the R/T) but a intro car. These cars do not have snycro's hence, you must double clutch.. (or monster blip) but they don't like that...

B

B-Line

Are you talking about the driving school or racing school? Cause I drove one of those skip barber cars into the BIG BLUE WALL at Daytona at about 70mph and smacked the **** out of the car. Not only was there no charge, they strapped me right back into a new vehicle and I was off and running. NO CHARGE..

I believe once you upgrade to the 2 day advanced course (R/T 2000) you have about a $3000 deductible if you wreck. However, the Skip Barber cars are usually not that expensive to fix. It's not like repairing a 997.

I also understand that your deductible changes based on your "rate" as a driver. If you crash a car every time you go to SKIP, they increase your deductible.

B

BiggerTwin

I am talking about the high performance driving school and it was a 997

Alan

ronmart

I'll confess, I have some Top Gear / Fifth Gear test drive moments intentionally sometime where I'm trying to break free and get some drift. Yes, drifiting isn't logical for good lap times, but it is freakin fun to do (even if you do lose some rubber ).

I don't plan on driving that way out on the track though. Doing it on an autocross where you are going < 50 mph is one thing, but that just doesn't fly when you are on the track. The consequences on the autocross is that you spin out and take out some cones, but no harm done. It's your car and possibly bodily injury on the track, so know that while I like to have fun I'm not a complete dolt!

ronmart

This is true. I saw this myself at the skills day but then again being on wet VHT makes that pretty easy to do! However, I got tremendous understeer with my car under those conditions. Turning off the PSM allowed me to get more oversteer and reduce the understeer for a much better skidpad circle.

It also allowed me to have fun giving it a good blast and bringing the car around as shown in the video I posted.

allegretto

I'm still unclear. A tire can actually only "roll" of course in the plane of its wheel no matter what. It can "travel" or "translate" in a different plane of course and that's what understeer or oversteer or drift are about.

What am I missing?

I just dont understand % as units in this equation. I would consider that it refers more properly to an "index" or "quotent" of some fraction or product (as %-ages are in math) but I dont understand the derivation...

ronmart

You need to buy this book:

http://www.speed-secrets.com/racing_publications.html

It'll tell you everything you need to know and teach you quite a bit about driving too. It is a short read and not horribly expensive.

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a 100% slip angle is perpendicular to the normal plane (90 degrees).
that gives you a point of reference to measure it as a percentage.
why the report it as a percentage instead of degrees, being that it is an angle,
i have no idea!

allegretto

so the conversion is % slip - slip angle X 10/9 ?

OCBen

I think this will help, Herman.

Imagine a model car's wheel and imagine a gummy tire mounted on this wheel with a straight axle attached and the other wheel left off. Now imagine pressing down on the axle to firmly plant the tire and then move the axle angularly forward and back while the gummy tire is still planted without slipping. You'll clearly see then that the plane of the wheel, which is rotating, is obviously no longer coplanar with the tire, which is firmly planted.

allegretto

Ben, yes thanks, I do understand that part. It describes the slip angle. Of course we both realize that the tire will not travel in the direction it is pointing because it will strip away from the wheel in one revolution. Instead it translates in some arc between the two directions of the axes (tire and wheel).

But that is not my question directly. My question is; what is the significance of slip angle as a %-age. As you know, a %-age is a ratio. I just wanted to understand the components of the ratio. I would think slip angle would be presented in degrees since that describes the phenomena we are speaking of. However some folks express it as a %-age and I wanted to understand the derivation. Not exactly the stuff of advanced math, just the simple case will suffice.

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if 0 degrees is 0% and 90 degrees is 100%
10 degrees would be 10/90 = 11.11%
yes, your formula works

porsche says 7% before psm intervention.
.07 * 90 = 6.3 degrees before intervention