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+--- Thread: New PPF Formula? (/showthread.php?tid=3242)
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- JoeP - 05-10-2012
I do this sort of thing all the time for business and manufacturing clients and would be happy to help. I'll PM you with my work eMail so that you can send the spreadsheet. If you want to tweak the underlying mathematics, you will also need clean measures of a diverse sample of cars and their corresponding track results.
Joe P.
- betegh9 - 05-11-2012
trevornaidoo wrote:
Quote:V had a good spreadsheet last year for determining our PPF. My suggestion is to look at that spreadsheet, the PAX formula and add grip, age to the formula.Trevor, don't lrt it get to you. Think of balance, add weight to the end that slips. If it is oversteering into a turn, try to place a bit less brake imput, and accelerate as you turn. Lift a little if the car is understeering.
fyi, I still haven't figured out how to get the most out of my car. After those spins on sunday, I think the car was getting the better of me.
- betegh9 - 05-11-2012
JoeP wrote:
Quote:I do this sort of thing all the time for business and manufacturing clients and would be happy to help. I'll PM you with my work eMail so that you can send the spreadsheet. If you want to tweak the underlying mathematics, you will also need clean measures of a diverse sample of cars and their corresponding track results.Joe, thanks for your attention to help out. NNJR uses a abriviated Parade Competition rules for medium size AX events. They have a large database of Porsches over the years and thus made up the PAX. Here is the raw times by class from the last weekend:
Joe P.
http://autox4u.com/results/2012/nnjr_pca_may6_classes.htm
and the PAX finishes:
http://autox4u.com/results/2012/NNJR_PCA_May6_Porsche_pax.htm
I don't know why, but my friend, Drew wins PAX all the time in his 911sc
hock:The more data you have, the more accurate the PAX is, so following NNJR's may be the way to go.
- arena - 06-05-2012
CarreraSupercharged wrote:
Quote:So your system allote the same weight for each component : 1/3 for weight of car, 1/3 for grip of the tires, and 1/3 for power. Which in reality, for autocross, handling is the most performance enhaning mechanism. This mostly comes from suspension and tires, and a great deal of the weight of the car plays in this equation. Although much less can be attributed to the horsepower of a car when comes to autocrossing. ( A good example is Chuck and Nick's car light weight and low hp). But to dedicate the sme ratio for HP, Grip, and weight, is a mistake in my opinion.Point taken.
This system disproportionatly advantage the cars that sits on the extrem range of each component.
May I ask why do we have to re-invent the wheel,....especially after the season has already started...:?
New PPF system shelved. We can revisit this in the off-season.
- JoeP - 06-06-2012
1) I am not an expert in automotive engineering, but it appears that a formula should normalize power and grip, not use them directly:
(HP/Weight) - This is a good predictor of acceleration. I assembled the attached chart while comparing different options for a DE car. I compared cars I have driven over the years against some available options and milestone racing cars. Although the devil is in the details, I was very surprised at the overall agreement.
(Grip/Weight) - I have no data on this, but I would think that a 235mm wide tire would have mucher higher absolute traction on a Mini than on an M5. -- But, how do you quantify "grip" between different tire compounds?
2) What about Aero? When I look at SCCA participants, some of them have billboard-sized airfoils on them.
- CarreraSupercharged - 06-06-2012
arena wrote:
Quote:CarreraSupercharged wrote:Quote:So your system allote the same weight for each component : 1/3 for weight of car, 1/3 for grip of the tires, and 1/3 for power. Which in reality, for autocross, handling is the most performance enhaning mechanism. This mostly comes from suspension and tires, and a great deal of the weight of the car plays in this equation. Although much less can be attributed to the horsepower of a car when comes to autocrossing. ( A good example is Chuck and Nick's car light weight and low hp). But to dedicate the sme ratio for HP, Grip, and weight, is a mistake in my opinion.Point taken.
This system disproportionatly advantage the cars that sits on the extrem range of each component.
May I ask why do we have to re-invent the wheel,....especially after the season has already started...:?
Wise decision,..
If you still decide to reform the PPF system, be aware that a large data set is much more revealing than just an average of 10-12 drivers/cars and their obvious differences.
Just one more thing on GRIP,.. it is so much more than just fat tires against skinny tires. When comes to grip a skinny tire with proper camber setting may be more effecient than a fat tire set at a 90 degree angle. Suspension geometry play a great deal in grip/traction of the car. Another variable when comes to grip/traction is the use of 2 wheel drive VS. 4 wheel drive.
So in short, there is tons of variables to think about when setting PPF value to a given vehicle.
- arena - 06-11-2012
JoeP wrote:
Quote:1) I am not an expert in automotive engineering, but it appears that a formula should normalize power and grip, not use them directly:
(HP/Weight) - This is a good predictor of acceleration. I assembled the attached chart while comparing different options for a DE car. I compared cars I have driven over the years against some available options and milestone racing cars. Although the devil is in the details, I was very surprised at the overall agreement.
(Grip/Weight) - I have no data on this, but I would think that a 235mm wide tire would have mucher higher absolute traction on a Mini than on an M5. -- But, how do you quantify "grip" between different tire compounds?
2) What about Aero? When I look at SCCA participants, some of them have billboard-sized airfoils on them.
Great stuff. I would love to see a simmilar graph on grip with regards to weight and tire section.
Regarding Aero- AX speeds typically aren't high enough for any aero to have an effect on a street car... Yes people put spoilers on, no I'm no convinced they do anything at 60 mph...
- betegh9 - 06-11-2012
trevornaidoo wrote:
Quote:V had a good spreadsheet last year for determining our PPF. My suggestion is to look at that spreadsheet, the PAX formula and add grip, age to the formula.
fyi, I still haven't figured out how to get the most out of my car. After those spins on sunday, I think the car was getting the better of me.
When you wana lift (because your're scares) squeeze down on the throttle to avoid the spin, adn chase with the steering wheel.
Trevor, at the next AX, I will take your car and get a feel for it and let you know what I think you are doing or what remedies you need. the solution may be just changing some driving habits.
- betegh9 - 06-11-2012
CarreraSupercharged wrote:
Quote:arena wrote:I agreee with much of this EXCEPT: 4 wheel drive vs. 2 wheel. 4 wheel drive units have lots of additional weight, so their only advantage is really under adverse weather conditions like snow and rain. Although 4 wheel drive has come a long way, only the high HP and modified cars rule in the dry with a GOOD DRIVER.Quote:CarreraSupercharged wrote:Quote:So your system allote the same weight for each component : 1/3 for weight of car, 1/3 for grip of the tires, and 1/3 for power. Which in reality, for autocross, handling is the most performance enhaning mechanism. This mostly comes from suspension and tires, and a great deal of the weight of the car plays in this equation. Although much less can be attributed to the horsepower of a car when comes to autocrossing. ( A good example is Chuck and Nick's car light weight and low hp). But to dedicate the sme ratio for HP, Grip, and weight, is a mistake in my opinion.Point taken.
This system disproportionatly advantage the cars that sits on the extrem range of each component.
May I ask why do we have to re-invent the wheel,....especially after the season has already started...:?
Wise decision,..
If you still decide to reform the PPF system, be aware that a large data set is much more revealing than just an average of 10-12 drivers/cars and their obvious differences.
Just one more thing on GRIP,.. it is so much more than just fat tires against skinny tires. When comes to grip a skinny tire with proper camber setting may be more effecient than a fat tire set at a 90 degree angle. Suspension geometry play a great deal in grip/traction of the car. Another variable when comes to grip/traction is the use of 2 wheel drive VS. 4 wheel drive.
So in short, there is tons of variables to think about when setting PPF value to a given vehicle.