Race Sim Central Forums - Alpine's Pacejka data

10-10-2002, 21:46	View Warnings #1
Seamus Super Moderator Join Date: May 2002 vCash: 7500	Alpine's Pacejka data A couple of months ago, Alpine posted some pacejka coefficients and other tyre information in the High Gear Racer Physics forum (this thread). I've copied over the meaty bits of the thread and edited out the chat. This data is apparently from a Michelin tyre test rig, and Alpine says that the tests were done 12 years ago. First up, a series of measurements that are NOT pacejka coefficients but which are interesting and relevant..... SI units are used throughout, and the italics indicate the values for which I don't have a clue what's being measured. The unknown words (caou, etc) are in French "shorthand" Code: 205/45 ZR 16, pressure=2 bars, load=2500 N ?? 2.2 8.3 0.00951 Free radius 0.295 Radius under load 0.287 Contact patch width 0.198 275 Contact patch length 0.0986 50 Vertical stiffness 263000 Vertical force (load) 2500 Long. carc stiffness 200000 Lat. carc stiffness 110000 11000 1.20 Tors. carc stiffness 10000000 Carros(?) carc stiffness 0.36 Long. caou(?) stiffness 105000 Lat. caou(?) stiffness 57193 1650000 8 Long. static friction 1.203 4.4 0.32 Lat. static friction 1.16 1.1 0.30 Rolling effort 1900 Code: 195/60 VR 15, Pressure=2.2 Bars, Load=3000 N ?? 2.0 11.11 0.0168 Free radius 0.3085 Radius under load 0.301 Contact patch width 0.129 212.7 Contact patch length 0.0640 38 Vertical stiffness 179000 39583.3 Vertical force (load) 3000 Long. carc stiffness 200000 Lat. carc stiffness 93000 12291.5 1.383 Tors. carc stiffness 10000000 Carros(?) carc stiffness 1.146 0.098 Long. caou(?) stiffness 105000 Lat. caou(?) stiffness 58155 500000 -2.75 Long. static friction 1.20 4.4 0.32 0.0037 Lat. static friction 1.36 1.11 0.32 0.0037 Rolling effort 1950 Code: 195/60 VR 15, Pressure=2.2 Bars, Load=4000 N ?? 2.0 11.11 0.0217 Free radius 0.3085 Radius under load 0.301 Contact patch width 0.134 189 Contact patch length 0.081 28.6 Vertical stiffness 184000 39583.3 Vertical force (load) 4000 Long. carc stiffness 200000 Lat. carc stiffness 94000 12291.5 1.400 Tors. carc stiffness 10000000 Carros(?) carc stiffness 0.895 0.098 Long. caou(?) stiffness 105000 Lat. caou(?) stiffness 66750 500000 -3.00 Long. static friction 1.20 4.4 0.32 0.0037 Lat. static friction 1.36 1.11 0.32 0.0037 Rolling effort 1950 Code: 255/45 VR 15, 2.2 bars, 4000 N - rear tyre of Alpine V6 turbo ?? 2.2 8.3 0.01096 Free radius 0.309 Radius under load 0.296 Contact patch width 0.211 373 Contact patch length 0.0601 134 Vertical stiffness 365000 Vertical force (load) 4000 Long. carc stiffness 290000 Lat. carc stiffness 110000 11000 1.20 Tors. carc stiffness 20000000 Carros(?) carc stiffness 2.00 Long. caou(?) stiffness 105000 Lat. caou(?) stiffness 73000 210000 0.40 Long. static friction 1.203 4.4 0.32 Lat. static friction 1.36 1.1 0.30 Rolling effort 5000 OK and now the bit that you're all keen for, the Pacejka coefficients themselves Note that not all of these sets of coefficients are complete - some have several coefficients zeroed out and most have the data rounded slightly... but there's probably not enough rounding to affect the in-game feel. Code: 205/45 ZR 16 on 6"1/2 rim, 2.5 bar - note no longitudinal values! ; Lateral force a0=1 a1=-106 a2=1629 a3=1843 a4=9.4 a5=0.013 a6=-0.336 a7=1.14 a8=0.019 a9=-0.019 a10=-0.18 a111=-20.7 a112=-0.021 a12=0.48 a13=12.2 ; Longitudinal force b0=0.000 b1=0.000 b2=0.000 b3=0.000 b4=0.000 b5=0.000 b6=0.000 b7=0.000 b8=0.000 b9=0.000 b10=0.000 ; Aligning moment c0=3 c1=-2.9 c2=-0.7 c3=0.24 c4=-2.52 c5=-0.36 c6=0.0037 c7=-0.026 c8=0.19 c9=-0.043 c10=0.14 c11=0.027 c12=0.038 c13=-0.66 c14=0.12 c15=-1.22 c16=-0.9 c17=-0.8 Code: 225/45 ZR 17 on 7" rim, 2.4 bar ; Lateral force a0=1.6 a1=-38 a2=1201 a3=1914 a4=8.7 a5=0.014 a6=-0.24 a7=1.0 a8=-0.03 a9=-0.0013 a10=-0.15 a111=-8.5 a112=-0.29 a12=17.8 a13=-2.4 ; Longitudinal force b0=1.7 b1=-80 b2=1571 b3=23.3 b4=300 b5=0 b6=0.0068 b7=0.055 b8=-0.024 b9=0.014 b10=0.26 b11=-86 b12=350 ; Aligning moment c0=2.3 c1=-3.8 c2=-3.14 c3=-1.16 c4=-7.2 c5=0.0 c6=0.0 c7=0.044 c8=-0.58 c9=0.18 c10=0.043 c11=0.048 c12=-0.0035 c13=-0.18 c14=0.14 c15=-1.029 c16=0.27 c17=-1.1 Code: 195/60 HR 15 on 6"1/2 rim at 2.1 bar ; Lateral force a0=1.3 a1=-49 a2=1216 a3=1632 a4=11 a5=0.006 a6=-0.04 a7=-0.4 a8=0.003 a9=-0.002 a10=0.16 a111=-11 a112=0.045 a12=0.17 a13=-23.5 ; Longitudinal force b0=1.57 b1=-48 b2=1338 b3=6.8 b4=444 b5=0 b6=0.0034 b7=-0.008 b8=0.66 b9=0 b10=0 b11=0 b12=0 ; Aligning moment c0=2.46 c1=-2.77 c2=-2.9 c3=-0 c4=-3.6 c5=-0.1 c6=0.0004 c7=0.22 c8=-2.31 c9=3.87 c10=0.0007 c11=-0.05 c12=-0.006 c13=0.33 c14=-0.04 c15=-0.4 c16=0.092 c17=0.0114 Code: 225/60 HR 16 ; Lateral force a0=1.9 a1=-41 a2=1210 a3=2180 a4=10 a5=0.014 a6=-0.023 a7=0.67 a8=-0.051 a9=-0.018 a10=-0.06 a111=-2.35 a112=-0.37 a12=4.3 a13=-14.9 ; Longitudinal force b0=1.5 b1=-5.2 b2=1190 b3=26.7 b4=255 b5=0 b6=-0.000093 b7=0.05 b8=0.49 b9=-0.007 b10=-0.23 b11=141 b12=-206 ; Aligning moment c0=2.53 c1=-3. c2=-6.6 c3=-0.56 c4=-8.9 c5=0 c6=0 c7=0.016 c8=-0.39 c9=0.35 c10=0.014 c11=-0.014 c12=-0.006 c13=-0.15 c14=0.023 c15=-0.89 c16=0.025 c17=-0.4 Here's how to read a tyre description: For a tyre such as a "225/45 ZR 16".... - 225 is the width of the tyre in millimeters. - 45 is a percentage meaning that the tyre sidewall height is 45% of the tyre width. So in this case, the sidewall height will be 101 millimeters (on the radius, not the diameter). - SR, HR, VR or ZR is the maximum speed rating of the tyre... SR = 180 Km/h, HR = 210 Km/h, VR=240 Km/h, ZR=over 240 Km/h - 16 is the wheel diameter in inches. From this you can calculate the tyre's radius (as need by Racer).... for this tyre the wheel radius is 8 inches = 203 mm, and you add the 101 mm sidewall to get a overall radius of 304 mm or 0.304 m. (This is actually the unloaded radius not the rolling radius). Alpine's comments on the tyres for which he has supplied data: These are all road car tyres. Tyres are not made specially for the front or rear. - 205/45 ZR 16 and 225/45 ZR 17 are sports tires. - 195/60 HR 15 and 225/60 HR 16 are all season tires. The Pacejka coefficient descriptions and units: Code: Shape factor ........................................... A0 Load infl. on lat. friction coeff (1000)... (1/kN) .... A1 Lateral friction coefficient at load = 0 (1000) ....... A2 Maximum stiffness ........................ (N/deg) ..... A3 Load at maximum stiffness ................ (kN) ........ A4 Camber infiuence on stiffness ............ (%/deg/100) . A5 Curvature change with load ............................. A6 Curvature at load = 0 .................................. A7 Horizontal shift because of camber ........(deg/deg).... A8 Load influence on horizontal shift ........(deg/kN)..... A9 Horizontal shift at load = 0 ..............(deg)........ A10 Camber influence on vertical shift ........(N/deg/kN)... A111 Camber influence on vertical shift ........(N/deg/kN*2) A112 Load influence on vertical shift ..........(N/kN)....... A12 Vertical shift at load = 0 ................(N).......... A13 Shape factor ........................................... B0 Load infl. on long. friction coeff (1000)... (1/kN) ... B1 Longitudinal friction coefficient at load = 0 (1000)... B2 Curvature factor of stiffness ............ (N/%/kN2) . B3 Change of stiffness with load at load = 0 (N/%/kN) .... B4 Change of progressivity of stiffness/load (1/kN) ...... B5 Curvature change with load ............................. B6 Curvature change with load ............................. B7 Curvature at load = 0 .................................. B8 Load influence on horizontal shift ....... (%/kN) ...... B9 Horizontal shift at load = 0 ............. (%) ......... B10 Load influence on vertical shift ......... (N/kN) ...... B11 Vertical shift at load = 0 ............... (N) ......... B12 Shape factor ........................................... C0 Load influence of peak value ............ (Nm/kN2) ... C1 Load influence of peak value ............ (Nm/kN) ...... C2 Curvature factor of stiffness ........... (Nm/deg/kN2) C3 Change of stiffness with load at load = 0 (Nm/deg/kN) .. C4 Change of progressivity of stiffness/load (1/kN) ....... C5 Camber influence on stiffness ........... (%/deg/100) .. C6 Curvature change with load ............................. C7 Curvature change with load ............................. C8 Curvature at load = 0 .................................. C9 Camber influence of stiffness .......................... C10 Camber influence on horizontal shift......(deg/deg)..... C11 Load influence on horizontal shift........(deg/kN)...... C12 Horizontal shift at load = 0..............(deg)......... C13 Camber influence on vertical shift........(Nm/deg/kN2) C14 Camber influence on vertical shift........(Nm/deg/kN)... C15 Load influence on vertical shift..........(Nm/kN)....... C16 Vertical shift at load = 0................(Nm).......... C17 Alpine*: Thank you very much, the Racer community is very grateful! If anyone has any comments, corrections, etc, please post away!

10-10-2002, 21:53	View Warnings #2
cubits Section Owner Join Date: Nov 2001 Location: Australia Age: 21 vCash: 7500	Mucho Gracias Signor Seamus.

10-10-2002, 22:12	View Warnings #3
Frank N. Oreskov Registered Join Date: Jul 2002 vCash: 7500	Seamus this thread deserves an A+, great stuff and beautifully edied so it is so easy to overlook. And to give a purpose of this post, is it possible to make the 205/45-16 tire values complete? This is the exact tire I need for both my own cars, the 206 and the Orion RS. Frank N. O.

12-10-2002, 03:32	View Warnings #4
Niels_at_home Registered Join Date: Aug 2001 Location: Netherlands Age: 26 vCash: 7500	Can't wait to use these tyres on Beta7 soon Since pictures speak thousands of words, here's screenies and pretty closely guessed 'optimal slip angle / slip ratio' needed in the car.ini As Ruud often mentioned, you need to enter the optimal values.. Racer probably refers to the default car.ini for these 2 values when you don't use them in your ini, and thats prolly not going to do any good to the car handling see attatched pic (if it attatches..) nope can't attatch pics :/ http://geocities.com/n_heusink/tyres.gif then copy paste url in a newly opened IE window to make it work.. sigh.. why can't i attatch this few kB worth of gif! Niels

12-10-2002, 04:04	View Warnings #5
Seamus Super Moderator Join Date: May 2002 vCash: 7500	(Niel's pic as linked in the post above) Last edited by Seamus : 19-10-2002 at 00:46.

12-10-2002, 06:45	View Warnings #6
cubits Section Owner Join Date: Nov 2001 Location: Australia Age: 21 vCash: 7500	I thought the peak values were just used for tyre squeal and smoke.

12-10-2002, 11:39

View Warnings #7

Frank H

Section Owner

Join Date: Jul 2001

Location: Lulea, Sweden

Age: 26

vCash: 4014

Quote:

Originally posted by cubits
I thought the peak values were just used for tyre squeal and smoke.

Nopes, it does affect those, but the handling on my AC really became different when I altered the optimal angles/ratios. This is due to the reason that racer uses the "Gregor Veble's combined Pacejka" method for getting the appropiate values.

At least this is how I have understood it.

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12-10-2002, 12:14	View Warnings #8
happyken Registered Join Date: Sep 2002 Location: Paris, France vCash: 7500	http://www.racer.nl/reference/pacejka.htm I think all other links available to pacejka science courses (if this exists) would be usefull. It's very difficult to understand the signifiance of certain values (what is exactly the signification of slip ratio etc..) specially if english is'nt your mother tongue, and if you're not a physics graduate. Pacejka is the major part of ini building, so i believe it's the part that needs the most to be explained, even if it's difficult. The Kankris explantion of pacejka was a very nice example of Pacejka pedagogy, but now it's incomplete on camber values and other. For example waht's the exact effect of the a6 value, "curvature change with load"?

12-10-2002, 15:43	View Warnings #9
cubits Section Owner Join Date: Nov 2001 Location: Australia Age: 21 vCash: 7500	Aaah, no, i see now. I didnt think it was using veble's model, but that it was an option. Cool, theres something that could help my ini's. Edit: the best way to learn the effects of pacejka is to take a nice curve (alpines tyres for example), then alter a number, and see how its affected by load (up the newtons force) or camber. You will see how the shape flattens/steepens with load with that setting, changing the peak value, and the falloff. Last edited by cubits : 12-10-2002 at 15:47.

12-10-2002, 20:29

View Warnings #10

happyken

Registered

Join Date: Sep 2002

Location: Paris, France

vCash: 7500

Quote:

Originally posted by cubits
Aaah, no, i see now.

I didnt think it was using veble's model, but that it was an option. Cool, theres something that could help my ini's.

Edit: the best way to learn the effects of pacejka is to take a nice curve (alpines tyres for example), then alter a number, and see how its affected by load (up the newtons force) or camber. You will see how the shape flattens/steepens with load with that setting, changing the peak value, and the falloff.

This is the typical trial and error method, that helped me to understand some parts of pacejka. But it has its limits, some effects are difficult to analyse just by playing around with the car.
We need sometimes something more precise.

12-10-2002, 22:49	View Warnings #11
CreeP Registered Join Date: Sep 2002 Location: Montreal vCash: 7500	'caou' would be the shorthand for caoutchouc, 'rubber' in french.

13-10-2002, 02:52	View Warnings #12
Mr Whippy Registered Join Date: Sep 2002 Location: United Kingdom Age: 25 vCash: 7500	Is all we feel with force feedback wheels the aligning moment of pacejka? A force feedback wheel helps a great deal, driving and seeing what pacejka has done, esp in the aligning moment values is much better than it was with a non FF... Hmmmmmmm

19-10-2002, 00:45	View Warnings #13
Seamus Super Moderator Join Date: May 2002 vCash: 7500	I just stickied this one because someone asked me to. Thanks again Alpine for the data.

19-10-2002, 03:43	View Warnings #14
Ryan T Moderator Join Date: Sep 2002 Location: United States vCash: 7500	Thanks for reposting this stuff. I had missed the definitions before. That's great. __________________ My Website 1967 GT500 1967 GT40 1968 Barracuda 1970 GTV 1750

16-11-2002, 19:49	View Warnings #15
Mr Whippy Registered Join Date: Sep 2002 Location: United Kingdom Age: 25 vCash: 7500	Just wondering if we are ever gonna be able to get the pacejka coefficients we need... For instance, if Alpine had never provided this, we would be much further back with decent handling cars then we are now... I'm really starting to think, is there much point trying to make any car.ini's representing cars with any other tyres than those stated? All we are gonna do is make things up, and just make things handle really badly as a consequence! I think we should either really be determined to get some decent data (slicks, hr vr zr rated road tyres, winter tyres etc) for various sizes... As it is, we can't even make a good guess what a 345/35 ZR18 curve will look like! Which is a problem since a Zonda has them on it's rear! Bah, what does LFS use, they seem to have good tyres!

18-11-2002, 00:37	View Warnings #16
Deyan Registered Join Date: Apr 2001 Location: Pasadena/California Age: 19 vCash: 7500	yeah, I already mentioned, that maybe we should switch to different method of tire model, its just too damn hard to get pacejka informantion... LFS aren't using pacejka, and they have damn good tire model...

18-11-2002, 01:10	View Warnings #17
Mr Whippy Registered Join Date: Sep 2002 Location: United Kingdom Age: 25 vCash: 7500	Well, after a little conversation with Mr Seamus, I decided to change my mind back to Pacejka! In the end of the day it's just another model to simulate a tyre, and pacejka is a pretty good one! The main problem is that we have to get to grips with the numbers to use for the coefficients... Some are common sense, and can be judged while driving, "do they FEEL right" etc... Main problem is that some need a guide, like magnitude, or trend, so you can make good guesses, and then tweak from those! Alpines data was invaluable for that, if he'd just given say 3 tyres that were all ZR, then a better trend could have been noticed! Also, the fact some coefficients were missing, like B5, which is quite important, means that we can only use wild guesses for those, instead of having a real-life value avaliable, it may be 10x bigger or smaller in magnitude than we are thinking/guessing! But as it is, it describes tyres behaviour in a very accurate and comprehensive way, we just need more time, more testing and trying out, and more looking for real data for evaluation and analysis! I think pacejka in Racer has come a long way in 6 months, and hopefully when Beta5 is in it's final release, the cars will handle better too, so we can focus on Pacejka even more! Also, just playing in the Pacejka player and seeing how things change, especially with load, is a very important thing to do, so we can understand the actual effects a tyre undergoes while being driven around... I'm sure it helps make a car.ini if you know more how the tyres work!!! Byeeee

18-11-2002, 01:19	View Warnings #18
Deyan Registered Join Date: Apr 2001 Location: Pasadena/California Age: 19 vCash: 7500	too bad not all of us have Murcielagos to see if it feels right

18-11-2002, 01:26	View Warnings #19
cubits Section Owner Join Date: Nov 2001 Location: Australia Age: 21 vCash: 7500	Yeah...but at least we'd have plenty of data on fiestas

18-11-2002, 02:14	View Warnings #20
Mr Whippy Registered Join Date: Sep 2002 Location: United Kingdom Age: 25 vCash: 7500	Well, if we can make a few road cars feel right, even just average ones, it means that Racer is getting pretty good! So all it would hopefully take then is practice to make a Murcielago that feels good.. Just make it feel loooaads better than a road car! Simple really, make a fiesta that FEELS like a fiesta (test drivers avaliable)... Then, try make it handle better and or FEEL better... That is then a Fiesta RS turbo Make it feel better again... honda s2000 make one that feels better still... ferrari 360 better.... lambo better... etc etc So as long as better cars FEEL better than the ones that are not meant to be as good, then it'll be OK I suppose.... Then again, maybe not!!!

20-11-2002, 00:53	View Warnings #21
Czapi Registered Join Date: Sep 2002 Location: Poland Age: 25 vCash: 7500	Maybe not. There are many cars we don't know how they handle. There's rather no possibility of checking that out. Maybe you could have a drive of a Ferrari... So what? You'd need at least a year to know how it handles... Now I'd really like that! But I don't think a Ferrari owner will just come to me and say "Michal, take this Ferrari, check it out for a year, so you can make the car handle better in Racer". So the FEEL gives us no good aproximation, and Racer is supposed to be a simulation which means really good aproximation... How about a small blackmail? Maybe if we told tire companies that we do have pacejka values of the Michelins, why shouldn't they give us their tires for comparision? Worth a try, still I don't think they'd even reply. __________________ Michal 'Czapi' Czapracki Projects: K-Shell Barchetta - held BMW E36 318ti - 80% done, beta released... BMW E46 325ti - ext done, willing to give it away! Audi A6 Avant C4 - Alpha released

20-11-2002, 09:24	View Warnings #22
happyken Registered Join Date: Sep 2002 Location: Paris, France vCash: 7500	Damned Geocities, the pic of optimal slip ratio and angle does'nt appear anymore. It would be nice to attach it to this forum...

22-11-2002, 21:32

View Warnings #23

Kirk House

Section Owner

Join Date: May 2001

Location: United States

vCash: 4000

Here it is

Attached Images

tyres2.gif (15.6 KB, 734 views)

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22-11-2002, 23:17	View Warnings #24
Mr Whippy Registered Join Date: Sep 2002 Location: United Kingdom Age: 25 vCash: 7500	I really don't think a picture can tell many words... These pacejka don't have b5 or c5 coefficients, and these are quite important variables as load changes, just like load sensitivity (a1 and b1)... If you use carlab to work out the load per wheel, then use that in carlab, it changes those peak slip ratios/angles quite alot! I really think all those varaibles should be done on the run, since when you accelerate, those loads can halve, and double under braking, and the slip ratio/angle can change by anything, and having them fixed is a bit silly really! Hmmmmmmmmmmmmmm...

22-11-2002, 23:31	View Warnings #25
happyken Registered Join Date: Sep 2002 Location: Paris, France vCash: 7500	Hey Whippy, you're certainly true, but truth is that pacejka behaves in a much more realistic way with those values. Certainly not perfect but better. There is a word in France that says= "Better is the worst enemy of good" Racer is certainly not perfect, but gets better with every betas.. Sometime it will be perfect BTW thanks, Kirk.

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