Developing a Proper Suspension Model
Although this effort may seem worthless to some 86ers, I'd like to start a thread that compiles known data about the stock vehicle and uses this to develop a virtual model of the car.
Available programs:
The goal would be to analyze the stock package and look at how various aftermarket options would perform. Since each person has a different goal (autocross, street, rally, drift, etc) their interest will push the project in that direction. I'll be pushing the limits of SCCA street tire. The Facts (in 'Murika units and Sissy units): Curb Weight (FR-S, no spare/tools/mats, minimal gas) = 2645 lbs or 1200 kg LINK Corner Weights: LF = 823 lbs (701 ideal) or 373.3 kg (318.0 ideal) or 3660.9 N (3118.2 ideal) RF = 684 lbs (701 ideal) or 310.3 kg (318.0 ideal) or 3042.6 N (3118.2 ideal) LR = 513 lbs (622 ideal) or 232.7 kg (282.1 ideal) or 2281.9 N (2766.8 ideal) RR = 625 lbs (622 ideal) or 283.5 kg (282.1 ideal) or 2780.1 N (2766.8 ideal)Unsprung Weight: (best guess - LINK ) 83 lbs or 37.6 kg or 369.2 N per cornerSprung Weight: LF = 740 lbs (618 ideal) or 335.7 kg (280.4 ideal) or 3291.7 N (2749 ideal) RF = 601 lbs (618 ideal) or 272.4 kg (280.4 ideal) or 2673.4 N (2749 ideal) LR = 430 lbs (539 ideal) or 195.1 kg (244.5 ideal) or 1912.7 N (2397.6 ideal) RR = 542 lbs (539 ideal) or 245.9 kg (244.5 ideal) or 2410.9 N (2397.6 ideal)Dampers = SHOWA non-inverted, twin-tube, low-pressure Nitrogen, conventional strut Shock Dyno: https://scontent-a.xx.fbcdn.net/hpho...01415143_o.jpg Suspension Spring Rates: LINK Front = 131 lbs/in or or 22970 N/m Rear = 211 lbs/in or 36998 N/mhttp://philbedard.com/pics/brzvsfrs.jpg Spring Dimensions: Link to Bordom.is.me's post FRONT: REAR:Tire Spring Rates: (FSAE guru states 350 N/mm for passenger tires at passenger pressures. I concur.) 30 psi = 6500 lbs/in or 114000 kg/m 45 psi = ~10000 lbs/in or 175000 kg/mSway Bar Spring Rate: Front = 141 lbs/in or 2467 kg/mEffective Wheel Rate (in roll, including sway bar): Front (FR-S) = 373 lbs/in or 6528 kg/m (70% from sway bar) Rear (BRZ) = 200 lbs/in or 3500 kg/m (39% from sway bar)Caster Angle: Link Front = -5.937 degRoll Center Height: Link Front = 3.140" (stock height) --> ground plane (1" of compression)Spring Angle: Front = 15.5 degSpring Motion Ratio: Front = 1.050 (2.5" compression) --> 0.997 (1.5" compression) --> 0.95 (OEM height) LinkSway Bar Motion Ratio: Front = 0.92Natural Frequency (in ride): Front (FR-S) = 1.24 Hz Rear (FR-S) = 1.54 HzNatural Frequency (in roll): Front (FR-S) = 2.27 Hz Rear (FR-S) = 1.95 HzTire Info: 215/45-17 Michelin Primacy HP LINK Section Width = 8.46 in or 0.215 m Contact Width = 7.5 in or 0.1905 m via TireRack measurement Contact Length (at 60 mph and stock pressure) = ~5.71 in or 0.145 m Overall Diameter = 24.7 in or 0.6274 m Load Rating = 87W SL (168 mph or or 270 kph) UTQG = 240 A A (hmm... A?) Max Load (at rated pressure) = 1201 lbs or 545 kg Max Rated Pressure = 51 psi Tread Depth = 9.5/32 in Material = Green X - Low Rolling ResistanceWheel Info: Wheel Diameter = 17 in or 0.432 m Wheel Width = 7 in or 0.178 m Wheel Offset = +48 mm or 1.89 in or 0.048 mTrack Width: LINK Front = 59.8 in or 1.51m Rear = 60.6 in or 1.54mRoll Bar Diameter: LINK Front = 0.71 in or 0.018m Rear = 0.55 in or 0.014mCenter of Gravity Height = 18.1 in or 0.46 m LINK Roll Center Height: Front = 2.1 in Rear = 3.8 inWheelbase = 101.2 in or 2.5705 m LINK Suspension Travel: Bump Travel = 2.5 in or 0.1 m Rebound Travel = 3.5 in or 0.15 m Max Roll Angle = +/- 2.3 deg Max Pitch Angle = 0.9 deg (braking) Roll Resistance on Front: 61% Braking on Front = 60% Anti-dive Under Braking: 5% (front) Anti-lift Under Braking: 196% (rear) Anti-squat Under Acceleration: 64% (rear)Steering Ratio: 14.3 (on center) - 14.4 (at 90 deg) Distance (axial) between lower strut bolts = 2.4" (or 60.5 mm) Thickness of lower flange = 1 in (or 25.4 mm) Distance (radial) from strut center to lower bolt = 2.4 in (or 60.7 mm) Distance (axial) from AST's lower bolt to hat mount = 15.4 in (or 392 mm) Upper strut thread: - AST = M12x1.25-25, with 1 mm of thread relief, 5 mm long (for camber plate) - KW = M14x1.5-30, with 0 mm of thread relief, 10 mm long (for camber plate) Length of AST's spring = 7.1 in (or 181 mm) Distance (axial) from lower bolt to sway bar mount = 4.5 in (or 115 mm) Distance (radial) from strut axis to sway bar mount = 1.97 in (or 50 mm) Diameter of sway bar mount hole = 0.4 in (or 10.2 mm) Here's a cool MATLAB function that helps you simulate shock dyno graphs: function y=critdamp(cwlbs,srppi,spmr,shmr,lsd,knee,hsd) %cwlbs=corner weight, lbs minus unsprung for more accuracy %srppi=spring rate, lbs per inch %spmr=spring motion ratio %shmr=shock motion ratio %lsd=low speed damping, percentage of critical %hsd=high speed damping, percentage of critical %knee=location of knee, in inch per second lbf2n=4.448; % 1 lbf = 4.448 newtons m2i=39.37; % 1 meter = 39.37 inch p2kg=0.4536; % 1 lb=0.453 kg if (spmr>1)+(shmr>1) disp('Motion ratios must be less than 1, but I''ll convert it for you') spmr=1/spmr;shmr=1/shmr; end wheelratestandard=srppi*spmr^2 wheelratemetric=wheelratestandard*lbf2n*m2i cd=2*sqrt(wheelratemetric*cwlbs*p2kg)/lbf2n/m2i/shmr^2 vel=(0:0.1:20); damp=lsd*cd*(0:0.1:knee); hispeed=damp(end)+(0:0.1:20-knee)*cd*hsd; damp=[damp hispeed(2:end)]; plot(vel,damp,'r','linewidth',2,'displayname',['LS:' num2str(lsd*100) '% Knee:' num2str(knee) ' ips HS:' num2str(hsd*100) '%']) legend('off');legend('show','location','east') Still looking for accurate suspension geometry coordinates (X,Y,Z). The current "best guess" is housed in a Google Docs spreadsheet: LINK Special Thanks to MLA163, Wepeel, and Boredom.is.me for contributing measurements and discussion. |
Saved for pretty pictures!
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The stock front swaybar is 18mm, rear is 14mm.
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The info I found from a Subaru forum suggested 17 and 13. Probably just difference in calipers and paint. Will change anyways.
How about a teaser, you say? Got the geometry style in... but no points or parameters have been entered. http://www.ft86club.com/forums/pictu...pictureid=3277 |
Updates made to suspension parameters, but not specific coordinates. Can I get a second set of eyes on this?
Requires peer review: Bump Travel = 4 in or 0.1 m Rebound Travel = 6 in or 0.15 m Max Roll Angle = 6 deg Braking on Front = 60% Tire Rolling Radius = 9 in or 0.225 m Still looking for suspension geometry coordinates (X,Y,Z), if anyone has logged them |
Right on brother.
I got 18mm / 14mm sways from measuring. I don't want to scuff up the coating to find pure steel, but would 1mm of powder coat be normal? |
I misspoke. Powdercoating is generally a couple mils thick, which would only give you 0.1 mm or so, even considering both sides and caliper inaccuracy.
Turns out that 3" bump, 4" rebound, 5 deg roll is more appropriate (for now). Front View http://www.ft86club.com/forums/pictu...pictureid=3282 Driver's Side View http://www.ft86club.com/forums/pictu...pictureid=3283 Top View (Passenger Side) http://www.ft86club.com/forums/pictu...pictureid=3281 Values are all still "eyeballed" from the pictures and general information. Next, the rear suspension~! |
ooohhhhh...
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Mac-Strut motion ratio STILL isn't 1.00... if you are going to bother being accurate, be accurate. ;)
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I've got an excel sheet I made as part of my senior project for my undergrad... I'll dig it up and run some of these numbers through and see what I get... We need an actual front motion ration though hehe
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According to racecomp, the front motion ratio is pretty darn close to 1. I'm not sure which side of one it sides on though.
-Acree |
:scared0012: Airline food, I mean come on...
You're correct SCCABRZ192, it will be slightly less than one. What value that is... I couldn't tell you without some coordinates or parts in front of me. This is not a traditional calculation for a wishbone, but the closest that I can imagine is to consider the knuckle and it's connections to be rigid. So, something like this: Motion Ratio = --------------------------------------------------distance from lower wishbone pivot axis to strut mount Maybe 0.9? The good news is that a kinematic solver doesn't care about the parameter of motion ratio, it just solves a bunch of free body diagrams and spits out positions.distance from lower wishbone pivot axis to spindle center If you have more precise coordinates, I'd gladly put them in. :D |
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