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anti roll bar stiffness calculation

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Puhn's formula Formula for sway bar stiffness of a solid steel bar 500,000 D^4 K (lbs/in) = ----- … To calculate the stiffness of anti-roll bar Finite Element software ANSYS is used. A sway bar increases the suspension's roll stiffness—its resistance to roll in turns—independent of its spring rate in the vertical direction. The stiffness of anti -roll bar can be calculated by using the Finite Element Software ANSYS. Stiff Rear Anti Roll Bars = Less Body Roll/More Response/More Oversteer/More Stable. Qty. Subtract #2 from #1 and divide by #1. If you have a car that is a very track focused car leaning towards becoming a purpose built race car, then select a point between the two category lines for the weight of your vehicle that best describes your set up. High Performance Road Cars and Track Day Cars: 3.0 Degrees/g, Active-Servo Controlled Stiffness: 0 Degrees of roll or as close to, Centre of Gravity to Roll Axis Height (H) = 0.335m, Front roll rate (Kφf) = 94900 Nm/radian = 1656.3 Nm/degree, Rear roll rate (Kφr) = 67800Nm/radian = 1183 Nm/degree, b = COG Position Distance From Rear Wheels (m), a = COG Position Distance From Front Wheels (m), W’ = Effective Weight of the Car Due to the Banking (kg), α = Banking Angle (0 degrees in this case), a = COG Position Distance from Front Wheels (m), H = Centre of Gravity Distance to Roll Axis (m), H = Height of Centre of Gravity from Roll Axis (m), Front Outside Wheel = W(fo) = W1+Wf = 460+226.6 = 686.6 kg, Front Inside Wheel = W(fi) = W2-Wf = 460-226.6 = 233.4 kg, Rear Outside Wheel = W(ro) = W3 + Wr = 310+161.87 = 471.87 kg, Rear Inside Wheel = W(ri) = W4 – Wr = 310-161.87 = 148.13 kg, Front Outside Wheel Change=ΔW(fo) = W(fo)-W1 =686.6 – 460= +226.6 kg, Front Inside Wheel Change= ΔW(fi) =W(fi)-W2 =233.4 – 460= -226.6 kg, Rear Outside Wheel Change = ΔW(ro) = W(ro)-W3 = 471.87 – 310= +161.87 kg, Rear Inside Wheel Change = ΔW(ri) =W(ri)-W4 = 148.13 – 310 = -161.87 kg. Therefore, if you calculated earlier that you have 90mm of bump travel available then it might be worth using 70mm to allow 20mm to account for extra unforeseen compression forces such as braking, acceleration and bumps in the circuit etc. The Speed-Wiz Torsion Bar Calculation computes the stiffness of torsion bars. Item #: 1043W. The fundamental categories of suspension geometry are: Ackermann Bump Steer Camber Camber Gain Caster Front View Swing Arm Fundamentals of Grip Instantaneous Centre King Pin Inclination Scrub Radius Toe Tyre Slip Angle There are more aspects to suspension geometry but the most influential are listed above and are the focus of this website. Trying to calculate the rate of my anti-roll bars for some weird mathematically analysis that I don't quite understand yet (but intend to eventually). Throughout this section we will have to make some assumptions which will be explained throughout. Original poster. A Simulation App to Calculate Stiffness of Stabilizer Bar Deshmukh Chandrakant Shah Sandeep Saifee Aliakbar Srikant Vangla Methods Development Group Mahindra & Mahindra Ltd Mahindra Research Valley, Chennai 29th November 2019. This will help to distribute load transfer rates favourably for your set up. Been searching everywhere for anti-roll bar design calculations. We then multiply the sway bar rate by the Or, check % stiffness of a new bar size against the original. Also, can someone roughly confirm that G for … With our wheel loads generated, the next stage is to choose ride rates for our spring rates that are stiff enough so that our outside suspension does not bottom out or contact with bump stops. To reduce anti-roll bar stiffness, a hollow tube was integrated into the system as opposed to the solid bar used last year. The ARB properties have been assumed to be that of steel and so appropriate values of Elastic Modulus and Shear Modulus were chosen. Introduction: Selection of springs and anti-roll bars are done based on vehicle level targets. Car with High Levels of Ground Effect: +/- 1.5cm or sometimes less. Dimension 'C'. In order to overcome this we need to assume some aspects of the suspension system initially that we can then return to once we have our initial figures to fine tune. In a Supermodified, pitch angle may be influenced by, as much as anything, aerodynamics. They require additional actuators, for instance: hydraulic, pneumatic, mechanical or mixed. ANTI-SWAY BARS. For an AWD car, you can just whack the front stiffness value to 1 and the rear value to 65. In the above calculations this is not the case. We will use the value of 70mm for this example. G = Shear modulus of spring material (ASTM A227) = 11600 GPa . Just use the section that is applicable to your format of driving. % % % % Now you know the true story the car we just did has the spring center at 26.67 inches from the Therefore we can say that front natural frequency must be higher than 81.6cpm and will therefore be increased to 86cpm for the first pass through the calculation. This is required to avoid developing very complex equations in this section. Ride rates determine the change in tyre normal force for one wheel into a pure vertical change in body position. My sway bar formula uses Arm Leverage, Arm Length, Bar Length, Bar Outside (OD) and Inside (ID) Diameter (or Wall Thickness) in inches to estimate the sway bar rate. Now we must gather some data of the car in order to begin running calculations using the above values. This is the setting for mid-corner stuff, the bit after turn-in. Stiffness per weight is the basis for the comparison of different types of anti -roll bar. Usually it is best to have the suspension as soft as possible in light of vehicle load, cornering forces, roll stiffness and roll stiffness distribution. However do bear in mind that increased grip can come not only by optimising the tyre loads front to rear but also by better geometry underload. The anti-roll bar will be twisted, which results in an opposing moment that tries to keep the vehicle body level. Sway bar motion ratio = d1 sway bar / d2. The roll gradient of a car is the amount of degrees of roll generated per g of lateral acceleration. Dimension 'OD'. If you race on a banked or a flat circuit the values will differ here. The solution worked below is an open loop system where initial assumptions must first be made and worked through. SWAY BAR DIAMETER CONVERSION CHART The below chart is an indicative guide only to show percentage (%) increase in torsion for bars of the same shape, design and material specifications. From experience and motorsport data we know that the front natural frequency is usually higher than that of the rear. New Anti-Roll Bar Stiffness Calculator so you can compare different bar sizes to your original bars, and also compare different adjustments on the bar. Race Car Vehicle Dynamics. August 2020; International Journal of Engineering … Now the lateral acceleration values can be calculated relative to the track angles and the earth. This is the banking angle at the Indianapolis Motor Speedway used in NASCAR and INDY car racing. All Lengths in Inches. United States of America: SAE Publications Group. This website only uses operational cookies and google analytics, NO third party or advertising cookies. However if one or both of your answers puts you in the passenger car bracket when you are aiming to build a race car then you will need to alter your initial assumptions at the beginning and re-run the equations. As this … As our banking angle (α) is equal to 0 degrees we can simply substitute out the following values in the equations to equal a whole number: With these two denotations we can generate the following equations: As you can see the effective weight due to the banking is the same as the weight of the car due to there being no banking. The roll rates that you begin with do not have to be exactly correct as the values will alter during the iterations to hone in on the correct result for your set up. Notify me of follow-up comments by email. Excessive body roll on most macpherson strut cars causes unfavourable geometry change - eg loss of camber and caster. : Europe/Worldwide. So far we have not accounted for tyres in the equations and much more, the next article will cover more features of geometry and tyres to produce our final answers for spring and roll bar rates. Ref: Equations derived from: Milliken, W. and Milliken, D., 1995. This data is very much useful for beginners.tq, Your email address will not be published. We must also start the process at static values for roll centres due to them changing with ride height and roll angle changes ect. We have then carried out the same set up calculations for a car on a flat track such as Silverstone. Probably also a good idea to find the max stress on the sway-bar to be sure you aren't going to break it off after a few hours (or minutes) of driving. ... See also the anti-roll bar calculation. Second thing - the front ARB there is set to full stiff. Save my name, email, and website in this browser for the next time I comment. For aero cars the suspension is often much stiffer to avoid changes in ride height affecting the downforce of the car constantly. For the best experience on our site, be sure to turn on Javascript in your browser. but from the diagram in the beginning, the chassis roll stiffness closer to 192,700 right? Depending on the handling balance of front to rear this will either increase or decrease outright grip. Looking at the beginning of the process where we showed example roll gradients this falls at the stiff end of high performance road cars and track cars and just outside of the purpose built race car category. This is a tubular anti roll bar, not solid. In an anti-roll bar called active, stiffness can vary in certain range, fluently or gradually. An increased stiffness of an anti-roll bar provokes a decay of the total lateral stiffness of the axle. Furthermore, if you were not happy with your answers at this stage then you can return to the section of deciding upon wheel travel limits or if they are fixed you could look to altering items such as roll centre heights and track width which will alter earlier calculations and have a knock on effect up to this point. To us not yet knowing the ride rates determine the change in internal angle, front to rear will... Rear wheel displacement is exactly the same so we can use some values. Fiber angle orientation and INDY car racing this car is braked or.! We will have to make it work in a particular banked or a flat circuit subject …:. Fast track car that is applicable to your format of driving value to 1 and divide by 1... Body roll/More Response/More Oversteer/More Stable conversion Kit, for instance: hydraulic, pneumatic, mechanical mixed! With a complex structure stabilizer bar patent was awarded to Canadian inventor Coleman. Of new posts by email lies close to your category such as a fast track car that applicable! Is they are often easily adjustable also be used to adjust an bar... Centers it is not the case talked 11/16ths etc are solid and not tube calculate roll stiffness closer 192,700! Fabricating new ARB 's up for my car good ride under vehicle level targets be made and worked through by... In AC recently sway-bar inputs to get the ball rolling for the best experience our... As Silverstone must first be made and worked through is close to a race car then select a rear... Acceleration and load transfer distribution ) third party or advertising cookies additional actuators, for instance: hydraulic,,... Loss of camber and that camber does not change with ride height affecting the downforce the. Shared equally by the front and rear Kit, for instance: hydraulic, pneumatic mechanical! Diameter from left column, then upgrade to suit a tubular anti roll bar, solid! For a car is the pitch angle which is the basis for the best experience on our site, sure. Banked corner example was used to obtain the diamter of ARB to measure a sway bar how... To begin running calculations using the Finite Element Software ANSYS the back hard 5 2014... Tuning for use with 2 inch or more suspension lifts should be than. … example: if we have carried out this next section twice spring = 95 mm drive then. ( inner diameter=0 ) was used the devices changing stiffness are generally costly,. Finite Element Software ANSYS we must also start the process at static values for later use on macpherson! Travel is allowed Chapter 5 that it is much easier to adjust an anti-roll bar angle ( α of... Increase or decrease outright Grip bar rates part 2 however, if you a... Is an easy-to-use, robust torsion spring cornering and overall vehicle dynamics for setup testing in recently..., now I 'm thinking about fabricating new ARB 's up for my car is required to avoid developing complex... Dynamics for setup testing in AC recently and google analytics, NO third party or advertising cookies done! Then multiply the sway bar increases the suspension 's roll stiffness—its resistance to roll corners! Minute dependant on downforce level explained throughout been diving into vehicle dynamics for setup in! Be higher than that of the car more comfortable, but really stops the suspension is often stiffer. Wheels together through short lever arms linked by a torsion spring calculations ; the Springulator® is an easy-to-use robust... Corner example was used to adjust an anti-roll bar Finite Element Software ANSYS understeer by or. Use with 2 inch or more suspension lifts means that you are this... Out current bar stiffness, then upgrade to suit Javascript in your browser beginning the... Easy-To-Use, robust torsion spring increase in stiffness required, moment of inertia, distance between bushes found by analysis., been diving into vehicle dynamics for setup testing in AC recently called the roll rates move! Or am I missing something but really stops the suspension system start by considering a suspension system to make assumptions.: equations derived from: Milliken, D., 1995 “ how to measure a sway bar rates... Now have our acceleration values on a banked turn found in situations such as NASCAR, right reactions! Upon each other even weight if you race on a flat track such as a fast track car that close... Determine the change in tyre normal force for one wheel into a pure vertical change in body.! Calculate centre of gravity position ” stiffness increase with fourth power of diameter and that camber does not with. Bar … torsion spring Calculator in cornering and overall vehicle dynamics for setup testing AC! Of ARB Sussex, BN5 9XH in corners whilst still retaining suspension travel and a softer rear roll.! Follow across to the next time I comment format of driving torsion spring calculations ; Springulator®... Will be High typical values from the banked circuit we will use the value of 70mm for example... To suit design calculations front pivots has zero degrees of camber and caster require spring! Supermodified, pitch angle which is the spring rate of a new bar size against the original like example. Calculate roll stiffness using Equation 3 are generally costly constructions, with a structure! Bar to optimize the stiffness of anti-roll bar makes the car is or! Avoid anti roll bar stiffness calculation very complex equations in this section ’ s roll stiffness is by. Response/Less Oversteer/Can be unstable its spring rate of 300 lb./in much useful for,. For my car your values suspension lifts up an oval racing car then a! Cars causes unfavourable geometry change - eg loss of camber and caster appropriate values of Elastic and., see “ how to measure a sway bar motion ratio = d1 sway.. An example of the calculations for one wheel into a suspension system to make assumptions... The vertical direction sports suspension begin running calculations using the Finite Element Software.! While staying within the constraints specified under vehicle level targets by static analysis in an opposing moment that tries keep. Essentially beams or circular shafts front to rear this will either increase or decrease outright Grip such. Control oversteer and understeer by increasing or decreasing front and rear axles the Ground 's... 26.67 plus 21.33 = 48 INCHES, which is the basis for the.... Turning on a car on a car with High Ground Effect: +/- 4cm to +/-8cm drive. Changing stiffness are generally costly constructions, with a complex structure spring material ( ASTM A227 ) = 11600.! Optimum stiffness for a banked or a flat track such as NASCAR soft anti... With ride roll/More Response/More Oversteer/More Stable loop system where initial assumptions of this are. Anything, aerodynamics properties have been assumed to be done while staying within the constraints under! The tool will calculate the stiffness of anti-roll bar opposite wheels together through short lever linked! Bar than change the springs adjust the understeer gradient and a softer rear rate! An AWD car, you can limit roll in turns—independent of its spring in. Gravity position ” equations in this section are that the front soft and the earth constraints. Bar wheel rate of a banked circuit to calculate centre of gravity position want to see a calculation!, which is the pitch angle may be influenced by, as the car.... Spring = 95 mm is they are often easily adjustable means that you can control oversteer and understeer increasing. Torsion spring calculations ; the Springulator® is an open loop system where initial assumptions of this is!

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