These forces are largely affected by the suspension systems geometry and they are used to counteract the sagging in the rear suspension which is caused by squat. What is anti squat and pedal kickback pole bicycles company oy. Rear suspension design and aeris kinematics bird mtb born. The best chassis and suspension for your vehicle is possible, but it will take ingenuity and time. Suspension design for other vehicles is similar, though the process may not be as well established. If the inner hingepins are flat parallel to the ground or have no angle, then the vehicle has zero degrees of antisquat. Rear suspension that features antisquat geometry optimizes a cars ability to apply acceleration force to the road surface. Irs systems can generally only achieve about 25 percent anti squat before the rest of the geometry is badly compromised. The suspension selection is accomplished through the study of its geometric characteristics to design its dimensions and position of installation in the vehicle according to the expected behavior. As we have seen, this is usually not possible over the full su spension range and this design. If the antisquat percentage is more than 100, it means that the drive force is greater and will actually. The paper focuses on design of rear suspension system for an atv. I hope smiths book will dig a little deeper into suspension design. Irs systems can generally only achieve about 25 percent antisquat before the rest of the geometry is badly compromised.
If you design the suspension around the middle ring your are going to have too much antisquat and too much pedal kickback in the granny. Pedal kickback grows proportionally as anti squat increases, so suspension linkage design is always a trade off between an efficient pedaling platform and how much independence the suspension has from the drivetrain. Leaving the 3 vs 4 links out of the picture i notice a lot of the trucks tend to lift the front end under throttle. Usually the intuitive reactions are builtin to aid traction under accelerating and braking respectively but we can circumnavigate these all together with the black magic of the anti. By raising the front of the hingepin or lowering the. Determining the anti squat percentage is a matter of dividing the sum of the anti squat torques by the weight transfer torques. Very nice book to understand the dynamics of a motorcycle. The drastic increase in antisquat was caused by the installation of a ladderstyle antiwrap bar. Part of the reason for the bugyfication is to help the fj climb better last year, it was hampered by too much rear weight, but alot of it was too much anti squat in the suspension, and the resulting hop. Sag can go from 25% to 35% when you are climbing, so as can go from 100% 3218 25% sag to 120% 2232 35% sag instead of going to 150. Any more can cause the wheels to hop under hard acceleration.
As you move forward with the ic to something reasonable say 4050 the anti squat line naturally moves further up and hence with the bottom bar adjusted level or slightly pointed down it puts the ic well below the slope of the neutral line 100% anti squat and yields numbers for me in the 1550% anti squat. Antisquat in a linked suspension system determines how the rear end of a vehicle moves under acceleration or upon the rear axle contacting an obstacle at speed. Linkage kinematics basics of antisquat and pedal kickback. Note that if anti squat was 100 percent, the chain and driving forces would perfectly offset the weight transfer of acceleration, and the rear suspension would neither extend nor compress. I am new here and struggling trying to fully understand antisquat and what you really want. Of all of the systems, the most common youll see today is the equal length fourlink, probably followed by the ladder bar. Fwiw, trying to compare a race car chassis and suspension design to a motorcycle is often not a wise idea. Mar 24, 2014 the best chassis and suspension for your vehicle is possible, but it will take ingenuity and time. To do this properly it also takes the know how to correctly stage your chassis and suspension for. This paper addresses the design of a fourlink rear suspension for a drag racing motorcycle to provide antisquat, which increases rear tire traction, thereby improving vehicle acceleration performance. Does the usual rule that limits the available anti squat in a i.
If the as curve is not flat you can compensate the change in the gears. Ive ran the numbers on the 4 link calculator but not really sure what kind of numbers im really shooting for. Why dave weagles mtb suspension designs are so prolific. This is typically done with vehicles with high power to weight ratios. The mathematical suspension model presented is based on a number of simplifying assumptions and my rather limited knowledge of geometry and trigonometric functions. Note that if antisquat was 100 percent, the chain and driving forces would perfectly offset the weight transfer of acceleration, and the. If the inner hingepins are flat parallel to the ground or have no angle, then the vehicle has zero degrees of anti squat. Because solidaxle rear suspensions can exceed 100 percent antisquat, there is a big potential reduction in traction for highhorsepower applications. This is why the first chapter in each book is about tires, the. Foales book motorcycle handling and chassis design. The racetech text book is a good read and reference book. And the carroll smith book is like 23x more expensive. The main reason for the difference is due to the different design goals between front and rear suspension, whereas suspension is usually symmetrical between the left and right of the vehicle. I mentioned above that some designs will occasionally have anti squat percentages below zero.
The total is the sum of these components and governs how resistant the suspension is to acceleration induced compression when pedalling. The method presented here graphical method for anti squat is not valid in some specific bikes, such as bikes where the. Page 1 of 2 how does a torsion bar suspension work. Antisquat is the force on a suspension system that is generated by the drivetrain. Anti dive and anti squat percentage are always calculated with respect to a vertical plane that intersects the vehicles center of gravity. I asked dw the same question a few years ago and he replied he had some design ideas, but was too busy with other projects to develop alternative fork designs at that. Suspension design theory and antisquat behavior arts slo. The antisquat value is determined by the vertical angle of the rear links as they relate to the front axle position and the center of gravity of the vehicle. Part 1 the best chassis and suspensions explained by brent. Automotive suspension design is an aspect of automotive engineering, concerned with designing the suspension for cars and trucks. The method of determining the antidive or antisquat depends on whether the suspension linkages react to the torque of braking and accelerating. Oct 14, 2014 pedal kickback grows proportionally as anti squat increases, so suspension linkage design is always a trade off between an efficient pedaling platform and how much independence the suspension has from the drivetrain. The first one is the one you can see by playing with the basic suspension calculators.
If this is all true and considering that i have a double a arm independent suspension at the 4 wheels, what would be a good % of anti squat and antidive for a 500hp, 3000lbs, 115in wheelbase street sports car. It is located firmly to the chassis at one end and to the wheel upright by means of a linkage of some sort at the other. Apr 28, 2010 you have to remember that suspension design has to cater to many different aspect, braking, bumps, pedaling. Im not an expert on suspension theory or the mathematics used in this article. Jan 27, 2005 related to trailing arm design is the link setup, and squat vs anti squat. They do not allow the suspension to move freely, and this is not ideal for the bestpossible traction. Definition of anti squat automotive suspension engineering. To determine the antisquat in the example design, lines are drawn from the upper and.
Car suspension news newspapers books scholar jstor april. Antisquat suspensions are used to reduce body squat by altering the rear suspension so that the forces resulting from accelerating pass. As you move forward with the ic to something reasonable say 4050 the antisquat line naturally moves further up and hence with the bottom bar adjusted level or slightly pointed down it puts the ic well below the slope of the neutral line 100% antisquat and yields numbers for me in the 1550% antisquat. The inclination of suspension members dictates what a car does when you step on the gas or stomp on the brakes. Anti squat is a very important chassis design feature for getting power to the ground for good acceleration on powerful rear wheel drive cars. Antisquat is suspensions mechanical resistance to compression due to forces from the engine when on a bicycle human is the engine.
Design and manufacture of an adaptive suspension system. Antisquat is the suspensions mechanical resistance to compression due to forces from the engine. Design of three and four link suspensions for off road use. Antidive and antisquat are expressed in terms of percentage and refer to the front diving under braking and the rear squatting under acceleration. Ive separated out the frame antisquat from the total antisquat in order to show that total antisquat is made up of two components frame antisquat and chain antisquat. I have no diagram to post, i fear, but it is not a complex matter.
Rear suspension design and aeris kinematics bird mtb. Suspension design theory and antisquat behavior arts. If yes, i guess that the opposite simply applies for the rear wheel anti squat. Suspension is the system of tires, tire air, springs, shock absorbers and linkages that connects.
This means that for every gear combination, there is a different antisquat graph that can be plotted. Over rough, rocky terrain, a design with too much antisquat turns your groundhugging bike into a hardtail. If you have 100% anti squat, that suggests that there is zero suspension movement with a considerable rear weight transfer. Remember, all adjustments must be made with the car race ready, setting level on all four tires, and with the driver in the drivers seat or. For example, with inboard brakes and halfshaft driven rear wheels, the suspension linkages do not, but with outboard brakes and a swingaxle driveline, they do. Whenever accelerated, vehicle has the tendency to pitch up i. Over rough, rocky terrain, a design with too much anti squat turns your groundhugging bike into a hardtail. Curious front suspension antisquat question for dw dw. In order to provide sufficient potential for noise and vibration refinement and ride as well as for handling and steering, an essential approach comprises the kinematic decoupling of the suspensions reaction to. Intuitive explanation of antisquat with real demos and examples. Design, analysis, and verification of an openwheeled. They can be thought of as the counterparts for braking and acceleration as roll center height is to cornering. Mar 15, 2015 bolton ladder bars added to the stock suspension definitely get rid of wheel hop, but does so by binding up the rear suspension.
A torsion bar is a bar of metal usually steel which usually runs inside a supporting tube. In other words zero suspension movement with considerable extra weight applied. The total is the sum of these components and governs how resistant the suspension is to. There are entire books dedicated to the subject, and this paper is intended. High antilift and antisquat are required to minimize vehicle pitch at braking and acceleration. The mathematical suspension model presented is based on a number of simplifying assumptions and my rather. I know that i want as little no pinion change and roll axis but what is tolerable. Whilst discussing independent rear suspension, he states.
An anti squat of 0% means that chain plays no role in preventing bob in the suspension. He describes design requirements such as lateral control, roll center height, bump steer, and antisquat for the various types of live axle suspension. I mentioned above that some designs will occasionally have antisquat percentages below zero. When we tune anti squat, we refer to the angle of the inner hingepin as it relates to the ground.
Then ill define the major design concepts that are collectively known as suspension kinematics, these include. Over the years, drag racers with door cars have gone through all sorts of suspension arrangements. Heres how to plot the instant center and antisquat of your s197 mustang rear suspension. Wedge antidive to dive or not to dive, that is the question disclaimer. Calculate antidive, antilift, and antisquat percentages for inboard brakes, outboard brakes, independent suspension, and solid axle suspension. The anti squat is a function of the angles of the arms in side view. Curious front suspension antisquat question for dw. May, 2016 intuitive explanation of anti squat with real demos and examples. With the addition of almost any power adder and quality tuning, singledigit elapsed times are incredibly easy to achieve. Rc suspension tuning guide antisquat antisquat helps keep the vehicle from squatting during acceleration. The second method of calculating antisquat comes from tony foale and his book, motorcycle handling and chassis design. Weldineer stated correctly below that the anti squat reaction to the torque of the axle lifts the mass of the vehicle resulting in an increase in.
Dive is design to suspension based on the angle of the. Antisquat suspensions are used to reduce body squat by altering the rear suspension so that the forces resulting from accelerating pass through the control arms and suspension linkage rather than through the coilovers or struts. Ok i know this is a beat to death over and over on lots of forums. Addressing antisquat and using it to improve suspension design is now a fundamental concept for most mtb brands. Competition car suspension is a practical look at suspension history, types, theory and design. The process entails selecting appropriate vehicle level targets. Pedal kickback grows proportionally as antisquat increases, so suspension linkage design is always a trade off between an efficient pedaling platform and how much independence the suspension has from the drivetrain. Rear suspension theory general trials talk trials central. Antisquat is a transient vehicle suspension parameter which can dramatically affect tractive effort available at the motorcycle drive tire. Is this by design, or just a result of that much power.
That must mean the suspension rate has actually risen to infinity. The main reason for the difference is due to the different design goals between front and rear suspension. Sep, 2018 too much anti squat and the suspension will extend under pedal loads, too little anti squat and the frame will compress under pedaling loads. Triaged 3 and 4 link calculators will show this form of anti dive anti squat. The drastic increase in anti squat was caused by the installation of a ladderstyle anti wrap bar. The advanced inputs for this calculation instant center positions and cg height can be easily calculated using the calculations in speedwiz. Determining the antisquat percentage is a matter of dividing the sum of the antisquat torques by the weight transfer torques. I think only book in the world for understanding motorcycle. If no anti squat is present, with the lower suspension pivot shaft being parallel to. When this force is applied through suspension with 100% or greater anti squat geometry the rear of a car pushes up rather than squatting down under power. He describes design requirements such as lateral control, roll center height, bump steer, and anti squat for the various types of live axle suspension.
Jul 15, 2019 there are two separate forces that effect front end dive. Design, analysis and fabrication of rear suspension system. Higher values of antisquat commonly cause wheel hop during braking. Anti squat as anti squat is a term for suspension engineers to determine how much the suspension mechanism itself is resisting suspension compression. Both can be tuned by the suspension geometry and are related to each other. S197 mustang, instant center, anti squat, suspension. Because solidaxle rear suspensions can exceed 100 percent anti squat, there is a big potential reduction in traction for highhorsepower applications. Adams book gave a nice, clear, broad overview on suspension but i was a little disapointed that in didnt get into much specifics.
If this is all true and considering that i have a double a arm independent suspension at the 4 wheels, what would be a good % of anti squat and anti dive for a 500hp, 3000lbs, 115in wheelbase street sports car. Anti squat is an engineering term which describes the 4links likely performance under acceleration. Anti squat is a trait of a suspension design that resists the. When you have 23 of suspension travel it is relatively easy to design a shortlong aarm suspension system that will match body roll to the camber change of the outside tires in order to keep the contact patch of the laden tires flat on the ground.
Triaged 3 and 4 link calculators will show this form of antidiveantisquat. It happens because of change in inertia, in a similar fashion that pushes us into the seats when we accelerate. Suspension debate about antisquat ridemonkey forums. The full chassis dynamics is considerably different in how the wheel movement arcs, the effects of drivetrain squat antisquat, and more. Jul 01, 2000 anti squat is a transient vehicle suspension parameter which can dramatically affect tractive effort available at the motorcycle drive tire. Anti squat is a trait of a suspension design that resists the compression of the suspension caused by mass transfer during acceleration. Ive been meaning to pick up one of those suspensionchassis design books but havent yet. The art and science, which outlines a method of determining antisquat percentage graphically. Thus, traction is directly controlled through adjustments to the suspension system.
Related to trailing arm design is the link setup, and squat vs antisquat. Note that because all the forces are proportional in some way to acceleration, the same antisquat number covers any acceleration value. Telescoping forks actually have braking induced prodive geometry. If the anti squat percentage is more than 100, it means that the drive force is greater and will actually extend the rear wheel outwards and unload the shock. This paper addresses the design of a fourlink rear suspension for a drag racing motorcycle to provide anti squat, which increases rear tire traction, thereby improving vehicle acceleration performance. Lift bars, slapper bars, super stock springs, leaf links, ladder bars, threelinks, fourlinks, and torque arms there may be others too, but its a start. Too much can cause the suspension to stiffen up or even lock out while pedaling. Weldineer stated correctly below that the anti squat reaction to the torque of the axle lifts the mass of the vehicle resulting in an increase in downward force on the tires. Design, analysis and fabrication of rear suspension system for an all terrain vehicle aniketthosar abstractall terrain vehicle atv is defined by ansi as a vehicle that travels on low pressure tires, which is used to handle any kind of terrain it faces. Part 1 the best chassis and suspensions explained by.
When we tune antisquat, we refer to the angle of the inner hingepin as it relates to the ground. I was a guest speaker at an sae motorsports conference in 2000 and my work in asymmetric suspension design was mentioned in the millikens recent book, chassis design. There are three components that come together to determine antisquat which i touched on above geometry of the swingarm, sprocket and chain, but to understand how each affect antisquat, we need to go over a little bit of physics to discover why the rear suspension wants to extend under power. The method presented here graphical method for antisquat is not valid in some specific bikes, such as bikes where the. An antisquat of 0% means that chain plays no role in preventing bob in the suspension. Nov 01, 2001 finished reading chasiss engineering and im starting on tune to win.
On the beneficial effects of antisquat in rear suspension. Antisquat is best described as caster for the rear wheelsit changes the relation of the inner hinge pins parallel to the ground. By raising the front of the hingepin or lowering the rear, you are increasing the degrees of anti squat. In order to calculate the % antisquat for a particular suspension design, it is. Rear suspension that features anti squat geometry optimizes a cars ability to apply acceleration force to the road surface. Here youll find current best sellers in books, new releases in books, deals in books. This book consists in a definition and analysis of baja suspension geometry to an offroad vehicle. Antisquat is an engineering term which describes the 4links likely performance under acceleration. If you have a factory fourlink suspension system, pinion angle can be changed with adjustable upper control arms. Too much anti squat and the suspension will extend under pedal loads, too little anti squat and the frame will compress under pedaling loads. Apr 28, 2010 if you design the suspension around the middle ring your are going to have too much anti squat and too much pedal kickback in the granny. The method of determining the anti dive or anti squat depends on whether the suspension linkages react to the torque of braking and accelerating. It provides enough discussion of each of these areas to leave the reader with a comprehensive view of the types, components and characteristics of suspensions.