At first glance this might sound like a cure-all, but beware of snake-oil salesmen fabricating racing chassis. If you think about corner entry with a high Ackerman car — as you start to turn-in that inside tire gets to a high steering angle, and therefore high tire slip-angle very quickly. Even a newbie can better understand the terminology and how everything works after viewing this video. All rights reserved. Trevor has a private pilot's license and is pursuing an MFA in fine art - specifically researching the aesthetics of machines, high performance materials and their social importance to enthusiast culture. Last in the alignment parameters is castor, and segways our discussion into the geometries you can not change with the turn of a wrench at an alignment shop. There are two basic formulas used in the vehicle dynamics world, one used for longitudinal weight transfer (front to back), and one used for lateral weight transfer (side to … What pittman arm, idler arm and drag link do I need on a 72 model chevelle clip with pinto spindles. Anti-squats and anti-dives give you geometric weight-transfer, and it happens through the control arms rather than through the compression of the springs. One last consideration in the steering design is scrub radius. Imagine the difference between standing on the inside edges of your sneakers (negative camber) with your ankles straight versus the outside edges of your sneakers (positive camber), if someone pushes you from the side, the opposite side of your foot will be the one to bear the load, and will pivot — flattening the sole to the ground for stability. Positive camber situations are inherently unstable, and promote the tire to tuck under and potentially role off the wheel bead. It’s no secret that not all cars are created equal in terms of handling characteristics. In a car with zero scrub radius the tire pivots around a central axis without dragging the tire forward or rearward. Currently, he presides over Thilenius Group, his third party testing company which conducts engineering and subjective evaluation for OEMs and support manufacturers. There is no one perfect geometry or suspension layout, everything is a compromise — and for more race cars an evolution, that changes from track to track and race to race. But the laws of physics remain the same. We spoke with seasoned ride and handling engineer David Thilenius, who among racing his own cars has worked in chassis development and testing for General Motors, Toyota, Hyundai, and Kia. 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The remaining variables fall into line with the addition of the dynamic components — arms, links, knuckles, and other bolt-on parts. Thilenius has worked on independent projects with Shinoo Mapleton of Sector 111. Changing the camber at static height is not the end of the story for most cars, camber gain under compression, into the negative spectrum, is commonplace and desirable for handling and stability. Front Suspension Set-up for Cornering. Understanding what’s happening when you apply a control input — with feet or hands — is the first step to understanding why a car reacts the way it does under the aesthetic wraps. As a car accelerates there are changes direction or velocity, and weight transfer occurs — loading and unloading different areas of the platform. By handling we, of course, mean cornering, but it is so much more than that. Even a newbie can better understand the terminology and how everything works after viewing this video. Photo source: Griggs Racing Products. In the performance aftermarket we are much freer to devise vehicle running gear and geometry to a specialized application. With an understanding of toe change and camber gain under bump and droop, we can begin to discuss topics like bump steer. The most common manipulative techniques to harness from roll centers are anti-dive and anti-squat. Photo source: Thilenius Group. “With the inclination you can define the instantaneous center of the suspension, and then the height of the instantaneous center relative to the height of the center of gravity determines how much anti-squat or anti-dive you have. The name bump steer may be a little misleading as it rarely acts like a steering pull, more often it upsets directional stability in a straight line. The angles, lengths, shapes, and mounting points of these extremities influence how the aforementioned weight-transfer we started this article with, is translated into movement or lack thereof. Usually the intuitive reactions are built-in to aid traction under accelerating and braking respectively — but we can circumnavigate these all together with the black magic of the anti. At GM we did it with some static negative camber and castor, at Mercedes they were doing it with zero camber and a lot of caster — that’s just a philosophical difference,” said Thilenius. All rights reserved. With modern CAD modeling, geometry can be worked out well before the prototyping begins. Widely recognized forms and designs like the Mustang II front end are common swaps for a reason, they work. The only thing that will change will be the pitman arm if you are running a metric box. “I basically jumped straight over from the School Series into the Firestone Firehawk series. Secondly it gets the front end super low to the track which has obvious aerodynamic benefits as well as weight transfer reduction in the front of the car. Heavy bump or droop scenarios expose bump steer. Without Ackerman understeer would run rampant, and turn-in would be hesitant. The most basic measurements that influence steering are the alignment parameters. “The beauty of Ackerman is that it really makes the car turn-in well. If I were to go to a fast open track like Willow Springs, I would run very little Ackerman. 2"| Page" Figure"2:Less caster,lesscaster"lead " " Figure2b:Greatercaster,greatercasterlead % When%cornering,% Z Á ] P Z v } v ] v P P [ } u ] v } Z } v ] v P ( } X d Z } v ] v P Crate Racin’ USA Late Model Special Set For November 5-7 At The, Summit Southern Nationals This Weekend At RPM, Bringing The Show To You: PRI Embarks On Cross-Country Road, Lawrenceburg Speedway Looking To Lease The Facility, Brandon Sheppard Scores Five-In-A-Row With Duck River, Strapping Your Race Car Or Hot Rod To A Trailer Just Got, Get The PerTronix Wiring Products You Need In Your, QA1 Releases 2.5-Inch I.D. By engineering an exponential steering angle gain the inside tire will be correctly angled to attack it’s tight arc, and the outside to follow it’s looser arc. © 2020 Power Automedia. “In lateral weight transfer you are talking about roll-centers and fore-aft weight transfer happen the same way,” Thilenius said. We promise not to use your email address for anything but exclusive updates from the Power Automedia Network. © 2017 Power Automedia. “I’ve been racing since 1984, I started off in the School Series with Formula Mazda. This quick-hitting video features a very-well versed explanation from his daughter. Chassis and suspension geometry are easy to mess up, but if you insist on starting from scratch these basics should get you going. Trevor is engaged with hands-on skill sets such as fabrication and engine building, but also the theoretical discussion of design and technology. There is a heim one the outside of the upper A arm and 2 heims on the tierod. Dirt is a whole lot more complicated and inconsistent than its prissy sister! A roll center is what determines the datum point around which all other suspension geometry moves. Trevor Anderson comes from an eclectic background of technical and creative disciplines. “One of the issues is long spindle length, which McPherson struts will give you. All rights reserved. The thing that you always hear, that you never want — toe-out at bump at the rear, is called reverse kinematics,” he concluded. The way chassis and suspensions systems are designed has a direct relationship to how these dynamics are translated into ride and handling characteristics. We came across another very well done video by Mike Higley, which explains front suspension and geometry on a racecar. This ambitious endeavor will involve fabricating a replacement base structure or chassis. Photo source: Thilenius Group. Most OEMs build cars to include some degree of toe-in because it provides reasonably forgiving, predictable and safe steering characteristics. © 2017 Power Automedia. “On a race track environment like a street circuit such as Long Beach — a track with slow 90-degree corners — I would probably want to run as much Ackerman as I could physically put into a vehicle because I want it to turn in and I don’t have to worry about the mid-corner understeer. A consequence of a compressed space between the arms is a lot of lateral movement in the contact patch, and a lot of toe change as the suspension cycles up and down through it’s range of motion,” Thilenius illustrated. If these two wheels where linked together for a completely linear steering relationship, the inside tire would always be scrubbing because it would not have enough inclination to roll through the arc. Photo source: Thilenius Group. Bump steer can be drastic under the worst circumstances, but designed out in racing applications. “There are three kinds of weight transfer in a car. The roll center is found by drawing lines in space through the control arms and intersecting them with lines drawn from the tire contact patch to instantaneous center (the projected intersecting point of the top and bottom control arms). The inner circle traced by the wheel on the inside of the corner and the outside diameter by the other wheel. I knew what 20-percent Ackerman felt like, and then I got to get into a car with 60 or 70 percent Ackerman,” Thilenius recalled. Weight transfer, traction, braking, acceleration, and other vital defining traits are heavily influenced by the chassis. The cosmos dictates that conservation of energy means all energy has to go somewhere, in some cases that can mean back to ground like electricity looking for an origin, which is generally not in our favor. 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Further than a quick-disconnect aftermarket wheel Dirt Maniac Total posts: 117 posted April,...
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