Talk:Slip angle

Slip angle is not the same as Sideslip angle

On the first sentence you say "Slip angle or Sideslip angle", which are two different things. Slip angle is that what you describe but Sideslip angle is the angle between the middle of the vehicle and the speed vector of the vehicle on the centre of gravity of it. So it is a similar concept but referred to the vehicle and not the tire/wheel.

-Jorge Jauregui TCS (talk) 12:11, 30 March 2020 (UTC+1)

Slip Angles and Geometry

Because the forces exerted on the wheels by the weight of the vehicle are not distributed equally, the slip angles of each tire will be different.

The idea that's attempting to be conveyed here is more or less correct, but, as stated, this sentence is wrong. Since (at a fixed steering input angle) the positions of the wheels relative to the vehicle are fully constrained, the difference between the four slip angles is purely a function of geometry (plus the vehicle's overall chassis slip angle). The turn radius, track widths, wheelbase, ackerman, C of M position, and the angle of the chassis relative to the direction of travel of the C of M determine the difference between the slip angles at each wheel.

A diagram would help explain this, and I will try to find time to turn my old hand-drawn sketches of it into something that can be used here. In the mean time, I propose to revise this sentence to the following.

The slip angle at each wheel is determined by the angle between the chassis centerline and the direction of motion of the center of mass, combined with the turn radius and the geometry of the chassis. The relevant chassis geometric parameters are: front and rear track widths, wheelbase, steering ackerman angle, and the position of the center of mass (relative to the axle centerlines). Naturally, on an asymmetrical car (such as most oval-track race cars) the asymmetries must also be factored in.

This would stand alone as a paragraph. The remainder of the current paragraph would become a separate paragraph.

--Tedd (talk) 00:50, 20 August 2008 (UTC)

You are ignoring roll steer and compliant and dynamic effects. I have just plotted the tire slip angles for a 0.15g swept steer at 120 kph and they are all different, primarily due to static toe in, but at the peak slip they also differ between axles and sides, albeit only slightly once the static effects are accounted for. I am sure the difference would be greater on a more extreme manouevre. Greg Locock (talk) 02:29, 20 August 2008 (UTC)

Yes, that's right, I'm ignoring compliance (and roll/bump steer) effects -- by design. I think it's important to begin with an assumption of rigidity, to simplify the theory. That's standard practice in engineering texts. Compliance effects can then be added once the reader has been given a chance to grasp the basic concepts.

However, at some point we should probably branch out into separate articles coving such topics as compliance-steer, roll-steer, and bump-steer. These are all important subjects that depend on an understanding of slip angle, but don't necessarily belong in the slip angle article. --Tedd (talk) 13:31, 20 August 2008 (UTC)

Understeer and Oversteer

The ratios between the slip angles will determine the vehicle's behavior in a given turn. If the ratio of front to rear slip angles is greater than 1:1, the vehicle will tend to understeer, while a ratio of less than 1:1 will produce oversteer.

Here, too, the concept that we're attempting to describe is correct, but the details are wrong. The two rear slip angles can't be the same as each other because the rear wheels have a fixed angle between them but the tire contact patches are on arcs of different radii. For similar reasons, the two front slip angles will only rarely be the same (when the ackerman effect just happens to be exactly right for the turn radius, overall chassis slip angle, and degree of understeer). So there can't be a single ratio of front to rear slip angles.

However, I think the concept we're trying to explain here is important. I believe there is an accepted, engineering definition of understeer and oversteer, similar to what is described here, but I don't have access to the texts that describe it. I'm hoping another editor can provide it.

--Tedd (talk) 00:53, 20 August 2008 (UTC)

Often people talk about axle slip angles rather than wheel slip angles. hence the confusion. Greg Locock (talk) 02:31, 20 August 2008 (UTC)

In the traction circle article we chose to restrict the content to a single wheel, so that the explanation of traction circle didn't get complicated with more global handling effects (such as load transfer or driveline configuration). It might be a good idea to do that here. But perhaps what we need to do is let the article expand a little, and then the places where it makes sense to spin off separate, more detailed articles might suggest themselves. --Tedd (talk) 13:43, 20 August 2008 (UTC)

Kinematic and Kinetic Factors

As this article develops, I think it will become important to separate kinematic and kinetic factors. For example, when considering only a single wheel and tire, we can talk about the relationship between normal load, slip angle, and lateral load. But once the discussion moves on to the vehicle as a whole the concepts become much more complex, and have to include both chassis geometry and global kinetic effects (such as load transfer and roll couple). We will need to decide at what point the discussion should be moved up to a higher-level article that would draw on this article and other low-level articles, such as the Ackermann steering geometry and traction circle articles. --Tedd (talk) 13:58, 20 August 2008 (UTC)

Aerodynamic coefficient of lift

The parenthesized statement that "This is directly analogous to the coefficient of lift in aerodynamics" is very confusing. What is "this" referring to? Because the slip angle is in no way analogous to the coefficient of lift. I have a fair bit of experience in vehicle dynamics, including tires and aerodynamics, and I have no idea what that sentence is talking about. Does the writer mean angle of attack? Even then, it's highly questionable as to whether it is "directly" analogous, as the force curves do not look similar mainly because they develop forces in completely different ways. —Preceding unsigned comment added by 98.209.17.37 (talk) 01:42, 20 September 2010 (UTC)

Error in the slip angle equation???

I'm reading the slip angle formula (arctan(vw/uw)). Fine, that makes sense...but wait: the diagram seems to show uw and vw on the wrong axes. If there's no slip, uw = 0, right? but vw > 0 if moving forward, and so (vw/uw) is infinity, and its arctan will be 90 degrees. I think that either the drawing or the equation needs to change.... — Preceding unsigned comment added by 173.233.10.149 (talk) 03:35, 15 August 2012 (UTC)

Yes, you are correct. Perhaps things got goofed up in the conversion from x and y to u and v (which are hard to distinguish in the font used to display equations). I'll try to straighten it out. -AndrewDressel (talk) 15:38, 15 August 2012 (UTC)

Load transfer

"This can be achieved by modifying the height of the roll centers,..."

I believe this line is wrong. Modifying the roll center height only changes the ratio of load transferred by the shocks to that by the linkages. The only thing that can be changed is the load transfer ratio at the front axle to the rear axle which only depends on the roll stiffness at either end. The total load transferred still remains constant as it is only a function of the lateral acceleration/force alone.