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Longitudinal force and slip ratio
For a tyre to produce a longitudinal force (driving or braking) it must slip (stretch then release). This means that its rotational velocity is not equal to its translational velocity. The amount of slipping “Slip Ratio” is expressed either as a fraction or a percentage.
SR = (Rotational Velocity / Translational Velocity) -1
The actual definition of slip ratio differs worldwide, depending on how the rotational velocity is calculated. Some notable ones are:
Rl= Wheel centre above the road surface, (loaded radius) Calspan
Re= Effective rolling radius (zero slip angle, free rolling) revs/m SAE
Free rolling, SR = 0; Braking limit, SR = -1; Driving limit, SR = +1
As with the 3D lateral response surface, the longitudinal response surface provides us with a wealth of information. The curvature of the surface with slip ratio, normal load and slip angle dictates how the car will respond to changes in parameters and its eventual CONTROL, STABILITY and HANDLING behavior.
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The three dimensional visualization of Longitudinal Force with Slip Ratio and Normal Load is shown in the diagrams. The chart on the left is for pure longitudinal force (zero slip angle). The chart on the right is for 3.5° slip angle.
As with the 3D lateral response surface, the longitudinal response surface provides us with a wealth of information. The curvature of the surface with slip ratio, normal load and slip angle dictates how the car will respond to changes in parameters and its eventual CONTROL, STABILITY and HANDLING behavior.
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| Started By | Thread Subject | Replies | Last Post | ||
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| Anonymous | Longitudinal force and slip ratio | 0 | May 29 2010, 1:31 PM EDT by Anonymous | ||
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Thread started: May 29 2010, 1:31 PM EDT
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I've found it hard to find real tire data for the Longitudinal Force with Slip Ratio as shown in the plots. Are the plots shown pretty typical for a radial tire? In the plot on the right, at maximum normal load, the longitudinal force seems to keep increasing beyond the limits of the chart. I wonder where it peaks. 13% or so?
Amazing that a tire can deform that much longitudinally. Certainly not something you can see with the naked eye. Although, I have seen photos of dragster tires where you can see the sidewalls crinkling under acceleration. |
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