Calspan tire data

[skumdum]

Hi,

Did somebody can tell me why, on brake-drive test, longitudinal force is going from negative to positive?? Maybe I don't understand the test well enough, can somebody explain me how it's done.

Also, considering road speed constant, most of the time the wheel is sliping from the surface (relative velocity between road and tire)?? Why taking these data, we don't want it.

Thanks a lot

Mathieu

[skumdum]

Hi,

Did somebody can tell me why, on brake-drive test, longitudinal force is going from negative to positive?? Maybe I don't understand the test well enough, can somebody explain me how it's done.

Also, considering road speed constant, most of the time the wheel is sliping from the surface (relative velocity between road and tire)?? Why taking these data, we don't want it.

Thanks a lot

Mathieu

[Christopher Catto]

unfortunately i dont have that tyre data. i'd like to buy it but i need to sort out other stuff first (laptop for example).

however, from what you describe, it appears to me that the data simply allows you to calculate slip ratio. then you plot the traction or braking force (one is neg., the other positive) against the slip ratio.

this data you can use for traction control for example (see post on Motec traction control).

if i am wrong http://fsae.com/groupee_common/emoticons/icon_frown.gif, then write clearly what name/label the data has, and what units etc.

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by skumdum:
Also, considering road speed constant, most of the time the wheel is sliping from the surface (relative velocity between road and tire)?? Why taking these data, we don't want it. </div></BLOCKQUOTE>
A slip ratio between tyre and road is required in order to generate a longitudinal force. It's the same principle as a slip angle being required to generate a lateral force.

If you want your car to move forwards and go round corners, you need slip ratios and slip angles... That's why they are in the data.

Regards, Ian