Relation b/w slip ratio and drag force.....Race car Vehicle Dynamics help...

Prashant_

hii guyz....

this is the first time i am posting on this forum and hope i ll get help....

I was going through Race car vehicle dynamics by milkins and found a relation given on pg 64
which says....

Drag force={(slip ratio +1)(Input Torque/loaded radius)} - Tractive force

I cant understand how does slip ratio gets involved in this reaction?

Any help would be appreciated as this concept has to be used by me for a project...
Looking for an urgent (plzzzzzzzzzzz) reply...

thnx....