the present invention relates to a method of shaping glass sheets , and more specifically , shaping a heated glass sheet by roll forming , such that undesired curvature may be selectively minimized / eliminated from desired portions of the glass sheet . for example , the undesired curvature may be removed from the trailing edge of the glass sheet . this result is achieved generally by utilizing a glass shaping system which typically has at least ( 1 ) a glass heating furnace for heating glass sheets 10 to a temperature sufficient to enable the glass sheets 10 to be shaped , ( 2 ) a substantially horizontal first roll shaping zone 16 , and ( 3 ) a second roll shaping zone 18 which is configured to be upwardly inclined at a predetermined angle or slope relative to the first roll shaping zone 16 . ( see fig1 .) more particularly , within the first horizontal shaping zone 16 , the shaping system of the invention utilizes one or more pairs of upper and lower shaping rolls 20 , 22 having a first substantially transversely straight configuration and , at one or more selected locations within the first shaping zone , one or more pairs of upper and lower shaping rolls 24 , 26 having a second transversely convexly arcuately curved configuration , as shown in fig2 and 3 . in addition to the configuration of the shaping rolls , the inventors have found , generally , that the shape of a selected portion of the glass sheet 10 to be shaped may be further altered by varying the contact time t between one or more portions of the glass sheet 10 with the selectively configured shaping rolls of the present system 20 , 22 , 24 , 26 . the contact time between the glass sheet 10 and a given set of shaping rolls is influenced by the rotational speed of the shaping rolls , which in turn influences the velocity of the glass sheet 10 as it is transported between the various sets of shaping rolls 20 , 22 , 24 , 26 . the present system is controlled by conventional mechanical and electrical means to allow for variations in the rotational speed of any of the shaping rolls , but preferably the rotational speed of the shaping rolls 24 , 26 having the transversely convexly arcuately curved configuration can be varied so as to cause the glass sheet being transported therebetween to vary between , for example , velocity v 1 and velocity v 2 , which velocity v 2 is less than velocity v 1 . velocity v 1 may preferably be between 0 . 3 m / sec . and 1 . 0 m / sec ., while velocity v 2 may preferably be between 0 . 05 m / sec . and 0 . 3 m / sec . increases and decreases in the velocity of the glass sheet 10 may be triggered by either the leading edge of the glass sheet 12 , or the trailing edge of the glass sheet 14 . it is also possible , and when bending thicker glass may be desirable , to operate the system of the invention where v 1 is equal to v 2 . a decrease in velocity of the glass sheet 10 , as previously noted , desirably translates into an increase in , for example , the contact time t between the leading edge of the glass sheet 12 and / or the trailing edge of the glass sheet 14 and shaping rolls 24 , 26 , preferably having the second convexly arcuately curved configuration . such contact time t at velocity v 2 may be on the order of 1 . 5 sec . to 3 . 0 sec ., whereas contact time t with the shaping rolls when glass sheet 10 is traveling at higher velocity v 1 is on the order of 0 . 5 sec . to 1 . 5 sec . such modest increase in contact time t can , the inventors have found , cause significant changes in glass shape while having little adverse effect on the overall cycle time for shaping a given glass sheet . the present system also provides significant flexibility in the number of different vehicle windows which can be formed on the system without making major changes to the primary components thereof . to more clearly describe the invention , it is useful to conceptually divide the first shaping zone into sub - zones , here called sub - zones a , b and c , as illustrated in fig1 . as would be appreciated by those skilled in the art of roll forming , to achieve the aforementioned objectives of the invention , various combinations of shaping rolls 20 , 22 having the first substantially transversely straight configuration and those 24 , 26 having the second transversely convexly arcuately curved configuration may be utilized . for example , sub - zone a of the first shaping zone 16 may include shaping rolls 24 , 26 having the transversely convexly arcuately curved shaping configuration while sub - zones b and c may include shaping rolls 20 , 22 having the first substantially transversely straight configuration . alternatively , it may be useful to place shaping rolls 24 , 26 having the second transversely convexly arcuately curved configuration in sub - zone c , while the shaping rolls 20 , 22 in sub - zones a and b have the first substantially transversely straight configuration . in yet another alternative , sub - zones a and c may contain shaping rolls 24 , 26 having the second transversely convexly arcuately curved configuration , while sub - zone b may contain shaping rolls 20 , 22 having the first substantially transversely straight configuration . of course , other combinations of shaping roll configurations may be possible and are within the scope of the invention . the shaping rolls 20 , 22 , 24 , 26 may be made from any suitable material ; however , a metal material is preferred . the shaping rolls may be solid or tubular ; i . e ., having some open space within an outer wall of the roll . steel is especially preferred . coverings for various purposes may be used to cover the outer surface of the shaping rolls , e . g ., thermally resistant and abrasion resistant materials such as fiberglass , stainless steel mesh and the like . as previously mentioned , the second shaping zone 18 is preferably upwardly inclined at a predetermined angle or slope relative to the first substantially horizontal shaping zone 16 . with such an arrangement , the glass sheet 10 can , in one operation , be bent in a plane substantially transverse to its direction of movement , and in a plane substantially longitudinal to its direction of movement . in the present invention , however , curvature in the transverse direction is desirably minimized / eliminated and the curvature to a predetermined radius is desirably limited to the longitudinal direction as effectuated by the inclined second shaping zone . in accordance with the provisions of the patent statutes , the present invention has been described in what is considered to represent its preferred embodiments . however , it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope .