the invention is embodied in the drive wheel arrangement of an otherwise conventional self - propelled combine . an end portion of the combine drive axle 10 and one set of dual drive wheels 12 is shown in fig1 . each end of the axle 10 includes axle housing 14 , one or more spacers such as the spacers 16 , and a planetary final drive assembly 18 . two identical wheel and tire assemblies 20 are secured against the mounting face 22 of axle flange 24 by wheel bolts 26 . in this exemplary embodiment , axial spacing of the dual wheels is arranged to suit harvesting of row crops planted in thirty inch rows and , in this case , on ridges 30 . thus , so that the dual wheels may straddle a row while providing at least minimum clearance for the side structure of the combine body 31 , the width of spacer 16 is chosen so that the center line 32 of the duals is spaced at a convenient multiple of half row spacings from the center line of the combine -- in this case seventy - five inches . thus the duals at the opposite ends of the combine drive axle straddle pairs of rows or ridges spaced five rows apart . when the crop row spacing is relatively narrow , and particularly when the crop is planted in the ridge as here , it is convenient for each tire of the duals to run midway between the rows . thus in this case , the center lines 34 of the dual wheel tires are spaced thirty inches apart . looking now in more detail at the structure involved in the dual wheel arrangement , each axle flange 24 includes a pilot boss 40 surrounded by a concentric set of threaded wheel stud holes 42 . the center or disk 44 of each each wheel assembly 20 is generally conical in form with an external circumferential rim of flange 46 to which is welded , in an offset relationship , a conventional rim 48 . rim 48 accepts a conventional tire 50 . at the center of the disk 44 is a wheel mounting flange 52 normal to the wheel axis and having a concentric pattern of holes 54 matching that of the axle flange 24 . a central bore 56 of the wheel disk center 44 is dimensioned for piloting onto the pilot boss 40 of the axle flange 24 . in final assembly , a clamping ring 58 and wheel bolts 26 clamp the pair of wheels to the axle flange 24 . as an aid in mounting the duals to the combine axle , a pilot stud 60 or preferably a pair of pilot studs is used as shown in fig2 . each stud is threaded at one end 62 and has a pair of transverse holes including an intermediate retaining hole 64 and a &# 34 ; wrenching &# 34 ; hole 66 towards its chamferred end 68 . also used in mounting is an elongated retaining rod 70 which has a hooked end or handle 72 . principle steps in mounting one set of duals 12 to one end of the combine axle 10 are as follows ( see fig2 ): 1 . two pilot studs 60 are threaded into axle flange holes 42 , spaced about 180 degrees apart as indicated in fig2 . 2 . the first wheel assembly 20 is guided onto the studs 60 with the rim and tire offset inwards . the wheel is slid inwards so that the wheel center mounting flange 52 is against the axle flange 24 . 3 . retaining rod 70 is passed through the retaining holes 64 in both pilot studs 60 . ( note that each retaining hole 64 provides a transverse bearing surface against which the retaining rod 70 bears to restrain the wheel .) 4 . the second wheel assembly 20 is guided onto the studs 60 followed by the clamping ring 58 ( this condition is indicated in fig2 ). 5 . wheel bolts 26 are then started in the holes not occupied by the pilot studs 60 and tightened sufficiently to retain the assembly in the &# 34 ; snug &# 34 ; condition shown in fig2 . 6 . the wheel assembly is then rotated so that the retaining rod handle 72 is downwards so that the retaining rod 70 may fall ( or be pulled ) out of engagement and the already inserted wheel , bolts 26 tightened . 7 . the pilot studs 60 are now removed for example , by inserting a tommy bar ( not shown ) in the outer hole 66 to assist in rotating the studs . the remaining two wheel bolts 26 are then installed and all wheel studs tightened to recommended torque . in an alternative installation procedure , which may be useful particularly for installation of larger diameter or heavier wheels , a first step is the insertion of short pilot studs 74 in the axle flange 24 ( see fig4 ). use of these shorter studs may facilitate installation of the first of the wheel assemblies . the first wheel may then be secured temporarily by using wheel bolts 26 while the short studs 74 are removed and the longer studs 60 installed . the remainder of the procedure described above may then be followed . procedure for removing the dual wheels is essentially a reverse of that described above except that in some circumstances it may be convenient to remove the pilot studs 60 before finally removing the inner wheel . as can be seen from the drawings and the above description , the structure of the wheels comprising a dual set is simple and clean in appearance , lending itself to economical manufacture . the use of identical wheel and rim assemblies for the inner and outer of the pair of duals has a potential for reducing manufacturing and inventory costs as well as errors in assembly . spacing apart of the wheels of the pair to produce the desired straddle position derives entirely from the deep dish offset concept used for the wheel center 44 . this not only simplifies the structure , in that no additional spacers or connecting members are needed ( other than the simple and conventional wheel bolts 26 ), but produces a large outwardly tapering open space 76 to minimize the possibility of mud and trash build - up between the wheels . an advantage of using pilot studs ( 60 , 74 ) in the mounting or dismounting of the duals is that operators are required to manipulate and / or control only one wheel at a time . the inner wheel may be safely secured and restrained in its proper location ( by means of retaining rod 70 ) while the outer wheel is being manipulated into and out of position . the combination therefore is one of simple and economical structure with good functional characteristics and convenient mounting and dismounting procedures .