referring now to the drawings , and to fig1 and 2 in particular , there is shown a multiple strand roller drive chain constructed according to the teachings of the invention . fig1 is a plan view of a section of the drive chain 10 , which chain is formed in an endless loop , and fig2 is an edge or side view of the drive chain . for purposes of example , drive chain 10 is constructed generally as shown in u . s . pat . no . 3 , 677 , 388 , and this patent is hereby incorporated into the present application by reference , in order to simplify and condense the description of the usage of the drive chain 10 in the intended escalator application . drive chain 10 has three strands in the preferred embodiment , a central or inner strand 12 , and first and second outer or side strands 14 and 16 , respectively . the outer strands 14 and 16 are driven by a sprocket arrangement , which is fully described in the incorporated patent , and which is shown generally at 18 in fig3 . the inner strand 12 drives an endless belt constructed of interconnected rigid , metallic toothed links , also fully described in the incorporated patent , and shown generally at 20 in fig3 . the endless belt 20 shown in fig3 is formed of interconnected toothed links 22 on each of its sides , with the two sides being connected together via step axles 24 , which also pivotally interconnect the rigid toothed links on each side . the escalator steps are attached to the step axles 24 . the drive sprocket arrangement 18 shown in fig3 includes a driven sprocket 26 , driven by a modular drive unit described in the incorporated patent , and an idler sprocket 28 , on each side of the sprocket arrangement 18 , with each side of the sprocket arrangement 18 having a drive chain 10 which loops about the driven and idler sprockets . the driven and idler sprockets each have first and second spaced rows of teeth which mesh with the first and second outer strands 14 and 16 , respectively , of the drive chain . returning now to fig1 and 2 , the pitch of the inner strand 12 is twice the pitch of the side strands 14 and 16 . thus , if the pitch 30 of the side strands 14 and 16 is 1 . 0 inch , the pitch 32 of the inner strand 12 is 2 . 0 inches . outer strand 14 is constructed of interlocking metallic pin links 34 and bushing links 36 , metallic pins 38 , which are associated only with strand 14 , and metallic pins 40 which extend through all three strands . the longitudinal axes 39 and 41 of pins 38 and 40 , respectively , are disposed in spaced , parallel relation . metallic roller sleeves 42 are mounted for rotation on pins 38 and 40 . in like manner , outer strand 16 is constructed of interlocking metallic pin links 34 &# 39 ; and bushing links 36 &# 39 ;, metallic pins 38 &# 39 ;, which are associated only with strand 16 , and pins 40 . metallic roller sleeves 42 &# 39 ; are mounted for rotation on pins 38 &# 39 ; and 40 . the inner strand 12 is formed by disposing roller assemblies on pins 40 , between bushing links 34 and 34 &# 39 ;, with every other roller , or alternate roller assemblies 44 , being of like construction , and the remaining or intervening roller assemblies 46 being of like construction , with the construction of the roller assemblies 46 being different than the construction of the roller assemblies 44 . more specifically , roller assemblies 44 each include a bushing 48 and a deformable , non - metallic , resilient roller sleeve 50 . for example , roller sleeve 50 may be formed of polyurethane having a type a durometer of about 90 . roller sleeves 50 have a first predetermined outside diameter 52 . roller assemblies 46 each include a bushing 54 and a substantially non - deformable , metallic , rigid roller sleeve 56 . they may be separate elements , or they may be one homogeneous part . for example , roller sleeve 56 may be formed of steel . roller sleeves 56 have a second predetermined outside diameter 58 , with the second predetermined outside diameter being less than the first predetermined outside diameter 52 of the resilient roller sleeves 50 . the difference between diameters 52 and 58 is selected to provide the maximum desired loading of the resilient sleeves 50 , as will be hereinafter explained . in the prior art drive chain described in the incorporated patent , the roller assemblies of the inner or drive strand 12 are all constructed as described relative to roller assemblies 44 . this resilient construction was preferred because of the load sharing aspects of resilient rollers , as well as for lessening noise and vibration . when the drive chain is new and its pitch is the same as the pitch of the teeth on the toothed links , the force on each roller engaged by a link is the same . for purposes of example , assume a 48 inch wide escalator having a 20 foot rise which distributes a total of 750 pounds across the engaged rollers with no passengers , and 1 , 875 pounds across the engaged rollers with rated passenger load . fig4 is a graph which illustrates the load on each engaged roller for no - load , and for rated load , with various amounts of chain wear per inch of pitch , from zero wear to 0 . 006 inch wear . the engaged rollers are referenced to the rollers shown in fig3 with roller 60 being roller position number 1 in the graph , and with roller 62 being roller position number 8 in the graph . curves 64 , 66 , 68 and 70 illustrate the force distribution over the engaged rollers for 0 . 000 inch , 0 . 002 inch , 0 . 004 inch , and 0 . 006 inch wear per 1 . 0 inch pitch for an unloaded escalator , and curves 72 , 74 , 76 and 78 illustrate the force distribution for similar wear for a fully loaded escalator . it will be noted that curve 72 indicates an equal force of about 230 pounds on each engaged roller , when the chain is new , i . e ., wear is 0 . 000 inch , and that when the wear reaches 0 . 006 inch per 1 . 0 inch of pitch , the force distribution is unequal . as illustrated by curve 78 , the force on the roller in position 1 is 600 pounds , the force on the roller in position 2 is 480 pounds , the force on the roller in position 3 is 360 pounds , etc ., with substantially no force on the rollers in positions 6 , 7 and 8 . the higher than normal loading on the resilient rollers reduces their useful operating life . the present invention enables the load on a resilient roller to be limited to a predetermined maximum value by alternating resilient and rigid rollers in the drive strand of the chain , and by providing the rigid rollers with a smaller outside diameter than the resilient rollers . in determining the difference in outside diameters , first the maximum desired load on a resilient roller is selected for achieving the desired chain life . for purposes of example , it will be assumed that this maximum load is 400 pounds . the deformation of the resilient material used for the resilient rollers which corresponds to a load of 400 pound is then determined . using polyurethane of the aforesaid durometer , a force of 400 pounds causes a deformation of 0 . 042 inch . then , the maximum chain wear per drive strand pitch at which it is still desired to maintain the load limit , is determined . for example , if it is desired to operate within the 400 pound maximum load limit when the chain is worn 0 . 006 inch per 1 . 0 inch of pitch , the wear per drive strand pitch , which in the example has a 2 inch pitch , would be 0 . 012 inch . the required difference x in radii between the resilient and rigid rollers is then stated by the following relationship : thus , the difference x in radii is equal to 0 . 030 inch . if the outside diameter of the resilient roller is 1 . 125 inches , for example , the outside diameter of the rigid roller would be 0 . 060 inch less , or 1 . 065 inches . fig5 is a graph which illustrates the load on each roller of the fig3 configuration , with no passengers on a 48 inch wide , 20 foot rise escalator , using a drive chain constructed according to the teachings of the invention . curves 80 , 82 , 84 and 86 illustrate the force distribution for chain wear of 0 . 000 inch , 0 . 002 inch , 0 . 004 inch , and 0 . 006 inch , respectively , per 1 . 0 inch pitch . with 0 . 006 inch wear per 1 . 0 inch pitch , curve 86 illustrates that the load is taken by the rollers in position 1 , 2 and 3 , with the roller in position 1 , a resilient roller , taking 400 pounds , the rigid roller in position 2 taking 200 pounds , and the resilient roller in position 3 taking 150 pounds . fig6 is a graph which illustrates the load on the same escalator used for developing the fig5 graph , except with a full passenger load . curves 88 , 90 , 92 and 94 illustrate the force distribution for chain wear of 0 . 000 inch , 0 . 002 inch , 0 . 004 inch , and 0 . 006 inch , respectively , per 1 . 0 inch pitch . with 0 . 006 inch / 1 . 0 inch pitch wear , curve 94 shows that the load is taken by the rollers in position 1 , 2 and 3 , with the resilient roller in position 1 taking 400 pounds , the rigid roller in position 2 taking 1 , 300 pounds , and the resilient roller in position 3 taking 175 pounds . thus , in summary , from no - load to full - load on an escalator , up to 0 . 006 inch wear per 1 . 0 inch pitch on the drive chain , the force on the resilient rollers of the drive chain is limited to 400 pounds , with the rigid rollers taking any excess . even when the chain is worn , the resilient rollers will carry the load most of the time , within the 400 pound limit , as the operation of escalators at full load occurs infrequently , and then for relatively short periods of time . since the major factor in the life expectancy of the drive chain using the prior art drive chain structure is the overloading of the resilient roller , the present invention extends the life expectancy by limiting resilient roller loading .