▁each ▁end . ▁Bog ies ▁were ▁commonly ▁used ▁as ▁load ▁whe els ▁in ▁the ▁tracks ▁of ▁army ▁t anks ▁as ▁id lers ▁distrib uting ▁the ▁load ▁over ▁the ▁terrain , ▁and ▁were ▁also ▁quite ▁commonly ▁used ▁in ▁tra ilers ▁of ▁semi - tra iler ▁tr uck s . ▁Both ▁t anks ▁and ▁semi - tra ilers ▁now ▁prefer ▁trailing ▁arm ▁susp ensions . ▁ ▁Design ▁ ▁The ▁ro cker - b og ie ▁design ▁has ▁no ▁spr ings ▁or ▁stub ▁ax les ▁for ▁each ▁wheel , ▁allowing ▁the ▁ro ver ▁to ▁clim b ▁over ▁obst acles ▁( such ▁as ▁rocks ) ▁that ▁are ▁up ▁to ▁twice ▁the ▁wheel ' s ▁diameter ▁in ▁size ▁while ▁keeping ▁all ▁six ▁whe els ▁on ▁the ▁ground . ▁As ▁with ▁any ▁susp ension ▁system , ▁the ▁t ilt ▁stability ▁is ▁limited ▁by ▁the ▁height ▁of ▁the ▁center ▁of ▁gravity . ▁Systems ▁using ▁spr ings ▁tend ▁to ▁tip ▁more ▁easily ▁as ▁the ▁loaded ▁side ▁yields . ▁Based ▁on ▁the ▁center ▁of ▁mass , ▁the ▁Cur ios ity ▁ro ver ▁of ▁the ▁Mars ▁Science ▁Labor atory ▁mission ▁can ▁with stand ▁a ▁t ilt ▁of ▁at ▁least ▁ 4 5 ▁degrees ▁in ▁any ▁direction ▁without ▁over turn ing , ▁but ▁automatic ▁sens ors ▁limit ▁the ▁ro ver ▁from ▁exceed ing ▁ 3 0 - deg ree ▁til ts . ▁ ▁The ▁system ▁is ▁designed ▁to ▁be ▁used ▁at ▁slow ▁speed ▁of ▁around ▁ ▁so ▁as ▁to ▁minim ize ▁dynamic ▁shock s ▁and ▁consequ ential ▁damage ▁to ▁the ▁vehicle ▁when ▁sur mount