▁back ▁as ▁the ▁Vel oc ar , ▁they ▁are ▁not ▁today ▁common . ▁ ▁As ▁of ▁ 2 0 1 7 , ▁there ▁is ▁at ▁least ▁one ▁ 4 - w heel ▁production ▁model , ▁the ▁Qu attro V elo . ▁ ▁Four ▁whe els ▁tends ▁to ▁further ▁hurt ▁aer od ynam ics ▁and ▁weight ▁compared ▁to ▁three ; ▁but ▁for ▁a ▁given ▁width , ▁four ▁whe els ▁is ▁much ▁more ▁later ally ▁stable ▁than ▁three ▁whe els . ▁ ▁Also , ▁four ▁whe els ▁can ▁be ▁placed ▁in ▁a ▁way ▁that ▁increases ▁lug g age ▁capacity ▁a ▁lot ▁compared ▁to ▁three - w heel ▁designs . ▁ ▁Most ▁vel om ob iles ▁drive ▁the ▁rear ▁wheel ( s ). ▁ ▁This ▁approach ▁is ▁simple ▁and ▁can ▁often ▁use ▁many ▁standard ▁b icy cle ▁parts . ▁ ▁Vel om ob iles ▁with ▁two ▁rear ▁whe els ▁may ▁drive ▁just ▁one ▁wheel , ▁or ▁may ▁drive ▁both . ▁ ▁D riv ing ▁a ▁single ▁wheel ▁is ▁the ▁simplest ▁and ▁light est ▁approach . ▁ ▁D riv ing ▁both ▁whe els ▁can ▁improve ▁tra ction ▁but ▁also ▁increases ▁complexity , ▁cost , ▁and ▁weight . ▁ ▁A ▁solid ▁ax le ▁may ▁be ▁used , ▁but ▁increases ▁fr iction / drag ▁in ▁corners ▁and ▁thus ▁can ▁slow ▁down ▁the ▁vehicle . ▁ ▁One ▁alternative ▁is ▁a ▁differential , ▁which ▁is ▁the ▁approach ▁used ▁in ▁most ▁cars . ▁ ▁A ▁second ▁alternative ▁is ▁to ▁use ▁a ▁pair ▁of ▁r atch ets , ▁where ▁the ▁slower ▁wheel ▁is