▁by ▁scen ery . ▁ ▁S lot ▁car ▁racing ▁was ▁a ▁popular ▁f ad ▁in ▁the ▁ 1 9 6 0 s , ▁with ▁sales ▁reaching ▁$ 5 0 0 ▁million ▁ann ually , ▁including ▁ 3 , 0 0 0 ▁public ▁courses ▁in ▁the ▁United ▁States ▁alone . ▁The ▁f ad ▁s put tered ▁out ▁by ▁the ▁start ▁of ▁the ▁ 1 9 7 0 s ▁as ▁am ateurs ▁felt ▁s que ez ed ▁out ▁at ▁races ▁and ▁stayed ▁home ▁in ▁add itions ▁to ▁compet itions ▁against ▁the ▁radio - control led ▁car ▁market . ▁ ▁Common ▁slot ▁car ▁scales ▁ ▁There ▁are ▁three ▁common ▁slot car ▁scales ▁used ▁for ▁competition : ▁▁ 1 : 2 4 ▁scale ▁or ▁ 1 / 2 4 , ▁cars ▁are ▁the ▁largest ▁slot ▁cars ▁commonly ▁rac ed . ▁A ▁typical ▁ 1 : 2 4 ▁car ▁might ▁be ▁ 7 ▁to ▁ 8   in ches ▁long ▁( 1 8 – 2 0   cm ). ▁ 1 : 2 4 ▁cars ▁require ▁a ▁course ▁so ▁large ▁as ▁to ▁be ▁imp ract ical ▁for ▁many ▁home ▁enthus iast s , ▁so ▁most ▁serious ▁ 1 : 2 4 ▁racing ▁is ▁done ▁at ▁commercial ▁or ▁club ▁tracks . ▁▁ 1 : 3 2 ▁scale ▁or ▁ 1 / 3 2 , ▁cars ▁are ▁smaller ▁and ▁more ▁su ited ▁to ▁home - s ized ▁race ▁courses ▁but ▁they ▁are ▁also ▁widely ▁rac ed ▁on ▁commercial ▁tracks , ▁in ▁h ob by ▁sh ops ▁or ▁in ▁clubs .