il ▁vehicles ▁are ▁normally ▁smaller ▁than ▁those ▁found ▁on ▁other ▁types ▁of ▁rolling ▁stock ▁( such ▁as ▁locomot ives ▁or ▁carri ages ). ▁This ▁is ▁because ▁the ▁wheel ▁has ▁to ▁be ▁stored ▁clear ▁of ▁the ▁ground ▁when ▁the ▁vehicle ▁is ▁in ▁road - going ▁mode ▁- ▁Such ▁whe els ▁can ▁be ▁as ▁small ▁as ▁ ▁in ▁diameter . ▁In ▁Australia , ▁whe els ▁for ▁road - ra il ▁vehicles ▁should ▁comp ly ▁with ▁the ▁requirements ▁of ▁AS 7 5 1 4 . 4 , ▁which ▁is ▁the ▁standard ▁for ▁infrastr ucture ▁maintenance ▁vehicle ▁whe els . ▁ ▁T ire ▁ ▁The ▁whe els ▁of ▁many ▁rail ▁vehicles , ▁especially ▁steam ▁locomot ives ▁and ▁older ▁types ▁of ▁rolling ▁stock , ▁are ▁fitted ▁with ▁steel ▁t ires ▁( or ▁ty res ▁in ▁British ▁English , ▁Australian ▁English ▁and ▁others ) ▁to ▁provide ▁a ▁replace able ▁we aring ▁element ▁on ▁a ▁cost ly ▁wheel . ▁ ▁T ire ▁installation ▁ ▁Rep la cing ▁a ▁whole ▁wheel ▁because ▁of ▁a ▁worn ▁contact ▁surface ▁is ▁expensive , ▁so ▁older ▁types ▁of ▁railway ▁whe els ▁were ▁fitted ▁with ▁replace able ▁steel ▁t ires . ▁The ▁t ire ▁is ▁a ▁ho op ▁of ▁steel ▁that ▁is ▁fitted ▁around ▁the ▁steel ▁wheel ▁centre . ▁The ▁t ire ▁is ▁mach ined ▁with ▁a ▁shoulder ▁on ▁its ▁outer ▁face ▁to ▁locate ▁it ▁on ▁the ▁wheel ▁centre , ▁and ▁a ▁gro ove ▁on ▁the ▁inside ▁diameter ▁of ▁the ▁fl ange ▁face . ▁ ▁The ▁inside ▁diameter ▁of ▁the ▁t ire ▁is ▁mach ined ▁to