ars ▁may ▁have ▁at ▁most ▁four ▁magnet s ▁( 2 ▁to ▁drive ▁the ▁motor ▁and ▁ 2 ▁" tra ction " ▁magnet s ▁for ▁additional ▁down force ). ▁Motor ▁magnet s ▁must ▁be ▁cer am ic , ▁tra ction ▁magnet s ▁may ▁be ▁polym er . ▁Motor ▁must ▁have ▁a ▁resistance ▁of ▁no ▁less ▁than ▁ 3 . 0 ▁ Ω ▁on ▁each ▁pole . ▁Pol ym er ▁Mod ified ▁( H OP RA )/ Rest rict ed ▁Open ▁( U F H OR A ): ▁C ars ▁may ▁have ▁at ▁most ▁four ▁magnet s ▁( two ▁to ▁drive ▁the ▁motor ▁and ▁two ▁" tra ction " ▁magnet s ▁for ▁additional ▁down force ). ▁All ▁magnet s ▁may ▁be ▁polym er . ▁Motor ▁is ▁un rest rict ed . ▁Ch ass is ▁may ▁be ▁sand ed . ▁Sh unt ▁w ires ▁may ▁be ▁used . ▁Un limited ▁( U F H OR A ▁and ▁H OP RA ): ▁No ▁restrictions . ▁Custom ▁ch ass is ▁permitted . ▁Six ▁ne od ym ium ▁magnet s ▁are ▁usually ▁employed . ▁T - J et ▁Super ▁Stock ▁( AK A ▁F ray - style ): ▁Aur ora ▁Th under jet ▁ch ass is ▁with ▁no ▁tra ction ▁magnet s , ▁modified ▁by ▁motor ▁magnet s , ▁changing ▁ax les , ▁front ▁and ▁rear ▁whe els ▁and ▁t ires , ▁and ▁the ▁body . ▁Limited ▁modifications ▁are ▁allowed . ▁ ▁In ▁the ▁UK ▁ ▁The ▁main ▁gover ning ▁body ▁of ▁UK ▁slot ▁racing ▁is ▁B SC RA