well dont know about were you race but in our south west winter series, what we call stock class in tc is 13.5 and and speedo setings you want and we all run sorex 28 but no set rule only have to use rubber tyres as for tc4 never had one but still got 2 tc3 and pro4 but moved on to xray t2009 as kept braking front diffs running a spool as no give with shaft drive cars were as belt drive you can get away with spool as belt will skip
