Tires you currently have on the bike are correct/original size and style for that year. There is a currently re-issued tire that coker has made for them that is a comparable replacement....the call it a 14x6 trials, yours are probably a 4.00x6 stamped carlisle made tire, they called that a "Knobby" but the Trials in 14x6 were the Asian made counterparts of the same era