Originally Posted by The Jerk
The original rear tire size according to the owner's manual is 130/80-18. Apparently the BT-45 doesn't come in this size (or motorcycle superstore just doesn't carry it). So what are people going with? The 120/80-18 looks like the closest option even though by my calculations it would cut sidewall height by 8mm.
Many people (like me) use a 120/90 rear. Feels a little nimbler but not unstable. Also the speedo will be less off (people say, haven't checked mine but plan to).