Don't go too big on the rear either a 120/80 - 18 or a 120/90 - 18 too large a tyre will rob power & effect the handling, 250cc dirt bikes need some slip on the rear, if you put too large a tyre on the bike won't turn.
I have been using MT21's on my WRR & D606's on the TTR, the MT21's on the WRR turn in really quick, the D606's don't turn in as quick & do have a small amount of slip or understeer on the front.
If you run the 120/90 on the rear drop the gearing to a 13T on the front to keep the gearing the same
Hi all just got a 2004 ttr250for reasonable price, the bike came with a 140 80 18 tyre on the rear my question is there any downside to this size in the rear, bike seems to ride ok and clear in the swingarm and gator
The gearing is 13 front 52 rear.any info appreciated.
A 140 is miles too big for a little 250, 120 max even 110 will turn better, find grip better and offer less power robbing resistance. Have a look at the link in the above comment. Asking about tyres is a bit of a minefield as everyone has a different opinion usually related to their differing uses and priorities and regular riding conditions. Good luck.
Rich.