Dunlop recommends the following for rear tire size usage:
100/90-19 rear for 125cc two-strokes, 250cc four strokes
110/80-19 rear for 125cc two-strokes, 250cc four strokes with 2.15 rim
110/90-19 rear for 250cc two-strokes
120/80-19 rear for 250cc two-stroke and 450F four-strokes
110/90-18 rears for 250cc four-stroke woods/trails off road use
120/90-18 rear for 450cc four-stroke woods/trails off road use

Pro Supercross/Motocross races
August 13        New Berlin NY, Unadilla AMA Motocross Championship Round 9
Typical conditions: Hard pack with rocks.
Front tire: MX71 90/100-21 with tire pressure of 12 PSI 
Rear tire:  MX51 with tire pressure of 13.5 PSI 
Support:   Dunlop Service Vehicle support, see Brian Fleck

Pro-AM Motocross (Qualifiers to earn AMA pro status):
Tire Recommendation - Dunlop MX51  12 -12.5 PSI for all events unless otherwise stated

August 12-14        New Berlin NY, Unadilla AMA PRO- AM Motocross
Typical conditions: Hard pack with rocks.
Front tire: MX71 90/100-21 with tire pressure of 12 PSI 
Rear tire:  MX51 with tire pressure of 13.5 PSI 
Support:   Dunlop Service Vehicle support,

August 14        Crystal Falls, MI   Valley Raceway AMA Pro-AM MX  906 367-0600
Front tire: MX51F 80/100-21 with tire pressure of 12 PSI 
Rear tire:  MX51 with tire pressure of 12.5 PSI 

Off-Road/Enduro/Scrambles and WORCS
Tire recommendations MX51 or D952 (unless noted)

August 19-20        Washougal WA,  Washougal MX Park  *WORCS Round 7
                                     Possibly MX71 front tire