I would go with the 9 tooth ski doo drivers.Great quality,plus cheap.Plenty of clearance with the 1.25 track.You will have to clutch and or gear to compensate for the bigger drivers.Also on the 151 it will correct your speedo(more realistic) Reduces wear on rail tips,front of hyfax.I had to lengthen the rear axle slots to get the track loose.I just did this with great results.I have a great setup for 151 at sea level and trail riding.