Check out some mods I did to a Hi-Max I owned. This was built by Gail Bean from PA. This plane flew great after these mods. I installed a 503 DCDI in place of the 447 SCSI. I removed the 15x5x6 wheels and tires and installed 22x12x8 tires with 8 inch wheels. Here is a short video of her flying Hi-Max with Rotax 503 DCDI - YouTube Before the upgrades this bird had bad ground manors. After these upgrades she handles so much better. Not one ground loop after these upgrades. It helped AOA when taxiing and I believe this helped. It also IMHO put more wind over the Vetical stab. I believe this was another big help. Not to mention how much smother she taxied and landed. Tony P.S. If you need a good Rotax call Rotax Rick out of Florida. He is the best and stands behind his products. He is the best.