a longer stem will make it easier on the rear wheel, but will make the front hard to pull up to start with. for bunnyhops, a short high front end is best. I dont know what stem you have on now, but if you can pop a few spacers under it, get those bars as high as poss. Also, rear sweep on bars is a godsend for bunnyhops. Also, having your brake lever set correctly can help too. Have fun