If you're 5'11, there is no way you'll fit on an A-Bike. I'm 5'7 and that bike was too small for me!! Why not look into buying a Xootr kick scooter? If there are no hills this kick scooter is much faster than an A-bike. Just wear gloves and knee pads because you will wipe out.

http://www.xootr.com/kick-scooter_mg.html

I had an A-Bike and sold it after 4 rides. Too slow, poor rolling and dangerous small wheels.