Hi - I just bought a Mitas 100/100 C-16 for my Beta 125 and it looks perfect. The bike came standard with a Metzeler 4.00 x 18 and the Mitas 100/100 is marginally lower profile but the same width. The C-16 is also DOT approved and not as dear as some others. See all of them at
www.motorcycletyres.net.au/shop/home.php?cat=255 and you can buy them online.
Thanks
Ken