I wouldn't have done this without the OK from a Major MC Tire Manufacturer. Metzler states it's ok to mix radials & bias tires on a motorcycle. BUT, the radial must be installed on the rear - never install a radial on the front with a bias in the rear.
So for $60.00 I put a Kenda K671 150/70-17 [OEM is 150/80-17] Rear between the forks. I believe tread depth is 10/32. The lower profile does incrementally affect indicated speed. According to my GPS I'm 5 mph under an indicated 55 mph.
Ground clearance is slightly reduced so maybe that will slow me down a bit!
It handles just great, I can't tell a difference that it's a bias. It's matched with a GoodYear Triple Tread on the rear.
Ordered it from JC Whitney
OUCH

Went to copy a link to paste. That tire went up $40.00. I must have gotten in on their winter pricing or some such dumb luck...Remember this is a bias mc tire. With item surcharge & shipping it was $78.00. Gee maybe I should check the sidewall date code since I haven't. I'm back - Well, it's dated 37th week of '09. Maybe that's the reason for discounting. Less then 16 months old is OK with me.
http://www.jcwhitney.com/k671-cruiser-st-tires/p2015164.jcwx?skuId=394281Mileage should be incredible. BTW I did reverse mount the directional rotation as suggested here.