Here's the thing...how about we spend the $10 to have the tire mounted and let the rider decide how it "feels"? I've had 190/50, 190/55 and 200/50 rear tires on my bike and I still like the 190/50 best even though the general consensus is that I "should" like the 55 series tire better. Oh and "O" is totally right, different brands and/or series tires can have completely different profiles to them. The "60" or "70" is only relevant to that particular tire. Who knows, the guy might appreciate a slower turn in...besides, even if you guys are right and the change will "flatten" the tire, it will also "lower" the front end which typically quickens steering. If it's any consolation, I have a 50% 170/70 Pirelli Diablo the kid can have...

I personally, don't see any "danger" in changing the tire...Heck, raise the tire pressure 3 lbs if you're worried about it...