I want to get a new PR4 to replace my rear bald pr3. My PR3 front looks like it still has a lot of life on it. Is it safe?

No.  Send it to me before you suffer a catastrophic tire mismatch.


Seriously though, it's fine.  I generally ran through 2 rears per front before switching to the GT-spec Bridgestones.  Rears still wear out faster than the front, but not twice as fast like they used to.

...... the GT-spec Bridgestones.  ...........

the 023 or t30 ??
ran a bunch of sets of the 023gt, trying the t30 this year.

Neither you or your bike will know the difference.  The front and rear almost always wear at different rates.  I have always changed mine (riding motorcycles for 57 years) when they were worn out.  On my C14 there is currently a Dunlop on the rear and a Continental on the front, my other bikes also have mismatched tires purchased at different times with price the deciding factor when choosing between tires of equal abilities. 

I want to get a new PR4 to replace my rear bald pr3. My PR3 front looks like it still has a lot of life on it. Is it safe?

There was recently a thread containing the same topic (although it is not in the topic name)

It is perfectly safe.

http://www.zggtr.org/index.php?topic=16198.msg198654#msg198654

the 023 or t30 ??
ran a bunch of sets of the 023gt, trying the t30 this year.

023 GT.  Running a 180/55 rear, turns in nicely, is lighter, and was available in GT-spec when I last installed new rubber.  Looking around, I see that a 190/55 rear is available in the GT tire now... might try that next go around.  They stick nicely all the way to the edges, and does 2-up just fine.  I run my rear tire at 43-44 psi cold, and it's great.  Of course after my first sportbike experience on Dunlop D204's, pretty much anything is light-years ahead.  I ran 003 RSs on my race bike, and have BT-016s on my Ninja 250.  Ran Pilot Powers on the Superhawk (the race bike) before the 003's, and based on those I'd be completely confident in a set of PR4s.  There are simply a LOT of good choices for tires these days.

I currently have a PR2 on the front and PR3 on the rear.