[nealperkins]

OK, my front tire (Metzler) is badly cupped and needs replacing.
My rear tire has plenty of tread, but has developed a more flat contour (vs. the rounder look.)
Is this significant and do I need to replace the rear now too?
Thank you.

 

[Closetchef]

First, how many miles on the tires?
Second, How much tread is left on the rear tire?
third, How much tread is left on the front tire?

 

[nealperkins]

There's about 16,000 on the tires.
There's plenty of tread (can't measure it w/o relocating to bike) and there would be no need to replace them w/o the cupping issue (bad) and MAYBE the issue referred to above.
So, what's the answer on the "squaring off?"

 

[cycledude]

16,000 miles doesn't really tell a lot because different riders wearout tires at different rates. Best to measure tread left to wear bars and proceed from there. I usually prefer to replace motorcycle tires in pairs, if one is wore out the other is usually not far from worn out and the job is all done in one smooth operation. 2 new matched tires will take full advantage of the engineering built into the tires.

 

[Closetchef]

Yep, 16k and you done good. I'd say replace them both.
If you're asking why the rear squared off. the rear always squares while the front wears out on the sides. if you think about it, the front wears out on the sides because there is only stress on the tire when in corners. And the rear when accellerating and decelerating. Mostly when straight up!

 

[Wingman26]

Why does the rear develop the flat spot in the center of the tread? Very simple, 99.999999999% of the time the bike is standing up as it rides down the road. Does it need to be replaced? As long as it has a safe tread in the center there is absolutely no "need" to replace it, the bike will handle better in the curves with a new tire, until it squares off too!

Tire tread depth has customarily been measured in 32nds of an inch, the rear tire should be replaced when the tread depth is down to 2/32" and the front tire at 1/32". Tire tread depth gauges are available at any auto parts store.