I just rolled into 49,000 miles on my 08 ZX-14. Probably about 30,000 miles of highway service, 10,000 expressway, 5,000 city and 5,000 sport riding. No consistent drag racing but of course, plenty of hard running, lots of down shifting, some power wheelies and an occasional fast take off in the clutch. I always pull the clutch lever the full travel and I don't do much clutchless shifts unless sport riding at higher rpm.

The clutch pack thickness looked pretty good from a visual check. I did not measure the clutch pack depth but the range from new to shot is only 1 mm so you can see how crude a visual inspection is. Even measuring the whole stack while installed is sort of an estimate.

In a nutshell, here's what I found micing each plate for thickness and feeler gauging each for warpage on a surface plate.

The steels were all EXACTLY at standard thickness. No wear at all, as expected. All steels had zero or almost zero warpage. The innermost steel had a hair more warpage than the other steels but still far less than the service limit.

Fibers: The innermost fiber had 100% life left! It was right at the specced standard thickness. It had a lot more warpage than all other fibers but the warp was far less than the service limit.

The outermost fiber and all eight middle fibers were at about 25% service life. The outermost had a bit less wear than the middle eight. All fibers had zero ~ .0015 mm warpage which is far less than the service limit.

No signs of discoloration or seizure. No unusual wear marks.

The innermost fiber and steel warped a slight bit but there does not seem to be much wear from friction there at all.

The outer nine fibers had very consistent wear. Middle eight were within .0005" of one another. The outermost wore least being .002~.0025" thicker than the middle eight.

I could let it go another 5,000 miles. That would be one more season. Guess it will depend on how likely it is that I will be pulling the clutch out again in the next year. I have a hunch I might go with smaller shims on the HD springs I'm installing.

Pushing 65K on the original stock clutch. No drag starts. no bangshifting. If it ever starts to slip, I'll replace the plates.

Not sure it would slip until the fiber pads were gone and the plates were rubbing steel on steel. You're probably safe at 65,000 but that's about where i'd plan to change.

There's nothing inherent to a zx14 clutch that it wears out in 65k miles. Someone that has a zx14 but might as well have a Ninja 650 (in terms of what they use of the power) should see a lifetime of the bike clutch wear or at least 100k+ miles, if along with their leisure riding style also exhibit actual good clutch habits.

I can imagine sport riding and especially people who do a lot of drag racing being much harder on clutches. But someone that just "rides" the bike clutch should last forever.

You don't hear of people who just ride wearing out clutches. It's mostly drag racers who wear them out. I don't think i'm exactly hard on mine but I have used up 66% according to the thickness of the frictions. I'm assuming that clutch friction thickness correlates to the amount of use but there may be other factors. Maybe the rate of wear slows down as the plates get older, IDK. If the rate of wear is pretty consistent over the life of the frictions, 65k is pushing it as far as I should go. i am leaning toward just putting them back in but i'll be keeping a close eye on it.