rear-shock & front fork lifespan

[b4cruz]

I read somewhere 20,000 miles for stock motorcycle forks and shocks
longer for sport bikes with premium suspensions.

Or is it better to judge by actual ware even past 20k?
Like if the shock is compressing more than normal with your wieght
or if its starting to leak oil?   How far should a shock go down under your own weight?

Also is it safe to buy older shocks? Probably more of an issue for the heavier 1200s than the 250/400s. How old is too old? Or should you always rebuild before you put a used shock -  no matter what condition the source gives it to you.

My applications are for the lighter b4 so I can probably be more lenient, but the heavier bikes?

[Red01]

Pretty broad questions... depends on many factors. For instance, the stock B12 shock is pretty much crap out of the box unless you weigh under 150 lbs. And by 20K it's probably spent. The same shock tossed onto a B4 will work well, mostly because it's dealing with a lighter weight package.

Better sportbike shocks are rebuildable, so when they start to show signs of performance loss, they can be restored.

[tacoman]

Forks can last a long time if properly maintained.  Usually what does them in is not changing the fluid.  Fluid gets contaminated with water and will start to corrode and pit the internals.  Like Red said, the stock shocks are meager at best. If you plan on keeping for bike for a long time and get into the 20k+ miles range, go aftermarket.