Inspection mirror and feeler gauge. Your FSM spells it out.

 

thanks guys, I see they do have wear indicators and they look great.
I should get 30k to 40 k out of these

 

Front pads may last 30 to 40k. T have the orignal pads on the front of my 08 Ultra, still good at 34, however I'm on the second set of the rear pads.

 

Like others have said you can measure them with taking them out but if you haven't done anything with them in 15k miles you could clean and service them per this link from Lyndall Racing Brakes. It is for the pre-Brembo calipers so you should have a SM too.

http://www.lyndallracingbrakes.com/service_tech.htm


Milage varies by riding style and you likely have some pad life left but while you have the calipers off you could upgrade to Lyndall Z pads or the Gold Plus.

 

also depends on your riding style, changed my rear pads
at 18K and the fron still are good for quite a while longer.
I tend to use the rear brake more you can tell, trying to
change old habits as the front are dual disc, oh well just
throwing my .02 in............

:icon_pa triot:

 

I use my front brakes more than the rear, but I still have to replace the rear 2 to 1 over the front. I can't explain why.