How do I know if belt wore out

[Il fog]

How do I know if I need to change belt? Belt on secondary is flush at top and has slop on primary?
Haven't done a thing to this sled

 

[Ruggybuggy]

How long has it been on and how many miles. Loose at the primary is normal.

 

[Il fog]

New to me sled 4000 miles on it it is same width as a new one just trying to learn this sled . With me on it and I mash it (I weigh 220) it seems to slip. It is stock track and studs other post on here says that I need a free ride. , just looking at all options. The takeoff is nothing like my rx

 

[Ruggybuggy]

If the previous owner didn't tell you how long the belts been on it's not a bad idea to change it. Your going to have to find out what's slipping, track or clutches. If not the track then clean your clutches and install a new belt.