im starting to wonder if my cycling shorts need to be retired. ive been running on the same ones for the trainer for a while now… maybe a couple of years cycling through 3 different pairs, all of them being the same brand and design.
Well, I am still using a couple pairs of at least 15 YO bike shorts. One is an old Performance and the other is Pearl Izumi. The Performance shorts are coming apart, but the PIs are still going strong. I am dumping both for bib shorts, whenever I get around to cleaning out my sport clothes drawer.
Reason #1- when I expect to be riding with other people and the fabric of my existing shorts is transparent enough to be considered lingerie
Reason #2- when I come across a kickass sale
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If somebody is coming up behind me to pass and I hear a reference to a full moon then I will know my shorts have worn through.
I have a couple of good bib shorts and a couple good shorts. Those are usually used for longer rides. For shorter trainer rides I grab whatever old shorts are in the drawer
I usually have about 3-4 pairs on the go … ones just for cycling/running training … a couple of race only ones. I usually replace them when the elastics in the legs/waist start getting worn and weaker. So my race only ones usually last longer and then become a training pair.
When you realize yer ass is showing and you can get some pretty good shorts for $35 bucks over at The Black Bibs
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I’ve got several old pair of shorts and bibs used only on the trainer that have been patched in the crotch. I tried fabric tape and failed but sewing has held up.
When they charge $150 to $200 for something that is less than $20 worth of material ya gotta make em last 
It depends but like others have said when the material starts getting too thin. I’ve had some De Soto ones last 8-10 years before that happened.