I guess you could hold the shorts up to the sun and check if they're visibly much thinner in the back than somewhere that doesn't get as much stretching. My tights are virtually seethrough in back in normal lighting, but I always wear them over something else anyway.
Best way is just to ask a trusted friend to ride behind and check
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett