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I'm 51 and the skin on my arms is thinning. Every time I ride past a sticker Bush tall enough to catch my arm, I come home with bloody arms and ripped vented jerseys. Believe It or Not, these fast food cups work pretty well and best of all they're (sorta) free!
I know they look a little hokey but the best part about getting old is you stop caring what other people think lol. I haven't been able to find anything light weight enough or not too bulky that I feel like using. Trust me, I have probably spent $200 or $300 on various "solutions" but in the end, I end up not liking. We ride in 90 degree heat half of the time and most arm guards are either too cumbersome or too hot.
I would love to hear from anyone who has come up with a better solution so that my riding Buddies won't bleed out in the desert because they refused to copy me haha.