Boy it didn't take long for someone to start in on the tri geek baloney. Seriously folks the OP asked would running hurt his cycling. Absolutely not would be my vote, plus along with weight lifting it's the only way to build bone mass in the legs. Really, unless you're racing, it's a bit embarrassing to be able to ride 100 miles and not be able to run a couple miles, or swim a few lengths in a pool with your kids.
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Non semper erit aestas.