I can't believe I didn't see this until this morning. It's been a busy weekend.
You can definitely train up to 13 miles running with your base. And you will likely have to do a run walk type of program. As long as you're not looking to do some blistering times on the swim and bike you'll be fine.
I'm really excited for you. Keep us posted on how your training is going.
Living life like there's no tomorrow.
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2007 Look Dura Ace
2010 Custom Tonic cross with discs, SRAM
2012 Moots YBB 2 x 10 Shimano XTR
2014 Soma B-Side SS