Originally Posted by
hhnngg1
Mainly because most triathletes suck at swimming so the gains are potentially big at first.
However, once you're even to middle-of-pack, gaining speed in the swim is the most work for least yield in triathlon. Cutting off 1 minute off your 28 minute Olympic swim might take 50% more swimming, whereas if you applied that same time to the bike, you'd gain 3-4 minutes. The exponential resistance of water means that going faster takes a LOT more energy and technique than it does for bike/run, so it's well known that once you're better than average, swim gains are extremely hard - harder than bike/run gains to the point that it's usually not worth pursuing those small gains if you haven't maxxed the run/bike. This is even for sprint/oly races where the swim isn't a small % of the race (like an IM).
I think this is correct in many ways. However, I personally find a HUGE benefit to my other sports from dedicated swim practice. I was a swimmer first, and I have a strong swim. But even so, the swim gives me a different type of training that complements the bike and the run. But, regardless, I love swimming, cycling, and running, and that's why I'm so into triathlon. I wouldn't do it if I didn't enjoy it; OP...if you are a crappy runner...train smart, get better on your form, and reap the rewards and personal satisfaction as you improve.
In terms of spending money on a tri bike? Slap on a pair of aero bars for your tri and call it a day. If it goes well, and the run improves, then think about it. If you go into triathlon with passion, not equipment, you'll go further in the end!
And the difference for a tri bike is the aero, mainly due to the riding position that is much lower as most tri cycling courses are generally flat.