I'm an ironman distance triathlete. I'm very good on the bike and run. My swimming is middle of the pack. For sprint races I will get my HB above my Lactic Threshold. I've developed this ability with my cycling background. I would suggest keeping your HB about 5 beats below LT for sprints. You still need your legs for the run. On the run you can keep it at LT +- 3 beats. Do lots of brick workouts after you've developed your aerobic engine.

Start any bike leg slower than your expected average then build up to your goal. Too many triathletes get over zealous and go out too fast. For cycling time trails I have the time to warmup, which starts the lactic clearing process. For triathlons you typically need to start this process during the event, so build slowly. Once your legs have adapted to the lactic clearing process you can push your HB closer to or above LT.

For 1/2 Ironman distances I will keep my HB 10 beats below on average on the bike. For Ironman distances I will shot for 10-15 beats below.