Very little, if any at all. How you train on which bike is really up to you. Some train on the road bike during the off season, and then phase out the road bike out as the season nears, preferring to do a majority of in-season training on the tri bike. Others will train on their road bike until a week or two before a race, then start using the tri bike. No matter how you choose to do it, the more you race, the more time you need to spend on your racing bike.

RP