ESTPs are always big people. ISTPs are usually not.
ESTPs are aggressive, unless life has beaten them down, and even then they either become apathetic and unhealthy or turn unstable and dangerous. They need to dominate their surroundings and other people. I don't think they'd say this if you asked; it's just what they do.
ISTPs are logical and thorough in their pursuits, although their wisdom at selecting pursuits is frequently questionable. These are the people who know everything there is to know about motorcycles, IMO. They like having fun, just like ESTPs, and they also might drift through life, also like some ESTPs. If they do have a goal, they'll work hard for it, but they don't look as visibly intimidating and "Move out of this train's way" like ESTPs on the way up.
ESTPs don't usually look smart, even if they are. They don't seem high class or educated or polished or academic no matter how high they climb. I find that strange because when they are focused they are just about the most effective type, but it is what it is. Perhaps it's because their interest in knowledge tends to be either 'this is a hobby' or 'I can use this'. They don't take ideas in themselves seriously. They're too reality-based.
ISTPs can look smart or not depending on what they are doing in life. If they are an engineer, they're going to know about engineering and look 'smart'. If they are a firefighter, they're going to become obsessed with motorcycles and look like your average guy.
Neither type is motivated by academics for its own sake, but the ESTP is most maladapted for academia and is likely to be persecuted by teachers for standing out and being an individual instead of an automaton. Neither type likes to be controlled, but this is written on the ESTP's face whereas the ISTP is more low key.
Many ESTPs, if they are in the mood, can be really funny and 'the life of the party'. Very jolly, like Santa Claus. ISTPs can't be Santa Claus.
These types are radically different. The orientation towards adventure and action is about the only similarity. One is mild, the other is fierce. One is a technician, the other is a warrior. Both could be pioneers, soldiers, and so on, but one is a "Viking" and the other is not.
I dont know anything about motorcycles. I have actually restricted myself from owning or having one
I am not a good example of your knowlegde. I learn everything and anything and can apply it almost instantly with very good at application of it. Engineer bored me because its not enough hands on. I want a balance of theory and hands on.