This depends significantly on your child, their behavior, interest in college, work ethic, etc.
My parents did something similar, making me pay for college when they could have covered it (it luckily wasn't too much being in-state with a scholarship). At the end of college they then gifted me the $10,000 they would have spent on college. The idea was for me to better appreciate my education, however, I think in their case it was flawed reasoning. I had an innate desire to learn that was independent of how much I spent on college. However, some of my jobs during college potentially interfered with my education due to the time commitment. Once I graduated I didn't need the money, but during college it would have allowed me to focus a little more on my education to not be working paultry paying jobs on the side (though honestly I did pretty well, so I don't know if the distraction of the jobs hurt me that much either).
My point though is that the stated goal, to make me appreciate my education more, did not apply TO ME. That is because of what my goals and motivations were. There are many children I met during college that did not appreciate their education because it was being paid for and wasted the opportunity. Each child is different, and how they respond to such assistance will be as well.
So rather then giving you a flat answer I would say first you need to ask a few questions about your son.
How much does he need the vehicle, and would lack of one make him struggle with college on his side jobs? (In my case no, I had no vehicle in college and it was a mild inconvenience on a few occasions, but not worth the cost of insuring it even if I had a free car).
Do you believe your son will be motivated to work hard and continue to excel in college on his own without any external motivator, like the promise of a vehicle if he does well, to push him to strive harder?
Do you want your son working a part time job in college, that is to say do you feel it's more important for him to have enough time to get the best grades in college, or do you think he can (and will) manage good grades in college while holding down a part time job as well? Alternatively do you think he needs to work a part time job as well to develop more work skills and/or prevent him from going out to keggers and goofing off in college?
Do you think your son already has a good work ethic and understanding of the value of money, or does he still need to learn some of that?
Do you possibly want your son to not have a vehicle his first few years on college, to keep him stuck on campus where he will be learning and/or focused on college encouraged activities instead of going out to parties and clubbing?
Again this depends a lot on your son, so it's hard to answer these questions for you. In general the first decision is rather he needs a car right now. If he is on campus I would argue he probably doesn't. However, if he has a good reason to benefit from a vehicle, such as his living at home and commuting to college or his already having a job/desiring a job that he would need to travel off campus to reach, he may have more of a need for one.
If you think he doesn't need a car immediately I would seriously consider saving it as a 'reward' for doing well in college. Perhaps even adding money towards his 'car fund' every semester based off of how well he does in college. This could give him further motivation to work hard and excel in college if you feel he needs that, and if at the end of the four years you pay for most/all of his car at least he will feel he 'earned' it with his grades rather then that it was something he was entitled to simply as your son. If you go this route I suggest actually having a 'car fund' and a policy of how much you add based off of how well he does, rather then a generic 'do well enough in college and we'll buy you a car after' promise. That way he will see direct harm from a poor semester in college by seeing less money go into his fund, and if he really works hard in college he can perhaps earn a cheap car before his four years are up. Plus, as I said, from my experience a car wasn't too important in college since everything is in walking distance, so it could save on all the car-ownership fees if he doesn't need to use a car.
If you instead feel he needs a car early in college, to help him do well in college. Or perhaps you simply feel he will do well in college no matter what you do and would like him to have the extra opportunities a vehicle would offer, then you may want to consider helping him to buy a car.
I say "helping" him, because letting him feel he had some effect in buying the vehicle will help him to appreciate it. Even if you end up paying 90% of the vehicle's cost, I would make him contribute some amount of money towards purchasing the vehicle himself unless I was 100% certain he had a very solid understanding of the value of money and never wasted it. Perhaps you could offer him a flat sum towards buying a vehicle which would just cover the cheapest car he could get, and let him decide if he is willing to chip in more of his money to buy a nicer car.
In general though the question comes down to rather he needs an object lesson in saving money / earning resources or if he already understands the importance of these concepts, and rather you feel having a bribe to motivate him to focus harder on his schoolwork would actually yield better returns. This is ultimately something only you can decide.