In a race, one car blowing a motor doesn't make the other cars run any better.
In an election, one candidate dropping out inherently means that one or more candidates are going to gain a higher percentage of the vote. That's inarguable.
So no, the analogy doesn't work.
The pundits are wrong time and time again in analyzing who is going to get which demographic of votes. It is laughable how they suggest that when Rubio drops out some majority of his voters will go to Cruz. They also suggest that Bernie supporters will go straight to Hillary though many claim they will stay home.
In the end things are very random, like the weather.
Trump, who I was not going to support no matter what, is pulling a lot of this randomness to himself. Just like the random luck of a car that just happens to randomly run better than all of the rest.
I still like the analogy.