When someone says "my kart is tight" they could have just as easily said "my kart is pushing" and anybody that has raced any time at all would picture, in their head, the same thing. Both terms explain exactly the same handling situation. Regardless of what term you use, in all likelihood, the solution to the problem would be exactly the same. To me, tight means the kart is pushing, pushing means the kart is tight. Absolutely no difference.