Running carrying weight - is there any point?

Did you train for this 'challenge' race carrying a tire (tyre)? In any case, if it is a question of your legs feeling like jelly, there are plenty of running workouts that will help you achieve that feeling that are more conducive to improving your running. Carrying a weight isn't a recognized training method because of the injuries it causes and of course time spent healing from an injury is time you aren't training and thus improving.