Thanks Dot.
Long structural member can be made articulated in more than one spot if needed like a lot of long trucks and buses. Because most races are started at the start of a straight the vehicle would pull up to a stop before the next bend and go off the course.
If a horse gallops and veers in this is the only time it could be a problem but most of the time they are pulled to the outside or at least straight back. The arms could also be made higher than horse and just have a cloth or plate or something hanging down for the horse to follow behind.

Just tell me to drop the idea if you don't see any benefit in it as it might be wasting time for the forum members. The only reason I raise it is because I personally do see the benefit in doing it. The first question to be answered should be - Will it make an improvement to the racing. While I think it would, it seems I might be a low minority.