This must be obvious but I'll say it anyway... If you plan on taking part in Forzathon Live challenges, do pick a vehicle that is suitable on and off road.
I took part in a Live round in a stock 2017 Ford GT - I didn't think much of it as it was the car I was driving during free roam and was suitably fast enough.
I realised my mistake when first challenge was the danger sign which places a ramp next to that otherwise-impossible-to-reach influence board on top of a house... On the grass. Due to the lack of traction, I couldn't find the right angle to hit it before the challenge ended and I have no idea when that exact challenge will spawn again.
One of the following challenges was a drift zone on a dirt trail which wasn't hard to do, but again, much better suited to an offroad vehicle.
But that doesn't detract from the fact that Forzathon Live is a very cool feature! I'm getting "Freeburn Challenge" from Burnout Paradise vibes 👍