Just use the tyres you'd use for any off road ride, it's not like it's a long ride.

Nothing too soft if you have that much road

I would worry about puncture protection more than anything else . There is no ideal tyre as there is a mixture of different surfaces but with all the recent rain there are a lot of sections that are pretty washed out with a lot of sharp pieces of slate that can easily shred your tyre . Good news is a good weather forcast and a tailwind for Sunday . 1000 competitors , could be tricky on the road section from the oint of Ayre to Ballaugh .