But they dont need to extensively test an on road vehicle wearing 35s. They need to test it off road to tweak its quirks and find its weaknesses. The Bronco is going at the heart of Jeep and its off roading finesse. The majority of pre production Broncos are wearing 35s because they are gunning...
As the first car producer to offer 35" tires from the factory, I suppose they want to be sure they get it right. The other guys rolling around on 32s and 33s have been doing so for decades from the factory.