thoughts for tires

well I went to the honda dealer where I bought my formans from, and started off by asking if a snorkle would void my warranty, he said yes, then I asked about taller tires, and what he said made a little sense, he said that with out a jet kit and pipe, the largest tires he would go with would be 26's because the tires would change up the gear ratio and that I would loose enough horsepower to notice it. what I want to know is who has an 06 forman, with tires taller than 26's, and if so what kind and what if any mods, and how well dose it preform.