Going from a 24 to a 26 inch tire will give you 1" more ground clearance, assuming that the tires you choose actually measure true to stated dimensions. Tire sizes include the tread in their measurements so a 26 will be 26" overall.
I installed a Perfex 1" lift and HL springs. Before I went with bigger tires I technically didn't have any more ground clearance as the rear dif and hitch was still the lowest point. I did have a lot more clearance under the engine and it made a huge difference.
Honda Foreman Forums: Discuss the latest Honda Foreman in our free Honda Foreman forums. Also talk about Honda's other ATV and UTV's including the Honda Rubicon, Honda Rincon, Honda Rancher and Honda Recon