1864 tire size
 

One of the front tires on my 1864 has a slow leak, and while looking I noticed that the previous owner put bigger tires on the front- 18x8.5 instead of the 16.5x6.5 indicated in the manual.
Pros/cons for having larger tires? Wouldn't that cause a mower deck to sit slightly tilted? Am I better off finding a set of stock 16.5?

The larger (18x8.50-8) sits a little higher and will throw the geometry off, as far as implements goes. However, most of the time, adjustments can be made in the implements, to offset the height difference.

The 1864 has Power Steering, thus should overcome the extra width.