9.25x10. There are some ag tires that will work, along with tires from the airforce bomb carts, but they will strictly have the ribbed treads. Here is a link to some new old stock I purchased last year of the proper tires:
http://www.mapleleafup.net/forums/sh...ad.php?t=34112
You can also google DC5NB which is a 9x10 tire by STA. That is the tire used on the munitions trailer and will work, although a bit smaller and does not have the aggressive tread of the originals.
There are also some forklift tires which will work, but I found them to be quite small compared to what should be on the gun.