File off a flat spot or look for resin aftermarket ones. Many modelers cross the line from a tire that is load bearing to simply flat or low on air. Modern aircraft don't have as much wheel bulge as do older aircraft. Aircraft that operate of grass or unimproved fields have tire with high floatation. Aircraft which operate of runways are typically hard sidewalls that are solid as rocks and yield little bulge.
If you look at John Vojtech award winning AC-130, you see there is little tire flattening or bulge. www.umm-usa.com
Gerald "Hawkeye" Voigt
http://www.hawkeyeshobbies.com
http://hawkeyes-squawkbox.com
http://imagesbyhawkeye.com
Its not the workbench that makes the model, it is the modeler at the workbench.