FS9 aircraft gear comes in two flavors: model and texture.

This means the gear is included in the Gmax model and textures (paint and rubber) are added to it. Without knowing the model to which you refer, it would be impossible to answer this question.

P.S. A screenshot might be helpful as well. I've used FS9 since the day it came out and have hundreds of addon aircraft and have never seen this anomaly.