EMB ERJ 135 ER/LR
Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Workload
Deviation / Discrepancy - Procedural Weight And Balance; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Human Factors
While loading the plane there were many issues with station operations; they seemed very short staffed; also the gate agent working the flight told our FA that people pick up overtime but refuse to do any work during their overtime shift. I did my preflight walk around (inspection) right after the plane pulled into the gate for a crew change. As I was near the cargo area they were still unloading the bags from the arrival. If I can; during my walk around I try to take a quick look to see what is getting loaded; [paying attention to] anything different than your standard bag or box. However; since I did the walk around as soon as the plane arrived; they were still unloading the bags. Nothing was ever [given for] the plane [on] our departing flight. The flight went smoothly; but during my post flight inspection I noticed 5 tires coming out of the cargo compartment; I went back up to the flight deck and pulled the cargo (bag sheet) from the garbage to double check if we were ever told about these tires; which [we were not.] I went and talked to the ground crew unloading the tires and questioned them on how they would tell a crew about tires; and they showed be on the bag sheet how it was done. I went and asked them if there was a way to tell how heavy each tire is. They pointed out to me that the tires are labeled as 100 LBS each; so therefore we flew with 500 extra pounds of cargo we were never aware of.Our weights and CG numbers [could have been off] because of the extra unknown weight.Learning from this event we can try to ask the ground crew when they hand us our bag sheet is there is any cargo that is not your standard bag or box. Also these tires were being sent from one maintenance facility to another maintenance facility; therefore maybe the company can set up some sort of way for maintenance control to have dispatch put a note in our release paperwork about the company maintenance cargo they are going to have us carry.
EMB-135LR FO reported noticing five 100 pound tires being offloaded after arrival that were not on the load manifest.