Higher reaction torque than input value

Hello everyone...

I'm running a simple analysis to measure the torque transmitted to a contact patch on a wheel in SW Simulation. In the image below I apply a 134 Nm torque to the shaft face about its axis, the shaft transmits torque to the wheel which has a fixed patch at its base.

The problem is that when I'm checking the reaction forces and torque, I'm getting a torque of 138 Nm.

I expected to get a bit less since the contact definition of the gear teeth is No Penetration with 0.2 coefficient of friction. So I'm wondering if it's just a margin of error or something.

In the image below, the torque is measured from a point on the axis

I've attached the Assembly as well.

Any help will be greatly appreciated

Kind Regards,

David

SolidworksSimulation