Trouble with animating a wheel spin

Hi everyone

I still consider myself as pretty new to Unity and I have trouble with animating the wheels of my car. I got the car model from the asset store and the wheels have a basic rotation of -90° on the X axis in order for them to be standing up (my English may not be good enough to explain it).

I tried to add an animation to rotate them around the Y axis, since it's the one parallel to the ground. But the spinning effect I get make the spin act like my rotation was on the X axis. Same goes for the Z axis.

I don't know how to bypass that. Does anyone have an idea?

Thanks in advance