Hi,

Are yours like one of these?
http://www.volvovic.org.au/wp-content/uploads/2014/05/alloy_wheels.pdf


Look for the rim’s drop center to see if it’s located off center to either side. Some do and in that case put that side up to accept the tire easier.
The drop centers are there to allow the rim to be inserted up into the tires sidewall deeper by shifting on the tire’s bead at an angle into that zone.
Most drop centers can be made to be closer to one side of the rim than the other.
I would like to say the face side should be upwards.
For this reason if you have aluminum rims one should use nylon shaped pushing horns, I call them that?
Other tools use the term shoes.

Here is what I have and these suggestions in this YouTube is an example of ways to get the job done.
https://www.youtube.com/watch?v=bUR401rlpUg
The man knows how to improvise!
I noticed the face is upwards.

If you have to put a rim down on it’s “pretty face” make sure you have that face protected with something with resilience and softness on the bottom
I use a rubber mat to prevent the rim from turning on the base below on my harbor freight manual machine.
I also lengthened my bars that come with the tool and anchor the thing to my concrete floor with plenty of room around it.
I saw one fool mounting his using a wooden pallet. Then you have something else lying around that is a trip hazard afterwards or actually during use.

I pull out the bolts from the red head anchors mounted flush in the floor when done.
It’s solid and the floor is open, when not on use.
The machine is put way with the bar.

Hope this helps others to respond.

Phil