Originally shared by Greg Nutt
Here’s something I just did to my printer built with 2020 rails yesterday that really made a big improvement in motion smoothness, at least for me. I removed the outer wheels from both the X rail and the Z axis, leaving the inner ones inside the frame only. I found that this allows freer motion with less visible artifacts and my print quality has improved considerably. In all, I now need 12 wheels less than what I started with.
Here is a video demonstrating it:
You can always try the WeldingRod Bot rebuild. It’s an exactly constaint printer which means that the constraint is only on one side of each rail.
Interesting. How do you ensure that the wheels don’t slip?
@Panayiotis_Savva weldingrod bot rebuild?
Here you go:
@Panayiotis_Savva , thanks. I had found this, but wasn’t sure if it was the “rebuild” or the “original”. 
@Rod_Shampine developed this rebuild of the CobbleBot.
@Dushyant_Ahuja I explain it in the video. But, really, I think it is just as it looks. Make sure that the wheels are in contact on both sides and tighten using the eccentric spacers. Not much else to it.
Admittedly, I am finding at times it is difficult to adjust the eccentric spacers such that it minimizes any slop, which seem to slip at times. I think the wider apart you can get the wheels, the better the stability will be. This configuration may not be for everyone.
After further tweaking, I discovered one more thing with this setup. There is a very exact point where the wheels are tightened correctly with the eccentric spacers. Too tight and it will stick at the opposite of the drive end, just enough to look like slop whereas too loose and it will slop. It needs to be tight enough to hold it secure so that the drive side will pull the whole rail aligned but loose enough that it isn’t going to bind against the support rails. But it does work. It is also very important that the rail is perfectly square to the support frame once the plate nuts are tightened down.