Why odd ball 21" Wheels, 20" is what they are spec for also larger wheels creates tons more expense and odds of rubbing something.
It's also hard enough to find good looking 20" Wheels going larger IMHO just don't look like they belong on a Car and more on a Truck.
The last thing is larger Wheels then the less Side Wall meaning Road Damage to the Wheels and ride like a Tank when you hit a bump.

 

None of what you replied to was what I asked for. I am aware of everything you said. Personally, I love a big fat sidewall on my Challengers like I had on my Super Stock. But with this build, I’m changing things up. I don’t go for cookie cutter builds. The car looks like it is swallowing the stock 20’s. They appear too small. I feel 21” is the sweet spot LOOKS WISE.

 

The thing about asking for advice on forums is that sometimes the best answer is the one you don't want to hear.

Or maybe reword your first post say that you are dead aet on buying 21” rims and you want people to validate your choice.

 

Probably not going to find any good answers here. 18, 20, 22" wheels are the norm. For an oddball size rim/tire combo that hasn't been done by many or any unfortunately sometimes you just gotta take your best guess based on your measurements and just actually buy tires and seeing how they work/fit and see what if anything you need to change. It's not cheap but you can only measure and figure so much Without actually looking at it.