Hi,
I have never seen such a combo on FT and wondering if such a combo would look good and didn't cause any issues to car systems.

 

21" front and rear works fine on mine

 

It is more of whether the tire height would be the same, as long as the tire height matches, then it should be no problem. I would talk to the service department of a dealer, they would know for sure.

 

do you mean the overall wheel and tyre height or the tyre sidewall height? I think the former might be slightly different anyway, anecdotally when I had new tyres put on mine (running 21's) they used the GLC AMG spec PS4's which are the same as the Macan spec PS4's apparently, anyway the rear sidewall height was slightly more than the previous tyres I had on the car and I noticed the front under guard scraping over driveways more, I guess from the back end being lifted a few cm and the front coming down slightly. It would only be a slight difference, but it led to a lot of scraping.

 

For those who don't know, the sidewall height is a percentage of the tyre width as shown by the tyre sizing, so a 295/30R20 would have a width of 295 cms and sidewall height of 30% of 295 - 88.5 cms - on a 20" rim (don't you love mixed measurements?). Because rubber is flexible and tyre shapes can vary across manufacturers, it's probably not an exact number that applies to every tyre of the same nominal size.

 

This is exellent page:
https://www.wheel-size.com/calc/
You can compare different sizes and aspect ration values.
The tyre circumference difference is important factor when using stackkered setup. (different sizes on rear/front axle)
The comparisation table bellow of the page shows nicely each value

 

Yeah at the time I was going (on rears) from 305/25/R21 to 305/30/R21 as there were issues getting the same setup with COVID shortages and my tyres were going hard and I was getting wheelslip accelerating at 100kph, the tyre guys thought it would improve traction, not affect speedo (which they thought was read from the front) and give about 15mm extra sidewall height all around, so I suppose that is overall height increase of 30mm but only 15mm rear ride height increase

 

You might consider upgrading to 19” wheels all around. Lighter, cheaper, better performance and of course they look better.