Ados

Going by this calculator, there doesnt seem to be major changes if changing the wheel sizes. So the original wheels where 245/45/19. Iv currently put on 255/35/20 which might even be too small, so if i go with the 255/35/21 im actually better off on the larger wheel???

Man my head is wrecked. Why do i like modding my car so much. It would be so much more less stress if i just stopped!!

John Simcox

As a rough rule of thumb if you go up 1" in wheel diameter you go down 5 on the Aspect Ratio. Your current 20" wheels are too small at 35 aspect ratio (should be 40), but 35 ratio should be fine for 21 inch wheels. 255/40 R20 and 255/35 R21 are the 20 and 21 inch tyre/wheel combination options offered by Audi in the UK

Glisse

If done correctly, there should be no change. The suspension, chassis control unit (Inc ABS, torque vectoring etc etc) is all based on a specific rolling circumference determined by the chassis engineers, much as mchltschr said. It doesn't matter if you have optioned 18/19/20 or 21" wheels on your A6 (which you can in some markets), they will all have approximately the same rolling circumference. So will a space saver wheel, if fitted.

There will be some minor variation, as sidewall profiles change by increments of 5 percentage points is not exact in every case. And there is also a surprising variation between tyre brands, wheels should be exact though.

If you want the wheel arch to look more filled, use a bigger wheel. Even if there is no change in the gap between top of the tyre and the guard, the wheel (as long as it is not black) gives the impression of filling in the space. You pay the price in terms of ride comfort, but this is a small price in terms of the C8 A6 - this is not a BMW or Mercedes, where your glass eye would fall out going to a bigger wheel/shallower sidewall. All the MLB Evo models cope surprisingly well on narrow sidewalls, and the longer the wheelbase, the better they cope.

You could use a taller sidewall profile to fill in the gap, which is what you seem to be considering. Not legal in some markets unless certified / tested. Just be aware that you will be raising the height of the car by exactly the same amount you have reduced the gap below the wheel arch. You may not like that.

As John has noted, you are using the wrong tyre size, you should be on a 40 profile for a 20" wheel, not a 35. At least you now know what the ride will feel like if you decide on 21" wheels!! And the drivetrain is designed for 21" wheels, so not sure where this extra stress on the engine idea is coming from. As long as the rolling circumference is correct, the engine and drivetrain won't care.

But in real terms, the look you seem to be chasing is best achieved by lowering the suspension, which you don't want to do. I think your car looks pretty good as is, although because you are using a 35 profile instead of 40, your car is lower than stock by 12.75mm - and the gap between top of tyre and wheel arch is 12.75mm larger than it should be. Sure you haven't been staring at that gap for too long?

Further to John's post, the correct (global) OEM specs for the C8 A6 are:
225/55R18 on 8.0Jx18 ET39
245/45R19 on 8.5Jx19 ET40
255/40R20 on 8.5Jx20 ET43
255/35R21 on 8.5Jx21 (prob. ET43, as ET is a function of wheel width)

Ados

You are probably right. Iv been staring at it too long 🤣 Ah I was just thinking of a small change by changing the wheels and if I'm going to do it, what my options are. Think I might try the 21s. **** it, sure ye only live once. If it don't like it or it doesn't work out, I can always go back to the ones I have.

Thanks all for the input. Glad to have a good community for advice!!

DadAudi

It also depends on the “ look “ of the wheels as certain ones give the appearance of being bigger then they are.

John Simcox

Interesting though that, in the UK at least, you could not have the 21" wheel option with the 40TDi engine option. Today you can no longer spec 21" wheels from Audi for the UK market with any of the engine options

mchltschr

Same in the US. 2019 offered optional 21" wheels on the A6, but from 2020 onward it has maxed at 20". I'm in a 2021 S6 which is standard with 21" wheels. Not sure if that is a supply issue driving A6 options (doubtful) or there is some implication by Audi on comfort and consumer preferences? To be honest in general I feel like if you're configuring a car in recent years on Audi's site the US options are very limited. Going through the Swiss website for example it's incredible how detailed you can get in your config.

John Simcox

In Europe emissions regulations are driving the way manufacturers do options. Each car needs to have its own unique CO2 calculation based on how it left the factory. To offer an open ended options choice would require the CO2 impact of each and every option and combination of options to be calculated which would be an absolute nightmare for the manufacturer and make it very hard to keep control of the EU requirement to reduce the overall CO2 total for all cars manufactured. Manufacturers, not just Audi are therefore reducing the options and usually bundling a number of options together to make this simpler. Likewise (in the UK at least) Audi no longer offers a choice of wheels (from the factory) it is one option and that is it, wider tyres mean higher CO2. What happens at the dealer or post sale is a different matter of course.

In the US Audi has always been very limited on option choices in part I think because of the culture that buyers expect to buy the car off the to and drive it home the same day. Factory orders take time and the long transit time make it unattractive to many buyers (those on this forum are probably the exception!).