Optimal ET for 17 inch rims?

[WeekendDriver]

Hi. I want to upgrade from stock 16" to some cool 17" wheels, but I can't figure out the right ET value. People from this thread have anything between 32 and 42 with no rubbing, so I know that fits. But what is the correct, factory-intended value? My understanding is higher ET puts more strain on suspension and hubs, resulting in its untimely demise.

I've found this webpage with a list of factory rim sizes for B6, but it makes little sense to me because it lists different ETs for different rim diameters while in reality the ET is determined by the hub, so every rim designed for the same hub should have the same ET regardless of the diameter.

Did Audi actually put different hubs on cars with different stock wheel sizes?
Do you know what the stock ET is for the sedan with factory 16" alloys?
Will 17" even fit with the same ET?..

[walky_talky20]

The different ET's have to do with the different widths. They are basically adjusting the ET to make sure the outer edge of the wheel ends up in roughly the same place. So a wider wheel gets a higher ET and skinnier wheel gets a smaller one.

As for ideal offset on an OEM 17x7.5 wheel, ET45 is stock, but there is a lot of room to move them out. I run 15mm spacers to arrive at ET30, but that is on a B5. Look around in the suspension and wheel threads for cars with 17x7.5's that have the offset/look you are going for and see what final ET they are running.

[moyenecorniche]

Notice that as the wheel and tire widen, the et is raised. On stock wheels that is for balancing the wheels centerline as much as possible while still clearing the calipers.

I would not be concerned with strain on hubs and suspension from an et of 32-45.
Strain occurs when camber and alignment parameters are changed. Not when fitting larger / wider diameter wheels ( lower profile tire ).

Choosing the wheels and tires is the result of several numbers... On an A4 17" is middle ground. 18" is optimal both for handling and not running such a low profile that any bump or hole becomes a possible disaster.

(1) Are you going to upgrade to better brakes ( to S4 brakes or BBK ) as in Porsche / Brembo 4-6 pot calipers. Now your wheel choice matters.
(2) Are you upgrading suspension ?
(3) will you lower the car on coils or air ?
(4) What type of driving are you intending... Routine commute or pushing the boundaries in the twisties...
(5) Are you raising the performance of the motor, if so then you definitely need brake upgrades, starting with pads and as far as a complete brake system upgrade.

Driving with 17" will improve the response of the A4. mainly because it is a wider wheel ( wider tire ) and the tires profile being lower, the sidewall will have less deflection from steering input and respond quicker...

You need to equate what your plans are for the A4 and then your choices are narrowed for your particular scenario..

[WeekendDriver]

Thanks for the detailed answers with explanations! First of all, I did not realize that lower ET value means the rim is further away from the hub (I thought it's the other way around).

18" is optimal both for handling and not running such a low profile that any bump or hole becomes a possible disaster.

The roads are actually pretty poor in my country. Enough that I've already been advised not to move from 16" to 17" for ride comfort reasons (and I'm not even against 16" all that much, but the stock design is so boring...).
Now let me reply to your questions:
1) No, I'm pretty happy with my stock 312 mm front brakes (and I've just switched to ventilated disks). The car has impressive deceleration as it is.
2) Nope.
3) Hell no! And I'm happy with my 1BR stock suspension (155 mm clearance, if memory serves).
4) Definitely no pushing. Besides, I already like how stable the car feels in speed turns even with this suspension, so no need to sacrifice comfort for now.
5) Not any time soon. If I were to tune the engine, it would of course be silly not to make the suspension lower and stiffer at least by a bit. But for now I just want to drive and enjoy the car without stressing it.

I just wanted a new set of rims for looks, not for performance reasons.

P. S. I like your systems thinking!