Can You Put Smaller Size Wheels/Tires on car w/20's?
 

Looking to buy an A6 w/ low pro 20's on it, not good in my area especially with DW driving. Can you install a smaller size or is the suspension calibrated for what came with the car?

Yes, usually you can but you need to be careful of 2 things.... 1) Brake caliper clearance. Make sure you new smaller rims can accommodate the size of your break calipers. 2) Speedometer - Make sure you new set up does not effect your speedometer. Any of the large web tire companies know all of this info and it would be wise to consult with them before purchasing.

When changing the car's original wheels and tires, the general rule of thumb is that you can go up or down by one inch.

Thanks for the reply. Didn't even think about the speedometer, I was thinking about the dealer blaming something that goes wrong with the car on the wheel size. I have 18's from an A5 with snow tires on them too, they looked a little small, more than 1" different. The stock low pro 19's blow out a little too easily.

When you reduce the size of the wheel, you need to increase the sidewall height of the tyre ("thickness").

If you lined up a 17"/18"/19"/20" Audi OEM wheel/tyre for the A6, you would find they are all the same height. It is important to maintain the same rolling circumference.

The other aspect you need to consider is the offset of the wheel - the offset determines where the centre line of the wheel rests relative to the hub. A lower positive offset number means the wheel sits further to the outside, a higher positive offset means the wheel sits further to the inside.

The Audi A5 (either B8 or B9 series) has a shorter overall height / rolling circumference than an Audi C7 A6. You would need to add a taller tyre (larger sidewall profile, for the same tyre width) to get the height to A6 specifications.

And the A5 uses a markedly different offset than the A6, so using an A5 wheel will have the wheel coming out towards the wheel arch, and this can adversely affect suspension geometry.

You can see the relevant specifications for different Audi models, with respective wheel options here:

https://www.wheel-size.com/size/audi/

And on this separate part of the same site, you can plug in the various numbers to see what you need to do to get the right rolling circumference, the right geometry etc, or alternatively how severe any differences may be.

https://www.wheel-size.com/calc/

You should be able to trade / sell your 20" (although you say 19" in your last post??) and get the next size down in OEM Audi C7 A6 wheels in similar condition to your wheels for, at worst, no outlay other than time.

And all the A6 suspension options should work without issue on any of the OEM A6 wheel / tyre sizes. Suspension calibration issues tend to arise when there is a large difference in the weight of the wheel and tyre (unsprung weight), not so much from sidewall compliance, or the lack of it. You will only have issues if you go outside of OEM configuration, such as using an A5 wheel/tyre size :)

Thanks for that, didn't know that. The 19" are on my '14 A6 TDI, the 20's are on a car that I want to purchase. That's a great site, the A5's don't show that they are in the US market, not sure why. I bought a new take off set of 4G0601025BF wheels and put a set of Pirelli 245/245/VR18 XL snow tires on them, when you put them side to side with my 19's they are more than an inch shorter. You are right about the wheels being different, my 18's fit an A6...great for me. I only mentioned an A5 because a loaner car that we drove looked like it had the same wheel so when I advertised the wheels I included the A5 in the title, I'll have to remove it. Seeing that Audi puts 3 sizes of wheels and tires on the same A6, and their overall diameters are different, there mighty be a difference in the suspension in order to keep the same height off the ground. If the larger wheels are an upgrade why would a Prestige package have the 18" wheels and tires? Better for me NOT to have the larger wheel w/ low pro's but just wondering why. Thanks again.

^^
It is a good site. Wheel specs are no different on US market cars, sometimes there are a few more versions for EU cars, usually because winter wheel sets are much more common in Europe than the US, where they are often not offered by Audi of America.

The Pirelli 245/45R18 tyres are the correct fitment for the 4G0601025BF wheel on an A6. And that wheel is the correct OEM 18" wheel for a C7 A6. It should only be 9mm, about a third of an inch lower than the OEM 19" wheel, assuming that wheel is fitted with the correct 255/40R19 tyre. If the difference is an inch, perhaps you have 45 series tyres mounted on your A6 TDI's 19" wheels? If so, they are too tall, rather than your new 18" wheels and tyres being too short. You are good to go with your new 18" set, and they will be fine with the A6 suspension. Although I can't quite understand which wheels you are now selling, not that it matters.

Bigger wheels are typically fitted to the sporty models, such as the S6, because they have larger brakes and need a larger wheel for clearance. Other than that, it largely comes down to aesthetics, some people like the look of a larger wheel, and are prepared (or not after living with it for a while!) to put up with a harsher ride. As for Prestige package, that is something that Audi of America have created for the local market, which packages the car in a certain configuration. Other markets have either their own packages, or else have wider access to the full option range and can build the car however they want. Seems a reasonable for them to have gone for 18" wheels as the standard fitment for Premium pack, as more people will buy the A6 for refinement and comfort than tearing around a racetrack. Those who want something more sporty without going up to an S6 can always add the larger wheel options.

I see on the new C8 A6 model that has just been released in the US, that Audi of America have made 19" wheels the "standard size", for all trim levels. With a 20" wheel as an option, which must also include getting Sports suspension. In Germany, the new A6 comes with 17" wheels as standard. You then have the choice of getting 18", 19", 20" and 21" wheels for added cost. With whatever suspension you like.

Best of luck with the potential purchase.

I'll have to compare them again, If they are a little smaller/shorter I would think that they could still be used...I think? Height of the car would only suffer half the amount of the difference. Does the TPMS system allow for a smaller diameter, will it allow the values to be stored in the system?

TPMS is not affected as long as all four are the same diameter, which they will be. Once your new wheels are on, and you have adjusted pressures as per the manual (not the door sticker if you are in the US), then save the pressures via MMI.

To be clear, I'll repeat the Pirelli 245/45R18 tyres are the correct fitment for the 4G0601025BF wheel on an A6. You are at OEM spec, and will have no issues.

Thanks, and I repeat that when put up against my 19's they looked too low/short. It would lower the car by half that amount but I'm still concerned. Not sure that you can swap out a 19" option with an 18" option, vehicle height with be slightly lower. At least that's how I see it. Right tire for the wheel but different size option for the car. Not saying that it wouldn't work but car may be lower where it may have not been if the 18's came stock on the car. You would probably know better that me.....just IMHO.

The 18" wheel did come stock on the A6, specifically the wheels you have bought are one of the OEM Audi A6 18" wheels. As I said, the 18" set will be around 9mm lower in total, but you will have around 8mm more sidewall. And I presume more sidewall is why you want to move from 19" to 18" - better ride, better wheel protection.The 18" and 19" are both within spec of the suspension, the ABS system, etc etc.

As I mentioned, the C7 A6 is made for 17, 18, 19, 20 and 21 inch wheel combinations. Audi do not change any setting with the car to accommodate different wheel sizes, as long as the wheel and tyre specs are correct to OEM. The 19" version is not the "magic number" the car was designed for.

If you have an acute concern with ground clearance, stay with what you have and get a more forgiving tyre. You could put a 235/50R18 tyre on the new wheels to give you a bit more than your current total height, and a lot more sidewall, if that is your primary concern. But that is not OEM spec and will throw out your scrub radius by 5 mm, if you used the calculator I linked for you. Probably okay, may have a slight affect on steering / braking response as it is 5mm positive on a car with front drive axles, which need to maintain an overall negative scrub radius. But obviously Audi feel 245/45R18 works best with those wheels on that car. Your call.

So, 9mm lower means 18mm total, it looks a little more than that but I might be wrong. I was thinking that Audi changed something on the suspension to keep the ground clearance the same with either option, so you think not. I have to try them, at least thanks to you I now know that they are the right wheel for the car and not an A5. I don't really want, or need, to buy any other tire as both sets are new. So how do you know so much about Audi's? Thanks for all the info.

Because I try not to buy anything unless I understand what it is I am buying. It's almost a curse :)