[crabman]

While this is accurate for the issue at hand, remember it isn't a universal rule that applies proportionally. EX: If you put 14" wheels on the F Pace, it will likely (read: surely) handle worse than 18" or 20", for many reasons.

Yeah, similarly if you put 35" mudders on 17s and mounted them you would be taking a big hit in the various benchmarks because the entire package would be heavier. It isn't the diameter, it's the weight that kills although to a lesser extent the same weight moved out from the center of rotation exacerbates the hit. Also going smaller you run into brake clearance issues at around 17 to 18" on most performance cars which limits how far most are going to go. As you know I was of course talking about wheels someone might reasonably be expected to run on a performance vehicle. The latter definition for this car I think is fair because it is marketed that way, people are indicating they are buying in because of the fun factor, it does walk the walk (comparatively) in this segment.

I made a couple mistakes in my post above, I was typing it on my cell phone and was losing track of my thoughts while scrolling back and forth trying to see if I covered it and the grand kids were visiting and sidetracked me several times. I greatly dislike misinformation on forums because soon enough they become the lore if not corrected and I would like to point out my own and correct them. First in the C/D test the car shod with 20s won out on more metrics than it lost and tied a few. This went down along party lines, for example the better rubber of the 22"s pulled slightly more lat G while the lesser unsprung weight of the 20s took all the acceleration benchmarks. It is a very interesting example of which nerf is greater, the rubber or the unsprung weight. At least on this car with these examples we know the greater unsprung weight was the bigger nerf. I said however that it won them all and that isn't correct, I started that whole thought talking about all cars in general, moved into the numbers on this one, then what happens with similar rubber and so on but I jumbled all of that together. The second thing is I used the word ignorance. I still sometimes use the word by it's actual meaning which is that the person(s) didn't know or were not aware which is different than the willful ignorance connotation people have nowadays. I never meant to stamp anyone with the latter label and being a pathetic old man I sometimes forget people cant see my face and gather my intent from that. If someone took insult from that I apologize.

Lets go back then and reiterate the facts while I'm on my PC to clarify some of these things.

I did not pull that 10lb barbell out of my keister. Anyone can wander over to Tire Rack or similar sites and compare the same wheels where available in 20 and 22 and they are going to see about a 10lb difference. Sometimes it can be a little more, sometimes a little less but it's a fair and reasonable number to throw at a wheel when bench racing.

You can't argue with the laws of physics. Strap that ten pound barbell on each wheel and there can be no good result. This is not because I say so and not because I want it to be so, to my knowledge the laws of physics have never been impressed by my thoughts or opinions.

Even where many think logically the wheels should match up with the same rubber they don't. This one is a little less well understood even on the car guy forums. Take the skidpad. You would think that with the same rubber at the same width you're going to get a very similar answer and you're right. The real world isn't a near perfectly flat skidpad however so you have to take into consideration the effects of road surface and road surface irregularities. Once you do that wheel control losses and lower conformity have the 22's losing every time.

Often misunderstood are some of advantages people think they have with larger wheels. Quicker turn-in is often cited and this one has at it's heart real truth. You will get quicker turn in real world but this is a diminishing returns factor that is in practical terms lost as you both go up and get closer in comparative wheel sizing. As an example if you compare a 1980 Camaro's with 15" wheels to this car with 22's you're going to see and feel a massive difference. When you get closer in wheels sizing however the benefits diminish because there is comparatively less sidewall to flex and the sidewall itself becomes stiffer as it gets smaller. When you get into sizing like you have here turn-in becomes a non factor with comparable rubber.

I could go on a long time here, I love cars, they're my hobby/passion. I have been told I get boring though so I'm going to stop myself.

 

[crabman]

Not correct, every single measurable performance metric gets worse as you go larger in diameter. This is a well known, well documented, fact that cant be argued away because physics works. C/D tested this exact car in both configurations showing those results while surprising absolutely no one because the math cant be circumvented. This despite having the weaker all-season rubber. Had the 20s been shod with similar rubber rather than the weaker all-seasons the 22s would have simply been beaten by a larger margin because there can be no other result. Similarly if you stepped down to 19s of similar construction and ran them with the same rubber they would outperform the 20s. This is why all the track rats over on the M3 forums, corvette forums, etc downsize from factory and you see the threads titled "Which 18" wheels will clear "X" brakes?" They do it because unsprung weight is a killer. Just to frame it in another way, stepping up from 20 to 22s is going to add about 10 lbs of unsprung per wheel with a wheel of the same type and brand. That is equivelent to duct taping a 10lb barbell to each wheel because the extra diameter serves no purpose, it's nothing more than extra weight that must be started in motion, kept in motion, stopped, turned, and suspended. And you t hink this is going to be a good thing how?

I get that some like larger wheels for the look. I'm fine with that it's their money and their choice but a lot of people on this type of forum are not aware what they are losing by choosing them in some cases this is because of information such as what you posted which is not correct. OEMs put them on cars because people like the look and wheel options are a huge profit item with high uptake. I'm not completely immune to it myself, I think those E92s with 18s look a little odd and it's not a choice I would make. I would be making that choice understanding it though, not in ignorance. It's all good if you go in eyes open.

 

[crabman]

In the case of ride harshness it isn't a matter of viewpoint, 22" wheels ride harsher with the same rubber while suspended the same way because physics will allow for no other result. There are of course a lot of different viewpoints on whether the increased ride harshness, loss of performance in every measurable objective metric, increased instances of wheel damage, lower wheel control, and other downsides of increasing wheel size are a nerf worth taking for those who prefer the esthetic.

 

[crabman]

How can we be so sure that the performance delta is due to wheels only since it wasn't the exact same vehicle? We've all seen instances were an early, highly flogged press vehicle performed differently in initial tests than a production vehicle once it's arrived. I'm not saying there isn't an impact, but we can't ignore the fact that testing was on different vehicles despite being the same trim.

We don't know, they were both highly flogged press vehicles but either one could have been better or worse than the norm. On the other hand they would seem to be fairly representative because we can simply do the math and the answers jive well with what you read and were expected. Performance is largely a matter of numbers at it's heart.