Exactly, it’s not the size of the wheel it’s the aspect ratio of the tire.

 

Well... Bigger wheels of like construction still reduce performance in every measurable metric. There is no getting around that and alone says everything I need to know.

 

Not really, larger diameter wheels and lower profile tires improve handling....but it is largely a style thing.

 

Back when we were on 14s yeah, but not true now, hasn't been true for years. You will hurt every measureable performance metric and that includes increasing resistance to turn in, longer braking, slower acceleration, less traction due to the reduced conformity, etc. The best wheel sizing now in performance terms is the smallest one that clears the brakes. Added bonuses include better ride comfort and less chance of failure when encountering road hazards. These things are not my opinion, the only way you get a larger wheel of the same construction to perform better is to find a loophole in known physics and exploit it with your previously unknown discovery. I'm not going to be holding my breath on that one.

 

I certainly believe you and feel much the same, but more from a “seat of my pants” perspective than of physics. These modern MB’s handle SO amazingly well, I laugh when folks talk about their need or desire for “better handling.” Are they pouring their S Class into city street turns at such high speeds that they need additional grip? I guess I can understand talk like this in the AMG forums, concerning the sports cars, but when it comes to my daily driver luxury sedan, give me the deepest, cushiest side walls I can get. I really lament the move to 4-Matic and the larger brakes as standard equipment in the USA, requiring 19” wheels. I would have so much preferred RWD, standard brakes and 18” wheels, as I had on my W222’s.

 

My own experience driving the same car on smaller and larger diameter wheels does not bear that out. My LS460 for example, I had an LS460 on 18s and an LS460L on 19s, the 19s handled sharper, turn in was better, car felt lighter on its feet. Every car I have bought over the last couple years I have tested on several different size wheels, and always found the smaller wheeled cars to feel floatier and boatier and number than the same car on larger diameter wheels, including the S Class. There is obviously a point of diminishing return, but the difference is there. I like a ride over handling also, thats why I chose 19s for my S560, the 18s were too small and werent available with the AMG package which was a must have for me, and the 20s hurt the ride too much, so I chose the 19s...and my car rides incredibly while still looking great. In a 223 I would probably choose 20s.

This is an interesting video, he found the same subjective feel differences that I described (largest diameter wheel had the best handling feel in dry, smallest felt best in wet, but in reality times were very close, he also found the middle tire the best combination of ride and handling and noise, which is what I found when shopping for my S560):

 

My GLB35 AMG came with 21" Conti 255/35R21 summer tires, so I have been following this thread as the wheel/tire sizes match... For winters I got 20" wheels as there was no 21" A/S or winter tires were available. 20" Alpin 5 winters felt better esp with softer compound. Later MB service recommended me to switch A/S tires for 21" which I did when Michelin PS A/S 4's became available in stock... Although better in comfort, the ride was still harsh. MB service lowered the air pressure below recommended 39psi and ended up with road rash from manholes, so I increased to recommended psi esp I didn't want to risk with potholes...

Finally I ended up with 19's with PS A/S 4 and definitely they are more comfortable and floaty due to higher sidewall with 4psi lower recommended air pressure. I don't feel the small cracks anymore and the stopping distance is similar. Maybe 19" may match the corner performance to 21" with higher air pressure, but it might kill some of the comfort. I might test it later and see. Other option was changing 20 winters with A/S, but then again the tire pressure may not be lowered as much due to road conditions though MB recommends same psi for 19 and 20's for GLB35... Lookwise 20" profiles look nicest on the car with AMG brakes, but comfort is better with the smaller 19" wheels... I had 19" Conti A/S on GLK350 and there was no problem with those even with big potholes...S-Class is heavier than the GLB/GLK.

 

The smaller wheels will always give a softer ride, the statement I was refuting was that handling gets worse when the wheels get bigger.

 

It isn't an opinion. Performance is reduced with bigger wheel sizing, the bigger you go the greater the losses when comparing like constructions at greater diameters. Anything else is a mathematical impossibility and cannot happen. These losses occur across every measurable metric and this includes the oft mentioned turn-in because you've increased rotational inertia.

If you want to discuss feel now you're talking about dynamics which is another subject. I'm not going to get into that one too much other than to say the big wheels equal better performance myth is strong and IMO people conflate the wagon wheel feel with good due to the myth at times. You have a generation of drivers who grew up with that myth now; they were raised to think big wheels with low aspect tires is what good feels like. But is it? Different story here than with performance, where the math rules. I'm not going to put myself in a place where I'm telling someone what to like but I would say it's interesting to ask yourself why you like something. It didn't happen in a vacuum.

 

Then explain how this person did not see diminished performance when he went up in wheel size? This isn't a math equation this can be measured in the real world and he measured it.

At the end of the day all that really matters is driving dynamics. Who cares about actual metered performance when you are going to be driving the car in a regular way every day, all that matters is how it feels. Instead of calling people stupid followers for liking what they like why not just accept that different people like different things?

I am not someone who wants the biggest wheels, or who feels that the biggest wheels give the best performance, but all I have to do is drive the same car on different sized wheels and the difference in how the car handles and feels is clear. Going up in wheel size in general sharpens the handling but hurts the ride. To me its about finding the sweet spot, which I really feel I have with what is on my particular car. I would never buy one of these cars on 21s.

I have driven many S560s on 18s, and they ride a little softer but they also feel a lot looser and boatier which overall hurts the way the car rides to me. I don't want to drive a Lincoln Town Car. If someone prefers that...thats fine...thats why there are options.

 

All things being equal, wheels of larger diameter than necessary to clear the brakes, of the same construction, will always reduce performance in every measurable metric because no other outcome is possible. The implication there is pretty obvious in regard to your wanting an explanation.

As to the rest, I'm not calling anyone stupid. In general, people believe a lot of things based on various "knowns" that are false. I count myself among that group and I catch myself up in it often enough, I don't think I'm clever but I don't think I'm stupid either. The big wheel myth is sold every day because it pays well and few bother to actually check what "everyone" knows; over the course of decades its become entrenched. More so I think because at one time it was true. If I gave the impression that I think people are stupid, I apologize. My intent was to provoke thought.

Let me rephrase: If you, by you, I mean anyone and include myself, like something based on a false premise what does that mean, and would you want to reconsider your position after you became aware? Keep in mind that if the myth didn't exist, you might still like the feel of lower aspect tires better because you may or may not have (wholly or partially) based your opinion on what you believed is better. In the real world however people tend to put strong emphasis on what they believe is better or true and it's hard to shake an opinion once formed. You know all that, what you may not know is that I myself like the feel of low aspect tires outside of comfort; but I can't say how much of that was colored by what I've read, been told, think I know.

I'm not too old to learn, I'll be wrong again, and I hope, do something about it. That boaty feel you mention used to be considered a good thing, the way a car should feel. Was it good? Or did we just tell ourselves it was good? See where I'm going here?

 

You continuing to say that over and over again with nothing to back it up doesn't make it true. I posted a real world test that refutes that statement which you ignore and you have provided nothing. Show us something that backs up what you are saying.

Not trying to have a philosophical discussion. I can drive a car and decide what feel I like without my decision being "fed to me by society" thank you.

 

You may as well have said "here is a test proving the world is flat."

 

If you can’t back up what you’re saying, then it is in fact simply your opinion. Sorry.

This guy found lap times within a second and the fastest lap time was the largest diameter wheels…how do you reconcile that?

 

Think about it for a second man, you've moved the moment of inertia further from the rotational center; what must inevitably result from that? Lol, I'm not going to spoon feed you. If you think known physics don't apply to cars I can't help you.

 

Set aside your assumption that you are smarter than me for a minute and read what I'm saying. The reality is what you expect will happen based on your understanding of physics isn't what plays out in the real world because you are looking at it the wrong way. We are not discussing larger overall wheel/tire combos, but just the size of a wheel within the same size wheel/tire combo. Overall diameter of the wheel/tire on the car does not change, all that changes is what part of that diameter is wheel and what part is tire. If we are talking about larger wheel/tire combos vs smaller, then of course you are right...but we are not.

Where you are missing why this turned out this way is the behavior of lower profile tires vs higher profile tires as they slide over in a corner. The less sidewall the less the whole wheel slides towards the outside of a turn while the tread maintains contact with the road surface. Increasing the diameter of wheels does not increase the overall diameter of the wheel/tire combo, that stays the same. The difference is what portion of that diameter is a material that has no give (the wheel) vs a material the deforms when put to a lateral load (the tire). The less the tire deforms under lateral load the more grip the tire has which is why lap times are shorter, you can confidently carry more speed through a corner. Feel is improved because the directional change is more precise since again there is less tire to deform. If you drove the cars flat out you would find that the grip is probably the same ultimately but the smaller slip angle increases handling feel and improves confidence which lets you drive faster.

This is called the slip angle. Lower profile tires have smaller slip angles.

https://www.suspensionsetup.info/blo...ip-angle-truth

From the article:

But please by all means keep spoon feeding me

 

One more thing to consider is the more square set up of the 20"/21" tire with lower sidewall vs 19" tire. For example, Michelin PS AS4 255/35ZR21 has tread/width of 9", section width 10.2" vs Michelin PS AS4 255/45ZR19 has tread width 7.9", rim width 8.5", section width 9.8" per tiretrack specs. 20" spec is similar to 21" but changes on 19" which gives a more different driving characteristics in comparison to 20/21" esp with lower tire air pressure required for 19... There was no AS4 255/50ZR18, so I checked 245/50ZR18 and it has similar thread width of 7.9" so it is more a manufacturing decision on Michelin. DWS06+ has tread width of 8.6" on 255/45Zr19.... So there is more variations in these tire tests depending on the tire manufacturers...

 

Not going to work. With current material technologies the wheel portion of the combo is heavier than the tire. Like for like at the same total circumference the combo with the larger wheel will always be heavier. This is a loss by itself. You've also moved the weight further out, another loss. Again, at equal circumference.

There's more, but I have to ask myself if it matters? You just tossed out a post which is incorrect at the most fundamental level based on a search that was based on what? A desire to support an argument that defies known physics? What am I supposed to do with that?

These things are real. Go to the truck forums and ask what happens when you throw the big wheels and tires on there. They'll tell you the truck will accelerate slower, your braking distance will be longer, the truck will resist turning due to that rotational inertia you pumped up. The latter can be so great you need to make upgrades to the steering. Think about it. The forces at work are different only in scale.

If you go to the track you'll see the track rats have downsized their wheels to the smallest that will clear the brakes. Doesn't matter if it's the M3 guys, the Corvette owners, Porsche, they all do it. Think it's because they're trying to go slower?

Maybe they're stupid, the real pros run the wagon wheels. Think about what you see on a race car, any race car; wagon wheels or something else?

I don't know where to go here. I like you so I'm going to give you the last word because I'd prefer an amicable relationship with an agreement to disagree to the alternative. Mine is that I didn't make the physical world or the physics that define it. I don't own this; the sun doesn't come up in the morning because I say it comes up in the morning.

 

I wonder if the designer of these cars was thinking smaller wheels might be better?

 

Again, I provided lots of information and source data to back up my position and you provide nothing. Everybody is wrong but you. I think we’re done here.

 

This was a development designed to get around regulations stipulating the maximum wing width at the front. There wasn't enough room for the gear and the drivers feet while keeping the wheels inside the wing width so some clever person came up with this one. It had the added benefit of increasing braking area without the losses associated with larger wheels. It didn't last long because rule changes stipulated no more than 4 tires total.

 

I wish it was this simple...

I've tried replacing the P-zeros with PS4S, which had thicker side walls. Still blew 2 tires on the first sizeable pot-hole I encountered out of town.

 

Then buy smaller wheels.

 

Did exactly that and would recommend to anyone still on 21s

 

Yeah I absolutely would not buy one of these on 21s, if there was an in stock unit I wanted on 21s I would make them swap them.