[M2Sky]

Originally Posted by m2not1LE

The thing is that BMW designed the rest of the suspension around the 19" front wheels (and the resulting sidewall height) and vice versa.

As always, maintaining absolute correct factory wheel offset is essential in any non-stock wheel choice because incorrect offset messes up the kinematics of the suspension itself. BMW M engineers go to great length in ensuring that each suspension components (and wheels/tire) componenets work synergistically with the others. I think way too many folks overlook that.

I also think many overlook the adverse effects of a "plus" wheel/tire configuration, as detailed in this article:

https://www.caranddriver.com/feature...-wheels-tires/

Best wheel upgrade for these cars is choosing a forged alloy wheel (6061-T6 aluminum is the most common) and keeping all other variables exactly the same as factory spec - offset in particular. This provides for lighter wheels, which in turn reduce unsprung weight, wheel/tire rotational inertia and overall vehicle weight.

You are correct regarding kinematics I won’t dispute that but this is taken to an extreme.

Your implying bmw set this car up to be the best it can be which they didn’t. They set it up to conform to what they want from it. Compromise of comfort to handling along with a cost budget and meeting dumbass EU regulations.

Any modification from stock would be a compromise in one direction for another or could just be crap in every direction except athletics lol.

I could have taken it the wrong way but the impression I get from your posts is your car will shit if you change your wheels to non oem fitment which simply isn’t true.

[Ronin76]

Originally Posted by M2Sky

You are correct regarding kinematics I won’t dispute that but this is taken to an extreme.

Your implying bmw set this car up to be the best it can be which they didn’t. They set it up to conform to what they want from it. Compromise of comfort to handling along with a cost budget and meeting dumbass EU regulations.

Any modification from stock would be a compromise in one direction for another or could just be crap in every direction except athletics lol.

I could have taken it the wrong way but the impression I get from your posts is your car will shit if you change your wheels to non oem fitment which simply isn’t true.

That is exactly what his posts imply.

[Geighty7]

I rub at full lock steering.

285/30/20 front
305/30/20 rear

Dialed down 1.4’ drop front and back.

I’ll likely shave some liner or buy the clearance aftermarket’s.

As for ride feedback- I just got them done yesterday so I do not have a ton. I also got much needed alignment…so overall my ride is excellent. I haven’t taken any fast turns or canyons yet (I likely won’t with these wheels) but I assume in all honesty 20 in front might decrease performance, but increase looks.

Reason I’m saying that is you have more meat on the tire of course from factory or going with a smaller wheel up front. It’s pretty standard way of thinking.

Will you notice? Depends if you track it. My car is a faux track speck- meaning it looks like it’s track ready, but it’s showroom track ready if you catch my drift.

If I was building a true track mule or canyon carver, I’d opted for 19 or 18 squared with 295 or 305’s.

For cars & coffee standouts, overall looks, and head turning…20 all around is the way to go.

[m2not1LE]

Originally Posted by M2Sky

You are correct regarding kinematics I won’t dispute that but this is taken to an extreme.

Your implying bmw set this car up to be the best it can be which they didn’t. They set it up to conform to what they want from it. Compromise of comfort to handling along with a cost budget and meeting dumbass EU regulations.

Any modification from stock would be a compromise in one direction for another or could just be crap in every direction except athletics lol.

I could have taken it the wrong way but the impression I get from your posts is your car will shit if you change your wheels to non oem fitment which simply isn’t true.

I've implied none of that. Rather, that is merely your emotional interpretation of what I stated.

I merely provided engineering commentary (I am a mechanical design engineer) backed by a third party source addressing the pitfalls of choosing wheels with offsets that differs from factory spec and/or employing spacers.

That it is. I'll also note that I've made suspension/wheel/tire altercations to many of my own vehicles. Thing is, I actually know what I'm doing in making those choices, rather than merely going for "the bling factor."

Now please post a supporting link detailing the specific "dumbass EU regulations" that impact wheel offsets and suspension kinematics.

[Ronin76]

[M2Sky]

Originally Posted by m2not1LE

I've implied none of that. Rather, that is merely your emotional interpretation of what I stated.

I merely provided engineering commentary (I am a mechanical design engineer) backed by a third party source addressing the pitfalls of choosing wheels with offsets that differs from factory spec and/or employing spacers.

That it is. I'll also note that I've made suspension/wheel/tire altercations to many of my own vehicles. Thing is, I actually know what I'm doing in making those choices, rather than merely going for "the bling factor."

Now please post a supporting link detailing the specific "dumbass EU regulations" that impact wheel offsets and suspension kinematics.

Please don’t ever get into teaching. 🤣

Your far more educated than I on this however due to my miss understanding of what you meant I was using it as an example of how cars are not necessarily the best they could be in one way or another due to having to conform to various requirements.

I’m interested to know as an engineer do you look at everything on your own cars from a performance / efficiency perspective or is there a subjective feel basis in there too?

[Ronin76]

Originally Posted by maxwell smart

Whoever thinks the M2 is setup perfectly from the factory would be mistaken.
If your intentions are to just cruise it, the package is close to perfect.
But if you take the car to the extreme you find it understeers like crazy, squealing the front tires all over in the places you want to hold speed, but you cant hold your speed.
I lowered the front of my car using the parts bin method , using oem bmw m3 competition front springs.
The car is still all oem but, I reduced the amount of oversteer getting very close to neutral with this change by lowering and stiffening the front .
One thing should be understood, BMW M2 vehicles are fully adjustable race cars if you understand how to make the changes.
oh, and I just installed 824m wheels as well, other direction from this post but super sick.

Oh man…now you did it. Sheldon is going to tell you all about him being a mechanical engineer, all the things he has published, and a bunch of articles to read.

[MineralGreyMetallic]

Originally Posted by maxwell smart

Whoever thinks the M2 is setup perfectly from the factory would be mistaken.
If your intentions are to just cruise it, the package is close to perfect.
But if you take the car to the extreme you find it understeers like crazy, squealing the front tires all over in the places you want to hold speed, but you cant hold your speed.
I lowered the front of my car using the parts bin method, using oem BMW m3 competition front springs.
The car is still all oem but, I reduced the amount of understeer getting very close to neutral with this change by lowering and stiffening the front .
One thing should be understood, BMW M2 vehicles are fully adjustable race cars if you understand how to make the changes.
oh, and I just installed 824m wheels as well, other direction from this post but super sick.

That is one thing I'm really noticing as a difference between F87 and G87.

G87 understeers way more than I'd like. Never experienced that with my F87.

What will help that?

[aerobod]

Originally Posted by maxwell smart

Hello MGM,
I believe the US cars are engineered specifically to not be as good as the m3 and m4. How did they do that you ask, they jammed us with tall and soft front springs . If the vehicle is tuned to be correct with lower stiffer front springs it takes on a new personality .
If you look at information to reduce understeer, lowering helps, and stiffening helps. there are other ways to reduce understeer as well, you have to research and find out what you can apply to your setup.

G87 has stiffer front springs than the G80/2 and the same slightly softer rear springs of the G81 to give it a bit more power-on oversteer. No "engineered specifically to not be as good as the M3 and M4".

[MineralGreyMetallic]

Will the 20" wheel with smaller/firmer tire sidewall help alleviate or exacerbate understeer, or too hard to know?

[Montaver]

The BMW wheel offsets are determined by EU requirements for snow chains. Given the choice they would develop a more aggressive offset to widen the cars track. All the manufacturers do this, look at Audi for example. If your spending money on aftermarket wheels there is no real downside to getting a more aggressive offset. A lighter wheel will be great for unsprung mass and has a ton of benefits (ride, suspension response etc).

[m2not1LE]

Originally Posted by M2Sky

Please don’t ever get into teaching. 🤣

Your far more educated than I on this however due to my miss understanding of what you meant I was using it as an example of how cars are not necessarily the best they could be in one way or another due to having to conform to various requirements.

I’m interested to know as an engineer do you look at everything on your own cars from a performance / efficiency perspective or is there a subjective feel basis in there too?

But I have taught, with many students strongly benefitting as a result, son.

I strongly urge you to better familiarize yourself with the rules of proper grammar.

Every other thing you stated or asked is equally off base.

We as a nation are doomed when the vast majority of others are either unwilling or unable to learn from those who know better through both formal education and decades of related real world experience.

[priitserk]

There is lot of myth in these posts. First of all, BMW does not develop M cars anymore for track use. Well they advertise this as a capable track car, but they itself have admitted that most of the M cars will never see the track. Just go through the posts and you see that most of them use them as daily drivers (why on earth I dont understand)
Additionally, they have strict EU rules.

I watched the BMW video in the first post with irony. The reason why the went with wider tyres is the weight of the car. Its much heavier than the prev gen and to offer similar performance, they needed much more grip. This is the only reason. Yes sure, different chassis, different suspension etc... but when we get more abstract or look at things higher level, the weight of the car is the issue.

Originally Posted by MineralGreyMetallic

Will the 20" wheel with smaller/firmer tire sidewall help alleviate or exacerbate understeer, or too hard to know?

You alleviate understeer with proper suspension and camber. 305R19 or 305R21 wont make much difference. R21 has considerable amount of more mass so on track it will perform worse than R19. But sure, lower sidewall equals stiffer tyre. You will a bit better lap time but imo this is just compensation of poor suspension.

If you are facing understeer on track and are already going relatively fast then you already are at level where you need coilovers and camber plates. G87 original suspension setup is crap (for track)

For my track setup Im going with R19 wheels and 305 tyre (both front and back). It seems the best setup. Best mass ratio, wide range of semis and slicks, coilovers allow to lower the car meaning the center of gravity will be also much lower than on 21 inch wheel. Add front aero details and you have wayyyyy more downforce at front.

[MineralGreyMetallic]

Good post above, appreciated.

My alignment guy said a similar thing about under steer. He recommended starting with a thicker front sway bar and then potentially camber plates.

Surprisingly I have noticed much better cornering predictability after an alignment, but that could be placebo.

[T-Rexx]

Originally Posted by MineralGreyMetallic

Wheel offset comparison between OEM and the wheels I posted

OEM
9.5x19 ET20 for 275/35 R19
10.5x20 ET20 for 285/30 R20

Aftermarket
10.5x20 ET14 for 285/30 R20
11x21 ET12 for 305/25 R21

I am not so sure about the other posts and their level of concern regarding BMW engineers have calibrated parts and suspension for a 19 and 20 set up only.
Consider BMW M themselves have made a 20 and 21 wheel combo to be fitted to the G platform. They call it the ‘M performance wheel’.

Therfore if BMW M performance team have made a 20 and 21 wheel, that contradicts the statement that BMW engineers have designed the car for 19 and 20 only so any alterations from that will me detrimental.

Furthermore , BMW themeselges have called this 20 and 21 wheel set for sale as their “M performance parts” therfore indicating that not only does it NOT hinder functionality, they are advertising it IMPROVES PERFORMANCE.

[MineralGreyMetallic]

Originally Posted by T-Rexx

I am not so sure about the other posts and their level of concern regarding BMW engineers have calibrated parts and suspension for a 19 and 20 set up only.
Consider BMW M themselves have made a 20 and 21 wheel combo to be fitted to the G platform. They call it the ‘M performance wheel’.

Therfore if BMW M performance team have made a 20 and 21 wheel, that contradicts the statement that BMW engineers have designed the car for 19 and 20 only so any alterations from that will me detrimental.

Furthermore , BMW themeselges have called this 20 and 21 wheel set for sale as their “M performance parts” therfore indicating that not only does it NOT hinder functionality, they are advertising it IMPROVES PERFORMANCE.

Agreed. I'm even less convinced by the doom and gloom of the mechanical engineer with regards to installing non-standard wheels and tires after reading through the manual's tire section.

It lists tire pressure recommendations for 20/21 with almost identical tire sizes to my aftermarket setup.

There's no warning about compromised performance using these configurations. There is nothing in the manual regarding offsets, so it's still an open question for me how my wheel's offsets have affected driving dynamics.

[T-Rexx]

Originally Posted by MineralGreyMetallic

Agreed. I'm even less convinced by the doom and gloom of the "mechanical engineer" with regards to installing non-standard wheels and tires after reading through the manual's tire section.

It lists tire pressure recommendations for 20/21 with almost identical tire sizes to my aftermarket setup.

There's no warning about compromised performance using these configurations.

Well there you go, even in the owners manual!

And again, BMW themselves have made a ‘M performance wheel package’ in 20 and 21 staggered configuration for ‘better performance’!

[MineralGreyMetallic]

Originally Posted by Montaver

The BMW wheel offsets are determined by EU requirements for snow chains. Given the choice they would develop a more aggressive offset to widen the cars track. All the manufacturers do this, look at Audi for example. If your spending money on aftermarket wheels there is no real downside to getting a more aggressive offset. A lighter wheel will be great for unsprung mass and has a ton of benefits (ride, suspension response etc).

I totally missed this post, and this is great info.

In fact, the only mention I found in the user's manual about offsets is in reference to snow chains.

[T-Rexx]

Originally Posted by MineralGreyMetallic

I totally missed this post, and this is great info.

In fact, the only mention I found in the user's manual about offsets is in reference to snow chains.

Bingo!

[TallGibbs]

MineralGreyMetallic here is a VERY generic statement from Les Schwab tires about how wheel offsets affect handling:
Too Much Negative Wheel Offset =
increased steering wheel kick-back
Additional stress on the entire suspension
Poor handling
https://www.lesschwab.com/article/wh...with%20braking.

Some other considerations mentioned in a Motor Trend article:
scrub radius affected, wheel kickback, "effective wheel spring rate", wheel bearing loading

So yeah, it seems like there is certainly evidence of wheel offset having various affects to suspension performance. However, we have all seen many cars on the road with all sorts of offsets/lowering/camber and the cars still drive. So, what is the true magnitude of these affects???? Hard to say without having all sorts of kinematic modelling and full suspension design models available.

These subjects are much more difficult to get actual data available on (as opposed to temperature based subjects where measuring data is much easier). BMW "M-Performance" options certainly seems like a highly reliable data point to what is "totally safe", and then reputable wheel suppliers seem like the next best option for validating a design choice. Third data point I would look to is people who are tracking their car with the wheel choice you are thinking because they have certainly stressed their system more than an average road use case.

[TallGibbs]

Originally Posted by MineralGreyMetallic

Good post above, appreciated.

My alignment guy said a similar thing about under steer. He recommended starting with a thicker front sway bar and then potentially camber plates.

Surprisingly I have noticed much better cornering predictability after an alignment, but that could be placebo.

I do have a question here about correcting understeer for those who track their cars: my experience with car handling/dynamics changes is only from FWD setup changes and then iRacing sim racing setups. My experience has shown that a STIFFER front sway bar (anti-roll bar) is going to ADD understeer, so I'm a bit skeptical on this advice from "the alignment guy."

Can anyone with track experience in the G87 M2 suspension verify setup changes/affect. How would go about "correcting" understeer in low to mid-speed corners (ignoring aero affects)? Stiffen the rear, or stiffen the front?

[ourlee]

The cars are not dialed in to some 'synergistic nirvana' that is and always will be world without end, amen...they are rather dialed into an average use case that also meets regulations across worldwide markets…

THIS is the proper response to “the BMW engineers know all” boys because these boys forget the finance (and government) guys sit in the engineering meetings.