[MineralGreyMetallic]

I've been searching, but I can't seem to find a great discussion on this topic.

What is lost and what is gained converting the front wheel from a 19" to 20"? A lot of people seem to be converting to 20/20 or 20/21 setup, and I'm confused as to how important it is to maintain the stock setup.

This video with a BMW M Tire Engineer mentions the stagger. I've tried to differentiate below.

Pros for 20" in front (larger diameter, smaller sidewall)
- More grip in the bends
- More grip when accelerating / braking in bends
- Overall greater axle stability

Cons for 20" in front (larger diameter, smaller sidewall)
- Reduced heat dissipation and braking performance in a track situation
- Reduced comfort for every day driving
- Reduced wet traction(?)

What's wrong here?

What's missing?

[M_Power Rob]

Many of us are running 20' all the way around (and some with 20s up front with 21s in rear).

I am on 20x11 in the rear and 20x9.5 up front. I do not track the car, and it is my daily. I am also on M Performance HAS. From a driving and comfort standpoint, no issues whatsoever. With my setup, I did have to address the cooling vents on the front fender inner liners as the tires would rub slightly at max turning position.

[MineralGreyMetallic]

Originally Posted by M_Power Rob

Many of us are running 20' all the way around (and some with 20s up front with 21s in rear).

I am on 20x11 in the rear and 20x9.5 up front. I do not track the car, and it is my daily. I am also on M Performance HAS. From a driving and comfort standpoint, no issues whatsoever. With my setup, I did have to address the cooling vents on the front fender inner liners as the tires would rub slightly at max turning position.

How did you address the rubbing? Did you just remove the vents? Also, what size tire are you running in the front?

The wheels I'm looking at are 20x10.5 ET14 in the front with 285/30 tire.

[M_Power Rob]

Originally Posted by MineralGreyMetallic

How did you address the rubbing? Did you just remove the vents? Also, what size tire are you running in the front?

The wheels I'm looking at are 20x10.5 ET14 in the front with 285/30 tire.

Depending on what your intended use is, not sure I would go that wide up front. I am on 275/30/20 in the front, 305/30/20 on the rears.

This is how the fender rubbing was addressed (note, this is not my liner but a liner my shop did for another car).

[MineralGreyMetallic]

The wheel manufacturer I'm working with says there should be no rubbing with the 20" on the G87.

I'm wondering if the different offset, which from what I understand is fairly aggressive on these wheels, avoids the issue.

I'm a bit clueless with this wheel fitment stuff at the moment, as you can tell.

[M_Power Rob]

Originally Posted by MineralGreyMetallic

The wheel manufacturer I'm working with says there should be no rubbing with the 20" on the G87.

I'm wondering if the different offset, which from what I understand is fairly aggressive on these wheels, avoids the issue.

I'm a bit clueless with this wheel fitment stuff at the moment, as you can tell.

I dont have the offset figures...they are Vossens based on their R&D.

Are you lowered at all? If not, may nit have an issue.

This is my car with MP HAS port setting (I will be adjusting in the next week or so and will have updated pics).

[MineralGreyMetallic]

I've seen various G87s with this same setup and no mention of rubbing.

I also spoke with M2 CCO , who is running the same wheel/tire, and he did not mention any rubbing issues.

[Habber]

I wonder if people bought 2 more OEM rear 20’s and put them in front without issues.

[M_Power Rob]

Originally Posted by MineralGreyMetallic

I've seen various G87s with this same setup and no mention of rubbing.

I also spoke with M2 CCO , who is running the same wheel/tire, and he did not mention any rubbing issues.

There have been many reports of rubbing with 20s once car is lowered (the vents they rub on are protruding out into the tires space, slightly).

[M_Power Rob]

Originally Posted by Habber

I wonder if people bought 2 more OEM rear 20’s and put them in front without issues.

Keep in mind, many are going with aftermarket rims for looks, fitment and weight.

[Ronin76]

Originally Posted by MineralGreyMetallic

I've seen various G87s with this same setup and no mention of rubbing.

I also spoke with M2 CCO , who is running the same wheel/tire, and he did not mention any rubbing issues.

Hi, I know you are thinking Edelweiss. If that who is your are referring to with the sizes you mentioned then you should not have any rubbing.

Also, nice choice. Their wheels look sweet. Do not have my car yet but am considering them even though I do not believe they are forged wheels.

[MineralGreyMetallic]

I don't drive a lot, and if I intend to track the car in the future I will buy a separate set of wheels/tires for that.

I'm mainly concerned with aesthetics, but I don't want to introduce issues or compromise performance significantly.

That is why I'm trying to understand what I gain/lose going from 19->20 in the front.

[Ronin76]

Originally Posted by MineralGreyMetallic

I don't drive a lot, and if I intend to track the car in the future I will buy a separate set of wheels/tires for that.

I'm mainly concerned with aesthetics, but I don't want to introduce issues or compromise performance significantly.

That is why I'm trying to understand what I gain/lose going from 19->20 in the front.

Front what I understand the 20s would provide more control (especially on curves or turns) due to smaller sidewall. Could be a bit more stiffer of a ride. The 19s will be a bit more comfortable due to the taller sidewall. I think aesthetically the 20/21 will look better.

I do not plan on tracking the car rather driving it as my daily so for that reason I will be going OEM sizes. Also if I get 20/21 then I will have a set of OEM tires just taking up space. I figure going 19/20 I can use the tires.

[AZG87]

Originally Posted by Ronin76

Front what I understand the 20s would provide more control (especially on curves or turns) due to smaller sidewall. Could be a bit more stiffer of a ride. The 19s will be a bit more comfortable due to the taller sidewall. I think aesthetically the 20/21 will look better.

I do not plan on tracking the car rsther driving it as my daily so for that reason I will be going OEM sizes. Also if I get 20/21 then I will have a set of OEM tores just taking up space. I figure going 19/20 I can use the tires.

Yup as long as not going crazy specs oem can be reused. I'm doing the same til the ps4s are worn then will upgrade those as well.

[M2Sky]

I run 20’s all round I used my stock rear tires on the front as my rears are 295 now. No rubbing. Didn’t feel any difference from the switch.

[m2not1LE]

Originally Posted by MineralGreyMetallic

I've been searching, but I can't seem to find a great discussion on this topic.

What is lost and what is gained converting the front wheel from a 19" to 20"? A lot of people seem to be converting to 20/20 or 20/21 setup, and I'm confused as to how important it is to maintain the stock setup.

This video with a BMW M Tire Engineer mentions the stagger. I've tried to differentiate below.

Pros for 20" in front (larger diameter, smaller sidewall)
- More grip in the bends
- More grip when accelerating / braking in bends
- Overall greater axle stability

Cons for 20" in front (larger diameter, smaller sidewall)
- Reduced heat dissipation and braking performance in a track situation
- Reduced comfort for every day driving
- Reduced wet traction(?)

What's wrong here?

What's missing?

Larger wheels don't decrease heat dissipation, but rather increase rotational inertia unless moving to a substantially lighter forging such as aluminum alloy 6061-T6. In turn, the brakes must generate more heat for any given braking condition. Very different than heat dissipation, though.

More grip isn't necessarily the case, either, especially on real world roads that are loaded with imperfections. More times than not, it's initial turn-in response that improves more than grip with a "plus" size wheel/tire combination.

Suggested read here:

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

Then there's the fact that BMW engineers spent a huge amount of time and effort (including advanced computer modeling/analysis) in deciding on the stock wheel/tire sizes, which in turn play large rolls in determining wheel rates, stabilizer bar size, damper rates and so on (and vice versa). In other words, each component is designed to work synergistically with the others.

I think too many people mod their cars on a piece part basis without considering this.

I'll be running my 2025 M2 (on order) with the bone stock wheels and tires, with no planned mods in other areas at this time. Should I decide to change wheels, it'll be by moving to higher weight forgings that are otherwise identical in spec to the factory units, with wheel offset being especially important.

Obviously this doesn't mean that all aftermarket parts detract from overall vehicle performance, with carefully selected examples actually improving it.

Anyone considering a wheel swap on these cars should focus on lower wheel weight without sacrificing wheel strength while keeping all other variables (including offset) precisely the same. I'm sure there are some good forged (6061-T6 aluminum) examples out there for these cars, though haven't yet researched the matter enough to make a recommendation. Various tempers in the 7175 aluminum class would be much better (assuming salted roads is a non-issue), though are seemingly impossible to find.

[m2not1LE]

Originally Posted by M2Sky

I run 20’s all round I used my stock rear tires on the front as my rears are 295 now. No rubbing. Didn’t feel any difference from the switch.

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.

[m2not1LE]

Originally Posted by M_Power Rob

Depending on what your intended use is, not sure I would go that wide up front. I am on 275/30/20 in the front, 305/30/20 on the rears.

This is how the fender rubbing was addressed (note, this is not my liner but a liner my shop did for another car).

20" fronts with appropriately shorter sidewalls mess with the spring and damper rates that were specifically engineered to work with the 19" wheels (and vice versa).

Then there's this:

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

[m2not1LE]

Originally Posted by MineralGreyMetallic

How did you address the rubbing? Did you just remove the vents? Also, what size tire are you running in the front?

The wheels I'm looking at are 20x10.5 ET14 in the front with 285/30 tire.

Do the wheels you're considering maintain the exact factory offset and are they no heavier (including tires that are on them) than the factory units? (Answer to both questions should be "yes.")

Way more to this than just going for "the look" and perceived overall handling improvements...

Recommending reading here:

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

As a now retired mechanical design engineer and life long "car guy," I'm keeping my stock wheels unless I decide to upgrade to forgings (for reduced unsprung and total vehicle weight plus reduced wheel/tire rotational inertia).

As I've mentioned elsewhere, there's way more to all of this than just "the look," and oftentimes even optimal grip levels on a billiard table smooth skidpad.

[m2not1LE]

Originally Posted by Habber

I wonder if people bought 2 more OEM rear 20’s and put them in front without issues.

Offsets are almost certainly very different and we know that wheel widths are, too. So I'd strongly recommend against doing this. BMW engineers would have done it if it made sense.

I''ll also note that switching to a "plus one" wheel/tire on the front will have other adverse consequences - even if factory offset an width are maintained, as detailed here:

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

[MineralGreyMetallic]

So, you're saying there is absolutely a negative impact, but what is it?

And if there is a negative impact, when does it come into play? At 50% of the car's limit? 85%? 95%?

I would not take these wheels on a track. If I wanted to track the car I would get OEM spec forged wheels.

That article you listed doesn't really go into any of the specifics you're trying to highlight - like affect of suspension characteristics and handling.

The whole article is based around the assumption that the larger rim will be significantly heavier. Their cons were things like ride comfort, fuel efficiency, and 0-60 decreasing because of the weight.

The wheels I'm going with (20/21 setup) weigh less than the stock wheels so some of those won't apply.

What I took away from the BMW Engineering video is they chose a 20" in the back to increase grip and a 19" in the front to increase comfort. Larger tire in the front should increase understeer, which your linked article also mentions.

[Habber]

Originally Posted by m2not1LE

Offsets are almost certainly very different and we know that wheel widths are, too. So I'd strongly recommend against doing this. BMW engineers would have done it if it made sense.

I''ll also note that switching to a "plus one" wheel/tire on the front will have other adverse consequences - even if factory offset an width are maintained, as detailed here:

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

I see some people have gone 21” rear and 20” front. Why wouldn’t they have just gone 20” all around?