19 Inch Wheel Dilemma

[Atomsplitter]

Currently have a 2017 750i with the MSport package. I'm not a fan of the tire options available to me with the 20" staggered setup. I know it's an unpopular opinion, but I like to run on run-flats for peace of mind. With the current wheels on the car, an all-season run flat option does not exist and I don't want the hassle of winter tires as I feel like i'd be changing them often due to weather weirdness and periodic trips to florida in the winter.

Looking for recommendations for a 19" wheel to run 245 45R19s as a square setup that will fit over the front brake caliper. Having a hard time finding options that I know will be ok with the calipers. Tirerack configurator doesn't even recognize that the 750 has MSport brakes like it does with other cars.

[Markr]

Are you able to access the 2017 brochure to see if the MSport brakes you have were conditional on 20” wheels or not.

[Qsilver7]

You could also use one of the online part database sites like realoem.com or bimmercat.com and input the last 7 digits of your VIN…then go to the wheel diagrams.

Look to see if there are any 19” wheel offerings…if they are listed, then click on the diagram and read the info to see if any of them can NOT be used with the sport pkg.

[AlteBMW]

OP: If you can't go to 19" but want to stay with RFT, there should be non staggered 20" options avaialable for All Season RFT. That may require 2 or 4 new wheels but you were willing to buy new wheels anyhow.

[Al Pinã]

I have a 2019 M Sport 750i with the stock 19" wheels. They are a squared setup with 245/45/19 tires.

These would definitely work on your car.

Wheel code is 647M

[Atavus]

On mine they show a 245/40/20 and a 245/45/19. The diameter difference is under a millimetre. It’s normal to increase the profile like that.

[Atavus]

That’s not the gap between the tyre and the arch.

[Al Pinã]

Originally Posted by LuckyW

Do you realize that you have to code the height of the suspension because there will be a gap between the tire and the wheel arch, your suspension is set to 20", not 19" ...

Nope, you're wrong. The decreased sidewall thickness on the 20's negates any ride height change.

You think that they would be setting the ride height different from the factory based on the several rim choices available? You can get 21's as stock too from the factory. You're saying these cars are higher up? Nahhhhh.

[Qsilver7]

Ditto…all of the wheel/tire recommendation listed in your owners manual all have the same rolling diameter/circumference. If you don’t believe us…just google for a wheel/tire calculator and compare the 19”/20”/21” tires and you’ll see how close in spec they are:

• 245/45/19
• 245/40/20
• 245/35/21

Another term you can google to get an understanding is “plus sizing”. As the wheel size increases, you decrease the aspect ratio of the tire…which will maintain the same rolling circumference.

[Shantosh Seewooruttun]

Originally Posted by LuckyW

Do you realize that you have to code the height of the suspension because there will be a gap between the tire and the wheel arch, your suspension is set to 20", not 19" ...

What? It is the inner diameter that changes to fit bigger rims. The outside diameter stays the same for 19, 20 and 21's unless a non-recommended tyre is used.

[Moopai]

I have the same setup for winter with Michelin run flats, no issues with the height or the rider. Not sure what the other guy is talking about!

Originally Posted by ALPINA_DREAMS

I have a 2019 M Sport 750i with the stock 19" wheels. They are a squared setup with 245/45/19 tires.

These would definitely work on your car.

Wheel code is 647M

[13M5F10]

Originally Posted by LuckyW

Any more comments ...

Attachment 2726982

I think you're missing the point.

When you maintain the stock wheel and tire sizes on 19,20,21… you don't need to calibrate the suspension. This is from personal experience as I have ran all 3 stock sizes and I am very familiar with the calibration system. You aren't changing the overall circumference of the wheel/tire combo. So suspension heights remain the same. Ask any BMW dealer to confirm.

If I were to go outside of those stock parameters increasing or decreasing overall circumference, then I will need to calibrate the suspension to adjust for the differences in sizes and keep a stock suspension setup and yes, it could impact safety systems and components if you're not running the proper parameters. Example, you decided to do 245/45/20 in the front and 275/30/20 in the rear. You'll have roughly an 8% difference in circumference front to back and difference in revs per mile which will throw systems off. They need to be in alignment and the rule of thumb usually is not more than 3%

[Atavus]

Measuring to that point on the rim guarantees you also need the rim size to calculate the ride height.

[AlteBMW]

Originally Posted by LuckyW

I don't need to ask because I'm sure about this, I am as sure of it as the gear transmision oil is replaceable and the dealer claims that it is not because it is lifetime

Everyone does with their car what consider right, because it is his money and whether it is correct, time will verify.

I do not share any more in this topic because I presented hard evidence that it should be configured and that is what I would do and what others do with their cars I do not care.

My car would be 1000% configured for the new rime size but this is my car, in which I change oil every 10,000 thousand kilometers, not every 30,000 thousand - (everyone does it as he wants, I try to give best advice that I would do for my car)

What hard evidence are you referring to? Opinions are not the same as facts. Plus sizing which results in the same diameter of the wheel/tire assembly has been going on for decades, and across literally millions of cars of scores of brands and types. If you are right, then there would be frequent reports of suspension issues with plus sizing. There aren't. That is the hard evidence.

[Atavus]

Good to put the shovel down.

[AlteBMW]

Ok, Lucky. You win. You are smarter than I am. In fact, you are smarter than everyone. Thank you for everything.

[paul.j.ghosh]

LuckyW

I accept that ISTA+ uses the rim size for calibration. I accept that the measurement A is from the rim edge at the bottom to the lower edge of the wheel arch labeled 1.

I ask you to accept that factory rim sizes with appropriate OEM tire sizes have a diameter that is equivalent and let's call it D. If it were not, your speedometer accuracy would change drastically with different wheels.

Let's call the height of the tire sidewall H such that the diameter D is the sum of rim size R and 2H.

Let's call the gap between the bottom of the wheel arch 1, to the top of the tire, X for ride height computation.

So, ride height, for these purposes, is D, the diameter of the wheel, plus X, the gap between bottom of the wheel arch and top of tire.

Since the calibration opted to measure A from the bottom rim edge it is logical that the rim size is required to compute X. I also submit to you that desired X, regardless of rim size with OEM suggested tire sizes, is consistent given the compression capabilities of the suspension in a given driving mode. Yes, X does become smaller by a certain amount when the suspension is stiffened in sport mode and the car is lowered.

If one were to compute the relationship between A and rim size R you will note that it is a strictly linear relationship. Yes, ISTA+ uses rim size R but only because it opted to compute using the rim edge.

D = diameter of wheel - rim and tire assumed to be a constant
H = height of tire sidewall
X = gap between top of tire and edge of wheel arch labeled 1 assumed to be a constant
R = rim size
A = distance from rim edge at the bottom to the lower edge of the wheel arch labeled 1

D = 2H+R
D = A+H-X

Solving for H in both...
(D-R)/2 = D-A+X

Solving for A...
A=X+D/2+R/2

Assumption is that D and X are constants.

Therefore:
A=K+R/2 where K is a constant.

Yes, your measurement A would vary with different rim sizes R, but that is expected because of the nature of A's start/end point. However, your ride height overall does not change with different OEM wheels and therefore no calibration is necessary.

[13M5F10]

Originally Posted by LuckyW

Millions cars are not pneumatic suspension (I do not say that there will be any problems during normal seasonal changes, only during permanent use) - but even then I would do rim change calibration...

If print-screen of ISTA+ BMW diagnostic program is insufficient proof for you, then you are simply intellectually limited.

This exists to make calibrate the suspension when it's out of calibration or to make adjustments. Yes you need wheel measurements so it can calibrate properly. If you have 19,20,21 in stock sizes they will all calibrate to the same measurements lol.

It's all good. You do you.

[paul.j.ghosh]

What happened to all the posts by LuckyW?

[Atavus]

Flounced.

[Atomsplitter]

Found a solution i'm very happy with. Drag DR77 19 inch, 8.5 width, 22 offset. Love the look and plenty of room between wheel and caliper.

Thanks for all of the input.

I did not get the suspension recalibrated

[LuckyW]

Originally Posted by Atomsplitter

I did not get the suspension recalibrated

Let me know how it works in off-road conditions