XDRIVE tire diameter question

Gio69 · 10-04-2022, 11:15 AM

Hi all,
I read limitless posts about XDRIVE breaking transfer cases from using mismatched tires or changing only 2 of them. There is a good one for you. How is my bmw XDRIVE M440i G26 equipped with 245/35/20 front and 255/35/20 back? It should be against any limits?
Yet it comes like that from factory.
Any taught? Can I run square winter setup?

NLJ · 10-04-2022, 02:07 PM

Quote:

Originally Posted by Gio69

Hi all,
I read limitless posts about XDRIVE breaking transfer cases from using mismatched tires or changing only 2 of them. There is a good one for you. How is my bmw XDRIVE M440i G26 equipped with 245/35/20 front and 255/35/20 back? It should be against any limits?
Yet it comes like that from factory.
Any taught? Can I run square winter setup?

The M240i is also available in 245/255 front/rear from factory.
So not sure why the M340i doesn't come with this option with the track pack.

HighlandPete · 10-04-2022, 02:36 PM

Quote:

Originally Posted by Gio69

Hi all,
I read limitless posts about XDRIVE breaking transfer cases from using mismatched tires or changing only 2 of them. There is a good one for you. How is my bmw XDRIVE M440i G26 equipped with 245/35/20 front and 255/35/20 back? It should be against any limits?
Yet it comes like that from factory.
Any taught? Can I run square winter setup?

Historically xDrive was very sensitive to tire sizing. BMW have improved the xDrive system through the generations.

Latest transfer case design has better heat and oil management, including an efficiency mode. Vehicles like the M440i don't use xDrive at all times. Much more of the time only the rear wheels are driven. An open clutch, (more of the time), won't be putting as much stress on the drivetrain.

One quote from BMW:

Quote:

The rear-wheel drive bias of BMW xDrive optimizes both the efficiency and the dynamic properties of the compact BMW M model. In driving situations where all-wheel drive is not necessary, the power from the inline 6-cylinder engine is sent to the rear wheels only.

G30M · 10-04-2022, 11:02 PM

They have planned to slowly kill the car within a few years after warranty expires is my only explanation.

Just like first oil change after 3 years and 20,000 miles when they sold me my M340i

Gio69 · 10-05-2022, 11:16 PM

I'm planning after I switch to winters, to check the diameter of the front and back.

Tomct123 · 11-21-2022, 07:11 PM

Quote:

Originally Posted by Gio69

I'm planning after I switch to winters, to check the diameter of the front and back.

Did you switch tires only or wheels/tires? What wheels?

M440i xDrive 20” wheels - looking to run 18” in winter but struggling to find a fit.

wdc330i · 11-21-2022, 07:44 PM

Quote:

Originally Posted by Gio69

Hi all,
I read limitless posts about XDRIVE breaking transfer cases from using mismatched tires or changing only 2 of them. There is a good one for you. How is my bmw XDRIVE M440i G26 equipped with 245/35/20 front and 255/35/20 back? It should be against any limits?
Yet it comes like that from factory.
Any taught? Can I run square winter setup?

Really? It’s about diameter. 35/20 is constant. Width is immaterial.

Downsizing makes sense for winter tires. Your limitations will be your rim widths and the brakes. There are fitment calculators that should help. Start off at the Tire Rack website and enter your make, model year, model and your OEM tire/wheel sizes and then search for tire/wheel winter packages.

upstate650 · 11-21-2022, 08:01 PM

Quote:

Originally Posted by wdc330i

Quote:

Originally Posted by Gio69

Hi all,
I read limitless posts about XDRIVE breaking transfer cases from using mismatched tires or changing only 2 of them. There is a good one for you. How is my bmw XDRIVE M440i G26 equipped with 245/35/20 front and 255/35/20 back? It should be against any limits?
Yet it comes like that from factory.
Any taught? Can I run square winter setup?

Really? It’s about diameter. 35/20 is constant. Width is immaterial.

No it isn't. The sidewall aspect ratio is expressed as a percentage of the section width. The sidewall aspect ratio of a 235/35 tire is 35% of the section width of 235mm. A 185/35 tire is not the same height as a 285/35 tire.

wdc330i · 11-21-2022, 08:57 PM

Quote:

Originally Posted by upstate650

No it isn't. The sidewall aspect ratio is expressed as a percentage of the section width. The sidewall aspect ratio of a 235/35 tire is 35% of the section width of 235mm. A 185/35 tire is not the same height as a 285/35 tire.

Find a calculator and plug it in. But the biggest issue is keeping the ratios the same, front and back.

Here’s one: https://www.1010tires.com/Tools/Tire-Size-Calculator

upstate650 · 11-22-2022, 06:57 AM

Quote:

Originally Posted by wdc330i

Quote:

Originally Posted by upstate650

No it isn't. The sidewall aspect ratio is expressed as a percentage of the section width. The sidewall aspect ratio of a 235/35 tire is 35% of the section width of 235mm. A 185/35 tire is not the same height as a 285/35 tire.

Find a calculator and plug it in. But the biggest issue is keeping the ratios the same, front and back.

Here's one: https://www.1010tires.com/Tools/Tire-Size-Calculator

I'm well aware.

ncskibum · 11-26-2022, 01:49 PM

I have the HP cooling and tire pkg with 19"s. pilot sport 4s
I've done 8 track events and the car is amazing but I need wider fronts for track days but don't really want new wheels.

My understanding is that any front to rear sizes need to be within 1% diameter in order to keep the transfer case happy.

current set up
225/40/19 dia 26.1"
255/35/19 dia 26" difference of .4%

looking at
245/35/19 front dia 25.8"
255/35/19 rear dia 26" difference of .8%

I used this calculator
https://tiresize.com/comparison/

I would go square 255/35 but my 8" front rims max out at 245/35.

If I go with new wheels I may jump to
255/35/19 26"
295/30/19 26" diff = 0%
Not sure if these will clear.

Now to find some 200 treadwear tires!

Comments??

10-04-2022, 11:15 AM	#1
Gio69 New Member 0 Rep 11 Posts Drives: 2022 M440i GC X Drive Join Date: Jul 2022 Location: Toronto iTrader: (0)	XDRIVE tire diameter question Hi all, I read limitless posts about XDRIVE breaking transfer cases from using mismatched tires or changing only 2 of them. There is a good one for you. How is my bmw XDRIVE M440i G26 equipped with 245/35/20 front and 255/35/20 back? It should be against any limits? Yet it comes like that from factory. Any taught? Can I run square winter setup?
	Appreciate 0 Tweet Quote

10-04-2022, 11:02 PM	#4
G30M Brigadier General 3784 Rep 4,135 Posts Drives: BMW M550i; Kia EV6 GT Join Date: Dec 2021 Location: Australasia iTrader: (0)	They have planned to slowly kill the car within a few years after warranty expires is my only explanation. Just like first oil change after 3 years and 20,000 miles when they sold me my M340i
	Appreciate 0 Quote

10-05-2022, 11:16 PM	#5
Gio69 New Member 0 Rep 11 Posts Drives: 2022 M440i GC X Drive Join Date: Jul 2022 Location: Toronto iTrader: (0)	I'm planning after I switch to winters, to check the diameter of the front and back.
	Appreciate 0 Quote

11-26-2022, 01:49 PM	#11
ncskibum ncskibum 11 Rep 17 Posts Drives: 2020 m340i xdrive, Join Date: Apr 2021 Location: North Carolina iTrader: (0)	245/35/19 fr and 255/35/19 rear 1% front to rear max difference? I have the HP cooling and tire pkg with 19"s. pilot sport 4s I've done 8 track events and the car is amazing but I need wider fronts for track days but don't really want new wheels. My understanding is that any front to rear sizes need to be within 1% diameter in order to keep the transfer case happy. current set up 225/40/19 dia 26.1" 255/35/19 dia 26" difference of .4% looking at 245/35/19 front dia 25.8" 255/35/19 rear dia 26" difference of .8% I used this calculator https://tiresize.com/comparison/ I would go square 255/35 but my 8" front rims max out at 245/35. If I go with new wheels I may jump to 255/35/19 26" 295/30/19 26" diff = 0% Not sure if these will clear. Now to find some 200 treadwear tires! Comments??
	Appreciate 0 Quote