[harnoor8940]

Hey guys
Im moving from Toronto to Vancouver (4400 km roughly) in couple of weeks.

I just realized i have 225 45r18 tires in front and 225 40r18 rear tires. I was wondering if that would cause any harm to the tires or overall vehicle while on the road.

I had them on for 3 months now, the shop told me it won’t cause much difference. Since i don’t drive much, i didn’t think about it but now i am concerned.

Please help..

[Llarry]

Originally Posted by harnoor8940

Hey guys
Im moving from Toronto to Vancouver (4400 km roughly) in couple of weeks.

I just realized i have 225 45r18 tires in front and 225 40r18 rear tires. I was wondering if that would cause any harm to the tires or overall vehicle while on the road.

I had them on for 3 months now, the shop told me it won’t cause much difference. Since i don’t drive much, i didn’t think about it but now i am concerned.

Please help..

Your shop was wrong. Particularly for an x drive, different overall diameters front and rear do harm the vehicle. The proper size -- depending on the year of your car -- is probably 225/45R-18. We need more info for a fuller answer.

[harnoor8940]

More info about what exactly?

[RockCrusher]

225/45/R18
Dia: 26.0"
Circ: 81.6"
Revs/Mile: 777

225/40/R18
Dia: 25.1"
Circ: 78.8"
Revs/Mile: 804

The difference in circumference is around 3.4%. My info is for at least some BMW AWD models it is 1%.

I don't think those tires are right for the car.

My 2024 BMW 230ix came with:

BMW 230xi tires:
Front P225/40 19
Rear: P225/40 19
Dia: 26.1”
Circ: 81.9”
Revs/Mile: 774

Both front and rear tires are the *same* diameter.

Think you need to have the car in to a BMW dealer and ask if the tires are ok.

[MineralWhiteF80]

Not sure what year your 330xi is so Ill speak in generalities.

Your front and rear tires on an all-wheel-drive BMW should ideally always be within 0.1 inches (2.5mm) diameter or a maximum limit of 0.6% (4mm, 0.16 inch) difference from each other. People typically round this number to a 1% maximum difference, which accounts for uneven front-to-rear tire wear over time since the drivetrain does not distribute 50/50 power to the front and rear axles all of the time (more like 40/60).

Your current tires are a difference of 0.9", which will put additional stress on the clutch packs inside your drivetrain's transfer case since your front tires are trying to turn slightly slower than your rear tires. You might not perceive any problem, but long term, you can prematurely wear our the transfer case clutch. If you tire sizes were wildly different, you would notice the traction control system intervening much more than normal.

Something else to consider: using the nominal size values of 225/45 and 225/40 is not a good idea because tires often differ in dimensions as the nominal size indicates. This means a 225/40 and a 225/45 could be very close to the same diameter if the 225/40 ran on the large size and the 225/45 ran on the smaller size. It's best to look at actual manufacturer specs for tire diameter to see just how different the diameters actually are.

If this was my car, I would be changing my tires and install FOUR of the same tire size/brand/model on the car. Driving short distances around town might not be enough time for the car to display problems, but driving 4400km might be enough to start overheating the transfer case clutches.

[Llarry]

Originally Posted by harnoor8940

More info about what exactly?

What is the year of your car? Tire sizes change over the years.

[jzeiler4]

If you want staggered you need to have 225/40 F and 245/35 R for an xDrive.

[M3SQRD]

Originally Posted by jzeiler4

If you want staggered you need to have 225/40 F and 245/35 R for an xDrive.

Stock sizes are:

M sport staggered
Front 225/45-18
Rear 255/35-18

Standard/Base square
Front 225/45-18
Rear 225/45-18

I’m surprised x-drive didn’t have an issue with 225/45 F and 225/40 R because that’s a -3.1% difference. X-drive can handle a +/-1.0% difference (preferably -1.0%, larger diameter R tire). Our ‘18 m240ix and ‘20 330ix would not accelerate if the % difference was 1.2%. The issue is the transfer case can’t handle a large % difference and if it calculates the rolling diameters to be different then it basically puts you in limp mode (unable to accelerate).

[jzeiler4]

Those were the stock sizes on my 2021 M240 xDrive when I got it new.

[G30M]

Originally Posted by harnoor8940

Hey guys
Im moving from Toronto to Vancouver (4400 km roughly) in couple of weeks.

I just realized i have 225 45r18 tires in front and 225 40r18 rear tires. I was wondering if that would cause any harm to the tires or overall vehicle while on the road.

I had them on for 3 months now, the shop told me it won’t cause much difference. Since i don’t drive much, i didn’t think about it but now i am concerned.

Please help..

change the tires they need to be the same circumference