Tire Options - Running Staggered M-tech rims -- 19s

[RocketyMan]

I always loved the look of staggered rims--which is why I got them for my X5 and was on a hunt ever since I got my X3. Once I got the rims for my X3 my next quest was to look for tires from the 18s that came with it.

Well looking for tires for staggered 19s is not an easy task, set-aside that they're two different sizes (obviously)--but rather odd ones. Evidently, the stock running sizes are very slim pickings for a matching set. In addition, there are more issues with the stock-staggered tire sizes.

[RocketyMan]

The stock 19 staggered actually are a terrible size suggestion for rolling revs per mile. I think I read somewhere that on AWD vehicles the wheels need to be within a 3% difference as to preserve the Xfer case (transfer case). When running 18s this is not a problem because inherently the rims are the exact same size in all dimensions, therefore, the xfer case isn't constantly differentiating front/rear.

In this example of the 19s, we see that the rear wheel is actually smaller in circumference, thus, more revs/mile is needed. This would put stress on the xfercase as it would have to constantly differential the front and rear drive shafts. The clutches setup in the xfer case are setup to have some slip when the actuator is fully unloaded. This probably might not be a problem if the OPERATOR/OWNER of the vehicle follows the strict maintenance schedule of changing out the xfer case fluid every 30k miles--but if not, then the clutches in the xfer case end up wearing out until nearly full actuation does nothing to transfer power to either front/rear axle.

[RocketyMan]

So the BEST option I found was to go up a size on both the front & rear 19s to a tire size that is more common AND equal rolling circumference. In the example below the front AND rear have equal rolling circumference. This is the most ideal for the xfer case as to preserve the clutches and also gives plenty of tire sizes that match both front and rear brand/model/etc.

Matching same tire brand/model is important as no two brands nor models are going to have the same wear characteristics.

[RocketyMan]

Now since these tires I found are technically a size up, there will be differences in reporting speed from the stock 18s. With the stock 18s, I already have about 4 mph "offset" from the reported speedometer speed vs actual. This has always been annoying, but in the case of sizing up on the 19s, I would now be more close to the reported speed--which is convenient. Albeit it is only 1 mph max @ 70mph, this is actually fairly reasonable!

[RocketyMan]

I love stock BMW rims as they have the correct bolt pattern, correct offset, and hub-centric. There are so many options for BMW rims that I really don't like any of the aftermarket ones as they just seem interior to me--namely the characteristics I mentioned above.

[RocketyMan]

So I went with the sizes of 245/45-19 and 275/40-19 for the front and rear respectively. The rims are 8.5" and 9" in width respectively. This allows for the up-size to be a little bit "meaty" as some might say. I'm OKAY with this as this will give me a tiny bit more "curb-protection" when someone (not me... ) will drive the vehicle. The X3 is already a fairly compact car and putting bigger wheels on the unit would be utilizing the wheel-wells to the max. From what I found, the rears were the tightest from any control arm or shock with a good clearance of 1/4" from any critical component interference.

[RocketyMan]

So far I haven't had any rubbing or weird noises of that nature from driving it. I'm fairly happy and content with this nice upgrade to 19s and not having to worry about tire sizes and availability.

[Bogart79]

What brand and model tire did you end up with?

Any noticeable difference with running that size?

I’m also looking at replacing my stock 19 inch staggered M wheels.


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[RocketyMan]

Originally Posted by Bogart79

What brand and model tire did you end up with?

Any noticeable difference with running that size?

I’m also looking at replacing my stock 19 inch staggered M wheels.


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Brand is nearly irrelevant in this example. The important thing would be to find the same brand and model for front and rear tires with the sizes of 245/45-19 FRONT and 275/40-19 REAR. Therefore, the circumference will be the same.

The whole point is to match the front&rear "revs/mile" as the transfer case will have less to differentiate (hopefully none) when going straight down the road. This will be the easiest on the Tcase clutches and prolong the life of the unit (you still need to change the tcase oil ever 30k miles tho regardless!).

The brand I went with was Fortune Viento FSR702. There are other brands out there. I didn't really notice any difference in the size.