[octodad]

I am the happy owner of a used F25 (30d) but the garage I bought it from seems to have sold me a Frankenstein.

On the FRONT it has Dunlop Sp Sport Maxx GT 245/45/r19 - Which turn out are summer tyres
(which seem to be well thought of tyres) on the front with 4 mm of tread

On the REAR it has new ACCELERA PHI2 275/40/r19 (a budget all-season tyre,I believe the opinion is mixed some say dog *** some say fine).

So do I get to matching tyres for the front, replace them all with a premium brand all-season tyre?

I’m guessing 4mm is not really much to say keep 2front summer tyres get 2 new summer tyres for the rear in April and get winter tyres for December-ish to march?
(I’ve never had two sets of tyres for a car)

Thoughts?

[doru]

Originally Posted by octodad

I am the happy owner of a used F25 (30d) but the garage I bought it from seems to have sold me a Frankenstein.

On the FRONT it has Dunlop Sp Sport Maxx GT 245/45/r19 - Which turn out are summer tyres
(which seem to be well thought of tyres) on the front with 4 mm of tread

On the REAR it has new ACCELERA PHI2 275/40/r19 (a budget all-season tyre,I believe the opinion is mixed some say dog *** some say fine).

So do I get to matching tyres for the front, replace them all with a premium brand all-season tyre?

I’m guessing 4mm is not really much to say keep 2front summer tyres get 2 new summer tyres for the rear in April and get winter tyres for December-ish to march?
(I’ve never had two sets of tyres for a car)

Thoughts?

"Normally" having 2 of the same tires up front and 2 same, but different brand than front for rears shouldn't be an issue. Until you have an X-drive vehicle.
Here you should be careful, because a drastic tire diameter difference between wheels can damage the transfer case. Some X vehicles have staggered tires - that minimal difference in diameter between front & rear is pretty much the tops. If you have on the same axle different tire diameters (a brand new tire, and one with 40% left for example), and especially they are on the front, you can bugger the T-case (If X-drive). Front/Rear I think the max diff is 1cm or so, but not 100% sure. Dealer should know better (maybe?)

[octodad]

Originally Posted by doru

"Normally" having 2 of the same tires up front and 2 same, but different brand than front for rears shouldn't be an issue. Until you have an X-drive vehicle.
Here you should be careful, because a drastic tire diameter difference between wheels can damage the transfer case. Some X vehicles have staggered tires - that minimal difference in diameter between front & rear is pretty much the tops. If you have on the same axle different tire diameters (a brand new tire, and one with 40% left for example), and especially they are on the front, you can bugger the T-case (If X-drive). Front/Rear I think the max diff is 1cm or so, but not 100% sure. Dealer should know better (maybe?)

Thanks for replying but different sizes is not really what I'm asking about all websites says it's ok to have those staggered tyre sizes. It's more about the types summer run flat and all season and advice on all season, brands if to go winter tyre for UK etc etc.

[doru]

Now I understand your question.
Answer might be a bit elaborate:
Concerning RFT & regular:
Not advised. Because (from horses mouth, aka BMW) the manufacturer apparently took into account the harsher properties of those tires to work with suspension. If mismatched, like fronts RFT and rears normal, or vice-versa, the car have the driving dynamics totally thrown out. Won't affect t-case, but can affect how the whole ride/balance of the car works.
If you use summer tires on one axle and winters on the other, this can affect the t-case - softer rubber & harder rubber, especially more noticeable side effects when the temp is dipping below 0°C. The summers will get hard and will slide even on dry pavement. Braking will be iffy. Now you hit a patch of ice or snow, or slush, or just cold wet, a bit of slippage and the whole ABS/Traction Ctrl whatever system you have will be out of whack and will try to compensate let's say on a slipping winter tire towards an even worse summer that is not slipping yet.

You can mismatch different brand of tires having same brand on one axle and both brands close/similar weather rating.

Hope this helps

[octodad]

Yes I thought it would be massive issue when discovered it (run-flats on front and all season on rear). So was hoping someone might have had experience of accelera phi2 if it's worth getting two of these for front or getting rid of all of the tyres and getting a new set.

[octodad]

As for mixed size like I say lots of online tyres websites seem to know this is ok and suggest this might be one of your options for example. go to https://www.mytyres.co.uk and enter a x3 reg. its will show a front 245/45/19 and 275/40/19 read and option.
which is what I have bigger (i.e.wider at the back) said radial size.

[WagonR]

Wow, this thread is an interesting ride.

First things first; yes, you do not want to run tires that have a different diameter (side to side, or front to back) on an xdrive bmw (or any AWD car with an active differential). The all wheel drive system will think the wheels are turning at a different rate (which it interprets as slipping) and will want to spit the power to the wheels that are "gripping." This can burn out the differential.

However, in this case, the front 245/45/19s and 275/40/19s are THE SAME DIAMETER. It's the reason BMW offered a staggered set in THESE EXACT SIZES for the F25 X3s. You're fine with the tire sizes.

To answer you question; yes, it's a bad idea to run the mix&match of front and rear tires that you have. Different tread depth (performance in rain), different compounds, run flat vs. non-run flat, etc. Outside of driving down the road, nothing is beneficial with your setup.

Realistically the rears were worn, and the dealer put on the cheapest tire they could. Only on the rear.

The cheapest option would be to replace the fronts with the same tire as the rears (assuming they sell it in the correct size for the front). This won't be the best setup ever for the car, but at least everything will perform the same (good, bad or indifferent). Alternatively, you could consider the tires a loss (fronts are worn, rears may not be that good), and then get a good set of all seasons, or put winters on (it's almost November), and then hope to find a complete set of summer wheels/tires in 4-6 months.

[oVeRdOsE.]

^^^finally!

yes those are same diameter.

- Op, you can simply check treadwear rating. this is not perfect science since a a measurement from the manufacturer, but it will indicate the tire wear speed. So all 4 tires can get even wear.

Anyway, you should be in the 1% diameter difference range, I'm not worried.

- You can also find a non-extensible rope and get yourself a pretty precise outside diameter measurement.

- Also, about different compound, well, those x3 are not supercars, its not 50/50 weighted, the assembly precision is not a F1 like. for all that, If you don't have super drag Mickey Thompson tires rear and cheap ass winter tire mix, I wont be worried too much. Those car are great in winter condition and I can assure you that all 4 tires never got same friction force, since the road is uneven (ice/snow/salt/gravel/asphalt and so on). xdrive will do his job under different tire grip condition.

- This has been said, its not recommended, but if tire overall performance are about the same, same wear, about same year ; keep it like that. If not, change it.