[428JPV]

Wasnt sure if I should post in the wheel and tire or X drive area. Im a newb so I will get scorned either way. Just purchased a 2015 428i Xdrive convertible. The previous owners for reasons unknown left me with this set up. Fronts are Pirelli PZero 235 40 18 95Y all season non run flat and rear are Pirelli P7 Cinturato run flat 225 45 18 91Y stock size. The car is on stock rims and the car is bone stock and will stay that way. I post here because I dont want to screw up my transfer case. I read about the 1% rule but I am not smart enough to understand any of the math. I just want to get this car square and not mess with the speedo or transfer case. My questions are
1. Is this set up safe to run for now regarding my transfer case?
2, While I have the chance should I move away from run flats?
3. Should I consider matching my Pzero fronts with same size Pzero rear even though they are not the stock size and would this affect the speedo reading?
4. These tires are different size and tread pattern is this messing with my transfer case?
If you guys need to ship me off to the tire thread area ....go for it.
Thanks

[StradaRedlands]

You can plug the sizes in here: https://tiresize.com/comparison/

Diameter is off by 2.4%, so that could be a problem. I've always heard the same thing about AWD, but I don't have any actual experience with this.

[ppointer]

I have an opinion on x-drive and tires, but very little experience. I had an e46 325xi for a few years, and front wheels were not engaged unless the rears were slipping, if I remember correctly. That implies that slight diameter differences wouldn't be a big deal. At least with your set up, it looks to me as if the higher-traction tires are up front, which is probably not advisable when looking at emergency braking.

Yes, I would move away from run flats. I seem to have to do it every couple of years when I pick up a new-to-me BMW. I just swapped Michelin Pilot A/S 4 go flats onto an e93 I bought last month, and the improvement in noise and ride is transformative. Probably in May I will get rid of the original run flats on our '22 G30, going with the same A/S 4s. In my experience, run flats cost more, make more noise, ride poorly, and fail to last as long as go flats. If I get a flat, I pull out my platinum triple "A" card.

I would go with stock tire sizes, whatever they are for your 428i. If you need to fill out the wheel well, consider going with wheel spacers. Most of my cars have them, and I don't see a down side as long as you are reasonable. If you go overboard with them, you'll get some tire rub, which is also a risk with over-sizing your tires. My e9x's typically get 10mm up front and 12mm in the rear, though my e93 M3 actually got 12mm front and 10mm rear. Search the forum for recommendations, which is how I arrived at spacer sizes for the M3.

Regarding speedo reading, by default most BMWs read a little faster than they are actually going. You can correct that with Carly or Bimmercode. However, if you get away from stock diameter tires, then you will be unable to correct the discrepancy with coding.

Hope that helps. Cheers.

[428JPV]

Thanks for the replying to a newb! I just realized I didnt even select the correct series to post in but you guys still hooked me up with replies. I appreciate that. Yep I will move away from run flats and get the ole girl back to square asap. Thanks

[StradaRedlands]

Originally Posted by 428JPV

Thanks for the replying to a newb! I just realized I didnt even select the correct series to post in but you guys still hooked me up with replies. I appreciate that. Yep I will move away from run flats and get the ole girl back to square asap. Thanks

E90 folks are the fun bunch that don't take themselves too seriously but have a ton of experienced knowledge. Nothing wrong with palling around with us!

[Onizukachan]

Not to mention, some of us have Fseries x drives.


Change the OEM to match the aftermarket go flat 235s, it will help reduce /eliminate the factory Speedo error, and ride better.

The xfer case is always engaged and active on f 3x series, so best to do this asap as they are not cheap to replace. Bonne chance and see you Over on f30 post!

[428JPV]

Thanks E90 folks! I appreciate y'all kickin it around with me. I hope the F30 folks are as cool as you guys are.