Plus sizing tire radius?

[agentrnge]

I am pondering running slightly larger diameter tires. Assuming clearance is not an issue, and you ignore speedo inaccuracy ( this would likely increase accuracy ) is this a no no? 2003 540i/6.

Presently ( for another week or so ) running on my winter wheels. 17x8 Rial with 245x45 Dunlop wintersports.
I am considering something like 225x55 - 235x50, or 235x55 to provide a little more pot-hole protection ( and ride comfort ) in winter. This would add 1 or 2 cm of radius respective. Also, as inventory on snow tires is low, so getting available sizes now is tough. I dont even see 235x50 on the Dunlops as an option. Eyeballing the wheel wells, this looks like it would not be close to an issue fitment-wise, even riding ~1 - 1.5" lower than stock sport.

I also plan on also raising it up an inch or so for next winter. I am on height adjustable Billy PSS coils overs.

Thoughts?

[Ramboo]

Larger diameter of tires have many problems so best for you to change your tire to a fix diameter for a reliable drive.Other than this Coils adjustments is also a good step for your car performance.

[agentrnge]

One month bump.

Ramboo: what sort of problems would a larger diameter tire cause?

Dont worry, I am not talking about running on donks. lol. +1-2 cm radius tops. Whatever size I went with, would be the same front and back, so it shouldn't confuse wheel speed sensors and DSC/ASC bits. 1/2 cm difference is about the same difference as a fresh tire and a used up tire. So its nothing drastic.

edit:
Looking at 235/55/17 Wintersport 4Ds for next winter. They will be 1.5" larger diameter. I cant imagine that being a fitment issue, except maybe when the front wheels are turned sharply. I'll need to see what sort of clearance I have now with 245/45s. Also, it is the recommended size for a 740iL ( which will very likely be my second/optionally winter car by then )

[Critter7r]

The front strut body and spring perch would be my areas of concern. See if there's currently more than 3/4-inch clearance to accommodate the tires you want. Otherwise, I'd not be worried about the increased diameter with regards to speedo accuracy, as you said, it'll likely just make it closer to an actual reading.

[Jim@tirerack]

Besides speedometer, odometer, gear ratio and shift points on an automatic you could have rubbing on compression of the shocks. As long as they are the same diameter front and rear you are ok with the anti lock brakes and traction control. You can go a little taller usually without issues but be careful. If I can help let me know.

[agentrnge]

Jim,

Thanks for the response. Eye-balling it looks like there is no shortage of clearance. There are plenty of e39s out there with solid 2" drop lower than me with much wider tires without rubbing. Its also a 2003 m-sport so its got a little more room in the liners/fenders as it is. +3/4" radius should not be an issue. When the time comes for me to order the tires I will ping you about the specific tires I am looking at and see whats up. It will either be this coming winter, or the next, as I might squeak another season out of my wintersports...

[Jim@tirerack]

Sned me an email or give me a call anytime.

[agentrnge]

FYI everyone. I went up a series size on the tires. I went with the Mich PSS 235/45/18 front, and 265/40/18 in rear on e39 M-Pars. I am riding 1-1.5" lower than stock on Bilstein B14/PSS. No fitment/rubbing issues. No interference at full lock. Will check clearances at some point. No rubbing over any bumps that I hit in my jaunt around test drive.

I hope it provides just a little more pot-hole forgiveness. It also fills out the wheel wells nicely. Will post pics tomorrow or soon.

[Jim@tirerack]

Be aware the speedometer will be showing slower than you are actually going. It may keep you out of a ticket.

[agentrnge]

Thanks Jim. Yes this is true, but it works to my benefit. The speedo had previously displayed ~5% faster than actual speed ( by design ) so now it will be ~2% faster. I roll past a radar speed sign on my way home from work. I'll see how close it is. But I do need to reprogram the speedo-vs-actual calc in my brain...