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      06-27-2020, 01:09 PM   #1
HomeIn2
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+5 Tire Sidewall Aspect Ratio?

I’ve got factory 21” wheels and Continental run-flat tires on my ‘20 X5 M50i. Been trying to find summer performance non run-flats to replace the Continentals. I’m having a heck of a time, however, finding anything in the factory size: 275/40 front, 315/35 rear. Looks like there are quite a few decent options though with +5 sidewalls. Tires I’m considering are same as factory widths, but with 45 front and 40 rear sidewalls.

Has anyone gone slightly taller than factory aspect ratios? By my calculations, +5 would add only around 1/2” to the sidewall. I realize the speedometer and odometer will be off just a little, and the ride may be a little softer, but are there any other noteworthy issues in going up just +5?

I’m considering this purely because of availability, not for increased comfort. I wouldn’t mind, however, filling out the wheel arches a bit more since I’m not considering a drop. Finally, in case it matters, my X5 has DHP. Thanks...

Last edited by HomeIn2; 06-27-2020 at 02:36 PM..
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      07-02-2020, 01:52 PM   #2
Raikkonen
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Quote:
Originally Posted by HomeIn2 View Post
I’ve got factory 21” wheels and Continental run-flat tires on my ‘20 X5 M50i. Been trying to find summer performance non run-flats to replace the Continentals. I’m having a heck of a time, however, finding anything in the factory size: 275/40 front, 315/35 rear. Looks like there are quite a few decent options though with +5 sidewalls. Tires I’m considering are same as factory widths, but with 45 front and 40 rear sidewalls.

Has anyone gone slightly taller than factory aspect ratios? By my calculations, +5 would add only around 1/2” to the sidewall. I realize the speedometer and odometer will be off just a little, and the ride may be a little softer, but are there any other noteworthy issues in going up just +5?

I’m considering this purely because of availability, not for increased comfort. I wouldn’t mind, however, filling out the wheel arches a bit more since I’m not considering a drop. Finally, in case it matters, my X5 has DHP. Thanks...
Same exact boat that I'm in. I take delivery of my M50i next week, w/ 21's and w/ dhp.

I've been looking to swap my RF's for non-RF's....tires in factory sizes are IMPOSSIBLE to find.

I was able to find Michelin Pilot Sport 4 SUV at Discount Tire Direct online, but that's it:

https://www.discounttiredirect.com/b...rProduct/86841

I'm ordering them...

To answer your question however, I would call your service dept. and have them speak to a tech....you MAY be able to adjust your rolling diameter settings (speedometer) in idrive...maybe.

If not, you'd have to spend the rest of eternity adjusting for the speed difference in your head while driving....that would be a horrible nightmare imho!

I also called Tirerack for non-rft summer options in factory sizes, and everything is back-ordered indefinitely....for some reason, the 21's are in a really strange size offering from the factory....it really limits your options while retaining factory rims...
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      07-02-2020, 02:13 PM   #3
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Originally Posted by Raikkonen View Post
I was able to find Michelin Pilot Sport 4 SUV at Discount Tire Direct online, but that's it...
Those happen to be the exact tires I’m searching for. Several online retailers show availability for both fronts and rears, but then I’m always told the rears are nowhere to be found. Please let me know if you are able to source the factory size 21” MPS 4 SUV tires...thanks.
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      07-29-2020, 02:29 PM   #4
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Quote:
Originally Posted by HomeIn2 View Post
Those happen to be the exact tires I’m searching for. Several online retailers show availability for both fronts and rears, but then I’m always told the rears are nowhere to be found. Please let me know if you are able to source the factory size 21” MPS 4 SUV tires...thanks.
Wow...just got my car last week, and called Discount Tire and Tire Rack, and both are delayed INDEFINITELY in stock sizes on the Michelin PS4SUV...no end in site....Tire Rack even said they've been back ordered since May 2019!!! (in the rear specifically- 315-35-21).

Both "experts" said as long as you go +5 on both the front and rear, you should be OK....I had asked about going +5 on the rear only (so 40 all around) and they both said that's a big no-no.

For Northern climates, Tire Rack now has a Vredestein winters in stock, and Discount Tire has Nokian winters in stock, both non-RFT in stock 21" sizes.

I'm going to retain my stock RFT Pirelli's for now, swap to factory sized winters in a few months, and then check again on availability of the PS4's next Spring....if they're not in stock, I'm going to run +5 on every corner next year...

Non-RFT Summers or All-season stock 21" sizes are true UNICORNS!
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      08-27-2020, 12:57 PM   #5
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Quote:
Originally Posted by Raikkonen View Post
Wow...just got my car last week, and called Discount Tire and Tire Rack, and both are delayed INDEFINITELY in stock sizes on the Michelin PS4SUV...no end in site....Tire Rack even said they've been back ordered since May 2019!!! (in the rear specifically- 315-35-21).

Both "experts" said as long as you go +5 on both the front and rear, you should be OK....I had asked about going +5 on the rear only (so 40 all around) and they both said that's a big no-no.

For Northern climates, Tire Rack now has a Vredestein winters in stock, and Discount Tire has Nokian winters in stock, both non-RFT in stock 21" sizes.

I'm going to retain my stock RFT Pirelli's for now, swap to factory sized winters in a few months, and then check again on availability of the PS4's next Spring....if they're not in stock, I'm going to run +5 on every corner next year...

Non-RFT Summers or All-season stock 21" sizes are true UNICORNS!

Did you change your tires? If so, I’m curious to know what you went with and why the performance results were... was their a change in comfort? A change in the speedometer/mileage?
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      09-03-2020, 02:06 PM   #6
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Did you change your tires? If so, I’m curious to know what you went with and why the performance results were... was their a change in comfort? A change in the speedometer/mileage?
Sorry Jrunr....just saw this post.

I'm waiting probably another 6 weeks or so, before I go to Vredestein winters (non-rft) or the Nokian winters (non-rft), both available in factory sizes.

I've been so impressed by the ride quality of the factory Pirelli summer runflats, that I won't be swapping them out for non-rt's until next summer....IF there are non-rft summer tires that are available in factory sizes...NO ONE has them in inventory now, it's insane!!!!

Fingers crossed for next spring...

I'll post after I install my winter tires in a few weeks as well, with some impressions.
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