[AudiA4]

If you wanted more sidewall, why not just increase the profile and go with 245/45R21 and 275/40R21? This would also almost perfectly correct the notorious BMW speedometer inaccuracy.

[MyfirstBMW_X3M40i]

Originally Posted by AudiA4

If you wanted more sidewall, why not just increase the profile and go with 245/45R21 and 275/40R21? This would also almost perfectly correct the notorious BMW speedometer inaccuracy.

Is this possible, that is would it work? I'm no tyre scientist, and would welcome your thoughts on this, did a quick search and the PS4 SUV are available in this size, a lot cheaper that the Bridgestone RFT. Also the Goodyear F1 Asymm 3 also available, run these on previous SUV and absolutely loved them, cheaper again!

Also, would changing from the recommended RFTs, would this affect BMW mtce in any way if something were to go wrong? Don't need to worry for now, still have thousands of miles to go before I replace.

[AudiA4]

Originally Posted by MyfirstBMW_X3M40i

Is this possible, that is would it work? I'm no tyre scientist, and would welcome your thoughts on this, did a quick search and the PS4 SUV are available in this size, a lot cheaper that the Bridgestone RFT. Also the Goodyear F1 Asymm 3 also available, run these on previous SUV and absolutely loved them, cheaper again!

Also, would changing from the recommended RFTs, would this affect BMW mtce in any way if something were to go wrong? Don't need to worry for now, still have thousands of miles to go before I replace.

You can run the diameter numbers, but according to my calculations this slightly increased sidewall height would almost exactly correct the 2.5-3 MPH overstatement typical of BMWs.

As far as run-flat versus standard, that's just up to you regarding risks when given a flat.

[Oldguysrule]

Originally Posted by AudiA4

You can run the diameter numbers, but according to my calculations this slightly increased sidewall height would almost exactly correct the 2.5-3 MPH overstatement typical of BMWs.

As far as run-flat versus standard, that's just up to you regarding risks when given a flat.

I see no reason this size won't work. Sidewall height will only increase by 4/10s of an inch. Rolling circumference is spot on so the X-Drive will be no problem. I see this as a perfect solution for getting a set of all season tires in the same width as stock. Thanks for checking!!

[Vote Quimby]

So I've been doing the same thing as many of you (255/40/21 & 295/35/21 MPS4S) for a season and loving it - thanks for doing all the heavy lifting for me.

Now that there are a few of us, what's the consensus on spacers?

[coolnesh]

Originally Posted by Vote Quimby

So I've been doing the same thing as many of you (255/40/21 & 295/35/21 MPS4S) for a season and loving it - thanks for doing all the heavy lifting for me.

Now that there are a few of us, what's the consensus on spacers?

I just did the same setup very recently 255/40/21 & 295/35/21, i do not feel any rubbing, so not considering spacers. Would the spacers in this case really be for a more aggressive looking stance? or another purpose that I may have missed?

[Oldguysrule]

Originally Posted by coolnesh

I just did the same setup very recently 255/40/21 & 295/35/21, i do not feel any rubbing, so not considering spacers. Would the spacers in this case really be for a more aggressive looking stance? or another purpose that I may have missed?

Yes, mainly asthetics.

[Vote Quimby]

Originally Posted by Oldguysrule

Yes, mainly asthetics.

For all intents and purposes, it's purely cosmetic.

Some will argue that they derive some minute but appreciable handling benefit from the marginally wider track, but to the best of my knowledge this has neither been proven nor quantified. Similarly, the additional strain on the wheel bearing is de miminis and can be ignored.

Actual pros: Fills out the fender better and unambiguously looks good. It's a subtle nuance and not divisive like wraps, wings, or canards.

Actual cons: Costs money, tires will rub at full lock if overdone, spits more rocks onto the side of your vehicle.

[freshxdough]

Originally Posted by Vote Quimby

So I've been doing the same thing as many of you (255/40/21 & 295/35/21 MPS4S) for a season and loving it - thanks for doing all the heavy lifting for me.

Now that there are a few of us, what's the consensus on spacers?

Like more flush but throws a lot more rocks on your paint

[Vote Quimby]

Originally Posted by freshxdough

Like more flush but throws a lot more rocks on your paint

Originally Posted by freshxdough

Like more flush but throws a lot more rocks on your paint

Sorry, I know what they are and do; that was someone else's question that I think we both answered.

I'm trying to glean if many of you are using them with these tires, and if so what widths, and if you're rubbing.

[freshxdough]

Originally Posted by Vote Quimby

Sorry, I know what they are and do; that was someone else's question that I think we both answered.

I'm trying to glean if many of you are using them with these tires, and if so what widths, and if you're rubbing.

There's no rubbing. I was running 15/15. I removed them recently to see how I like it without. Seen people running like 18 as well and not rubbing. No matter what option you choose, you won't rub.

[Vote Quimby]

Originally Posted by freshxdough

There's no rubbing. I was running 15/15. I removed them recently to see how I like it without. Seen people running like 18 as well and not rubbing. No matter what option you choose, you won't rub.

Thank you - that makes it easy!

[Ice9]

This is a repost of an article I wrote in April that might be helpful. I have now lived with the tire decision, and am very pleased with the results. Smooth ride, good fit, and longevity (8500 miles and maybe 30% wear):

(pictured is my M40i. Tanzanite Blue with PPF and Ceramic Pro, Shadowline, M diff', H&R lowering springs with 15mm spacers. No mods to exhaust or computer, warranty is a priority for me. Also, my supercharged R8 takes care of those primal needs)

21 Inch Relacement: 275/35/21 (OE) vs. 295/35/21 (Michelin)
For those looking for replacement options for your OE 21" wheels, here is proof that the 255/40/21, 295/35/21 solution works.

Michelin Pilot Sport All Season4 tires
H&R Sport Springs (not yet installed) (now installed)
H&R 12mm hubcentric spacers (replaced with 15mm. both sizes fit)
Alignment

I will post a complete set of pictures later, after I finish other projects, but for now, here are a couple of pictures comparing OE tires to new ones.
car sitting with new tires, lowering springs, spacers all installed
B/A: the 275 sitting next to the 295

First, thanks to all who took the plunge on oversized tires, and gave me the assurance that they would fit! I hope this post passes forward the solid information that I got.

I wanted the OE 21" wheels, but I didn't want run flats, nor did I want the spare tire (hump). I had to take the P Zero run flats when I took delivery of my '22 M40i. The P Zeros were not nearly as "hard" as I anticipated, and served me well for 500+ miles of car break-in. They will now work well for a lady enthusiast in Kentucky who swears by run flats.

The Michelin Pilot Sport All Season 4's are just what I wanted. They fit (first of all), are quieter, smoother, less harsh over rough terrain, and actually cost less. I can't report on how they handle, as I am still breaking in
the car. I will be on the Utah track in two weeks, and will report then.

The Michelin's, although "All Season," are still "ultra high performance." They can also be had in this size in the "Maximum Summer Performance" Pilot Sport 4S. I have those tires on my R8, and they are fabulous, but not usable in cold weather. My M40i needs all seasons.

RIM/TIRE FITMENT:
The 255's are within recommended range for a 8.5" rim, and fit fine. The 295's, ideally, should be on at least 10" rims (OE are 9.5), but they do fit, and the tires do not look "pinched." The 295's come "close" to the strut, but do not touch. Even so, I recommend at least 12mm spacers, which I installed (with, of course, longer studs). There is NO fitment issue with the tire with the spacers. The hubcentric spacers from H&R are beautifully engineered and fit perfectly.

There is still plenty of room from the top of the tires to the top fender lip. I think that the truck looks a lot better with less wheel well showing. Next week, I am going to install H&R Sport Springs, which will lower the car 1.4 inches front, and .8 inch rear. I will follow up with more photos and a final report on handling differences.

And tire pressures.. I am trying 36 front, 41 rear, cold. we'll see. Oh yeah, be sure to get at alignment after all this.

It is STILL a proximate answer to my needs for an SUV, but a little lower and a little wider is always a good thing.

[Oldguysrule]

How much space do you have between the coils in front and the tire? Stock RFT its a little over 1/2". 255/40/21 looks to be about a half inch taller in diameter so 1/4" closer to the coil plate.

[Vote Quimby]

Not to be overly pedantic or adversarial, but since when does a forum post constitute an "article"?

Originally Posted by Ice9

This is a repost of an article I wrote in April that might be helpful.

[SimSimma941]

Originally Posted by Ice9

This is a repost of an article I wrote in April that might be helpful. I have now lived with the tire decision, and am very pleased with the results. Smooth ride, good fit, and longevity (8500 miles and maybe 30% wear):

(pictured is my M40i. Tanzanite Blue with PPF and Ceramic Pro, Shadowline, M diff', H&R lowering springs with 15mm spacers. No mods to exhaust or computer, warranty is a priority for me. Also, my supercharged R8 takes care of those primal needs)

21 Inch Relacement: 275/35/21 (OE) vs. 295/35/21 (Michelin)
For those looking for replacement options for your OE 21" wheels, here is proof that the 255/40/21, 295/35/21 solution works.

Michelin Pilot Sport All Season4 tires
H&R Sport Springs (not yet installed) (now installed)
H&R 12mm hubcentric spacers (replaced with 15mm. both sizes fit)
Alignment

I will post a complete set of pictures later, after I finish other projects, but for now, here are a couple of pictures comparing OE tires to new ones.
car sitting with new tires, lowering springs, spacers all installed
B/A: the 275 sitting next to the 295

First, thanks to all who took the plunge on oversized tires, and gave me the assurance that they would fit! I hope this post passes forward the solid information that I got.

I wanted the OE 21" wheels, but I didn't want run flats, nor did I want the spare tire (hump). I had to take the P Zero run flats when I took delivery of my '22 M40i. The P Zeros were not nearly as "hard" as I anticipated, and served me well for 500+ miles of car break-in. They will now work well for a lady enthusiast in Kentucky who swears by run flats.

The Michelin Pilot Sport All Season 4's are just what I wanted. They fit (first of all), are quieter, smoother, less harsh over rough terrain, and actually cost less. I can't report on how they handle, as I am still breaking in
the car. I will be on the Utah track in two weeks, and will report then.

The Michelin's, although "All Season," are still "ultra high performance." They can also be had in this size in the "Maximum Summer Performance" Pilot Sport 4S. I have those tires on my R8, and they are fabulous, but not usable in cold weather. My M40i needs all seasons.

RIM/TIRE FITMENT:
The 255's are within recommended range for a 8.5" rim, and fit fine. The 295's, ideally, should be on at least 10" rims (OE are 9.5), but they do fit, and the tires do not look "pinched." The 295's come "close" to the strut, but do not touch. Even so, I recommend at least 12mm spacers, which I installed (with, of course, longer studs). There is NO fitment issue with the tire with the spacers. The hubcentric spacers from H&R are beautifully engineered and fit perfectly.

There is still plenty of room from the top of the tires to the top fender lip. I think that the truck looks a lot better with less wheel well showing. Next week, I am going to install H&R Sport Springs, which will lower the car 1.4 inches front, and .8 inch rear. I will follow up with more photos and a final report on handling differences.

And tire pressures.. I am trying 36 front, 41 rear, cold. we'll see. Oh yeah, be sure to get at alignment after all this.

It is STILL a proximate answer to my needs for an SUV, but a little lower and a little wider is always a good thing.

A sincere thank you to everyone (especially Ice9) who contributed to this thread and others! I just purchased my M40i certified and was told they don’t make an all season for the 21” rim so I went with the 19”. Now I know I can get the 21” rims (718M) with an AS non-run flat and be fully content with my purchase. I love the width the the 295/35 and the stance looks great.

There was a mention of a speed rating with the larger MPS4-AS tire on the 9.5” rear rims. At what speed is the tire in the danger zone? I don’t plan to drive at high speeds often but want the option and to feel safe doing it.

**Also I will be selling my 19” 698M with RF-AS less than 1,000 miles on them. Could be a good rim to throw true winters tires on but I don’t have the space to store them.

[HeatJoey]

curious what you all do without the RFT's (which I agree are terrible), just plug kit & compressor and hope for no blow out or keep a spare in the back?

[glennbk]

Originally Posted by HeatJoey

curious what you all do without the RFT's (which I agree are terrible), just plug kit & compressor and hope for no blow out or keep a spare in the back?

Several members have added a compact spare tire in the back. One person is going to get a full sized tire and rim to see how much space it'll take. I ordered a compact spare with my new build, full knowing that non-RFTs were in my future. Limitation on the compact spare is 50mph max for a 50 mile max. About the same distance you'd get from a deflated RFT. Otherwise, consider getting towing assistance (AAA offers flatbed for up to 200 miles, I think??).

[Artdnj]

Real stupid question here, but I am curious. I am waiting on my X.3 that is coming with 20 inch 699M wheels with 20 inch run flat performance tires I plan on changing to all season, continental most likely, but need to know if I can go square with the existing wheels or do I have to stay with the staggered tire size? I believe the answer is I have to stay staggered unless I change the wheels but that won’t be an option. Just trying to confirm what I think is right.

[mjX3]

Originally Posted by freshxdough

There's no rubbing. I was running 15/15. I removed them recently to see how I like it without. Seen people running like 18 as well and not rubbing. No matter what option you choose, you won't rub.

Freshxdough, what kind of tire pressures are you running on the 255/40/21 and 295/35/21 setup? I just got these installed myself.

[freshxdough]

Originally Posted by mjX3

Freshxdough, what kind of tire pressures are you running on the 255/40/21 and 295/35/21 setup? I just got these installed myself.

OEM tire spec. Idk like 35/35. These tires have lasted me about 20k miles now and still going. I drive hard and I’m really surprised at how well they’re lasting. Probably need to replace at end of this year.

[mjX3]

Originally Posted by freshxdough

OEM tire spec. Idk like 35/35. These tires have lasted me about 20k miles now and still going. I drive hard and I’m really surprised at how well they’re lasting. Probably need to replace at end of this year.

My OEM recommendations at 41psi front and 48psi back which I think are pretty high. No wonder my tires in the past have been wearing quicker in the middle.