[iManu]

So, my Bridgestone Alenzas are at 1/32 in the rear and 3/32 in front. I really loved the overall comfort vs. performance of these tires even if they only lasted me 6 month/12000miles. I want stickier tires because the Alenzas slip sometimes when launching. I can hardly find any other tires except the Pirelli's bit I do not have good experience with them so I'd like to not go that way. I'm really interested in the Michelin Sport 4S but they do now make the right size.
My 21 inch stock size are: 245/40/21 and 275/35/21. What other tires can fit?

[verysideways]

Originally Posted by emmanuel.yoo

So, my Bridgestone Alenzas are at 1/32 in the rear and 3/32 in front. I really loved the overall comfort vs. performance of these tires even if they only lasted me 6 month/12000miles. I want stickier tires because the Alenzas slip sometimes when launching. I can hardly find any other tires except the Pirelli's bit I do not have good experience with them so I'd like to not go that way. I'm really interested in the Michelin Sport 4S but they do now make the right size.
My 21 inch stock size are: 245/40/21 and 275/35/21. What other tires can fit?

The X3M competition appears to be fitted with 255 fronts and 265 rears, in a Michelin PS4S.
Worth investigating further.

[iManu]

Originally Posted by verysideways

The X3M competition appears to be fitted with 255 fronts and 265 rears, in a Michelin PS4S.
Worth investigating further.

I saw that to! The front rims are wider on the X3M. The rear rims are wider to... I doubt I can go 255 on the front. I'll try 265 in the rear maybe.

[verysideways]

Originally Posted by emmanuel.yoo

I saw that to! The front rims are wider on the X3M. The rear rims are wider to... I doubt I can go 255 on the front. I'll try 265 in the rear maybe.

My 245 winters are on a 7.5" rim, my 245 summers are on an 8" rim, I'd be happy to fit the 255 fronts to my 8" rims.

And I'd also be happy to downsize the rears from the 275 to the 265.

Fingers crossed the PS4S are openly available by the time I need them 😁

[iManu]

Originally Posted by verysideways

My 245 winters are on a 7.5" rim, my 245 summers are on an 8" rim, I'd be happy to fit the 255 fronts to my 8" rims.

And I'd also be happy to downsize the rears from the 275 to the 265.

Fingers crossed the PS4S are openly available by the time I need them 😁

For under steering, do you think 255 in front will help? My car tends to understeer in tight corners at the track then when the rear starts going, the car loses control and spins out.

[verysideways]

Originally Posted by emmanuel.yoo

For under steering, do you think 255 in front will help? My car tends to understeer in tight corners at the track then when the rear starts going, the car loses control and spins out.

If you're getting understeer at the moment then going up a size in front and down a size at the back will certainly reduce that tendency to understeer.

[iManu]

Do you think if I get 20 inches rims, my car will be lighter and be able to accelerate faster?

[supersebbo]

Originally Posted by emmanuel.yoo

Do you think if I get 20 inches rims, my car will be lighter and be able to accelerate faster?

I think the difference is going to be absolutely marginal at best.

Plus it depends entirely on the rim. I thin-spoked 21" rim may well be lighter than a bulkier 20" rim.

You'd be exchanging some lightweight alloy for more rubber... I think it would in the in 100s of grams overall.

[skier219]

Originally Posted by emmanuel.yoo

Do you think if I get 20 inches rims, my car will be lighter and be able to accelerate faster?

Agree that it's not a function of size, it's a function of wheel weight and tire weight regardless of size.

On a lightweight sports car with manual transmission, I was able to detect a difference with lighter wheels and tires, but it was feel only -- no noticeable improvements in acceleration outside the margin of error. I doubt you'd even feel it on a vehicle like the X3, plus the auto transmission is a layer of molasses between you and the wheels.

[Presario]

I tried running 255 40 21 and 285 35 21 Conti's non-runflats. The ride was much nicer and much more comfortable than the runflats. It's the right size if you want to go a little wider without going outside the X-drive parameters. If you like the look of a little more rubber, this was a nice setup.

Here are some pics of the wider rubber on 21x9 and 21x10.

[iManu]

Nice setup you got there! I'd like to keep my stock oem rims, they're only 8.5 and 9.5 inches, do you think the 255 and 285 will fit without causing side to side wobble? I once had 255 on a 8 inch rim and on the freeway the car felt unstable due to the wide tires.

[Presario]

Originally Posted by emmanuel.yoo

Nice setup you got there! I'd like to keep my stock oem rims, they're only 8.5 and 9.5 inches, do you think the 255 and 285 will fit without causing side to side wobble? I once had 255 on a 8 inch rim and on the freeway the car felt unstable due to the wide tires.

Thanks bud! Yup, the 255 and 285 minimum width size is 8.5 and 9.5 so you're good. You shouldn't have to worry about side wobble.

[calintexas]

Originally Posted by supersebbo

I think the difference is going to be absolutely marginal at best.

Plus it depends entirely on the rim. I thin-spoked 21" rim may well be lighter than a bulkier 20" rim.

You'd be exchanging some lightweight alloy for more rubber... I think it would in the in 100s of grams overall.

Car & Driver did testing several years ago. You're correct that a 1" diameter difference doesn't do much, but as the wheel diameter difference expands, so does the effect. Even a lighter larger wheel can take more energy to accelerate than a smaller heavier wheel because the rotational inertia of the larger wheel will likely be higher (more weight(mass) further from the center of rotation - requiring more energy to both accelerate and slow down the wheel).

Car & Driver article: https://www.caranddriver.com/feature...-wheels-tires/

Enough science & engineering to make you want to go blind:
http://hpwizard.com/rotational-inertia.html

[iManu]

Originally Posted by Presario

Thanks bud! Yup, the 255 and 285 minimum width size is 8.5 and 9.5 so you're good. You shouldn't have to worry about side wobble.

Thanks! Also what do you think about the bmw xdrive tire difference tolerance? I heard 1% is a rule of thumb to respect but I was wondering if I can go 2%. Cant find the right tire size here...

[Presario]

Originally Posted by emmanuel.yoo

Thanks! Also what do you think about the bmw xdrive tire difference tolerance? I heard 1% is a rule of thumb to respect but I was wondering if I can go 2%. Cant find the right tire size here...

255 40 21 and 285 35 21 is 29” and 28.9” respectively so it’s less that 1% difference. It’s perfect for x drive setup.

[iManu]

Originally Posted by Presario

255 40 21 and 285 35 21 is 29" and 28.9" respectively so it's less that 1% difference. It's perfect for x drive setup.

I was looking at the Michelin super sports, they come
In 255/40/21 and 265/40/21 only its 1% flush do you think it will be okay?

[gordonyz]

My wife - same tires as OP's at 9.5k mi, has 7/32 left..
Mostly hwys

[iManu]

I was on the tirerack website, Michelin 4s makes new sizes now! 275/35/21. Just need to wait for the 245/40/21 to come out! I really loved the Alenzas for the wet handling but for dry handling I find the 4s sports are more comfortable and quiet!

[shinyred]

Seeing the X3M being fitted with 255 fronts and 265 rears for both 20" and 21" wheels. I'm curious how the M40i are fitted 245 and 275 respectively

can the M40i run the same tyre configuration as X3M, or are the rims different in size?

thanks in advance

[xyvyx]

Originally Posted by shinyred

Seeing the X3M being fitted with 255 fronts and 265 rears for both 20" and 21" wheels. I'm curious how the M40i are fitted 245 and 275 respectively

can the M40i run the same tyre configuration as X3M, or are the rims different in size?

thanks in advance

Yeah, I'm curious too...

I think Tirerack will only show a staggered set available if they have the OEM config w/ both sizes. But they do carry the Mich PS4S in the 255 front / 275 rear widths... and it sounds like the larger fronts will fit w/o looking funny.

I'm at about 10k miles and I've got a screw in one of my back tires. I might see if I can get it patched, but if I have to replace 'em, I'm not yet sure what I want to do. For RFTs, the OEM Alenza's weren't horrible... not as bad as I remember from my Z4 many years ago.

[Driving for Charity UK]

So will the following sizes work on a X3 M40i?

255/40/21
265/40/21

[X3M40i_Nev]

Originally Posted by shinyred

Seeing the X3M being fitted with 255 fronts and 265 rears for both 20" and 21" wheels. I'm curious how the M40i are fitted 245 and 275 respectively

can the M40i run the same tyre configuration as X3M, or are the rims different in size?

thanks in advance

There are some opinions that the reason the X3M has a narrower rear track so that the “drive” in cornering can feel more engaging.

Can’t see any reason my these profiles and tyres cannot go on M40i and some have done it with MP4S’s