Ditching Runflats and gaining sidewall, how much is too much???

[Johnny_B]

Hey everybody. New member to Bimmerpost and to BMW as well. Just purchased a 2018 650i Grand Coupe 2x4 with 68k. I love the car and I'm trying to familiarize myself with all of BMW's 'qwerks' as far as function (single door lock button on dash, windsheild wiper lever operation, etc..). But I hate to say that the ride of this car has been more than disappointing. Coming from a 2014 Lexus LS460L to this has been one extraordinary change as you may imagine. One month in and have already had to replace 2 tires thanks to Louisiana's less than satisfactory road conditions. So I'm looking to ditch the runflats and up the sidewall. I currently have 275/30/R20 on rear and 245/35/R20 up front. As I previously stated I'm in a 2 wheel drive version but still would like to keep the tire ratios close to equal in front and back due to the spare I'm purchasing ability to be used in both situations. My question is, what is the optimal tire size that can be used with out rubbing or other complications? Any info is much appreciated and I hope I can contribute to the forum in the future.

[Milu]

255/35 and 285/30 fit ok. They give a little more sidewall. Combined with non RF will help a lot.
Do you have VDC?

[Qsilver7]

Originally Posted by Milu

Do you have VDC?

Since the OP is new and this was his 1st post...he may not be familiar with BMW option abbreviations...as well as some older owners, too.

VDC = variable damping control (aka EDC...electronic damping control)...where there is an electrical connection to the struts/shocks that can allow for different damping characteristics/parameters.

If your F chassis six series has VDC/EDC...you can easily verify your car has this option by scrolling through the various driving dynamic selections (using the driving experience button next to the gear shift lever)...if you have COMFORT+ then you have VDC.

VDC shock/strut/dampers can soften or stiffen based on selected drive experience settings, all 6 series come with the drive performance control, but cars optioned with VDC/EDC will have the additional option of "Comfort+" setting.

Without VDC/EDC:

• Eco Pro
• Comfort
• Sport
• Sport+

With VDC/EDC:

• Eco Pro
• Comfort
• Comfort+
• Sport
• Sport+

See info below about the front & rear EDC dampers/struts/shocks (respectively):

[Johnny_B]

It does have the Comfort+ option and that seems to help somewhat but still feels like a 10lb sledge whaling against the undercarriage everytime I hit a pot hole. And the road noise is akin to that of my Duramax with 10ply All Terrains not to mention the tapping sound from tge bubbles I have gotten on the sidewall. Sorry to complain so much. It's that I just got this car and I was expecting more in means of comfort and queit. Got a whole other issue of a tap while under acceleration but thats for a different thread. And thanks for the replies. After some more scrolling, I see this topic has been covered before. I just didn't see anyone give a sure answer on what would work.

[Qsilver7]

Just an FYI... a summer or all season non run flat tire will usually make the ride more compliant...but she's still going to be like a BIG girl wearing 5" spiked high heels. The 20" wheels make her look flattering...but that's a lot of weight on thin rubber...the effect/affect is much like that big girl trying to sprint across a gravel parking lot...it's not going to be pretty & more than likely will end with twisted ankles.

I run 18" winter tires and 20" summer tires. The winter tires ride is much more compliant...but the summer tires are a lot more sexy. If you're going to stay with the sexy look...learn how to lookout for & avoid the pot holes (if possible) as well as uneven road surfaces.

[Johnny_B]

Nice analogy. I love a big girl but not in this sense! The 20's are nice on the eyes but I guess I'd rather sacrifice the look for the feel. Unfortunately I'm not willing to sacrifice the $ on a new set of rims to alleviate the problem to the best of ability. Milu, I appreciate the advice but would the sizes you gave increase sidewall? Or just width? I thought the first # was width and the second # was the % of the width as the sidewall? Not sure if I'm stating that correctly but I'd have to lay blame partly on the person that developed this method of measuring tire size! Could we have made it a little more laymen friendly? Not all of us think in terms of coefficients in physics!

[rorz12]

Originally Posted by Johnny_B

Hey everybody. New member to Bimmerpost and to BMW as well. Just purchased a 2018 650i Grand Coupe 2x4 with 68k. I love the car and I'm trying to familiarize myself with all of BMW's 'qwerks' as far as function (single door lock button on dash, windsheild wiper lever operation, etc..). But I hate to say that the ride of this car has been more than disappointing. Coming from a 2014 Lexus LS460L to this has been one extraordinary change as you may imagine. One month in and have already had to replace 2 tires thanks to Louisiana's less than satisfactory road conditions. So I'm looking to ditch the runflats and up the sidewall. I currently have 275/30/R20 on rear and 245/35/R20 up front. As I previously stated I'm in a 2 wheel drive version but still would like to keep the tire ratios close to equal in front and back due to the spare I'm purchasing ability to be used in both situations. My question is, what is the optimal tire size that can be used with out rubbing or other complications? Any info is much appreciated and I hope I can contribute to the forum in the future.

I'll give you a simple answer. Get Michelin PS4S 255/35/20 for the fronts and 265/35/20 for the rears and you're sorted. The 275s and 265s are literally the same width so don't worry that you're gonna get narrower tires, I checked them side by side at the shop and you can't tell the difference.

This combo was perfect and gives you good side wall and ratio.

[Bavariane31]

Did your Lexus have 20” run flats as well? You have to compare both cars with the same tires for an even comparison. Can’t slap on concrete tires on a Rolls Royce and then complain about the ride! Runflats are known to have harsher rides. They basically effectively reduce the sidewall of the tire. Google Runflats blowing up. Side walls rupture and irreparable damage happens often and ride quality sucks. I swapped to 19” wheels on Michelin PS AS. Rides pretty nice.

[Milu]

Originally Posted by Johnny_B

Nice analogy. I love a big girl but not in this sense! The 20's are nice on the eyes but I guess I'd rather sacrifice the look for the feel. Unfortunately I'm not willing to sacrifice the $ on a new set of rims to alleviate the problem to the best of ability. Milu, I appreciate the advice but would the sizes you gave increase sidewall? Or just width? I thought the first # was width and the second # was the % of the width as the sidewall? Not sure if I'm stating that correctly but I'd have to lay blame partly on the person that developed this method of measuring tire size! Could we have made it a little more laymen friendly? Not all of us think in terms of coefficients in physics!

You’re reading it correctly. But of course the 30/35% of either 255 or 285 is about 3mm extra sidewall. It’s not much but I think you can feel the difference

[Johnny_B]

Thanks for the straight forward answer rorz12. I assume you work somewhere with access to tires so in your opinion, is that the tallest tire that would fit WITHOUT rubbing (sorry for the emphasis but that'a a big no no!) and is it possible to sacrafice a very little amount of width to gain height and not curtail the overall preformance of the car? Buvariane31, my Lexus did not have runflats but it did not have 20" wheels or a magnetic dampening system either. I realize the difference in equipment but I guess I always assumed that BMW was luxury and I equate luxury much with comfort. Not trying to trash the car as a total P.O.S. It certainly is higher end vehicle with good preformance in general and would most likely leave my Lexus in a 1/4 mile (Unless the Lexus had turbos, and then well..). The ride just really suprised me. But let's hope these tires help a good deal and I at least get rid of that bumping sound my right front tire is making due to the 2 bubbles on the sidewall. Which are most likely not helping the wheel bearing that I hope is not roaring on that side but can't determine becuase of tire noise. Lol. I see what you're saying Milu. After didn't put in to play that aspect. I had initially thought of putting 285/35 on back and 255/40 on front but I guess keeping the original manufacturers' ratio would be best.

[rorz12]

Originally Posted by Johnny_B

Thanks for the straight forward answer rorz12. I assume you work somewhere with access to tires so in your opinion, is that the tallest tire that would fit WITHOUT rubbing (sorry for the emphasis but that'a a big no no!) and is it possible to sacrafice a very little amount of width to gain height and not curtail the overall preformance of the car? Buvariane31, my Lexus did not have runflats but it did not have 20" wheels or a magnetic dampening system either. I realize the difference in equipment but I guess I always assumed that BMW was luxury and I equate luxury much with comfort. Not trying to trash the car as a total P.O.S. It certainly is higher end vehicle with good preformance in general and would most likely leave my Lexus in a 1/4 mile (Unless the Lexus had turbos, and then well..). The ride just really suprised me. But let's hope these tires help a good deal and I at least get rid of that bumping sound my right front tire is making due to the 2 bubbles on the sidewall. Which are most likely not helping the wheel bearing that I hope is not roaring on that side but can't determine becuase of tire noise. Lol. I see what you're saying Milu. After didn't put in to play that aspect. I had initially thought of putting 285/35 on back and 255/40 on front but I guess keeping the original manufacturers' ratio would be best.

I don't have access to tires.. but I compared different sizes at the shop when I was changing my tires.

At the time I couldn't find OEM sizes (245/35/20, 275/30/20) anywhere where I was living, so I had to choose something else and also at the same time I wanted a beefier side wall.

255/35/20 in the front fills the rim better and gives you a straight sidewall which I think looks good.

Paired up with 265/35/20 in the rear keeps the staggered dia. and circ. at 1.1% difference. 285 or 295 doesn't look good on the 9" rear rims, I didn't like the bulge.

Most of the difference is going to come from switching from run flats to non-run flats. It's a world of a difference. And the tire sizes above work well, with no rubbing. No issues with stability or slip. And gives you that extra bit of sidewall height.

Some people keep the widths and just bump up the sidewall ratios from 35 to 40 in the front, and 30 to 35 in the rear. That will give you more sidewall than the combo I gave you, I don't know about rubbing though. I doubt you'd have any issues.

But to be honest, 255/35 and 265/35 is more than enough sidewall. Note, I can only speak for Michelin Pilot Sport 4S in these sizes. Other brands might have different measurements (despite the same ratios).

Photos below.

[Johnny_B]

Nice pics! Alpine white I assume. Mine is the same color except I believe my wheels are a little darker on the inside. So after all this contemplating I think I'm gonna end up just bumping that mid-number by 5 from a 30/35 ratio to 35/40 on width. That makes the widths and rotations identical but not that it matters seeing how mine is rear wheel only. Thank you all for the input. It is much appreciated. Oh and just for some irony, All this focus on tires has obviously manifested itself in the form of a torn 18 wheeler recap that decided to play pinball on a walled part of the interstate yesterday. And I got to play the part of the 'flipper' and smacked the hell out of it. It was 2 lane on the elevated section with no choice but to lock up the brakes and cuase a pile up or try to hit it with the corner instead of dead center. Not sure which is better. Both suck. Broken grille insert and sidemarker/reflector amongst the casualties of the day.

[PixelVogue]

Continental Sport Contact 7s, they are afew levels above the "old tech" Michelin PS4S and cheaper!

[Smooth6]

I'm pretty much sold on the Continental extreme contacts. But I'm in the same situation meaning I want to increase the aspect ratio and my question is by how much can I increase them by. Mine's an extra drive 640i says it should run on 245 40 19. I'm trying to put on 245 45 19. But I'm having a hard time finding any information on that. I just called the dealership and they just gave me the runaround saying that the stickers and the door jamb. They were much help at all. That and I got to get rid of these god-awful run flats

[rorz12]

Originally Posted by Smooth6

I'm pretty much sold on the Continental extreme contacts. But I'm in the same situation meaning I want to increase the aspect ratio and my question is by how much can I increase them by. Mine's an extra drive 640i says it should run on 245 40 19. I'm trying to put on 245 45 19. But I'm having a hard time finding any information on that. I just called the dealership and they just gave me the runaround saying that the stickers and the door jamb. They were much help at all. That and I got to get rid of these god-awful run flats

You have plenty of side wall with that ratio and 19s.. you really don't need to increase it more. Just switch to a good non-run flat tire and it will be night and day difference.

Anyway if you still want to increase the ratio, you should not have any problem increasing the ratio by 5, it is a miniscule difference. 245/45/19 and 275/40/19 will be a perfect pair up and give you identical diameter, circumference and sidewall height.

[Johnny_B]

Got a set of Continental Extreme Contact DWS6 plus XL for $1009.00 shipped. Would have went local but they were pricing me $1300 before tax and mount. Thanks again for all the input!

[Smooth6]

Yeah I'm excited to see the difference. Everybody says how it's night and day. I'm trying to find a vibration going on it's going on in the seat at low speeds and speeds around 70 mph. My first troubleshoot is the fact that it could be a balancing issue with the tires. If it's not that I'm thinking the guibo.