Tire size question (upsizing)

[nitin100]

Hello
I have to change my tires on 21" rims.
It came with 245/35/21 + 275/30/21.
I have successfully used 245/40/21 + 285/35/21 earlier. But due to puncture, went back to original size presently.

I want to fit 255/40/21 +295/35/21. Is anybody using this wide tires? I am a bit worried on shocker support on front, which has got very small clearence.

I am using 629 wheels.

Thank you

[BMWDriverX]

Originally Posted by nitin100

Hello
I have to change my tires on 21" rims.
It came with 245/35/21 + 275/30/21.
I have successfully used 245/40/21 + 285/35/21 earlier. But due to puncture, went back to original size presently.

I want to fit 255/40/21 +295/35/21. Is anybody using this wide tires? I am a bit worried on shocker support on front, which has got very small clearence.

I am using 629 wheels.

Thank you

I've got custom 21's on order and was told to use 255/35 on the ffront and 295/30 on the rear. The sizes you called out will fit width wise but far as height goes you should be fine if you're not lowered. If the car was lowered i would say stick to the size normally used on 21" wheels

[jokerswld34]

Hello
I have to change my tires on 21" rims.
It came with 245/35/21 + 275/30/21.
I have successfully used 245/40/21 + 285/35/21 earlier. But due to puncture, went back to original size presently.

I want to fit 255/40/21 +295/35/21. Is anybody using this wide tires? I am a bit worried on shocker support on front, which has got very small clearence.

I am using 629 wheels.

Thank you

You will have some speedo issues with the increased tire heights as well added rolling resistance. Width wise, you'll have no issues but I would keep the tire height the same as OEM (e.g. 35 not 40 / 30 not 35).

[nitin100]

Thank you for responses. When I was using 245/40/21+285/35/21, the speedo was dead accurate.
With OEM, it was around 5% faster (ie, real speed = 95, speedo showing 100).

[g11hoonigan]

The site https://willtheyfit.com/ should give you an idea on the differences.

Height doesn't necessarily increase rolling resistance. It might add unsprung weight, if the tires are heavier though.

[bimmerdude79]

Originally Posted by g11hoonigan

The site https://willtheyfit.com/ should give you an idea on the differences.

Height doesn't necessarily increase rolling resistance. It might add unsprung weight, if the tires are heavier though.

Hello, when you say "un-sprung weight if the tires are heavy"? what do you mean by that?
I'm currently running on my 750ix bmw, style 629 Staggered 21's...... front: 255/45/21, rear: 275/35/21 It's not lowered, but with this setup currently is it going to cause more gas consumption an/ or damage to the Xdrive system?

Only reason I went with this setup was to fill in the wheel well gap more. Both front and rear tires have the Pzero Pirrelis.

[g11hoonigan]

Originally Posted by bimmerdude79

Hello, when you say "un-sprung weight if the tires are heavy"? what do you mean by that?
I'm currently running on my 750ix bmw, style 629 Staggered 21's...... front: 255/45/21, rear: 275/35/21 It's not lowered, but with this setup currently is it going to cause more gas consumption an/ or damage to the Xdrive system?

Only reason I went with this setup was to fill in the wheel well gap more. Both front and rear tires have the Pzero Pirrelis.

Unsprung weight is the added load not carried/supported by vehicle suspension. Heavier tires/wheels are not carried by the suspension but add to driveline load and its effect is not the same as the equivalent sprung weight. For example, a 30-lb additional 'unsprung' weight effect is higher than that of a sprung load (e.g. grocery items) that weigh 30 lbs. Also factor in the tires rolling resistance - this metric isn't typically published.

[bimmerdude79]

[QUOTE=g11hoonigan;30589265]Unsprung weight is the added load not carried/supported by vehicle suspension. Heavier tires/wheels are not carried by the suspension but add to driveline load and its effect is not the same as the equivalent sprung weight. For example, a 30-lb additional 'unsprung' weight effect is higher than that of a sprung load (e.g. grocery items) that weigh 30 lbs. Also factor in the tires rolling resistance - this metric isn't typically published.

Thank you for your explanation. I went ahead and changed my tire setup to front 255/35/21and rear 295/30/21. Michilin pilot 4s. Beamer runs much smoother and throttle response much improved in handling and ride quality.

[BIGTEX72]

I had new, wider tires installed yesterday evening. Salesman said wider size was approved to fit by Michelins current info. He also said system would not show tires unless size was ok to install. Went from 245/40/20 on the front to 255/40/20 and from 275/35/20 to 285/35/20 on the rear. upon pulling out at closing time, the car started shuddering/lurching in first / second gear. No warnings appeared though. I drove it gingerly home. I went back first thing in the morning to the tire shop. Manager says take it to BMW to see if they can reprogram. Service manager talks to a few techs and says no can do. He said install prior size back on immediately and hope the transfer case and transmission are not damaged. My first question is why can't I go wider on the tires and secondly, why is it causing the transfer case and transmission to act up? Still want a wider tire but not at the expense of the trans and transfer case. I checked tire size calculator and the bigger size tires were about a 1/4 of an inch taller. Would a different size tire that is wider than what I had on but not taller taller work...and if so, what size?
Flummoxed in OKC
2018 M760i Xdrive
Frozen Gray
Fiona Red
57k miles

[BlackM750i]

Originally Posted by BIGTEX72

I had new, wider tires installed yesterday evening. Salesman said wider size was approved to fit by Michelins current info. He also said system would not show tires unless size was ok to install. Went from 245/40/20 on the front to 255/40/20 and from 275/35/20 to 285/35/20 on the rear. upon pulling out at closing time, the car started shuddering/lurching in first / second gear. No warnings appeared though. I drove it gingerly home. I went back first thing in the morning to the tire shop. Manager says take it to BMW to see if they can reprogram. Service manager talks to a few techs and says no can do. He said install prior size back on immediately and hope the transfer case and transmission are not damaged. My first question is why can't I go wider on the tires and secondly, why is it causing the transfer case and transmission to act up? Still want a wider tire but not at the expense of the trans and transfer case. I checked tire size calculator and the bigger size tires were about a 1/4 of an inch taller. Would a different size tire that is wider than what I had on but not taller taller work...and if so, what size?
Flummoxed in OKC
2018 M760i Xdrive
Frozen Gray
Fiona Red
57k miles

Something else is going on. I'm running Michelin AS4 in the same sizes with zero issues and I have spacers installed. I've driven from MD to FL and back with absolutely zero issues. You can run as wide as you want if they will fit as long as the specs are within 3% range of the OEM tire size. There is nothing to "reprogram". I am actually going with 295/35/20 in the rear when the 285's needs to be replaced. @furlow is running 295/35's in the rear as well.

[Raimo5]

Originally Posted by BlackM750i

Something else is going on. I'm running Michelin AS4 in the same sizes with zero issues and I have spacers installed. I've driven from MD to FL and back with absolutely zero issues. You can run as wide as you want if they will fit as long as the specs are within 3% range of the OEM tire size. There is nothing to "reprogram". I am actually going with 295/35/20 in the rear when the 285's needs to be replaced. @furlow is running 295/35's in the rear as well.

Is your car xDrive as well?

[BlackM750i]

Originally Posted by Raimo5

Is your car xDrive as well?

That's correct.

[Raimo5]

Originally Posted by BlackM750i

That's correct.

Then that sets the precedence. I have heard of similar symptoms due to inapropriately sized tires.

BIGTEX72 Did you refit previous tires and did it solve the issue?

[m760iM5]

BigTex, what rims are you running on your M760i and I assume PS4 tires? If you have 8.5 f and 10 r, your set up is only different from mine where you have 255s vs my 245s in the front. Either the extra front width threw something off or it's something not related. I would say not related, the Alipina's come with 255 in the front, but 21's.

I'm surprised to hear that you guys can fit 295's on a 10 inch rim. I have PS4s on my M760i (245/40/20 and 285/35/20), I wonder if the Michelin's make a difference in width vs. Pirelli. I haven't considered putting 255/40/20's on the stock fronts and I've been looking for aftermarket wheels with a 9-9.5 inch front so I can get 265s. I feel like the 265s will fill the front better. I want to go 295, maybe 305 in the rears and I need a 10.5 inch rear to do that. Aftermarket rims for the G12 are tough to find with my picky preferences.