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.