Stock Rear Bar - Solid or Hollow?

[tsk94]

Is anyone able to confirm if the stock M4 (non-comp) rear sway bar is solid or hollow? I haven't removed it to judge it based on weight, and the weight on Realoem of 3kg is having me think it's hollow. But those weights are often not accurate.

If anyone is able to confirm it would be greatly appreciated.

[Skiy]

Originally Posted by tsk94

Is anyone able to confirm if the stock M4 (non-comp) rear sway bar is solid or hollow? I haven't removed it to judge it based on weight, and the weight on Realoem of 3kg is having me think it's hollow. But those weights are often not accurate.

If anyone is able to confirm it would be greatly appreciated.

how can i confirm? i have one laying in my garage.

[tsk94]

Originally Posted by Skiy

how can i confirm? i have one laying in my garage.

Realistically, if you could weight it that would likely be the best indication.
Say it does weight ~6lbs, I don't see a solid bar of that size and diameter weighing on 6lbs, so it's likely hollow. If it's say 15lbs, then it's likely solid.

[Skiy]

I measured it roughly at 6.5 lbs with the bushings. If I'm holding it in my hand and tap it I can feel it vibrate. Id say its hollow.

[tsk94]

I'd say that's hollow.
Appreciate you checking that for me - thanks!

[x.shell]

The sway bars are hollow. A solid bar would be heavy af while adding no benefit — only penalties. Since the sway bar's main function is accomplished through torsional rigidity, it makes no sense to use a solid bar as the center of bar will contribute very little to it's torsional performance. If a stiffer sway bar is needed, they just up the radius.

[Skiy]

Originally Posted by x.shell

The sway bars are hollow. A solid bar would be heavy af while adding no benefit — only penalties. Since the sway bar's main function is accomplished through torsional rigidity, it makes no sense to use a solid bar as the center of bar will contribute very little to it's torsional performance. If a stiffer sway bar is needed, they just up the radius.

You you know much much stiffer front and rear zcp bars are compared to base bars?

[TractionControlDelete]

Originally Posted by Skiy

You you know much much stiffer front and rear zcp bars are compared to base bars?

https://f80.bimmerpost.com/forums/sh....php?t=1295680

Front sway bar is the same thickness but the narrow section is shorter on the ZCP. Rear sway bar is 25.26mm on ZCP vs 22.9 on non ZCP.

[Skiy]

Originally Posted by F82KPowers

https://f80.bimmerpost.com/forums/sh....php?t=1295680

Front sway bar is the same thickness but the narrow section is shorter on the ZCP. Rear sway bar is 25.26mm on ZCP vs 22.9 on non ZCP.

I am aware of that, I replaced both of mine. But wondering if anyone has % data or maybe bmw published this somewhere.

[TractionControlDelete]

Originally Posted by Skiy

I am aware of that, I replaced both of mine. But wondering if anyone has % data or maybe bmw published this somewhere.

Gotcha. I'm curious myself too now. While I was checking for data I did find out the following more detailed information on the bars:

Front Stock Competition Bar thickest portion is 28.5 millimeters. 25.0 in the center and 24.5 on the ends.

Rear Stock Competition Bar thickest portion is 25.3 millimeters. 22.3 millimeters in the center of the bar and 21.0 millimeters on ends.

Might help in comparing sway bars to aftermarket options that have similar dimensions to gauge approximate changes compared to OEM bars.