E92 Removing Rear Seats effects the rigidity?

[ashutoshkotha]

I'm trying to understand if removing the rear seat will effect the cars rigidity on track?

Technically it should but tying to know up to what extent. Can I go to track days like that without a half roll cage?

[DukeofAlexandria]

Originally Posted by ashutoshkotha

I'm trying to understand if removing the rear seat will effect the cars rigidity on track?

Technically it should but tying to know up to what extent. Can I go to track days like that without a half roll cage?

Why would you think that?!?

Explain your thought process here.

-Duke

[ashutoshkotha]

I want thinking that because the seat is structure that is in the center the car.

[DukeofAlexandria]

Originally Posted by ashutoshkotha

I want thinking that because the seat is structure that is in the center the car.

And what is that structure made out of?

1/4” cold rolled steel, or a small simple wire frame with wrapped cushion material and some leather?

It will help with weight reduction and that’s it. It has zero impact on suspension geometry or unibody chassis.

-Duke

[ashutoshkotha]

Got it. I’m just getting started on my build. That is what I hoped it’d be.

Thanks for responding!

[DRLane]

Beware, It’s addicting to just keep taking shit out! ashutoshkotha

[ashutoshkotha]

Damnn thats 🔥🔥🔥

[DRLane]

Originally Posted by ashutoshkotha

Damnn thats 🔥🔥🔥

One day it will be, right now it’s just a mess… Have fun

[ashutoshkotha]

Thank you. Good luck with the build.

[wyatth]

Originally Posted by DukeofAlexandria

Why would you think that?!?

Explain your thought process here.

While it makes no/little difference on E9x cars, his thought was not unreasonable, as the rear seats could make a material difference in torsional rigidity on E36 and E46 models.

Example on the E46:
Sedan (w/o folding seats): 18000Nm/deg of torsion
Sedan (w/folding seats): 13000Nm

[ashutoshkotha]

Originally Posted by wyatth

While it makes no/little difference on E9x cars, his thought was not unreasonable, as the rear seats could make a material difference in torsional rigidity on E36 and E46 models.

Example on the E46:
Sedan (w/o folding seats): 18000Nm/deg of torsion
Sedan (w/folding seats): 13000Nm

That was my thought process. Mechanically it makes sense that it should affect the rigidity since the car is mostly OEM. But I wasn't sure to what extent it might even affect the rigidity. I finally decided to remove the seat when I install the half roll cage.

[SYT_Shadow]

Just remove the rear seat and get the slon workshop reinforcement panel!

[M3SQRD]

Originally Posted by wyatth

While it makes no/little difference on E9x cars, his thought was not unreasonable, as the rear seats could make a material difference in torsional rigidity on E36 and E46 models.

Example on the E46:
Sedan (w/o folding seats): 18000Nm/deg of torsion
Sedan (w/folding seats): 13000Nm

The type of support structure is very different between fixed vs. folding rear seats (one has structural welds, the other doesn’t). Removing a folding seat from the rear of a car will have an insignificant, if no, change, in bending and torsional stiffness. If you’re looking to increase torsional stiffness then add the Slon bonded in reinforcement CF panel as suggested by SYT_Shadow.

[Redd]

I have a cheap Ultra Racing rear strut bar and it helped with rear rigidity even with my folding seats in place. Yes I know it doesn't tie in with the rear strut towers (which are lower) and yes it's not triangulated to the floor etc etc but it works and is noticeable. You can try that if you're worried about rear rigidity without the seat in place.

[M3SQRD]

Originally Posted by Redd

I have a cheap Ultra Racing rear strut bar and it helped with rear rigidity even with my folding seats in place. Yes I know it doesn't tie in with the rear strut towers (which are lower) and yes it's not triangulated to the floor etc etc but it works and is noticeable. You can try that if you're worried about rear rigidity without the seat in place.

Please describe how you measured the change in rear rigidity and was it…Bending? Torsional? Lateral? Or magically all three DOF?

A front strut brace doesn’t increase torsional stiffness like 99% of the internet thinks - it helps to keep the outside loaded strut tower coroner from flexing outward by using the stiffness of the much less loaded inside strut tower.

The ultra racing rear strut tower bar is mimicking what a front strut tower bar does. I doubt it increases the stiffness in any DOF by any significant amount.

[Redd]

Originally Posted by M3SQRD

Please describe how you measured the change in rear rigidity and was it…Bending? Torsional? Lateral? Or magically all three DOF?.

Absolutely nothing scientific. I had a creak from my parcel shelf every time I went over a bump. After the rear strut bar no more sound. I also noticed some additional rear stiffness and less body roll, something like an arb. So something somewhere stopped flexing.

[M3SQRD]

Originally Posted by Redd

Absolutely nothing scientific. I had a creak from my parcel shelf every time I went over a bump. After the rear strut bar no more sound. I also noticed some additional rear stiffness and less body roll, something like an arb. So something somewhere stopped flexing.

Your shock bar is a two-force member so it’s going to act similarly to how a front strut tower bar works by, for example, while turning left, the right rear side will want to deflect outwardly but the stiffness from the less loaded left side will help to minimize the right side deflection by allowing them to combine stiffness - basically it gets the two sides to act together in tension/compression and, therefore, have some small measurable effect on lateral stiffness. The rear shock tower assembly is a lot closer to a “closed section monocoque” with the c-pillar, side quarter panel & shock tower, roof and floor all helping to stabilize the deformation of the shock towers.. so a shock tower bar will be a lot less effective on rear lateral stiffness compared to the stiffness added by tying together the two front “open section” towers with a strut tower bar.

However, it won’t have a measurable effect on rear bending and torsional stiffness.