Rear torsion/sway bars

I don't know if this is helpful, but this is a quote from one of the Ford Engineers who worked on the Fiesta ST from a video discussing the suspension of the car-
The [REAR] twist beam is about 75% stiffer, and the twist beam on a twist beam car it's like your stay [SIC,=SWAY?] bar, it's your roll stiffness. So the stiffer the twist beam is, it's like putting a bigger stay bar on it. There’s no extra stay bar.. we did it all on the beam.
View: https://www.youtube.com/watch?v=M7YKS9CnpJg

Th


Thanks!! Yes the torsion beam is basically one massive spring/strut mounted sway bar. My question is just: in practice how do the two styles of “torsion stiffeners” change the handling dynamics of our car? Does one yield greater results than the other? One more mild than the other? I’d imagine they both do the same thing just to varying degrees.

They basically do the same thing by adding stiffness to the torsion beam. Straight bar (pierce/tb/etc) beam stiffeners tend to have a slightly milder effect than the external bars which can be beefier with more solid mounting points. You could in theory make a stiffer straight bar, but at some point you’re just relying on two 1/2”’ bolts loaded in shear

Some very approximate numbers I came up with for increase in stiffness vs the 2014-2015 torsion beam. Obviously there’s some measurement error so take with a grain of salt.

2017-19 rear beam: +27%
Pierce 19mm (3/4”) tube stiffener: : +24%
19mm (3/4”) DNA/UR rear “sway bar”: +37%
22mm (7/8”) Hotchkiss tubular “sway bar”: +58%
(7/8”) 22mm Whiteline solid “sway bar”: +70%

as you can see, the Pierce (TB is probably similar) is roughly equivalent to upgrading to a 2017+ rear beam.

If anyone is curious, here are numbers for the front (again baseline is 2014-2015 front 19mm bar)

21mm 2017+ front bar: +49%
22mm (7/8”) UR front bar: +87%
25mm Eibach front bar: +200% (holy understeer Batman!)

You can use the above to compare a given bar setup to the understeer/oversteer of the stock setup

The 2017+ bar/beam combo has slightly less liftoff oversteer than the earlier setup based on the stiffness ratios. The Pierce beam stiffener in addition to being roughly equivalent to the later model rear beam, is also about enough to give a later model car the same liftoff bias as the 2014-2015 setup.

The Eibach front bar is way too stiff for anything but a serious track car with a massive front aero splitter, even with as much rear bar combination as you can possibly add.

They basically do the same thing by adding stiffness to the torsion beam. Straight bar (pierce/tb/etc) beam stiffeners tend to have a slightly milder effect than the external bars which can be beefier with more solid mounting points. You could in theory make a stiffer straight bar, but at some point you’re just relying on two 1/2”’ bolts loaded in shear

Some very approximate numbers I came up with for increase in stiffness vs the 2014-2015 torsion beam. Obviously there’s some measurement error so take with a grain of salt.

2017-19 rear beam: +27%
Pierce 19mm (3/4”) tube stiffener: : +24%
19mm (3/4”) DNA/UR rear “sway bar”: +37%
22mm (7/8”) Hotchkiss tubular “sway bar”: +58%
(7/8”) 22mm Whiteline solid “sway bar”: +70%

as you can see, the Pierce (TB is probably similar) is roughly equivalent to upgrading to a 2017+ rear beam.

If anyone is curious, here are numbers for the front (again baseline is 2014-2015 front 19mm bar)

21mm 2017+ front bar: +49%
22mm (7/8”) UR front bar: +87%
25mm Eibach front bar: +200% (holy understeer Batman!)

You can use the above to compare a given bar setup to the understeer/oversteer of the stock setup

The 2017+ bar/beam combo has slightly less liftoff oversteer than the earlier setup based on the stiffness ratios. The Pierce beam stiffener in addition to being roughly equivalent to the later model rear beam, is also about enough to give a later model car the same liftoff bias as the 2014-2015 setup.

The Eibach front bar is way too stiff for anything but a serious track car with a massive front aero splitter, even with as much rear bar combination as you can possibly add.

Those are helpful numbers. I do believe that the stiffer rear beam and the bigger front bar started early in the 2016 model year.

What was the build month/year for the Sync 3 update?