I have zero experience with twist beam rear suspensions as I've mostly tried to avoid them. However, I feel the time has come to break the cherry and embrace my inner economy car.
So questions. a) Are they as awful as I assume? b) How much lateral deflection do they typically suffer? c) How does one control/adjust the roll center with a twist beam? d) How hard is it to convert one to a solid axle with a panhard bar?
I raced VWs with twist beam rears. Changing the rubber bushings to spherical ball bushings will help with lateral deflection. A large rear sway bar and shimming the hubs to adjust the toe both helped. There are bars available to keep the trailing arm part of the beam from flexing laterally. There are several suppliers of racing VW parts where you might find pictures for reference. I had looked at how much the rear beam of my son's 2009 Kia Rio resembled the VW setup with the intent of upgrading the handling. He never went further with it.As for going to a solid axle/panhard set up , anything is possible I suppose.
I don't mind the beam in the Forte. Makes things simpler in terms of "dialing it in" IMO because I set the rear to full stiff and soften/stiffen the front and adjust tire pressures to help over/understeer.Oddly enough, I'm running a much closer tire pressure F/R on this car than I have with any of my previous IRS cars.
So it's not a death sentence, basically?
I had been looking for a 2nd gen Accent when I found a pretty good deal on a Hyundai Getz 1.6 DOHC. It runs an Alpha engine, which is what I want. It weighs barely 2000 lbs, which is what I want. It has decent factory brakes, which is a big advantage over the Accent. It runs identical "bones" in the front suspension to the Accent and the tuning doesn't matter because I'm going to redo all the springs/shocks/bars anyway. It's also a significantly stiffer, stronger and safer car than the Accent, which I'll certainly take.
The only thing I'm worried about is the twist beam in the Getz vs. the 4 wheel struts in the Accent. I've had a lot of success suspension tuning by playing with roll centers and I'd like to continue using this technique. If I can't change the roll center on the Getz, I'll just have to hope it's high enough stock. If it's low, I've got to figure out a new way to tune suspensions that probably won't work as well.
Don't know if this matters, but the entire rear suspension will swap between a Getz and any Kia Rio from 2005 on up to the current model.
Wife has an 08 Rio sedan. Very neutral car bone stock if that helps any.
Not a death sentence, but I don't know much about them. Quite a few cars with decent handling have them - latest Fiesta, older Sentras off the top of my head...the RunX (JDM-only model) has one on the rear.
VW used them for decades.
They suck, but you can either stiffen them up to the point of essentially being a Kart chassis or you can soften them to try and keep the wheels in contact with the road at the expense of body roll. Your choice.
This may help.......http://www.cobaltss.net/forums/suspension-67/thoughts-rear-twisting-beam-sway-bars-202507/
I had one in a POS Pontiac Sunfire, it was fun in a "poke me again and I'll come around and kill you" sort of way. Very end swappy at the limit, liked to hop all over the road in bumpy corners. With practice, controlled lift off oversteer was doable.
DaewooOfDeath wrote: I have zero experience with twist beam rear suspensions as I've mostly tried to avoid them. However, I feel the time has come to break the cherry and embrace my inner economy car. So questions. a) Are they as awful as I assume? b) How much lateral deflection do they typically suffer? c) How does one control/adjust the roll center with a twist beam? d) How hard is it to convert one to a solid axle with a panhard bar?
a) no. it's not that bad. And on a smooth track it's even less "not bad." Depends a lot on the car though. I never had any issues with the back end hopping, but then again mine was in a heavy car. b) depends on what the center mount configuration looks like c) uh.... d) it's not super-hard if someone makes the right parts. For example, several guys with 4th/5th gen maximas have done it (including my rallycross co-driver in his i30).
Add a big rear sway, and the maxima guys liked to "bend the beam" to get more camber (though I didn't go that far myself)
It looks like you calculate the roll center by drawing a virtual arm through the chassis mounting point, to the top of the cross beam and then extending that line over the axle.
This makes me think it's not adjustable, but might be high enough not to matter.
Kenny_McCormic wrote: I had one in a POS Pontiac Sunfire, it was fun in a "poke me again and I'll come around and kill you" sort of way. Very end swappy at the limit, liked to hop all over the road in bumpy corners. With practice, controlled lift off oversteer was doable.
Sort of like a strut or multilink with a way too big swaybar?
DeadSkunk wrote: This may help.......http://www.cobaltss.net/forums/suspension-67/thoughts-rear-twisting-beam-sway-bars-202507/
Thanks, very helpful.
In reply to DaewooOfDeath:
More like a cross between a solid axle and trailing arms.
It only tried killing me a couple times unprovoked. Once when the front right tire got pulled into a puddle when I wasn't paying attention, and once on a unfamiliar dirt road with an off camber corner with the apex at the top of a short steep hill.
The wife's Rio does not hop over humps/bumps/expansion joints, but the springs are relatively soft. The Forte hops with the stock suspension because the factory shocks suck donkey di.... umm... they're bad, MMMKay? The K-sports with really stiff springs do not hop but it will easily lift a rear tire when braking/turning. As soon as you reapply power it's right back down on the ground and away it goes.
Roll center can be changed with beam peak position..........if peak moves more to front - RCH moves down, if peak more to down - RCH moves down similar effect like semitrailing arms(also always affected camber gain and bumpsteer)
Look what I found... Intelligent Conversation about twist beam
and found another source of info about clamping a steel bar to your axle beam... clamp a bar to axle
It's a twist beam, that means it's attached to a FWD car, so your first priority is maximizing front grip. If you manage to get enough front grip to get oversteer, like that's going to happen, then you can worry about the rear suspension.
I need to worry about the rear suspension right away, unfortunately, because a bad roll center axis will mean I need to do really radical, very suboptimal things to the front AND rear to get it to grip.
twist beam roll center position and understeer are coupled,
higher roll center create rear wheel lift=extra understeer,
higher roll center=more camber gain=extra understeer,
higher roll center=more bumpsteer=extra understeer
FWD low roll center is good idea 
youngfg wrote: It's a twist beam, that means it's attached to a FWD car, so your first priority is maximizing front grip. If you manage to get enough front grip to get oversteer, like that's going to happen, then you can worry about the rear suspension.
That might be the silliest thing I've read on here in a while! I've yet to have a FWD car that didn't have some oversteer when stiffened up/lowered/decent tires. In fact, the Forte had that bone stock with sticky tires.
You'll need to log in to post.
