obsolete
obsolete None
March 14, 2012 11:39 p.m.

Hey GRM, this is my first post here.

I run a Chevy Beretta (or should I say THE Chevy Beretta, there are currently no others) in LeMons & Chump. The rear suspension on this car, which I think is officially called a twist beam, is basically just a piece of angle iron between the hubs, with a trailing arm on each side. Springs and shocks are mounted separately. With the body supported and the wheels off the ground, if you lift one side of the suspension, the other side droops a surprising amount. For this reason, I call it the "wet noodle" rear suspension. It's semi-independent, I guess? Like IRS with a big rear bar? Other than the springs being too soft, it seems to work fine on the track.

Last year we upgraded the car by buying an Olds Alero for parts. We swapped in the running 3.4L V6 and the front spindles, and scrapped what was left of the shell. Before we hauled it to the recycler, I also pulled the rear independent suspension.

Installing the Alero IRS would require some fab work, but my team and I could do it if we wanted to. It has trailing arms with a pair of fairly long lateral links for each spindle. It has a sway bar and coil-over struts. I believe it gains some negative camber in compression.

My question is, should I bother with the IRS at all? Right now it's sitting my garage taking up space. Our plans, if we keep the good 'ol wet noodle twist beam, is to bolt a piece of pipe into it to stiffen it up (GM did something similar on later/sportier Berettas) and find some better springs/shocks. Does this make sense to y'all, or is the IRS just inherently better?

jimbbski Reader
March 14, 2012 11:53 p.m.

On most FWD cars the rear only just holds up the back end. You do all your acceleration, turning, & braking with the front end. IMO it's not worth it. Save your budget for something else.

LopRacer Reader
March 15, 2012 6:42 a.m.

Having zero experience with the Berretta, the system you describe sounds very similiar to the design used on MK1, MK2, (maybe on up to modern day) VW Rabbits and Golfs. the big bar running accross tieing both sides together. It has worked for VW for years upon years and they had some of the best handling FWD of all time. I don't think it's worth the trouble unless oyu have nothing better to do with your time.

92CelicaHalfTrac MegaDork
March 15, 2012 6:55 a.m.

It's FWD, the rear is just along for the ride, i wouldn't bother touching it.

failboat Dork
March 15, 2012 7:03 a.m.

I googled and one of the first links that came up was http://grassrootsmotorsports.com/forum/grm/intelligent-conversation-about-twist-beam-axle-swa/10872/page1/

ProDarwin SuperDork
March 15, 2012 7:04 a.m.
LopRacer wrote: It has worked for VW for years upon years and they had some of the best handling FWD of all time.

Huh?

I agree with others, I wouldn't waste a ton of time/money/energy retrofitting an IRS. That said, IRS is definitely the superior setup.

HappyAndy Dork
March 15, 2012 7:10 a.m.

Lots of great handling FWDs have a beam type rear suspension. Concentrate your efforts on tuning what you already have.

alfadriver UberDork
March 15, 2012 7:31 a.m.

If you are worried much about it, you can quickly add a panahrd rod to keep better control of the rear beam. Much easier to fabricate....

The question if IRS superiority is very dependant on how good it is, and how well it's matched to the front of the car. That goes quadruple on a FWD car.

dinger Reader
March 15, 2012 7:33 a.m.

One of the Tri Point Mazda World Challenge engineers once said "The rear suspension on a FWD car is there to keep the trunk from dragging on the ground." Stiffen up the rear, then focus your efforts elsewhere.

93EXCivic UltimaDork
March 15, 2012 7:59 a.m.

Stiffen the rear and add a panhard bar.

mad_machine MegaDork
March 15, 2012 8:05 a.m.

you would be surprised how many front wheel drive cars use a similar set up.. I would not sweat it

Schmidlap HalfDork
March 15, 2012 8:07 a.m.

Does your car have any poor handling traits that could be fixed by going IRS? If the rear end is not holding you back, upgrading it isn't going to do much.

Are the tracks you race on particularly bumpy? I always thought that IRS and solid/semi-solid rear axles were fairly equivalent on smooth racetracks, it was on bumpy streets that IRS prevailed (see solid axle Mustang GT vs IRS Cobra).

Streetwiseguy SuperDork
March 15, 2012 8:08 a.m.

I believe it was Colin Chapman that said something along the lines of, "Any suspension design can be made fast if it is not allowed to move." Greg Amy's take on that was to run 1000 lb/in rear springs in his ITA NX2000.

Gearheadotaku SuperDork
March 15, 2012 8:41 a.m.

There are sway bars that fit. Earlier cars had them as an option. Maybe find a really big bar (close to the size of the whole axle) and add that somehow?

ProDarwin SuperDork
March 15, 2012 8:54 a.m.
Streetwiseguy wrote: I believe it was Colin Chapman that said something along the lines of, "Any suspension design can be made fast if it is not allowed to move." Greg Amy's take on that was to run 1000 lb/in rear springs in his ITA NX2000.

"Any suspension will work if you don't let it."

Javelin UltimaDork
March 15, 2012 11:00 a.m.

IRS's superiority doesn't start to count until you hit rough roads, uneven surfaces, and what not. If you are just driving on a smooth racetrack you may not even notice a difference at all if you swap the IRS. Twist-beams can be made to handle road course work very well. I'd leave it.

obsolete
obsolete New Reader
March 15, 2012 2:00 p.m.
Schmidlap wrote: Does your car have any poor handling traits that could be fixed by going IRS? If the rear end is not holding you back, upgrading it isn't going to do much. Are the tracks you race on particularly bumpy?

Nope, the car doesn't have any bad habits, and is very easy to drive. It is on the understeer side of neutral, but some liftoff oversteer can be provoked. LeMons tracks are generally smooth, and the ones we race are pretty flat as well.

I guess I'll finally haul that IRS cradle to the recycler so I can quit tripping over it.

Moparman HalfDork
March 15, 2012 4:45 p.m.
Gearheadotaku wrote: There are sway bars that fit. Earlier cars had them as an option. Maybe find a really big bar (close to the size of the whole axle) and add that somehow?

It is not diffcult to make a sway bar for the beam axle, just u-bolt a flat steel bar to the axle.

mad_machine MegaDork
March 15, 2012 5:22 p.m.
obsolete wrote:
Schmidlap wrote: Does your car have any poor handling traits that could be fixed by going IRS? If the rear end is not holding you back, upgrading it isn't going to do much. Are the tracks you race on particularly bumpy?

Nope, the car doesn't have any bad habits, and is very easy to drive. It is on the understeer side of neutral, but some liftoff oversteer can be provoked. LeMons tracks are generally smooth, and the ones we race are pretty flat as well.

I guess I'll finally haul that IRS cradle to the recycler so I can quit tripping over it.

If you are on smooth tracks and the car is not exhibiting any sort of strange habits.. I would stay with the current suspension

Ian F UltraDork
March 15, 2012 5:35 p.m.

The IRS on wannabe-luxury cars like the Alero were more for ride comfort than handling performance.

If you need another arguement against, compare the sub-system weights - IRS usually weighs more. I'm assuming your Lemons car engine doesn't have a lot of power to spare to lug around any more weight than it has to.

turboswede SuperDork
March 15, 2012 7:19 p.m.

Most FWD cars need work on the front end as many tend to move poorly due to oversized sway bars, mounts incorrectly.

The suspension tends to bind when loaded and the inside front, which is already unloaded, can actually get stuck and run out of droop. Result? Lots of inside wheel spin and if you're unlucky, blown axles or differential.

Focus on making sure both front tires have the ability to move easily and that the sway bar doesn't bind up the suspension when loaded.

The rear is just there to follow along, teach everyone about left foot braking and FWD driving styles and some may find some missing speed :)

Good luck!

Toyman01 UberDork
March 15, 2012 7:56 p.m.

Spend your efforts changing the lower intake manifold gasket on the 3.4 before the crank case fills with coolant.

If it's anything like my wife's van, it should scoot pretty well.

A big +1 on the big rear bar, otherwise it's going to vaporize the inside front tire.

81cpcamaro Reader
March 16, 2012 8:21 a.m.

The Showroom Stock guys did pretty good with the 91 Olds 442 (Calais) and 92-3 Achieva SCX, both had the twist beam axle setup. My 92 SCX handled pretty good, the rear never did anything funky, so I'm not sure the IRS would make enough of a difference. The Achieva is basically the same car (more or less) as the Beretta.

I did upgrade my car with custom Bilsteins, coilovers and larger rear sway bar, all from Mantapart. But I would strongly suggest that you avoid them, plenty of info on web and BBB about how bad they are. It only took them a year and three months to get the parts to me.

Vigo SuperDork
March 16, 2012 8:17 p.m.

Late to the party here but yeah, IRS would be wasted effort unless you raced on bumpy tracks.

As for attaching steel plates to the bottom of a twist beam.. 3 of my current cars are modded thusly.

I have a rear bar from a Cimarron kicking around. I THINK your rear suspension is the same as a j-body? I dunno. If interested, lmk.

friedgreencorrado PowerDork
March 16, 2012 9:06 p.m.

http://www.amazon.com/Front-Wheel-Driving-High-Performance-Advantage/dp/0879382988

Dated, but the basics are correct.

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