What's a "Torsion Beam?"
 

I keep hearing the rear suspension referred to as "Torsion Beam" but I've always thought torsion anything referred to suspension like on bigger trucks and older muscle cars, like this:

http://www.allpar.com/photos/dodge/1...rsion-aire.jpg

But the rear suspension is what I would just call "Coil springs and shocks/semi-independent suspension," like this:

http://www.shockabsorbersworld.com/g...ndent-rear.jpg

This Torsion Beam thing is a total new one on me.

Someone enlighten me?

ge8 doesnt really have that, it has a solid rear axle (if one wheel goes up the other has to go down. vice versa) the spring and shocks are seperated but idk y. you could make them a "coil over shock". other then that the ge only mounts the rear axle off 2 mounts, ( i believe this is why the car shakes at high speeds, the mounts are too soft.) with out a stabilizer ("panhard bar") for side to side movement the fit is shaky. the rear shocks kinda help reduce side to side movement but since the shocks use a soft single mount i believe they flex as well. if they used a solid mount or even 2 bolt mount instead of 1 i believe the fits handling would improve drasticly. the fits rear suspension is pretty basic, kinda the most basic it could be, its a dead axle with springs holding the car up and bearings for the wheels w/ brakes attached hahah :rotfl:

Attachment 33384


ge8 rear = solid

It's the crosspiece
 

"Torsion Beam" or "twist beam" refers to the large cross-piece that runs across the car between the two trailing arms that are on either side.

This beam is not connected directly to the car; it's attached to each trailing arm and moves up & down (although only a little bit since it's so close to the body pivots) along with the wheels.

The beam does two things:
1. it locates the trailing arms; keeps them from twisting around on their own & sets the overall suspension geometry in the back, and
2. provides an anti-roll function when it gets twisted by the differing angles of the trailing arms as the car leans.

That last twisting function is the source of the name "torsion beam/twist beam". Lots of cars from many different makers use variations on this basic design; that twisting portion can be anywhere from right up close to the body (Honda Fit, original MK1 VW Golf) to directly between the wheels (late Toyota Tercels) to somewhere in between.

Thanks guys! So it's not that it was anything special from what I was saying, it's just a different name for the same thing.

Cool. I already knew the rear was a solid axle, and more than understand what that is, though. Just saw on Honda's website it called it a torsion beam. But that makes sense now.

4thCorener: + reps Good post, thanks.

Here's another good read for those curious...

2009 Honda Fit Sport: Suspension Walkaround

Remember when just about all Hondas had double-wishbones (unequal-length A-Arms) front and rear. McPherson struts and twist-beams were found in bargain-discount Cavaliers.

The advantage of the twist-beam is that it doesn't take up much space and doesn't cost as much, and for a car that's designed primarily for utility and economy over performance, it works. But I do see it as kind of a sign that the magic that Honda had has slipped away.

See link I shared. The Fit's suspension (both front/back) is really about as simple as things get, ie. very few bits, lowest cost design.

Definitely nothing near the legendary double wishbones.

Although Honda did really make the double wishbone standard in budget cars...

280Z's had fully independent suspension when about the only other cars in the American markets that had it were of Corvette calibur. Hehe.

There are pluses and minuses to every suspension layout. In the end the tuning probably has more to do with the final handling result than the basic design.

Reminder: BMW's for the longest time had a very simple, basic suspension design: McPherson struts in front, semi-trailing arms in back. Everyone raved about how those cars handle. The magic is in the tuning -- basic spring rates, front/rear roll-stiffness balance, bushing compliance, steering responsiveness.

The overall handling balance of the Fit shows that Honda engineers get this, too.

Honda hasn't had the double wishbone in anything inexpensive since 2000 when the EM1/EJ/EK (if not in the us) model went away.

IIRC the TSX was the last semi-affordable small car to get double wishbone.

I thought Civics/Integras had it till 2001, but still minor details there, its just a year after 2000. So really 2002 model year (late 2001) is when the huge shift began.

Well, the design used on the Fit isn't really a "solid axle". The placement of the twist-beam and the resulting geometry make it closer to a "pure trailing-arm" design.

If the twist-beam was located directly between the two wheel hubs, it would be a solid "axle": the beam would move up and down with the wheels and the wheels would remain vertical to the ground no matter how much the car was leaning in a curve.

The Fit's twist-beam makes the rear wheels change camber when the car leans. Being close to the body pivots means that the inside end of the beam is lifted when the car leans. This makes the outside wheel tilt into positive camber in a corner (a good thing on a FWD car).

Having the beam close to the body pivots also drastically reduces the range of the beam's vertical movement, and its unsprung weight -- also a good thing.

Good point, the Integra had it in 2001 (although it was still the same car from 1994) the Civic lost it after the 2000 MY.

So 2001 Civics and the 2002 RSX are when the DWB left cheap Hondas.

The rear suspension is a u shaped structure that is a torsion bar between the trailing arms that aren't firmly attached to the crossmember.. That way the two trailing arms can go up and down somewhat independently as the inner attachments tend to float. Its cheap and fairly effective.

The old Chrysler torsion bars were twisted rods instead of springs to provide the support; the Fit uses coil springs on trailing arms from a ridgid crossmember pivoting from the chassis like a horizontal door on hinges.

considering honda was coupling lower-end cars with double wishbone suspension with crappy tires like RE92's it really made no difference. :D

Some things never change - the crappy tires are still there. :p

RE92's were like butter compared to the Michelin XGT-V4 tires used on the Integra GS-R and Civic Si. Nothing like slapping the cars that Lived their Glory in the tuner age with horrendous tires.

Still miss the GS-R. It was a dream on the Direzza DZ101s The only thing I wanted to do to it was add a thicker sway bar.

~SB

yah, but at lower cost overall for a similar sloppy car, why not? :D

yah, i had a Gen5 lude at the time and they came with my car. first thing i changed... lol i ran dunlop SP8000's at the time on 17's. they were great grippy tires for the price. :)