Torsion beam rear axles explained 

Agreeded. I was wondering about my honda fit with the modified twist beam. What do we call this then. 3/4 twist?

They are really good.

Hope you enjoy it!

You’d enjoy the book!

Far rom dead I would say. Lower spec Mercedes A-Class, Golfs and their SEAT/Skoda, even Audi equivalents use one, as does the Peugeot 308 and its clones, pretty much all supermini class cars like the Polo etc. And since cars like the Golf moved from multi-link independent rear ends to this two-tier system of twist beam for low-spec cars, you could say it's more common now than before. Perhaps it will die however - nice to see the new Renault 5, despite its size, having an independent rear end.

I think Toyota still uses them too. I remember I saw one in 2012 Yaris. I just noticed it after I got fascinated by this axle type after one in my Golf got broken and how easy it was to replace. At least compared to the multi-link rear axle on my wife's Audi which always has some bushing or link worn out.

Thank you. You might want to look at some of the 200+ videos already produced.

The book’s even better!

Glad you liked it. You might want to also check out some of my 200+ other videos.

Don't forget to check my 300+ previous videos.

@@JulianEdgar watched many today. Really like this content!

Yes that is correct.

For the Astra VXR/OPC they are commonly replaced with spherical bearings which add minimal NVH for a huge upgrade in rear end feel and stability. Definitely something I want to do to mine.

Afaik that's been a original design in quite a few cars. But I'm not sure except some Opel/Vauxhall models. Seems like a rather simple but worthy upgrade for sure.

Yes, most rear suspension designs have 'steer' capabilities.

You are welcome!

More likely inadequate damping. Lack of lateral stiffness in a rear torsion beam more likely to lead to rear toe (ie rear steering) changes, I think.

@@JulianEdgar oh ok

Yes.

I have no technical information on the Opel Astra J.

Yes and no: there will still be a relatively flexible trailing arm component unless the torsion beam is acting only as a dead axle.

That was the answer to my question since I just bought a 206 and wondered why the trailing arms are on individual bearings if they are supposed to be rigid. My thought was something like what you stated but was not sure.

The 306 also had a passive rear wheel steering mechanism as part of the bushing arrangement.

I do not agree 100% about the low maintenance, the family 106 needed a replacement of the entire system because it rusted together, leaving the car with no suspension at all. The replacement version had multiple lubrication spots to fill op the torsion beam system with grease, to prevent the system from rusting into a solid piece again. The same system generally works well on a lot of trailers though, so designing it correctly is key.

@@larsjrgensen5975 Just because YOUR suspension system wasn't reliable, doesn't mean ALL of them were unreliable. Most cars I've seen with 200k with no work needed to be done on the suspension. That does take a lot of doing!

@@khalidacosta7133 Just because YOUR suspension system was reliable, doesn't mean ALL of them were reliable. I wrote that it works very well on trailers, but it is not a 100% perfect system. If they spend time and money on developing a way to renovate the system on a peugeot, there must be a market and need for it. The 106 had around 160.000km on it, when it locked up and became very dangerous to drive. A friend of mine had a Renault 19 with the same design, one side broke at 190.000km. A 306 in the family locked up like the 106, but i do not know about the km, so it does not count. We have a bad climate here, with a fair bit of road salt, that could maybe explain some of the higher failure rates.

Not a depth I am going into here. I can recommend several textbooks and papers if you're interested.

@@JulianEdgar if you have them. That would be great.

@Michael Stanbrough The references I used when writing the section on torsion beam suspension were: Held, V. & Hiemenz, R., Designing Twist Beam Axles in Encyclopedia of Automotive Engineering, John Wiley and Sons, 2014, and Heibing, B. & Ersoy, M., Chassis handbook : fundamentals, driving dynamics, components, mechatronics, perspectives, Vieweg + Teubner, 2011. However, I am not sure they will fully answer your questions.

Not easy to answer eg depends in part on the unsprung weight of the two different suspension designs.

Yes, covered in my book.

Yes, many cars with torsion beam rear suspension have an anti-roll bar within the beam.

@@JulianEdgar You said there wasn't one on the VW beam and you are correct for all but the GTI models. I did see you mention other vehicles. I just felt like commenting as I was a VW mechanic for 35+ years. 👍

Depends how long the dampers are, but yes normally that would be the case.

Thanks for your reply! This applies also when the damper and the spring work separately? I mean when it's not a coilover.

I mean a design Similar to the design your are describing at 6.06 of your video

The length of the dampers dictates the preload (if any) on the spring. Fitting spacers to the springs would normally change the preload, because the dampers don't get any longer.

It depends how the independent suspension is arranged - torsion bar springing can be used with a whole variety of suspension systems. (I don't know the Pug system in any detail.)

@@JulianEdgar I was going to ask about the difference between Torsion Beam and Torsion Bar. I *assume* they are different?

@@zonoscopePictures 'Torsion beam' refers to a type of suspension system, as covered in this video. 'Torsion bar' refers to a type of *spring* - a bar that is twisted. So anti-roll bars (sway bars) are torsion bars, and torsion bars can be used as the main springs in all sorts of suspension systems eg double wishbones, semi-trailing arms, etc.

What is double balljoint suspension? Double wishbones?

@@JulianEdgar I seen some Audi have 2 upper ball joints

@@JulianEdgar en.m.wikipedia.org/wiki/Multi-link_suspension

OK, multi-link suspension. Pretty common these days, especially on the back on RWD cars. Yes, they have benefits in holding toe angles and giving defined camber curves - but I often think the benefits are a bit overstated. Multi-link suspension is covered in my book.

No. Digital books immediately get pirated.

@@JulianEdgar I only buy digital books now (Kindle or Apple Books; easier to highlight, reference, read anywhere), but I had to make an exception for your book Optimizing Car Performance, and now I know there is no point in waiting for a digital version of this. Thank you!

It can involve differing bush hardness in different planes and the bush orientation - but also inclination of the trailing arms to horizontal, use of additional toe control links, etc.

It depends on the car and how much effort you want to go to, but usually, yes.

Yes, you can shim the hubs where they bolt to the axle.

Allows easy manufacturer adjustment for different models. Just change the bar, not the whole torsion beam axle.

Yes, cars with anti-lift rear suspension will rise when the handbrake is applied and the car attempts to roll backwards.

Pretty sure the Citroen AX used torsion bar setup which was independent. Very different to a torsion BEAM suspension.

@@khalidacosta7133 The forces involved in anti-lift - which lead to lift when the car tries to roll backwards - are exactly the same, though. Now, with Citroen being Citroen, it's likely that the spring rates were quite soft, which amplifies the amount of this motion.

Because all cars need front and rear grip, irrespective of their driveline configurations.

Anything is possible but it would be a major engineering exercise.

@@JulianEdgar If it piqued your interest and lets say intellectual curiosity, as someone that knows a lot on car suspension, i could suggest tackling this idea, thinking a "what if, how i would do such a change". Not needing a large EV motor (like lets say a tesla or any other powerful beasts) but one that could serve every day driving in a phev, like a 9 inch electric motor or an 8 inch one, with some 20-30 odd kW output...or maybe smaller hub motor setup in each rear wheel, which might not involve any suspension change

To be honest I think the days of doing home-brew electric conversions is gone. Depending on where you live, it would likely cost a lot more than buying a secondhand electric car. And as for a hybrid, you could never match a Prius in outcome - and they're now very cheap indeed.

@@JulianEdgar yeah, factory electric cars are not too appealing, they have devolved in terms of quality plus they use everything integrated, only touch screen, minimal buttons and very expensive to repair. In fact the EV conversion will just start to bloom, because plenty of owners of older cars would want to continue to use them and enjoy upgraded performance of the EV tech as opposed to the new low cost EVs at stupid overpriced price tags. A conversion is 10k-15k using tesla batteries (so expensive) Ah, there are shops that charge for a EV conversion 3 times that from the snobs that don't care, that is a different story, but with 10k an EV conversion is a realistic price. What used EV do you find with such a low price? Nissan leaf is junk, was a failed engineering from the start, Now, then you get to keep your beloved current vehicle that has much higher comfort than the sparse plastic cans of the first gen EVs and also the benefit of electric drive.

In short, double wishbones as a suspension system are superior to MacPherson struts, irrespective of age.

@@JulianEdgar but those old cars have heavy arms and probably not that good geometry. I am not an expert, those are just my thoughts :). Thanks for the reply btw.

@@Random-nf7qb My reply stands: double wishbones are intrinsically a better suspension system than MacPherson struts. Plenty of old double wishbone systems were light and had excellent geometry. You'd enjoy the book, I am sure.

@@JulianEdgar Ok, thanks!

I wonder if you cover the Holden HQ in your book. It has interesting double wishbone front-end geometry. I think there are some issues with 4-link live axle rear suspension, such as a high roll centre, some roll-steer effects etc. Not the best for stability. The Holden VB with Macpherson struts is likely to be an upgrade.

Yes, good packaging.

Better than what?

Less?

No, quite different. Torsion bars provide the springing medium; in a torsion beam system the springing medium is completely separate. Perhaps you'd enjoy the book?

@@JulianEdgar so what exactly does the torsion in "torsion beam" refer to? Doesn't torsion, by definition, refer to a twisting action which is what differentiates a torsion beam axle from a beam axle?

Torsion bars provide the vertical movement's suspension springing. A torsion beam axle does not use its axle in torsion to provide vertical springing; it uses its torsion to provide roll resistance. A torsion beam suspension is nothing like suspension using torsion bar springing - torsion is used in completely different ways in the two systems. Therefore torsion beam suspension is not just a variation of the torsion bar suspension.

@@JulianEdgar so a torsion beam is a glorified anti-roll bar.

Yes, that is a better way of putting it than suggesting it is just a variation of torsion bar suspension. However, unlike an anti-roll bar, the torsion beam is solely responsible for the wheel location as well. Have you actually watched the video?

On many cars with torsion beam rear suspension you can adjust the alignment eg by shims behind the stub axle mounting plate.