Semi trailing arm suspension explained

Used on millions of cars - BMW, Mercedes, Ford and even Rolls Royce - semi-trailing arm rear suspension had some huge advantages. But it also had downsides that were nearly impossible to overcome.
Buy my book on the history of car suspension here - www.amazon.com/Car-Suspension... (or from Amazon in your country)

[@ganeshmohan]

My imported R31 Nissan Skyline had semi trailing arm rear suspension (with Nissan's early implementation of HICAS too). My biggest issue with this suspension layout is the propensity to squat under hard acceleration. When fully loaded with people and things in the boot, you could almost hit the rear bump stops when you launch it. Thankfully the rear suspension design got completely revamped in the R32.

[@HannyDart]

funfact: VW is actually using a "längslenker" aka semi trailing arm in their newest VW T7 Van. They use GIANT cast aluminium links with the spring actually mounted behind the rear axle.

[@arrindaley3714]

I implemented a semi trailing arm on my mini, previously with trailing arm, primarily to raise the rear roll centre, it drives beautifully IMO and no need for a rear roll bar or progressive bumpstops. All I read was about datsun 1600s and BMWs reducing thier sweep angle where I was looking to increase it drastically, then I realised they are RWD and as the rear squats negative camber change means the rear tyres lose traction so they were forced to run smaller sweep angles. As a front wheel drive this wasn't much of a concern so I was able to pick a sweep angle and camber curve that best matched camber change due to roll.

[@JulianEdgar]

An interesting story!

[@brucescammells2817]

Nicely informative article. Triumph used this very effectively from 1963 with their 2000 sedan.

[@ArchOfficial]

The effect of elastokinematics shouldn't be understated. In addition to the natural toe-out and +ve camber tendency of the wheel hub and wheel rim present in all assemblies, there is also a significant toe-out tendency on lateral and braking torques present in semi-trailing geometries that can be tuned out in strut/double wishbone/multilink geometries, or even reversed into toe-in. For this reason some makers have adopted control methods like Mazda's DTSS for the FC3S.

[@blurglide]

I'm reliving my senior project...1999 SAE Mini Baja (basically a small UTV). I was responsible for the rear suspension...but I did the front as well (and the final drive) because my teammates were incompetent. I trusted them to at least do the steering. First couple laps...we were dominating the pack. We could corner AND absorb bumps like no other team. Then...turns out the steering interfered with the suspension on hard bottom outs and we broke tie rods. If you want something done right, do it yourself. Today I make sure dangerous things don't do their dangerous thing when they're not supposed to.

[@johnbarker5009]

Great and thorough explanation, thank you!

[@JulianEdgar]

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

[@johnbarker5009]

@@JulianEdgar I've checked out a few others already, and will certainly look at more of them. Good stuff!

[@A.A.HadiWhite]

thank you for explaining

[@seshachary5580]

very educative. thank you regards

[@OldSkoolUncleChris]

Fantastic end to the video

[@tiitsaul9036]

Thank you for sharing. Well presented as always. My daily driver has semi trailing arm suspension and it definitely feels “alive” when driven hard. Holden is the last car with semi trailing arm suspension I can think of. Lasted til 2002 or 2003 or something.

[@billmanagerbunson3123]

Wrx kept it till 2007

[@tiitsaul9036]

@@billmanagerbunson3123 interesting. I did a quick google search and couldn’t find any Subaru with semi trailing arm suspension.

[@billmanagerbunson3123]

Ah actually this is my mistake, they are traditional trailing arms. It makes me wonder how much more alive they would feel if they were semi trailing instead, however that seems like it would complicate the driving dynamics brought on by the AWD system

[@bgnukem]

Another problem with multi link rear suspension is the cost of replacing all the bushes and balljoints! Semi trailing system is way simpler and cheaper to refresh!

[@Rose_Butterfly98]

Wonder why they don't bring back trailing arms. At least not on normal cars, I know some buggies like the CanAm Maverick trailing arms. With what we've learnt from mountain bike suspension designs, we could make very comfortable suspension. Plus since cars aren't chain driven and we have crankshafts that can extend, some of those weirder MTB suspension designs that have chain tension issues won't be a problem.

[@jamsbong]

This could be a good reason to own an old classic car

[@JulianEdgar]

Yes I think doing so adds immeasurably to evaluations of current cars.

[@TheSoundsnake]

Thanks for sharing! But I’d like to comment on the trailing arm design. Many French cars offered a famously comfortable ride with trailing arms, and were equally well known for their road holding capacities. This goes for e.g. all Citroëns with hydropneumatic suspension (exception C6), including the Moose test record holder Xantia. The Xm and Zx even had passive steering built in. Also the famous Peugeot 205 and 405 used trailing arms. It was extremely compact too, so I still don’t know why they stopped using it. Maybe because tires have a wider low profile today. My main complaint is that all this bulkiness only eats up our resources faster, and I’m pretty sure people don’t enjoy their drives more now then people did in the past, any period.

[@JulianEdgar]

Trailing arms have a ground level roll centre - typically not what is wanted. Most cars have had passive rear steer for many decades. Not saying that Citroen suspension isn't very good, but fans of one make tend to overlook other cars a bit.

[@TheSoundsnake]

@@JulianEdgar thanks for your reply, didn’t know about the ground level roll centre, that’s interesting. And agreed, I’m a Citroën fan and own one of this old big Cits. But maybe I wasn’t clear, I do understand that more sophisticated links systems could do a better job. However, in most cases it’s not worth it, or the implementation is not even good enough to seriously outperform Peugeot and Citroen. I remember many cars being advertised back in the 90’s with super multilink etc., but in real world people either don’t drive them in a way that it makes any difference, or they simply even weren’t as stable as those old frenchies. Add to that the space savings of trailing arms, and for most cars and drivers this cheap and simple setup would be optimal. Circuit driving is a completely different story… So my remarks were not about saying that trailing arms are the best, I think it’s the best compromise for regular street cars, or maybe semi-trailing arms, that’s probably compact too. I do regret all the natural resources that are put in the building of huge big heavy cars, with all sorts of complicated systems not required to enjoy a trip, with less interior room then you’d expect… Safety would be the argument, but that’s a race to the bottom where every next generation must be bigger and heavier, impacting the environment more and more, so pointless.

[@arrindaley3714]

@@JulianEdgarI just read the section of your book on semi trailing arms, were there any FWDs equipped with semi trailing arms? If not any reasons why?

[@JulianEdgar]

@@arrindaley3714 Yes, Volkswagen Transporter is an example. However, the vast majority were on RWD cars.

[@bikeaddictbp]

@@arrindaley3714 Nissan and Subaru used rear semitrailing arms on their early FWD cars (1970s and into the 1980s). First generation or two of FWD Nissan Cherry and Sunny/Sentra had them. The first Toyota Tercel (1980ish) used pure trailing arms.

[@realnutteruk1]

Of course, major camber change is much more of an issue with modern wide tyres. The greatest handling cars of all time... the 2CV and the Issigonis Mini, ran such narrow tyres with relatively huge sidewalls that camber change on fully trailing arms wasn't an issue...

[@ArchOfficial]

Where did you get that idea from? Data shows that while the peak is at a lower angle and there is less to be gained from optimal camber, you will still lose a ton of grip being at a very unoptimal angle on old high-sidewall, flexy tires. Some sources like RCVD have camber sensitivity curves for bias-ply tires but the tests are probably flawed as there is no perceivable trend, so I think heating etc. wasn't taken into account.

[@mackquack2929]

The Corvairs produced from 1959 to 1964 used a semi-trailing rear suspension. Currently a friend of mine is racing this "early model" Corvair and is doing fine against later, more sophisticatedly suspended Corvairs in vintage racing. His car number is 362, a tribute to racing legend, Bill Thomas's 1960 model racing Corvair. The upgrade is 1000lb. springs at 2-3 degrees negative static camber and good radial tires. The dampers must be properly matched. These guys all use spherical bushings as pivot points.

[@JulianEdgar]

Yes, I cover the Corvair in detail in my book.

[@288gto7]

They used swing axle until 64 , then in 65 it received semi trailing arm from the c2 corvette

[@tylerkimberlin194]

looking at the toe graph, is the imaginary line from hub to pivot on the 280zx horizontal, and going down from hub to pivot on the 300zx?

[@Dr_Reason]

I have always believed the "swing axle Corvair" had a 45 degree semi-trailing arm. The suspension had too much un-spung weight as it was designed to hold up under the van and pickup versions with heavy springs and big loads. Pontiac copied this for 62-61 Tempest but in 63-64 the changed to a lighter arm and moved the pivots to get about a 30 degree from longitudinal semi-trailing arm.Critics thought it handled much better than the early model. The Corvair stayed with the original arm through 64 and applied several band-aids to limit camber change.

[@JulianEdgar]

The Corvair is covered in detail in my book.

[@shinequashie393]

You absolutely need to analyze the Aptera vehicle

[@JulianEdgar]

Won't be happening until it is a production car and proper information is released on it.

[@bilaltariq7819]

Does the back of the car lift up and go into the rebound part of the curve for the 300sx when braking? If so, wouldn’t the toe out cause rear instability especially under hard braking?

[@JulianEdgar]

Yes, but look at the graph scales.

[@andrewroland8491]

Mr. Edgar, have you ever heard or thought about a diy "fric" suspension. I'm working on a 93 WRX, and honestly I just want to do something different and interesting from the rest of my autocross competition.

[@JulianEdgar]

I cover two dry front rear interconnected suspension systems in the book.

[@helixworld]

Is there built in anti-lift under braking? I wonder if it can help to reduce undesirable geometry changes.

[@JulianEdgar]

Yes, under braking the semi-trailing arm tries to pull the back of the car down, so there is some anti-lift.

[@ArchOfficial]

@@JulianEdgar There is often A LOT of anti-lift. Most STA cars will squat the rear hard under handbrake application, although footbrake application depends more on the brake setup ie: torque bias.

[@288gto7]

I think It was first used by lancia aurelia in early 50s and not by bmw

[@murraymadness4674]

Does your book have anything about leading arm suspension? I am building a mid-engine car and the trailing arms pivots are in the way, so I swapped them into leading arms. I spent a lot of time thinking about and trying to find what problem this may cause and found nothing about it. The newer ford trucks using leading arms in front.

[@JulianEdgar]

As far as I know, leading arm front suspension has only ever been used on the Citroen 2CV. Do you have a link showing the suspension on newer Ford trucks?

[@murraymadness4674]

@@JulianEdgar I tried to find it earlier, I had a F550 and recall it did, but it actually has a straight axle with leading arms, so not an IRS like the 2CV, which btw, saw your video on that.

[@avoohanian]

The E link rear end of the v6 Mazda 929 (whilst documented as multi-link) used to have quite pronounced camber change under load. Even a moderate takeoff from stop would tuck those rears in very much like a swing axle. I always found that a little unsettling in the wet compounded by the softness of the rear springs. Made for a very plush ride though.

[@compu85]

Guessing you have a W123 Estate? Those had rear SLS as standard.

[@JulianEdgar]

Close - W123 230 sedan with optional SLS rear suspension.

[@compu85]

@@JulianEdgar Cool! I wish my W126 had it. It was standard only on the 560 in the US market. Mercedes got rid of the anti-squat rear suspension in the 560 for the 1988 model year - from what I read the standard semi trailing arm setup - virtually identical to your 230, introduced in 1968 with the W114/5 gave a softer ride. I've seen some people on forums retrofit it though, seems like an easy enough rear subframe swap!

[@chuckgoodwin87]

I believe they’re on the the VW Transporter too

[@JulianEdgar]

Yes, and they're good handling vehicles, too! (We have a T5 Transporter.)

[@billmanagerbunson3123]

The Subaru wrx kept it till 2007 and I ADORE it. It feels strong and alive, love all the characteristics of it Edit: Subaru never used semi trailing, only trailing.

[@JulianEdgar]

No that is not correct.

[@billmanagerbunson3123]

Ah yes my mistake, they are traditional trailing arms. Still adore them regardless

[@JulianEdgar]

Not that, either!

[@billmanagerbunson3123]

What do you mean? The Impreza uses trailing arms for its rear suspension

[@JulianEdgar]

A trailing arm suspension has one forward pivot point axis (like a hinge) and the wheel follows directly behind this suspension arm pivot point (eg like the rear suspension on an old Mini - see www.minimania.com/images_temp/80060000121a392_r.jpg ). No Impreza has run a purely trailing arm rear suspension. (In the Impreza the trailing arm is just one of the links used, not the only one.)

[@ckb6.3]

Hi, What will happen if the rear is softer than front? Isn't it the same?

[@JulianEdgar]

The same as what?

[@ckb6.3]

@@JulianEdgar same as front is softer than rear..

[@JulianEdgar]

@@ckb6.3 Differing front rear softness has major implications for both ride and handling.

[@NamishIslands]

Isn’t it about Lancia’s rear axle from 1947?

[@JulianEdgar]

Very interesting - I didn't know about that car's rear suspension. I'll include reference when I do the second edition of the book. Thanks.

[@godfreypoon5148]

I thought a Semi-Trailing-Arm was a maneuver performed by a particularly lazy driver (or passenger) with their window open.

[@vincentbaelde-millar670]

Don't lift!