Trailing arm rear suspension pros/cons?

[Brett]

Hi,

I've been thinking a lot lately about the rear suspension in my car (MA61), as I'm starting to see a few people swap out whole subframes and do all types of crazy modding just so they can fit real coilovers instead. I can't say I've really seen an explanation as to why trailing arm suspension is so bad, or why coilover type suspension is so much better.

It looks like this if you're unfamiliar:

(Thanks to Rob's spring replacement thread)

Sure there are things like bad static negative camber if you run short springs, and the lack of height adjustability, both of these I can understand, but the first can be fixed relatively easily and the second doesn't bother me enough to warrant a swap to coilovers. Then you get onto things like the weight of trailing arms, but that kinda goes out the door when you see huge new subframes, or new towers being welded in.

The only viable argument against trailing arm suspension I've heard is about camber deflection, how the camber of the wheel can change over bumps, but I don't fully understand why this is considered a bad thing. The way I see it, camber deflection sounds like a positive thing, especially on long banked corners and hitting ripple strips, isn't it ideal that the camber changes to suit angle of the road surface?

I've heard of really nasty things about Porsche type trailing arms, where under heavy braking or acceleration, the toe would change, and I can see why that's a bad thing, but I can't for the life of me work out why our type of trailing arms are worth ditching! I'd love an explanation as to why they suck, or why coilovers are better (in more ways than adjustability and off-the-shelf availability)

Cheers.

[WDE_BDY]

I think you are confusing a couple of things here. Coilovers is simply how your springs are mounted, its still a trailing arm setup and a coilover setup will not address any of the geometry short comings. It just makes height and spring rate changes much easier. Remember, the shocks do not play any part in the geometry of th trailing arm setup.
As you have noted, the camber problem can be adressed relatively easily. So you are left only with the issue of geometry changes through the suspension travel. For a road car, once the camber is set appropriately at ride height I doubt you would ever notice a problem, under race conditions it will be even less critical as generally suspension travel is even less. Yes a double wishbone arrangement can be set up better and more consistent, however whether the difference is noticeable or the costs justified I am yet to be convinced.

Callum

[brett_celicacoupe]

main reason im using coilovers is because they can be easily be changed. the spring diameter is common so many rates and lengths will be available. the MA61 type spring is pretty limited (2 or 3 types)?

im running HKS fully adjustable coilovers to suit a Z30 soarer (they were very cheap).

[Brett]

Thanks for the replies So moving to coilovers isn't really an effort to stop the geometry changing? Is it just the design of the subframe (angle of the trail) that dictates whether camber will change through suspension travel?



From what I can gather, it seems that changing to a coilover style setup won't effect the geometry at all if you're still mounting to the original arm, unless you swap in a different type of subframe, like the top one.

I think spring choice is more than sufficient for the stock layout, you can get custom springs at any height or rate. I'm not so sure about shocks, but the road and track surfaces are so inconsistent down here that I probably wouldn't benefit from having 16 way adjustable shocks compared to 6 way or whatever

I really respect what you're doing brett_celicacoupe, but I just thought there would be something more to it than what I've seen listed. Even the idea of swapping a whole new subframe in doesn't sound that enticing, as Callum said, there'll be very little movement anyway with decent rate springs. If I can get the spring height and rate I want, and shocks that match it, it seems as though I won't really be regretting not swapping a new subframe in. I guess I just needed to clear that up before I spend all my money on making my trailing arm suspension better, as I was under the impression that I'd be polishing a turd

[WDE_BDY]

Put it this way, I have transplanted the trailing arm setup from a TA63 (same as MA61) into a Starlet. There simply weren't enough benefits to chase down a double wishbone setup instead.

Callum

[Norbie]

For a road car, once the camber is set appropriately at ride height I doubt you would ever notice a problem, under race conditions it will be even less critical as generally suspension travel is even less.

I disagree. On a race car especially you want as much consistency and predicatability as possible when it comes to wheel angles; if the camber is changing every time the rear end squats, lifts or rolls there's no way you can optimise your setup for all conditions.

The only advantage of semi trailing arms compared to other IRS systems is (a) they're cheap and (b) they're relatively light. More sophisticated setups like double wishbones are always going to perform better, although on the street 99% of people probably wouldn't notice the difference.

[RObErT_RaTh]

I thought I recognised the pic from somewhere Brett

[oldcorollas]

the problem of any IRS is that if you set it up for cornering.. ie gaining camber with bump to maintain a flat contact patch, then you also gain camber on squat.
that can be partially negated by having "antisquat" dialled in,but the optimum camber curve for straightline and cornering traction are different.

trailign arm should be better straight line, but semi trailing should be better for cornering

[The Real Roadrunner]

the problem of any IRS is that if you set it up for cornering.. ie gaining camber with bump to maintain a flat contact patch, then you also gain camber on squat.
that can be partially negated by having "antisquat" dialled in,

but you will never get anywhere near 100% anisquat with an IRS setup and the most you are likely to see is 50%.

there are heaps of reasons semi-trailing rear ends suck but probly aesier to find the info rather than me posting it (if i had the time)

and i don't think there would be much of a weight difference between the 2 as the trailing arms themselves would weigh asmuch if not more than the arms and uprights in a double wishbone setup.

cheers
linden