Trailing Arms Again, Sorry !

[cossie350 0]

Please dont shoot me down, i have searched and searched, resulting in me ending up even more confused than when i started !!!

 

Car is used on track only and never see's the road.

 

Im in need of a pair of trailing arms and about to put an ad in the wanted section, but unsure as to what i really want in terms of rear toe, i think im right in saying that the zx arms with no toe are the quickest option of getting round a corner, but is there any chance of finding a pair of them now ?

 

Whats the next best option that im lightly to get mt hands on 306 1.8 16v ? As ive read posts that state when fitted to a 205 all the info on them is basically useless as they sit completely different than when fitted to a 306.

 

I understand that having the arms machined is the "money no object" way to go, but would it hurt to heat and bend them to what you desire, or to acheive camber even run a grinder through the top of the arm close the gap and weld it. I know this may sound crude but in reality the arm is still going to be a million times stronger than the stub axel.

 

Why im asking questions about bodging lol, why doesnt anyone ever move the mounting points out for the front wishbones(on subframe) rather than going the rose joint route on the other end, it seems like a free solution to the losing camber whilst trying to gain caster problem when using essentric top mounts, i know its not adjustable, but it is free.

 

Cheers

 

[allanallen 528 2 Cars]

Zx rear arms do not give zero toe on a lowered 205, there aren't any that will.

 

Petert heats and bends arms, no idea how you do it accurately, IMO it's a bodge as is cutting and welding?!

 

People do move the pivot points on the front subframe, moving them outwards alters more than just the camber though so do your homework before getting trigger happy with the welder.

[petert 549]

Not heating bending now, preferring to re machine for zero toe and -3 deg camber.

[cossie350 0]

Oh i never realised the zx arms altered when fitted to the 205 beem too, has the info ever been posted as to what camber and toe is given with the other models arms when fitted to a 205 ? I see alot of people say that it changes so people must have measured it but never seen the results.

 

Getting back to my original question, machining not being an option, what is the best off the self arm to use.

 

Thanks.

[DanteICE 72]

If I'm not mistaken it's the negative camber that comes with the ZX arms that affects the toe when lowered. In theory at a certain height it would give zero toe and some degree of negative camber, but I'm guessing that would be quite high on a 205.

[allanallen 528 2 Cars]

Very high on a 205! Arm angles are very different

[petert 549]

It's hard to imagine how the toe could alter. If it's zero at one angle, surely it must be zero at any angle?

[welshpug 1,621]

it would only be zero toe at any angle if there was zero camber too.

 

as you go lower with some camber you gain toe in.

[Anthony 1,000]

Whilst I can understand how it changes, how much is the real-world impact on tow/camber as the suspension moves through its normal travel and/or the car is lowered though?

 

I'm sure that I could work it out with a bit of thought, but logically it can only be a few minutes variation assuming say a 20 degree movement of the trailing arm can't it, with the lower the car goes the more toe it gains at the expense of some camber (on a ZX arm at least given that it's nominally zero toe - I haven't had enough caffeine to work out a 205/306 arm where it has both nominal toe and camber)?

[allanallen 528 2 Cars]

The arm angles of a standard height 306 and a lowered 205 are massively different. A 306 sits with the stub axle well bellow the centre of the beam whereas a lowered 205s stub axle is well above the centre line of the beam. Yes we're talking fairly small toe changes, im guessing around 1mm with zx arms. I'm more getting at the point that you can't just swap arms willy nilly and expect them to give X amount of camber and X toe.

To be honest we see a lot of rear arms and the few sets of zx arms I've seen wouldnt give zero toe on any car! Difficult to know what you're buying with rear arms!

[welshpug 1,621]

the likelyhood of a zx having its original beam is low, and given a 306 beam fits...

[j_turnell 134 3 Cars]

I would try a few different setups, a set of arms is pretty inexpensive. We can talk about figures until we are blue in the face, it's how it suits your driving style that matters. There are also lots of other factors to bear in mind such as ride height, tyre compound, spring rates and ARB's.

[Tom Fenton 1,524]

I have just bashed up a quick sheet at dinnertime. Its fair to say i am quite suprised with the results. Graphs to follow which show -90 to +90 arm angle, this is assuming that 0 means that the stub axle is on the same plane as the pivot pin. Then the base readings of toe and camber are stated at that point.

Then the -90 is the geo you would get with the arm dropped with the stub axle directly below the pivot, +90 vice versa.

Ok these values are not realistically achieveable on the car, maybe +/- 30 degrees is.

But the variation is large and complex.

[Tom Fenton 1,524]

 

 

Look carefully in the lower left corner you can see the numbers I used for each graph

[petert 549]

You'll need to explain it more fully. I've been drawing an arm with a -3 deg stub axle and zero toe during the day. I've rotated it through +/- 20 deg. A line has been drawn from the axle to 3 o'clock on the wheel. Thus in theory, there should be three lines when viewed from the top view. However, there is only one.

[Tom Fenton 1,524]

The way I consider it is this.

 

First calculate camber change from toe. Assume 0 deg camber at a horizontal arm. To use your figures we will use toe = 0 deg.

 

Move this arm so its now standing vertical. What was the toe figure when it was horizontal is now the camber as you've moved the arm through 90 degrees arc- after all camber is measured "north-south" whilst toe is measured "east-west".

 

So your camber change in this instance is 0 throughout the arc.

 

Now look at toe change from camber. Assume 0 deg toe @ horizontal and we will use your camber of -3 deg.

 

Again stand the arm vertical, you would now have -3 toe.

 

My graphs plotted above are the two figures added together at each point of arc movement. So toe change from camber plus toe from toe. And likewise. I used 0-30-45-60-90 for ease. But you get the idea.

[Tom Fenton 1,524]

 

Here's my graph for your -3 camber 0 toe scenario. In my mind it works but could be rubbish.

[petert 549]

Here's my investigation. I drew a horizontral arm with a -3 deg stub axle and zero toe. I rotated it down 10 deg and up 20 deg. The toe measurement remains at 1239.67mm each time. Am I missing something?

[allanallen 528 2 Cars]

You are peter yes, the change is very obvious on arms with -3.

Some of the guys running -3/-3.5 with our arms have several sets machined for running at different ride heights.

Edited July 10, 2015 by allanallen

[j_turnell 134 3 Cars]

It would probably be easiest to simulate this on a decent wheel aligner, you could see the changes in toe and camber at a given trailing arm angle and also look at bump steer. What sort of changes in ride height are you talking Allan? as I'm assuming they won't be huge, surprised that requires different arms.

[allanallen 528 2 Cars]

I'm talking between around -20 and - 50, the toe noticeably changes with -3 degrees camber.

 

Ive had several people who buy our 306 arms second hand, fit them to a 205 and then have a rant at me that they've got loads of toe in and they've been machined wrong!

[Tom Fenton 1,524]

Peter, using your model. Rotate the arm 90 degrees.

You should then have zero camber and 3 degrees toe per arm.

If you don't then for whatever reason your model isn't right.

[cossie350 0]

I havent used this forum for a few years now due to building a house and other things, i was slightly disappointed with the first couple of replies. But now im glad to see things havent changed, the knowledge and intelligence of the people on here is outstanding compared to any other car forum i have been on.

[petert 549]

If rotated through 90 deg, indeed the camber does become 0 deg. However, the toe measurement remains the same.

[petert 549]

Having said that, you can clearly see the change in toe from the front view.