1600's, 280ZX's, Z31's, below is a link to a BMW site, yeh they used semi trailers too. For anyone serious about getting this suspension working well in a race situation this article is very relevant.

Also check out the other Suspension articles, more useful info there.

http://teslacoils.org/e30m3performance/ ... /index.htm

<Edited by SR20Datsun: link now up-to-date>

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Richard... http://www.youtube.com/watch?v=rqM9_Wq-TKc

This link is very good.

I've spent some time going over it for quite some time.
It seems our Datsun 1600 rear semi-trailing arm suspension is approximately 25 degrees for the cross member "sweep angle" instead of the 15 the BMW E30 guys run. I also know the M3/Race DTM E30 runs 12 degrees which means it is closer to a trailing arm suspension. (so less camber/toe change as the suspension travels). The Toe curve and Camber curves are different by a fair amount with the 25 -vs- 15/12 degrees.






I've attached some graphs I made up (using his formula) comparing the Datsun 1600 rear to the BMW.

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1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

With my semi-trailing arm suspension on my 1600, I raised the pivot points (evenly both the inner and outer mounts) so that the roll centre was raised due to me wanting to lower the car. Effectively the amount I lowered the car was more than I could raise the pivot points, so unfortunately the roll centre was a little lower overall.
The next batch of modifications will be to follow the pictures above and move one (or both) of the pivot points so I can raise the roll centre more to reduce the roll couple and increase roll stiffness further. I haven't thought out what effect this will have on the graph just yet, but I am also thinking of reducing the angle of the cross member currently from 25 down to something like 20 (if possible). This would need some modifications to the axle section (toe correction and possibly camber correction) which would require cutting the arms and re-welding them (a pain) and this would require a jig.
I'd have to find out where this would place me on the graph and how much change I would be getting over the suspension travel.

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1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

Here's something similar and quite a clever design allowing 'bind free' suspension travel.

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1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

I really like the rear end on this Datsun over in the US.
He's made aluminium arms and raised the inner pivot. This effectively raises the roll centre, but there's a whole bunch of mods required to do this.....(damn it!)

I think the link is here:

http://www.the510realm.com/viewtopic.php?f=3&t=13582

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1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

Good stuff getting this topic going again Nick!

I raised both pivot points as much as i could to the body. Basically the crossmember sits on the body.
The two ends of the crossmember were cut off and flipped 180 degrees. This raised the pickup points around 10-15mm

The outer piviots of the trailing arms had around 10mm removed and welded back together to reduce toe to 0 with low ride height.

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Circuit Race 1600 in the build

I thought of getting this started pretty much with your comments on your build. I'm keen on building something more custom than what i currently have (have to remove the x-member anyway due to r200 diff potentially going in). Just thought i would see what others are up to.

Let the discussion continue...

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1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

I would like to do something similar to to photo below.
It would allow adjustment of the roll center without affecting the camber on the rear wheels.
I suppose the ideal position for the trailing arm at ride height is perfectly horizontal. This would be in the sweet spot where camber and toe do not change radically. There is exponentially more camber and toe the further you move from horizontal.
The camber change is probably not much of a problem for a race car like mine. Camber gain on bump is very desirable. Its the toe change that is not very good.

I have always wondered if the trick to add more toe in on the rear to get the car to turn in actually has more to do with the raising of the roll center. More toe in increases the sweep angle and should raise the roll center. The rear ends seem fairly sensitive to the roll center change so it might make a difference

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Circuit Race 1600 in the build

I have been studying that design Lampy and reckon it's not too bad. For race use the Heim / Rose joint has a fair bit going for it, but I would like to use the poly-urethane joint to soak up a small amount of the road noise.
In some instances it may be necessary to use rubber due to it having a bit more compliance (depending on the design obviously) It would be good to design something that is 'semi-active' (such as the Weissach system on the 928) which moves in the right direction under load instead of what we have which the Toe moves in the opposite direction..

The camber gain should be proportional to the body roll change ideally. Squat though is where compromise kicks in. Ideally if it's a circuit car (rolling start???) then squat doesn't really matter too much, so you can design around it..

I've also thought that increasing toe manually had something inadvertently to do with changing the roll centre, but looking at the diagrams above the change in toe -vs- roll centre change would be minimal. I think greater change in RC height would be due to camber change??? Happy to be corrected...

Does anyone on here have camber and toe curves for other Semi-Trailing arm cars (such as a VS-VX commodore)? I'm also trying to find camber/toe curves for multi-link rear end suspensions.

(Where are all the guys who used to be on the forum -beef- -thehelix- etc. who used to talk about this stuff???)

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1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

My opinion at the moment is to raise the pivots as much as possible, and unfortunately put up with the camber/toe curves, unless I can reduce the x-member sweep from 25degrees to say 20 or less without too many mods which moves the curves favourably towards the M3 style suspension.
The only other option is to use multilink wizardry such as the Mazda RX7 FC which add a toe and camber link. The upper link would foul on our chassis, but you could put a bend in it...

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1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

Changing the inner pivot by 12.5 mm (up or down) gives approx 1 degree of camber change.

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1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

I have been thinking really seriously about doing something similar to the group c bluebird touring car.

It would consist of a trailing arm from the original outer pivot on the crossmember to the knuckle and then two lateral contol links to a rear plates on the diff.
It would be fairly simple to fabricate except for the knuckle.
A custom make alloy knuckle incorperating a silvia rear hub/bearing could be potentialy doable.

I suppose this type of modification would be fairly hard to engineer for a road car

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Circuit Race 1600 in the build

Very interesting. What are the benefits of this in terms of camber/toe change compared to the semi-trailing arm system? Considering the suspension travel these guys would be getting (compared to a road car...) the difference would be interesting.
Very interesting none-the-less though!

I have attached what the HR31 Gibson car did with their rear end (photo borrowed from somewhere I can't remember - apologies to whose it is). I like the adjustment idea and this could be fairly easily transferred over to road legal if you did it right....

I have also attached a few photos of the DR30 rear end for comparison....

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1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
viewtopic.php?t=6579
#SR20Datsun @SR20Datsun

Hmm I will have to try and think about the camber and toe changes for the bluebird design.
It looks to be tunable for roll center, static camber and dynamic camber through the length and position of the lateral links on the diff.
I wouldnt think toe would change very much due to the trailing arm being nearly longitudinal to the car

here is some more photos of both the skyline and the bluebird

https://www.flickr.com/photos/drdatto/s ... 125188355/

Interestingly the bluebird was earlier than the skyline. They basically went back to the semi trailing arm. Maybe this was due to homoligation of the fj20 in the skyline??

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Circuit Race 1600 in the build

This is a very interesting photo.
This is the second of the bluebird touring cars.
http://www.dairally.net/fury_bird/pages/Bluebird030.htm

Looks like they have used the semi trailing arm but left the bolt out in the inner pivot on the crossmember.
The links to the diff provide lateral support.

More interesting photos in the link above

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Circuit Race 1600 in the build