23 replies to this topic

[76lxhatch]

Judging by that, the holes are in the middle (neither top which is UC or bottom which is LX RTS) so either LH or pre-RTS LX.

Yes it is worthwhile changing to the UC top arms to gain a bit of caster. If you do this you will need the UC steering arms, if you don't you won't.

There is no real down side to caster but how much you can achieve depends mostly on wheel clearance to the firewall, anywhere between 1 and 4 degrees positive should be achievable with the UC top arms. Camber should be negative, how much depends on how hard you drive the car and what sort of tyre wear you are willing to put up with, normally I'd say 3/4 to 1 degree negative for a street driven car. Static toe in depends on what sort of bushes (how stiff your front end is), rubber bushes require a little more than polyurethane as the aim is to get zero toe under load/when moving - around 2mm for rubber bushes is a good start.

[ls2lxhatch]

I you have a UC front end then I would use the whole UC front end.

The UC and LX stub axles are the same so it will not affect your brake setup. The UC lower control arms are lighter, have larger shock holes and the UC steering arm bump stops. The UC rack is solid mounted and as 76lxhatch recently found is a different width compare to the LX rack to suit the UC upper control arm mounting postion.

[its Paul]

Sorry to hijack the thread but when I had my front end rebuilt I supplied both UC upper control arms and the UC steering arms. When I got it back they hadn't fitted the steering arms as they said I don't need them and it won't make a difference?

So what model did they end up using?

Did they give a reason as to why it makes no difference, every one on here who has spent gobs of time setting up and calculating the geometery says the best setup if using UC front end and Torana stubs is UC steering arms.

Paul

Edited by its Paul, 03 June 2012 - 10:05 AM.

[76lxhatch]

Absolutely it makes a difference! I've just been measuring bump steer for a rack conversion this afternoon and did a comparison using HZ power steering arms - the UC ones give me around 1.8mm toe change over 130mm of suspension travel, whereas the HZ ones were more like 57mm! Obviously there isn't quite as much difference to the LX arms but you get the idea.

However - something I only became aware of recently is that the UC rack is slightly wider than LX, I would highly recommend keeping upper control arm, steering arm and rack either all UC or all LX.

[ls2lxhatch]

To some extent it will depend on the caster alignment used. The main difference between the LX and UC steering arms is that the UC arm is bends down lower than the LX. I believe this is to compensate for the extra caster in the UC factory alignment. Adding caster raises the steering arm.

Picture by dangerous

[76lxhatch]

Yes and height of the tie rod end makes a big difference, I should dig up an LX arm to compare while everything is set up

[76lxhatch]

Take a look at some of the other threads in this forum, has been discussed in detail

[its Paul]

Has anyone lowered the position of the top arms in a UC and found it to handle better??
I guess i can just drill both set of holes and try both settings.

Thats what you do to get the A9X setup, but use A9X steering arms & HQ stub axles, with every thing else UC.

Paul.

[its Paul]

Look up toramamatt, im sure he's looked into the steering arms.

[76lxhatch]

I believe he's talking about the upper control arms rather than the steering arms. (Because the HQ stub axle is taller it alters the geometry somewhat along the same lines as this mod). As discussed in other threads here (there is also some more detailed stuff on roll centres on Toranamatt's cardomain page, http://www.cardomain...n-torana/page-2) lowering the mounting point of the upper control arm assists with better (negative) camber gain through suspension travel, and raises the roll centre very slightly (almost negligible).

[ls2lxhatch]

There are too many variables, steering rack, UCA mount position, caster alignment.

The only way to know for sure is to align the car with the LH steering arms and measure the bump steer. Then align the car with UC arms and measure the bump steer.

[76lxhatch]

^ I've just done that about half an hour ago and it looks like I might have to eat my words about the LH/LX arms; they are wrong, but not _that_ bad...

Important: this applies specifically to my front end alignment and components as noted in the graph subtitle. If your alignment is different, the result will be different (although this still gives you an idea).



The UC steering arms show a max of 2.75mm toe out at full compression (this is hard on the bump stops, unlikely to get quite that far), and just a touch less at full droop. It has a nice curve and only shows toe out which is perhaps preferable to toe in for best control. +/- 40mm from ride height the bump steer stays within 1mm (half of what most people would set as static toe in to allow for bush deflection) so pretty good.

The LX steering arms (on a UC configured front end, remember) give a similar amount of bump in compression but its toe in rather than out, but not too bad. In droop we get toe out but anything over about 25mm travel becomes excessive and maxes out at just over 8mm toe out. During normal travel it is definitely a bit worse than UC, so if you had the arms you'd definitely use them. I don't recommend it but I can't see the bump steer sending you off the road if you stuck with the LX arms.

[76lxhatch]

Yeah, toe out on turns (also known as Ackermann angle) allows the wheels to travel different directions as they are effectively on different arcs (forgetting slip angle etc for the moment). It shouldn't really be provided by bump steer though.

You are unlikely to get both a lot of lock and a lot of suspension travel at the same time except maybe hitting driveways on an angle at low speed. The worst part would be high speed cornering; very little wheel lock but the suspension travel could potentially cause a change in direction that the driver didn't anticipate. In this case it largely depends on the suspension travel available (lowered Toranas tend not to have a lot) but say you really hooked into it and got 40mm either way you could get a quarter degree steering change you didn't ask for. It would be toward the inside of the corner and it doesn't sound like a lot so I guess again while not recommended the LX arms aren't so bad...?

If on the other hand you used HZ power steering arms with the above combination, you could end up with over 4 degrees of steering change toward the outside of the corner along with 6mm more toe in than static (which would probably help add a bit more understeer)... scary!