17 replies to this topic

[76lxhatch]

This is more for interest's sake than anything else, but it might help people pick which steering rack they want to match up to their front end.

OK so I've been working on a power steering conversion (more on that later) which has brought me to an interesting discovery. I've read most of the suspension and steering stuff on this site and I'm pretty sure I haven't seen any mention of this?

I have a UC cross member with a second set of holes drilled for the upper control arms, approx 25mm lower in the LX RTS position. I have a UC steering rack, and an LX RTS steering rack.

It occurred to me as I was taking various measurements that lowering the upper control arm actually changes the axis of the inner suspension pivots quite significantly. It was immediately obvious that this could affect bump steer (mainly because that's what I was measuring for to start with!) - check out the different in the string lines, and the horizontal difference at rack height:

(please ignore the crap in the garage, I'm a messy worker...)

Now you'll also notice in the pic above that I have two different length racks - the one bolted up being UC and the bare one sitting on top being LX RTS. There is approx 15mm difference in overall length (~7.5mm per side, LX 620mm and UC 635mm) which appears to correspond with the difference in the suspension axis:


From what I can measure on the housings, there is no difference in the height of the rack mounting position between the two, and the housings are externally the same. However, the LX housing does have more depth machined into the ends of it so that the rack gets similar travel to the UC one (so the steering lock between the two should be much the same despite the length difference). I don't see any reason why the UC rack couldn't go into the LX housing but you'd lose lock/travel if you didn't machine the inner ends.

Clearly there is an effect on bump steer and I would assume that Holden had some idea of what they were doing, so it seems that you would be best using a UC rack with the upper control arm mounted in the top position, and the LX rack with it in the lower position.

I haven't take enough measurements (not to great enough accuracy anyway) to calculate the bump steer properly and confirm the last statement, I think I will have to now (I will measure it directly when I get to the new rack). Some quick calcs give me around 0.2mm difference. Of course it needs to be stated for the record that the different steering arms also play a part (probably a larger part). Also I am aware that pre-RTS LH/early LX had slightly different upper arm mounting points again, I don't have access to any steering racks or measurements from these earlier cars to see whether they are different again.

[ls2lxhatch]

This could explain why the A9X used the LX style rack.


It also makes me wonder about the effect of fitting the new style rack ends to either the LX or UC rack. The pivot ball in the new rack ends may actually sit out further than the pivot ball on the factory rack ends. There is enough thread that you could shorten the rack on a lathe when using the new rack ends.

Edited by ls2lxhatch, 31 May 2012 - 02:41 PM.

[76lxhatch]

Given that the pivot on the Torana rack sits hard against the rack end and the ball retainer goes over the rack that seems right, you'd want to short the rack a little to allow for the extra inner length a self-container pivot adds (or use the shorter LX rack).

It occurs to me now though that its backwards - the shorter rack was fitted to the front end with the top arm mounted further out, while the longer one had the top arm further in. Its hard to look at just one part of course, time to dig out the LX steering arms and see whether there was any change in offset. Maybe it was just wrong in the earlier models and the full RTS treatment included some improvements?

[axistr]

Guys I did heaps of different combos and bump steer curves to try and get the perfect set up and I come to the conclusion that if you got it perfect then fitted a 10mm wheel alignment shim to correct a bit of camber or caster that allown through the best set up out the window. Most of the tests I carried out were on LX & UC because thats what gear I had hanging around the workshop.

I got my rack inner tie rod balls to centre line between the lower & upper control arms bush mount bolts half way between the UC & LX. then stick the 10mm shim in and look at how much it effects the lines, or turn the steering wheel three degree (slight bend in the road) and also look at the effect. Sure get it close but more inportant is to get the rack level to the outer tie rod ball centres at ride height is much more important. If you get them all in the same plain the bump steer is only very minimal not noticable, and with heavy duty spring & shocks the travel isn't enough to induce bump steer in corners.

On my hatch I got the angles perfect, spent months f**king around mechining spacers inner stops moving the rack left & right then added shims to increase positive caster the buggered around again to correct the difference. I moved the rack backwood & foward to try and change toe out on turns and got the sweet spot.

The second rack coversion I did was no where as close as mine because I didn't do as many mods to the rack and the car steered like a go kart. The owner didn't have much money to spend and I was doing him a favour, He was stoked at the difference in the handeling and I couldn't pick the difference between his and my cars steering. The third one I did we couldn't get positive caster on it as we were flat out geting decent cambers, so we had to let it run 1 deg negitive caster both sides and to my amazement it also steered fantastic, but positive caster may have improved it slightly. still very happy with it's handeling.

Now if you look at the angles between the steering arms and lower ball joints this area is just as or more important than the inner tie rod. in this area many owners stuff up by putting all sorts of different arms and stubs and bending steering arms to clear brakes. I tell owners if your running LX use all LX gear, UC use UC gear, ect UC top arms yes as you can add more caster without stuffing up camber. You must use A9X steering arns with lower stubs (HQ) or you are asking for problems.

The only way to get decent to out on turns with Torries is to modify the steering arms. The Subaru rack I use fitted to the Forester has almost 5 deg of toe out on turns but when fitted to the Torana only manages 1/2 - 3/4 toe out, same as with standard rack. If you were to bend the steering arms out you could improve toe out, but to get enough you would have them hitting the disc rotors.

It's hard to explain all the angles without turning this into a 20 page boring read, but I hope this helps, by tryng to get the perfect curve you might leave behind the simple things that may make the car handle and steer much better.

This has been my experience with the Torries

Lenny/

[76lxhatch]

Thanks Lenny, I definitely understand that its more important getting the outer ends right and I won't be leaving the simple things behind. I just found this interesting because I haven't seen it mentioned anywhere in the various discussions, especially the difference in rack lengths (ratios have been discussed various times).

I spent some hours setting up a lot of the calculations to work out the interactions between various parts so as soon as I can get all the measurements to some accuracy it will be a lot quicker and easier to see the effects of changing various items. Even with the margin of error I have at present its quite amazing to see that while the numbers are quite poor by modern engineering standards, the car handles reasonably well (less suspension travel means less bump too I guess!). Since I will be cutting into the cross member to fit the new rack one thing I would like to do is get it just a bit further back to help with the toe out on turns, we will see.

If you don't mind me picking your brains just a little, one thing I'm curious about is the scale of bump steer that is acceptable, or what did you achieve/aim for? I see that Toranamat's cardomain page shows plots of around 4mm variation which seems like a lot, if my figures are right then some factory Torana combinations could be up to 6-7mm! (Once I get sorted I will measure the original setup bump steer before changing anyway.) Info I've been finding on the web suggests figures around 0.015" to 0.020" maximum which I can't see as practical in this case - like you say, altering the alignment shims could throw this out easily. I'm thinking that most of these references are pretty serious race car type stuff rather than a practical road car.

[axistr]

To keep the bump steer low you need the outer tie rod end ball centre & lower ball joint centre the same height (apart) as the inner rod and and pivot point/ inner lower control arm bolt. If Holden made the top & botttom control arms the same length there would be a lot less bump steer. But the angle of the steering arms effect this by trying to toe out a bit at the same time as the control arms are trying to turn the steering in, there by reducing the amount throughout the travel. Hope you understand the above as it can be a bit hard to explain.

It was some time ago that I carried out the bump steer figures, but from memory I think I achived 2.5mm per side through out the travel & through out normal driving this would only be around 1mm per side in the straight ahead position on my vehicle.

I got my rack to sit as far as I could trying to keep the the rack not only level in relation to the tie rods bars but also in line looking from the top view. This will reduce bump steer and excessive load on the rack, and that's why I used UC steering arms for my hatch. If you have the rack sitting to far foward like the other rack kit seen recently this will cause toe in under braking or any drag created from the tyres or even pot holes unless you have almost zero movement of flex in the front end.

When I moved the rack foward to see what effect it would have on the toe on turns it didn't make that much difference, this is determined by the steering arms angles. When I first started doing wheel turns to check toe in/out on turns I thought I had it all planed out but soon found out that the rack inner tie rod ends had to be exactly the same distance from the cradle or ball joints as even 2mm difference could change the toe out by 1/4 deg.

I am sure you already know, but using the lower inner top control arm mount bolt holes will induce more negitive camber on the outer wheel & more positive camber on the inside wheel, this may be good in some cases depending on you alignment setting and ride hight and how much sway bar tension you have, but could also induce bump steer depending on many factors and make things worse. Adding them alignment shims again can change things a bit. adding positive caster will raise the steering arms up. If I could I would perfer to run heaps of positive caster and run higher top mount positions, stiff sway bar and use caster to give the same effect, but with the Torana front ends this is not possible without major mods. Just for a comparison My Beamer runs 14 deg positive caster.

Over the years I have seen some shockers for bump steer from new. The Nissan Navara front ends are about the worst I have seen, On my car alignment mechine I can push up on the bumper bar and record 7mm toe in, then I hang off the bumper bar and I'm only 89kg and the toe goes out to 7mm out, that's 7mm each side through out the normal road wheel travel 14mm in total. Just think how much it must alter going four wheel driving.

Boy these reply's are getting long I hope I'm not boring everyone.


Lenny

[76lxhatch]

Thanks again, not boring me at any rate. For some reason I find suspension and steering geometry very interesting! Around 2mm total sounds a lot more achievable than some of the other stuff I've been reading and lines up better with Toranamat's figures, if that's in line with or better than the standard Torana specs I'm sure it won't be an issue. Interesting about the Navaras, I'm not much into that sort of vehicle as they drive like boats, with those sorts of issues I can see why!

Although the angle of the steering arms is the main factor in the toe out on turns/Ackermann angle, as you've said there isn't much that can be done here which is why I'm looking to move the rack back a little as an alternative. It won't have a lot of effect but I figure some is better than none. I hadn't thought of the effect on bump steer though as I was only thinking in two dimensions at a time - but of course the tie rod end will move in more of an elliptical rather than circular arc as the rack moves off centre. I will have to update my calculations on this one, it may not work as I had planned. I've got a spreadsheet I've been working on which includes a line graph of the top and bottom ball joint and outer tie rod end arcs throughout suspension travel, which I find useful for visualising the bump steer and camber gain. I will post a copy once the bugs are ironed out if anyone is interested.

When I put the 17x9s with 255/40s on the front I had to do some cutting so I took the opportunity to work around the best static alignment specs I could achieve. With the top arms in the lower position using Torana stubs with UC steering arms and maximum safe shim stacks I've got approximately 4 degrees of positive caster and -1.5 camber. It handles the best it ever has and I will be looking to keep these settings and make any minor tweaks with the rack to suit. Outer tie rod end (steering arm) height is one issue I will need to keep an eye on as it has quite an effect.

Side question: is it safe to bend cast steering arms much? Probably not I suppose, maybe it would be possible to machine up some wedge shaped washers/spacers to tilt the arm and move the tie rod end outward a bit, I have a touch more room than factory with the brake conversion sitting the rotors slightly further out. Although I'm getting ahead of myself here I think...!

Hopefully put some bushes and ball joints in some upper and lower arms tomorrow and have a play around with real measurements instead of calculations!

[axistr]

G'day,

My first engineer said it was ok to heat and bend the arms but I would prefer to do any bending cold. I fitted washers behind the rear mount bolt to see the effect and made bugger all, only slight change. You would need to move it a fair amount to get what I would consider to be good toe out figures.

There is a way to check the correct angle.

1 measure the wheel base on your car. Lets just say 3m.

2 from the centre of the steering rack(using you cradle on the bench) in a straight line to the rear make a mark on the concrete as per measured wheelbase. example 3m.

3 with the test cradle set up in the straight ahead position ( you will need zero toe), put a string line from the centre of the steering arm tie rod hole to the 3m marker on the floor, this 3m marker is the position of the centre of the diff housing if you were trying to check this angle in the car.

4 if the string line goes over the middle of the lower ball joint the Ackermann angle is correct, if not pull the string line left or right at the steering arm end till it does and see how much it's out and how far it needs to move to get it right.

Example;

When we see trucks that have had the chassis rails extended ( changed wheel base) we sometimes change the steering arms to correct this problem.
This can be a real problem with twin steer trucks when people just throw a second axle under a truck and both axles have the same steering arms.
Rockwell make 3 different steering arms for there steer axles for this reason.

So if you have front of axle steering the arms need to be outside the ball joint and rear steering behind the axle need to be turned in further the shorter the wheel base is.

If you have any problems getting you head around this let me know and I will try and add a drawing.

I made up brackets to simulate bending out the steering arms out but this buggered up my bump steer curve.
I also found when I had all my alignment gear hooked up to the test mule I could do too or three sweeps and get slight variations without moving any parts, so you have to be super accurate when trying to check any alterations. I started using plumb bobs and chalk marks on the concrete to try and get more accuracy and consistancy when checking.

[axistr]

P.S I would try and keep your cambers lower around 1/2 deg (30 min) neg on the left & around zero to 15min positive on the right and keep a bigger tyre foot print on the road, even caster if the drive thrust angle is zero, and 1.5 - 1.8 mm total toe.

[76lxhatch]

My first engineer said it was ok to heat and bend the arms but I would prefer to do any bending cold.

Interesting, all the more so because I didn't get quite as far as intended today because the steering arms (not the ones currently on the car) are already bent out of shape! Ideal candidates for a test in the press since they are buggered otherwise.

There is a way to check the correct angle. <...> So if you have front of axle steering the arms need to be outside the ball joint and rear steering behind the axle need to be turned in further the shorter the wheel base is.

Yep all good with that, as you've mentioned previously its not really possible to get the ideal angle due to physical limitations (such as the brake disc being in the way), just working on the best compromise for my specific combination.

I made up brackets to simulate bending out the steering arms out but this buggered up my bump steer curve.

I'm guessing you would have needed to lower the outer tie rod end to make up for the longer tie rod?

I also found when I had all my alignment gear hooked up to the test mule I could do too or three sweeps and get slight variations without moving any parts, so you have to be super accurate when trying to check any alterations. I started using plumb bobs and chalk marks on the concrete to try and get more accuracy and consistancy when checking.

My plan is to use a laser pointer on the stub axle at a right angle - this will mean that any horizontal movement will be bump steer only (not camber gain or normal suspension travel) and by placing a board to mark the positions some distance away it will magnify the movement and make it easier to measure small amounts... in theory. A bit of basic maths will get me the real figures from there.

P.S I would try and keep your cambers lower around 1/2 deg (30 min) neg on the left & around zero to 15min positive on the right and keep a bigger tyre foot print on the road, even caster if the drive thrust angle is zero, and 1.5 - 1.8 mm total toe.

I would have preferred to be a bit closer to 1 degree negative camber but that's a limitation of the front end with the amount of caster I want. There's not a great deal of long straight roads around here and plenty of tight corners which is a factor, the last set of tyres wore slightly more on the outside with around 1 degree negative so not too worried about it. I also prefer even left/right alignment, we've got just as many off-camber roads as normal camber, it tracks fine.

[76lxhatch]

OK found a nice straight steering arm and set up the front end:
* UC rack, steering arm, upper (and lower) control arm
* Upper control arm mounted in the lowest position
* 12mm rear shim stack, 0 front shim stack (on the hatch this gives me around 4 degrees caster)
* new polyurethane bushes in the arms (destined for the four door, good for slop and bind free testing)
* Torana (UC) stub axles

Now my methodology doesn't allow for an extremely high degree of accuracy but I measured three times and got the same results. I ran a threaded rod though the shock mount hole so I could carefully control the travel without unwanted movement and the laser pointer as described above onto a piece of paper attached to a fixed board, and simply put a dot at 18 points throughout approx 125-130mm of suspension travel. I was pleasantly surprised to get a nice curve centred at approximately ride height, with around 1.8mm of toe out at full compression and the same at full extension (so overall movement the same, 1.8mm). So there's nothing wrong with the UC steering arms for this setup that I can see!

For interest's sake I did a quick test with some HZ power steering arms I had laying around (no other changes). They move the tie rod down some 35mm and inboard around 5mm. The result: 26mm toe out at full compression, and 42mm toe in at full extension (overall movement around 68mm)!

In practical use the suspension is unlikely to travel the full 130mm (more like 90-100mm I think) so that reduces the above figures a bit too. If I can get the same figures with the new rack as with the UC one I will be happy. Toe out on turns/Ackermann angle as also discussed above is a separate matter which I will see if I can improve, provided I can stay within these limits for bump steer.

[76lxhatch]

Actually it occurs to me that the numbers above should be doubled... there are 2 wheels

[76lxhatch]

I posted this in the other thread about front ends but thought I would update here too. Improved the accuracy of my measurement by increasing the distance and fine tuning my methodology. I compared the LX steering arms (with no other changes) for interest's sake.



Obviously the UC arms are about as close to ideal for this configuration as any factory part will be, I'm quite surprised how good they are considering I have quite a bit of extra caster over the factory specs. Max of 2.75mm toe out at full compression (hard on the bump stops, unlikely to get quite that far), and just a touch less at full droop. Nice curve with toe out only, no toe in. No more than 1mm toe out +/- 40mm from ride height.

Figures are repeatable and don't show any unusual variation so this is my final benchmark.

[axistr]

Well done mate, it will be interesting to see the difference in swaping the alignment shims to under the front mount bolts and see what the difference is. It looks like you have come up with the same results that I had when I did test on my old Jig. Which further explains why I don't have any bump steer issues.

[76lxhatch]

Good to hear that the results are reasonably consistent.

I swapped all 12mm of shims to the front (zero at the back) for maximum negative caster - I expected a comparitively poor result but not quite this bad...

Obviously the LX arms would be better, but this is partly so bad because its very excessive - no one in their right mind would put this much negative caster on a Torana if they could help it. By my rough calculations if you did this and managed to tip the car into a corner that compressed the outside suspension 40mm (at the bottom ball joint) and lifted the inside 40mm you'd get nearly 1.5 degrees of bump steer toward the outside of the corner. However in a way this straight-line bump steer is relatively safe - assuming this scenario where the compression and extension are equal amounts then the overall toe is maintained. As long as it occurs gradually you just need to add more steering lock; the bump steer simply presents as more understeer (to add to the already ridiculous amount caused by the positive camber gain due to the negative caster...). I think that makes sense?

Its also worth noting that with the LH/LX configuration not only do the steering arms position the tie rod end higher to make up for the lesser caster, but the shorter rack results in slightly longer tie rods giving more toe out either side of level (not a lot of course).

[76lxhatch]

I'm afraid I have neither HQ stubs (other than the ones on my ute!) nor A9X steering arms to hand, so I can't measure it.

Toranamatt did graph the UC vs A9X steering arms on an HQ stub though - check out the last graph on this page, and the text just below it:
http://www.cardomain...n-torana/page-2
(this graph: http://carphotos.car...60192_large.jpg)
You would have to scan the text a bit more to confirm that he didn't make any other changes, because he did try a lot of different stuff.

At any rate he says that was measured at 3 degrees caster, and reckons that 4 degrees would be ideal for the A9X steering arm and 1.5 degrees for the UC arm. This agrees with my info above in terms of the caster change effect on bump steer, and the fact that (at my lowered ride height) it seems like 4 degrees of caster gives a nice curve with the UC setup despite factory alignment being somewhat less than this.

The general consensus in the front end threads seems to be that A9X steering arms are ideal, but you can get away with UC arms in a slightly less than ideal situation. The lesser caster mentioned above is slightly less than ideal but not a significant issue, all of this info seems to line up well enough.

Bottom line - you wouldn't be making the most of the suspension but if you limited caster to around 1.5 degrees max as stated by Matt then you should get away with using the UC steering arms rather than splashing out for the A9X ones. At the very least you could be happy with driving it while you save up and then dial in some decent caster one day if/when you change them over.

Also I think I saw in your A9X steering arm thread that someone else in NZ had managed to order them direct from Harrop at a somewhat better price.