27 replies to this topic

[fuzzypumper]

Due to bent arms and mistakes on my part, I have been running LX steering arms on my UC front end & UC sterring rack for a few years now.
The cons of this was reduced turning circle and heavier steering. However I always had a good feel of how planted the front wheels were on the road.
I recently acquired and installed the correct UC steerings arms. Before I did, I compared and measured the offset of the LX and UC arms tierod hole position to acertain how far the Toe adjust will change, which was only about .5mm diff so I proceeded thinking it wont be too drastic.

Well now I have considerably lighter steering and smaller turning circle but the front wheels feel like theyre going under and skipping on tight corners, e.g. when going around roundabouts and not even at full lock. In a straight line steering is great, steady and unchaged so I'm assuming the TOE adjustment insnt far off.

To me it seems and looks like the front outer wheel has too much positive camber when turned so should I attempt to apply more negative castor?

[76lxhatch]

I don't think you want negative caster; positive caster is when the bottom of the axis is further forward than the top, which is generally desirable and what the UC top arms provide.

Hard to give any advice without knowing what the settings are at present but it does seem most likely that you've introduced positive caster (sounds like the opposite though). Does it hold really steady at high speed in a straight line, or does it seem quite light/skittish then too?

If the toe has changed at all you'll want to fix that too, the tyres will thank you (in fact, maybe you had toe in before and you've fixed it?).

[fuzzypumper]

I don't think you want negative caster; positive caster is when the bottom of the axis is further forward than the top, which is generally desirable and what the UC top arms provide.

Sorry your right, that is what I meant.

Hard to give any advice without knowing what the settings are at present but it does seem most likely that you've introduced positive caster (sounds like the opposite though). Does it hold really steady at high speed in a straight line, or does it seem quite light/skittish then too?

If the toe has changed at all you'll want to fix that too, the tyres will thank you (in fact, maybe you had toe in before and you've fixed it?).

Im pretty sure toe was correct before as I had a wheel alignment done not long ago. So I trust the TOE was good back then and I will get it checked. The tyres look ok and wearing relatively flat ( no saw tooth wearing on the outer blocks). But you can never trust whether they do CAMBER and more so CASTER adjustments when you ask them too on a V8 torana or whether they notice to the fact you mention "Its a UC front end not an LX".
I will check the high speed test feel when I get a chance, but I do have my thoery right, dont I?
Thanks.

[rodomo]

The front wheels feel like theyre going under and skipping on tight corners, e.g. when going around roundabouts and not even at full lock.

Toe out on turns is adjusted by the steering arm (akerman) angle.
Maybe the different arms and the fact that you haven't had the toe in re-adjusted is making the skipping?

http://en.wikipedia....eering_geometry

[76lxhatch]

I will check the high speed test feel when I get a chance, but I do have my thoery right, dont I?

Its a strange one because the symptoms do seem point to too much negative caster as you've said, but how can that be when the only change you've made would introduce positive caster...?

[fuzzypumper]

With the old LX arms the turning circle was bad and the wheels never turned as far as they do now with the UC arms back on. Im not saying there wasnt the feel of some wheel skipping before but it was minimal and only right on full lock. Now its seems to happen alot earlier and coupled with the tigher turning cirle and lighter steering feel its seems like front is just gonna give way around corners, especially in the wet.(I may have found my answer right here.... doh)

I dont see how changing steering arms would affect castor anyway.
To me castor is the adjustment made to the geometry when the wheels are straight that effects the wheels camber when turned.
The wheel is still turning on the same axis (upper and lower ball joints) as it was before the arms where changed.

[76lxhatch]

Sorry I've just realised that you are talking about steering arms only, and not upper A arms, doh! Disregard the comments about changing caster, there won't be any change.

The longer/lower UC steering arms are designed to make up for extra caster and negative camber so you may well want to add some. My opinion (take that with a grain of salt!) now is that the skipping was there before but is now more obvious due to lighter steering. The longer steering arms will cause this with a bit more leverage, and allow movement at the road wheel to pull on the steering wheel more than it used to.

I think a certain amount of shimmy at higher speeds due to lots of positive caster is acceptable, but around a corner it should be more planted, not less. Personally I like at least 1 to 1.5 degrees of positive caster on a road going Torana, this should be easily possible with UC RTS and UC steering rack shouldn't be too heavy around that setting.

[fuzzypumper]

In that case I may just remove some shims from the forward upper control arm bolts to set the upper pivot points back more, thus introducing more positive castor, and see how it goes. I realise this may introduce same extra negative camber.
Does that make sense?

Next question is, how many degrees can I except the castor to change by removing a .030 or .059 shim?

[76lxhatch]

Not sure if I'm reading the chart right, but looks like around .060 onto the back and same off the front will give a degree of caster. You should aim to do it that way rather than take it all off the same set of shims if you don't want to muck with the camber too much. Do you have much idea of what the alignment is at present though? It really seems like you need a good baseline to start from.

Edited by 76lxhatch, 16 March 2009 - 07:50 PM.

[fuzzypumper]

I got round to adding some positive caster and rather than doing a small change I gave it heaps so I could positively detect the difference.
I removed .060" off the front UCA bushes and added .120" on the back. My home made wheel alignment tool showed camber was unchanged at -1.5deg but the tool showed I had added +1deg caster to the wheel while straight.
However I suspect this means I probably added quite a few degress of true caster but with good results.

With the wheels at full lock I now measure a camber of -1deg on the outer wheels and a test drive proved it worked.
No skipping of wheels while turning, steering wheel has stayed steady at high speed and steering wheel heavyness is even from
lock to lock, unlike before when you turned more the steering got lighter as I suspect the from wheel was going under and the forward
motion af the car was helping push the steering to lock.

Does anyone see a problem with what I have done?

[76lxhatch]

Unless you drive it quite hard that's a touch more negative camber than I'd like to run on the street but adding caster is all good; add as much as you like/can provided nothing hits and you have enough strength to turn the wheel!

Sounds like it sorted your problem and you should also notice less understeer pushing through corners. What is the absolute caster measurement now?

[fuzzypumper]

Unless you drive it quite hard that's a touch more negative camber than I'd like to run on the street but adding caster is all good; add as much as you like/can provided nothing hits and you have enough strength to turn the wheel!

Sounds like it sorted your problem and you should also notice less understeer pushing through corners. What is the absolute caster measurement now?

I actually cant get anymore positive on the camber as the left hand side has no shims on the front UCA bush atm.
I still have my UCA mount holes in the original factory UC holes (up high on the tower).
I suppose if drill a set of lower holes I could bring the camber back to -1deg and be able to apply more caster if needed.

I couldnt tell you what the absolute caster is as I didnt know whatit was to begin with and my home made measuring that isnt that elaborate.
Unless you know of a way I could measure it at home without a machine?

With steering heavyness I went from one extreme with LX arms(really heavy) to UC arms( really light with the wheel alignment issue).
Now Im somewhere in the middle.

[76lxhatch]

Chopper I do agree, I settled on -1 as being a good compromise, above setting is -1.5 which is probably fine too just a whisker more than I'd use as tyres are getting expensive these days.

fuzzypumper no idea how you'd measure the caster accurately at home, I guess as long as you're happy with how it is now it doesn't really matter I was just curious.

[fuzzypumper]

I had made this aligning tool when I rebuilt another front end on the bench and did a crude pre alignment.


I just butted this tool to the front wheel on the car when i did the adjustment to check whether my camber changed.
If I can use this to figure out my caster that would be handy.

Edited by fuzzypumper, 14 April 2009 - 05:14 PM.

[fuzzypumper]

Thanks chopper, I will try it tomorrow time and weather permitting.

So effectively Im swinging the left wheel 40deg total, starting from 20 deg left, through centre/straight, to 20 deg right ?
Also what is the factory caster setting suppose to be on a UC front end?

Edited by fuzzypumper, 14 April 2009 - 10:45 PM.

[76lxhatch]

Factory UC caster is around +0.5 from memory but don't quote me on that.

In your pic above what is the suspension sitting on? Or is it at full droop?

[fuzzypumper]

Factory UC caster is around +0.5 from memory but don't quote me on that.

In your pic above what is the suspension sitting on? Or is it at full droop?

In the picture I had the frame sitting on a wooden trolley. I didnt have the springs in and but I had lifted the arms
to the position where I expect my springs to be sitting once in the car and on the ground, basically with steerings Tie-rod arms being horizontal.

Edited by fuzzypumper, 15 April 2009 - 10:59 AM.

[76lxhatch]

Mine's still nice to drive (lighter than the LX rack and geometry ever was) with around +1.25 deg caster. Just have to watch as more caster is added more clearance is required at the firewall with full lock.

I like your homemade alignment tool fuzzypumper, simple but effective. I guess if you could position the upright equidistant from the centre of both upper and lower ball joints then you would get absolute caster measurements...?

[fuzzypumper]

Thanks Chopper. However I suspect for me achieve a desired +1.25 caster, my guage would need to acurately measure .25deg intervals.
I doubt its accurate to .5deg at best.
Having said that I measured from 0deg @ 20deg turne left to about -2.4deg @ 20deg right which by your calculation makes it +7.2deg caster...........oops! That cant be right. That would mean I need POP-EYE arms to turn the steering wheel.

76LXHATCH, The tool worked well enough for the front end outta the car and no wheel but for what I'm doing now it does requires a rework.
If I have time I might modify it so it grips the inside rim and centre the I only rum 205/60/13 tyres so the clearance to the firewall lip isnt an issue when the whwwl is turned and excesive castor. I have at least
25mm clerance.

[rodomo]

Stub axle inclination? (Was known as king pin inclination when I was at trade school)