11 replies to this topic

[Nugget]

I have a set of A9X style stubs(3695/3696) +Harrop arms, an lx front end drilled and splined at both regular positions.

and a UC front end complete

 

All other things being equal(koni shocks, matching final spring ride hight, rubber bushes, 3-spot at front or LCA and superpro outriggers);For cornering, tyre wear and high speed stabability which will perform best?

 

Thanks in advance

[Bigfella237]

If you hadn't already shelled-out for the Harrop steering arms I'd say go with the complete UC front end.

 

The Holden (aka "A9X") stubs will drop the ride height around 1 inch (25mm) without any change to the spring length, so if you're looking for a super-low ride height but still with some suspension travel then that might help. On the other hand, the Torana stubs have a much better SAI (or what used to be known as kingpin inclination) if you want to run wide offset/deep dish rims and manual steering.

 

Otherwise it kinda depends on what brakes you want to run.

 

If it were me I'd be selling the "A9X" bits, which would likely pay for your complete suspension rebuild on the UC front end, but it all depends what you're aiming for?

[Heath]

Your A9X setup if it's got a "shelby drop" (lowered inner pivot point on the UCA) is possibly going to be a bit hard on tyres if you're doing highway use... you might not be able to lose enough of the static camber? (I could be wrong there, but I see a lot of cars with HQ stubs and they have a lot of negative camber even though they're like... pro street cars and stuff haha so obviously not benefiting from the geometry)

Does that "A9X" type front end have the UC upper arms? That's an important part; because for a road car, you want the castor they facilitate, so you can go without big static camber to improve tyre longevity on the highway, but you do want a lot of camber gain on steering of course.

It will have more travel as Andrew said if you want to do road racing or generally have the car very low. 

 

Your UC front end in standard form is going to have less camber gain (but that's easily fixed by re-drilling the uppers of course). It will definitely have the ability to give you a decent amount of castor, which is important.

And of course that front end can drive well. It may also give you a bit more space for brake calipers?

 

Other than that, there's not that much difference between them. How you align it will influence how it drives as much as anything!

 

I would probably recommend using the UC one with a re-work, the best shocks you're willing to shell out for, and cashing in on the A9X bits, unless you wanted to use a HQ-type brake kit.

You might want to keep the steering rack off the earlier car if it's a bit faster, and solid mount it, although I think LX racks might be the same as UC anyway (LH is a touch faster) - if they are the same ratio just use the UC one because it's already solid mounted.

[axistr]

As Heath has said the wheel alignment will play a big part on how the car handles and tyre ware. Unfortunately trying to find a good wheel alignment guy is getting very hard, plenty of them tell you they are a wizard but don't even know the effects of caster, camber and thrust angles. Ask them about scrub radius and KPI and I generally get a very blank look.

 

If you do have original A9X stubs than you have gold in your hands. My theory on A9X stubs is Holden simply used the HX stub axle casting (current at the time) including the part number and drilled the top and bottom ball joint holes to suit the Torana KPI of 9 degrees. Due to low numbers of A9Xs it would have been the easiest way to get a lower centre of gravity that didn't require a special casting. They only needed to cast a unique steering arm to reduce bump steer due to the the 25mm lower ride height and off the shelf HX brakes. (low cost improvement) Every time I see a torana with two or three degrees of negative camber its a dead set rigger it has HG-WB stub axles. No A9X come from factory with three degrees of negative camber. The guys racing them probably used HQ stubs for extra negative camber due to the extra grip of slicks and mid corner speed load up of the suspension.

 

Its not hard to check if you actually have original A9X stubs by measuring the KPI. Put the stub axle in a vice and set it so the wheel bearing mount faces are level. Put a straight round bar through the top and bottom ball joint stud holes and measure the angle with an angle indicator. if you have close to 9 deg combined with a 25mm higher spindle height you have just won lotto. If you get an angle around 7 deg you have HX stubs.

 

Using HQ stub axles doesn't only effect the camber it also effects the scrub radius. Front wheel rims with lots of negative offset will make the car walk around much more with the lower HQ KPI stubs. However if your hell bent on fitting HQ stubs than fitting Whiteline offset bushes to the front of the lower control arms allows for adding lots of positive caster and reduce negative camber at the same time. These offset bushed were designed to change the diff pinion angle when fitted to the rear trailing arms, however they are the same dimensions as the lower front control arms. Further benefits are the dragging of the control arm in a forward direction gives better clearance between tyre and firewall on turns. This also allows further adjustability at the top control arms and wheel alignment shim stacks. Customers fitting these bushes have reported between 4 & 6 degrees of positive caster and cambers of zero and 1/2 degrees of negative camber. High positive caster will help with the difference in KPI. The downside is the steering input will get very heavy, the more positive caster the more weight of the car is added to the steering. Adding power steering would be the go with high positive caster. It should also be noted the larger the overall diameter of the wheels the more the KPI will alter the scrub radius. (worse with HQ stubs).      

 

 

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[Shiney005]

I looked at the topic title and thought "I've no doubt read all this before". But no. There is always more to learn.  Thanks Lenny. 

[UCSLE]

HX stubs only have 15mm higher spindle height than the LX Torana stubs . Where are people getting 25mm from ? 

[claysummers]

Noted the other day Hoppers Stoppers quote the HK to WB spindles being 25mm higher than HD HR in their Holden brake blurb. I don’t know if Torana are same height (different KPI). Maybe HR and Torana are being confused Troy.


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[UCSLE]

I dont know about HD HR stubs , dont have any to compare

 

Was thinking it had something to do with different camber not being taken into account .  

[Heath]

Lenny, that is a smokin' hot reply.

 

Some really excellent information there.

[RIM-010]

Comments like that, Lenny, is exactly why this forum remains an invaluable resource.

[76lxhatch]

They only needed to cast a unique steering arm to reduce bump steer due to the the 25mm lower ride height and off the shelf HX brakes.

 

Worth noting that static caster also affects bump steer quite significantly due to how much it moves the steering arms up and down, lowering the outer tie rod end maintains better bump steer with a lot of positive caster. LH/LX steering arms are no good with any more than a degree or so, UC arms are of course better and you can ream the tapers to drop the tie rod end in the arm a few mm if need be too.

[axistr]

Yep 100 % LX76hatch. I advise customers that fit control arm offset bushes to fit harrop arms even with lx lh steering arms to compensate for the outer tie rod end increased height.