38 replies to this topic

[mugginz]

So I did a quick trial fit of a rear flare on the car.  Then placed the max VCOP allowed 255 rubber underneath to see what kind of offset would be needed to be used to make the tyre not look ridiculous.

 

 

Looks like it would be mandatory to use the L34/A9X offset of -6.25mm (which is still not quite enough dish for the flare to look appropriate.)

 

So, with those two parameters determined, I'm wondering if anyone run into any regulatory problems running the L34/A9X offset on a non factory L34/A9X car.

 

Looks like I'm going to have to get custom wheels made up if I want a descent looking set of -6.25 offset wheels in Torana pattern.  To get a noice set of Japanese made wheels in this configuration I'm going to be up for thousands.  So, I'd hate to fork out all that money only to find I'm going to run into hastles with the plod.

 

In addition to plod troubles, I'm also wondering about increased load on the wheel bearings.  Anyone had a bearing failure due to offset?

 

Thanks.

[myss427]

Cheaper to shorten the diff? I run 3 3/8th offset with 11inch wheels, no bearing issues.

Edited by myss427, 12 September 2017 - 11:36 AM.

[mugginz]

Cheaper to shorten the diff? I run 3 3/8th offset with 11inch wheels, no bearing issues.

 

Stress on the bearings increases with movement from positive offset into negative so if you're running 3 3/8th inch negative offset without issue that makes -6mm seem pretty poutltry.

 

Without being prepared to pay for an engineer to pass a tyre bigger than 30% larger than 200mm (255mm) I'm stuck with VCOP regulation size.  Given that, to get get the tyre sidewall as close as possible to the outside edge of the bolt-on I need to run as much negative offset as I can get away with.  If engineers reports weren't so dear down Geelong way I'd be more inclined to investigate that.  At this stage I think I'm stuck with 255 tyres so I might need to reconsider the bolt-ons if the offset isn't kosher from a rules enforcement perspective.

Edited by mugginz, 12 September 2017 - 12:00 PM.

[Oversteer]

Increase in rear track will make it handle like shit....looks over safety.

[mugginz]

Increase in rear track will make it handle like shit....looks over safety.

The intention is to increase both the front and back the very same amount in order to maintain the front to rear track relationship as per factory.

I'm aware that increasing the rear more that the front is likely to increase understear and Toranas already ship from the factory with enough of that.

[myss427]

If your trying for rego, you can only go 25mm over track of an A9X (being the widest tack). I have two sets of wheels with different offsets, my rego wheels which is what the car is engineered with are 9 1/2 rears with 17 x 255. where my fun wheels are 17 x 11 with 315 drag radials. But mi diff is 2 inches narrower than factory.

[mugginz]

Firstly, let me say that this tyre to bolton relationship looks roughly perfect. Nicely done.
 

 
 

Hi mate, I've been through this with my car in the ACT for engineering as per NCOP and VSB14 guidelines.

255 is the largest engineerable size tyre to meet these requirements based on the largest rim width, size and tyre size from factory being the A9X.

 
This is my understanding as well.
 
 
 

For me my diff was longer than standard by 40mm which came in the car which was a 9 inch. The easiest way to find out the offset to use on a 10 inch rim (that is the widest rim a 255 can mount on) is to measure from the mounting face of your drum or disc to the inside edge of the flare to get your max.

 
That'd give me the offset I require but that might be different to the offset that's considered legal.
 
 
 

Keep in mind you can't increase track width over VSB14 spec so the L34 flare is perfect, the A9X flare (which is wider) won't look as good.

 
Gotta agree here. A9X flares need more rubber which makes running legal rubber and offset look silly.
 
 
 

To meet A9X spec track width I needed to run HQ stud pattern. If you run Torana stud you are limited to L34 spec which has a narrower track

 
This doesn't make much sense on the face of it. Sounds a bit arbitrary from an engineering point of view considering the following statements from http://www.ls2lxhatc...cifications.htm are likely true.
 

The "Holden Torana Performance Handbook" lists the rim offset as -0.25" for the A9X and +0.25" for the L34, this appears to be a typo as the GMH L34 service bulletin lists the rim offset as +0.25".

The "Just Holdens" track figures for the A9X are different to the L34 track figures. I would expect the front track figures to be the same for the L34 and A9X as they have the same front suspension and rim offsets. "60 years of Holden" list the same track for L34 and A9X. The A9X diff could had a different BUF measurement to the L34 diff.

VCOP states that you're allowed to run a track increase of 25mm but one engineer wouldn't let one guy run 25mm over A9X track for some unlisted reason. Would let him either run +25mm over standard or up to but not over A9X track.

It's hard to get clarity on this as the track and rim offset figures seem a little rubbery but it's heartening to hear that you don't have to have an L34 in order to run L34 offset.

[mugginz]

Looking at the L34 Supplament issued by Holden, the figures listed on http://www.ls2lxhatc...cifications.htm for L34 are correct. But...

Given that A9X has the same front suspension as L34 bar steering arm and upper control arm the figures listed for A9X don't seem possible.

Either when assuming correct wheel offset for A9X is actually the same as L34 (+0.25" / +6.34mm) the A9X front track doesn't jive with L34 and if we assume that the listed A9X figures of -0.25" / -6.34mm offset aren't a typo, the figures still don't jive.

[myss427]

A9X had a alloy girlock caliper which was in a different position and had a wider girth than the cast PBR used on the L34, tracks alowed are different, but stub axles were the same? go figure.

[mugginz]

I'm gunna need to find measurements of an actual A9X wheel I think.

At this stage I'm gunna assume the A9X wheels are the same dimensions as L34 and so where http://www.ls2lxhatc...cifications.htm lists them as the same I'll assume that's correct and where it mentions they're different I'm at this stage gunna assume that's incorrect but will keep looking for an authoritive source.

Edited by mugginz, 13 September 2017 - 02:09 PM.

[myss427]

I remember this same discussion about track and also wheels, had a thread here a few years ago with some proof, as in books and paper work displayed on the forum. Time for a search maybe?

[mugginz]

I remember this same discussion about track and also wheels, had a thread here a few years ago with some proof, as in books and paper work displayed on the forum. Time for a search maybe?

Looks like I've got some work to do when I get home

[Bigfella237]

NCOP11_Section LS Tyres, Rims, Suspension and Steering, Page 47/LS85 states:

 

Track. Where non-original axle or suspension cross-member components are fitted,
the offset of the wheel in relation to the axle or hub assembly used must not be
increased by more than 12.5mm each side of the vehicle based on the specifications of
the axle components used. If an axle assembly is shortened then the track width limit
is taken as the axle manufacturers original track dimension, less the amount the
assembly has been narrowed, plus 25mm.

 

If you have a Ford 9" diff fitted, then the Torana A9X track width specs have nothing whatsoever to do with it!

 

You take the track width of the vehicle that the diff came from (be it a Fairlane, LTD, F100 or whatever), add or subtract the amount that the diff was widened or shortened (respectively), then you are allowed 25mm over that measurement.

[Bigfella237]

I've been scouring the documents some more and it seems like rim width is one area where it sucks not to be in NSW!

 

Under the NCOP (section LS 4.2.8):

 

 

Tyres fitted to passenger cars or passenger car derivatives must not be more than 30% wider
than vehicle manufacturer’s widest optional tyre.

The rim width must not exceed the recommendations for the tyre fitted.

 

But in NSW, which is still under the old NSW LVCOP, Section 3.8.6 Rim Width says:

 

 

Allowable rim width increase above the widest
optional wheel available as original for the axle
assembly used

 

So if you shorten a 9" diff out of an F250 or something with dual wheels, then:

 

 

If a vehicle is originally fitted with dual wheels and is to be
changed to single wheels, then the rim width must not exceed the
maximum permitted for the mass of the vehicle in the table on the
previous page based on the original rim width being the addition of
the widths of each rim in the dual wheel assembly

 

So you should be allowed to add the width of both dual wheels, say they were 5" wide each, that equals a single wheel 10" wide, then you can add 2" over standard to that!

 

But getting back to the NCOP, I believe a similar caveat was intended to be included in section LS5 but it seems to have been omitted somehow?

 

Under REAR SUSPENSION MODIFICATION (DESIGN) CODE LS5, on Page 66/LS85 it says:

 

 

The following are designs that may be prepared under Code LS5:
- Design of rear beam axle modifications including shortening, differential and axle
substitution and revised location arms, rods, bearings, bushes and mountings;
- Design of independent rear suspension modifications using different struts, trailing
arms or uprights;
- Design of a conversion using a complete suspension assembly from a different vehicle
model;
- Design of a complete rear suspension assembly using components from different
vehicle model(s); and
- Alternative wheel and tyre specifications for vehicles with modified axles or suspension.

 

But that's it, I can't find any further information on alternative wheels for modified axles? It seems like they intended to add a clause similar to the NSW LVCOP but never got around to it?

Edited by Bigfella237, 14 September 2017 - 06:40 AM.

[mugginz]

So you should be allowed to add the width of both dual wheels, say they were 5" wide each, that equals a single wheel 10" wide, then you can add 2" over standard to that!

Sounds like one way to get legal 12" wheels under a Torana in NSW.


Some of those design constraints would seem to be designed in order to maintain the structural integrity of the axle assembly by not allowing the introduction of axle components (wheels) that would induce too much load on axle components. But then there's also the aspect of altering vehicle dynamics by changes to overall track.

Track widths as relating to handing should be basically determined by what the manufacturer released to the public and therefore should allow for the L34/A9X tracks to be used on any 74-80 Torana. This would have to be the most important determinant in my mind.

And then underneath those constraints you'd have the ones relating to durability such as deviation of offset so as to not overload wheel bearings and other suspension components. The durability issues are the only ones that I think could impact a Torana without L34 components running an L34 track (either front or rear.)

L34 rear BUF to BUF measurements are listed as being 11mm wider than a Torana without an L34 diff housing. If this is due to different brake drum thickness and not due to housing width changes then I think it'd be valid to run L34 rear track on the normal housing as centreline would be the same distance from bearing mount but if the L34 housing is actually wider then that might put a cat amongst the pigeons.

As for the front suspension. Front track increase for L34 is mostly due to wheel offset changes with the possibility that some of the last 15mm increase being either due to geometry differences or thickness of the HQ rotors so L34 front track shouldn't load the front bearings differently as HQ stub axle bearing mounting face relationship should basically be the same as Torana stub axle.

Edited by mugginz, 14 September 2017 - 10:10 AM.

[mugginz]

I think I might've found the source of the anomaly between the L34 dimensions and A9X dimensions as listed on http://www.ls2lxhatc...cifications.htm

Interesting the Cams amendment 21/12E states.

Front track is 1485.9 +10
-22

Rear track 1450.34 +13
-13

Does anyone have a copy of Cams amendment 21/12E?

Edited by mugginz, 14 September 2017 - 10:53 PM.

[mugginz]

When The Baron measured his spare A9X diff this is what he found an actual physical diff to be.

I measure 1438mm.

The diff still has the discs and calipers on.

The measurement was taken from the spigot ends of the diff axles which the wheels should sit on. They protrude from the wheel mounting up face by about 1mm max.

Width would be about 1436 -1438mm.

Sort of close to stock diff width.

Not sure what measurement technique was used by him.


I'm prepared to make a measuring trammel wide enough to accurately measure an A9X or L34 diff if anyone's got a car around Geelong/Melbourne area they want to have measured.

The written documentation seems to be so inconsistent as to be almost useless as far as the road going cars is concerned.

Edited by mugginz, 15 September 2017 - 10:17 AM.

[StephenSLR]

it's heartening to hear that you don't have to have an L34 in order to run L34 offset.

 

Correct me if I'm wrong. The SL/R models had different track widths due to the different rims and/or front geometry in the case of A9X; so if you increase the track width by 25mm from a track width that was already increased from standard; wouldn't that be non-complying?

 

i.e. if you had full A9X front geometry you could increase by 25mm but if you have standard Torana geometry you'd have to stick within 25mm of standard Torana track width?

 

s

Edited by StephenSLR, 15 September 2017 - 12:03 PM.

[mugginz]

I'm not sure you should be able to run the +25mm increase over A9X track width.

The A9X's front track increase was largely due to rim offset from what I can glean from the various docs I have but at this stage I have a few concerns about the documentation that's floating around.

Holden deemed it fine to run +32mm (standard 5" rim), +19mm (standard 4 1/2" rim) and +6mm (L34 rim) offsets on the bearing sets they shipped which I believe were Timkin brand.

I currently have problems with the figures listed for A9X which should at least be the same as L34 for front track. I'm not sure you could install enough negative camber on a Torana front end to account for the differences listed in Cams amendment 21/12E as mentioned by The Baron (I don't have a copy myself)

Those figures seem to have ranges depending on how you read The Barons post. Those track ranges may be because of different wheels holden deemed OK for A9X perhaps. I'd love to a look at the original docs but I love to accurately measure a real A9X and L34 even more.


Bottom line for me at the moment is I'm not able to find definitive measurements for bolt up face to bolt up face surfaces for A9X. I suspect they should be exactly the same as L34 for at least the front.

[mugginz]

Rear diffs for stanard, L34 and A9X all have different brakes so I can see how the rear BUF to BUF measurements could be different.

Holden could have used front wheels with different offsets compared to the rear wheel in order to maintain front track to rear track relationships but that at least seems pretty clear it wasn't the case. Everything I've read suggests front and rear wheels were the same offset as shipped from Holden

That being the case, the figures for L34 and Cams amendment 21/12E seem a little inconsistent (and probably not possible) depending on how you read The Barons post

Edited by mugginz, 15 September 2017 - 12:20 PM.

[StephenSLR]

I'm not able to find definitive measurements for bolt up face to bolt up face surfaces for A9X. I suspect they should be exactly the same as L34 for at least the front.

 

The A9X had HQ discs, different steering arms to accommodate the difference in length, RTS geometry, etc. so how could the distance between BUF's be exactly the same as L34?

 

... or did L34 also have HQ discs, etc.?

 

s

Edited by StephenSLR, 15 September 2017 - 02:00 PM.

[mugginz]

 
... or did L34 also have HQ discs, etc.?
 
s

Yep.

[mugginz]

Passenger side rear BUF to outside of body is 133mm on my car.

With an additional (and minimal) 20mm to fill the flare that makes at least 153 from BUF.

So it's not looking good for this car as far as a 255 tyre on legal offset filling flares.

[Bigfella237]

If your diff width is 1445mm (BUF), plus 2x 153mm out to your flare, then your total from the outside of one flare to the other is 1751mm (I've seen wider flares but that seems about right).

 

*IF* your maximum allowed rear track measurement is L34 at 56.82" (as confirmed by GMH Service Bulletin) plus the 1" over allowance, that's 1468mm

 

(1751 - 1468 = 283) / 2 = 141mm from the outside edge of your flare to the centre of the rim (where the track is measured from). 283mm rounds down to 11", minus 1" for the inner and outer bead flanges, means you need (what's known as) a 10" wide rim.

 

Then (1751 minus the BUF of 1445) / 2 equals 153mm (6") of frontspace, leaving you needing 5" of backspace (4.5" plus ½" for the inside flange).

 

So to achieve your goal you should need a 10" rim (which actually measures 11") with a 5" backspace?

 

Then if your original SL/R diff was designed for a track measurement of 54.4" (1382mm), that means you are actually 86mm (3.39") over your "standard" track, that's a long way outside the 1" allowance if a copper refuses to accept the L34 figures on the side of the road!

 

So just for the sake of interest, if we do the same sums using the SL/R track spec it would be (1751 - 1407 = 344) / 2 = 172mm, meaning you would need (what's known as) a 12.5" rim (which actually measures 13.5") with the same 6" of frontspace, leaving you needing 7.5" of backspace, which wouldn't physically bolt on without chassis mods and wouldn't be legal anyway?

 

After all that you may then want to widen the front track by the same amount to keep the front to rear ratio the same? SL/R track measurements had the front 0.9" wider than the rear; L34 specs had the front 1.1" wider than the rear.

 

But if you take the L34 front track, add 1" and apply it to an SL/R front end, you're gonna end up with a massive scrub radius. That would also affect the handling, perhaps more noticeably than having a lesser front track compared to the rear?