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#26 Oversteer

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Posted 03 July 2015 - 09:47 PM

Little goggling ;

 

 


L34/A9X
Rim 14x6" Offset -0.25" ( 6.37 mm ) PCD 5x4.75" Stud 7/16" UNF Source: Unconfirmed
DR70H14 (Approximate metric equivalent is 205/70/14) Source: Unconfirmed
Track Front 57.2" (1452.88 mm) Source: "45 Years of Holden" Terry Bebbington and Michael Malik 1994 p 93 and 96.
Track Rear 56.1" (1424.94 mm) Source: "45 Years of Holden" Terry Bebbington and Michael Malik 1994 p 93 and 96.

In theory the diff width including brake drums should be 1424.94 mm + ( -6.37 mm x 2 ) = 1412.2 mm

A9X Hatch & Sedan
Rim 14x6" Offset -0.25" ( 6.37 mm ) PCD 5x4.75" Stud 7/16" UNF Source: Unconfirmed
DR70H14 (Approximate metric equivalent is 205/70/14) Source: Unconfirmed
Track Front 59.5" (1485.9 mm) Source: Just Holdens Toranas collectors series. A9X edition pg 23
Track Rear 57.1" (1450.3 mm) Source: Just Holdens Toranas collectors series. A9X edition pg 23

 

 

 

 

So as you can see holden actually got something right in the mid 70's on the A9X and made the rear track significantly narrower than front...on a race track this would be a way to make a car handle predictable and neutral(for a rwd car)

 

Problem comes when people put aftermarket rims on and go for a staggered approach.....screws everything up, and if you have driven an LH with 500+hp on the two different tracks you feel the handling difference with your eyes closed....if your used to well handling modernish cars it feels so wrong.

 

Guess its another case of looks over legs lol.



#27 EunUCh

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Posted 03 July 2015 - 09:58 PM

^... so that is to say that the OEM designers actually knew something about geometry when they built these things ?, not only a "horsepower" issue, only need to change wheel size without keeping within the guidelines of of OEM to work that out ?



#28 Oversteer

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Posted 03 July 2015 - 10:20 PM

Yeah your right....you don't need horsepower to noticed the significant issure, just rolling around a corner at 30kmph doesn't inspire confidence !

 

With 500hp....is plain frOcking dangerous ! 



#29 Bigfella237

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Posted 04 July 2015 - 01:35 AM

Little goggling ;

 

Unfortunately you can't trust everything you find by "goggling"...

 

L34/A9X rim offset was +0.25" not minus, this is an excerpt from the GMH service bulletin on the L34...

 

Attached File  L34 Service Bulletin - Wheels.JPG   44.02K   5 downloads

 

I can see how the mistake was made, but it's still a mistake. The words aren't Offset minus ins, it's Offset dash ins.

 

If you take an accurate track measurement from Dr Terry's book and do the math (which I can do yet again here if you really need to see it), the offset has to be +.25", it just doesn't work out any other way.



#30 76lxhatch

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Posted 04 July 2015 - 06:57 AM

So as you can see holden actually got something right in the mid 70's on the A9X and made the rear track significantly narrower than front...on a race track this would be a way to make a car handle predictable and neutral(for a rwd car).

Moot point though as no doubt the race wheels changed the track quite a bit, there's a lot more room outboard than inboard from a standard wheel on the back of an A9X

#31 Oversteer

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Posted 04 July 2015 - 12:13 PM

Unfortunately you can't trust everything you find by "goggling"...

 

L34/A9X rim offset was +0.25" not minus, this is an excerpt from the GMH service bulletin on the L34...

 

attachicon.gifL34 Service Bulletin - Wheels.JPG

 

I can see how the mistake was made, but it's still a mistake. The words aren't Offset minus ins, it's Offset dash ins.

 

If you take an accurate track measurement from Dr Terry's book and do the math (which I can do yet again here if you really need to see it), the offset has to be +.25", it just doesn't work out any other way.

 

Fair enough those other offset figures did seem out of wack, but the overall track figures would be right still, so +.25 pushes the wheel inwards more. 



Moot point though as no doubt the race wheels changed the track quite a bit, there's a lot more room outboard than inboard from a standard wheel on the back of an A9X

 

I would be almost certain that the race wheels also widened the front track ;)



#32 Bigfella237

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Posted 04 July 2015 - 01:41 PM

Fair enough those other offset figures did seem out of wack, but the overall track figures would be right still, so +.25 pushes the wheel inwards more.

 

Yup, the same GMH Service Bulletin gives track figures for the L34 of:

 

Front: 57.89 in. (1470.4mm)

Rear:  56.82 in. (1443.2mm)

 

I'm pretty sure the A9X was the same. That's a difference of 1.07" (27.2mm) front to rear (SL/R & SS RTS are 0.9" different, again front wider).



#33 ls2lxhatch

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Posted 04 July 2015 - 05:10 PM

It appears you cannot service bulletins either.  6.3768 feet is 1.9436 meters but the service bulletin has it at 1.9636 meters.

 

There are quite a few variations for track figures for the A9X. I have listed some of them on my website.

http://ls2lxhatch.co...cifications.htm



#34 76lxhatch

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Posted 04 July 2015 - 09:08 PM

I would be almost certain that the race wheels also widened the front track ;)

No doubt but the point was that its all different, we don't whether the original difference in front/rear track still applies (there's always the possibility but my bet would be otherwise)

#35 Bigfella237

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Posted 05 July 2015 - 04:45 AM

It appears you cannot service bulletins either.

 

Yeah it seems someone at GMH still didn't have a handle on the metric system in '74, but you'd think they'd have proof-read their docs before release? I won't hold it against them though, they've still managed to turn out some nice cars over the years!

 

I've spent too many hours on the subject of calculating accurate track measurements but I arrived at the conclusion that the GMH Service Bulletin has the correct figures for L34 & A9X (nothing really surprising there)

 

L34 & A9X Track Front: 57.89" (1470.4mm) = front hub-to-hub width 58.39" (1483.1mm)
L34 & A9X Track Rear:  56.82" (1443.2mm) = rear hub-to-hub width 57.32" (1455.9mm)

Difference of 1.07" (27.2mm) front to rear

 

And the LX Torana Owner's Manual appears to have the correct figures for LX SL/R & SS

 

LX SL/R & SS Track Front: 55.3" (1404.6mm) = front hub-to-hub width 57.8 (1468.1mm)
LX SL/R & SS Track Rear:  54.4" (1381.8mm) = rear hub-to-hub width 56.9 (1445.3mm)

Difference of 0.9" (22.8mm) front to rear

 

ls2lxhatch confirmed that the Owners Manual was correct by physically measuring an LX diff at 1446mm (give or take a decimal point).

 

That means:

 

L34/A9X front suspension hub-to-hub width is 0.59" (15mm) wider than an SS

L34/A9X  rear suspension hub-to-hub width is 0.42" (10.6mm) wider than an SS

 

I assume the HQ stubs & discs account for the difference up front and the rear disc brakes for the back?



#36 ls2lxhatch

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Posted 05 July 2015 - 12:49 PM

I've spent too many hours on the subject of calculating accurate track measurements but I arrived at the conclusion that the GMH Service Bulletin has the correct figures for L34 & A9X (nothing really surprising there)

Have you seen a A9X service bulletin with track figures? I have only seen a L34 service bulletin.

I expect that the L34 & A9X have the same front and rear track but I would like to get confirmation from a GMH document.

The A9X had a different diff and the rims where made by a different manufacturer so there is potential for a track change.

#37 Bigfella237

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Posted 05 July 2015 - 08:33 PM

No but I would like to see the A9X bulletin if anyone has a copy tucked away somewhere?






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