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Rim Offsets

Started by antelopeslr5000 , Apr 14 2006 02:04 AM

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8 replies to this topic

#1 antelopeslr5000

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Posted 14 April 2006 - 02:04 AM

Hi all,

I'm currently looking at a brake upgrade for my Torana (LX) which will also include changing the stud pattern to that of a Commodore.

Would a 'standard offset' Commodore rim fit under a frontend of a Torana (I not even sure if there is such a thing as a 'standard offset'!)?

I guess what I'm trying to say is do Commodore and Torana rims have the same offset just with different stud patterns?

Thanks in advance.

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#2 _CHOPPER_

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Posted 14 April 2006 - 11:30 AM

Years ago I converted my LX to VK 4 wheel discs. The hub from the Commodore disc sits out an extra 5 MM than the Torana discs. This alone increases front track by 10 MM, assuming you use rims with the same offset that is already on there.

I ran VK front discs with 15x6 Commodore rims with garden variety ( 99.99% ) offset of +43. With 225/50R15 tyres, they just touched the sway bar on full lock. And I mean JUST. I tried using 15x6.5 BMW rims with +47 offset. These rims sit in an extra 9.5 MM. These just missed the top ball joint, but the normal wheel weights didn't. I fixed the problem by using stick on weights and then everything cleared. By using basic maths, this means that the 15x7 ute steel rims from VU onwards won't fit.

Feeel free to sak any other questions.

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#3 _devilsadvocate_

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Posted 14 April 2006 - 11:44 AM

Sorry dont know the ans to your question antelope, but it got me thinking about how to measure offset easily, I scoured the net looking for info on how to do it, but wasnt enlightened, especially if the tyre was fitted to the wheel and/or the rim width unknown.

Here's a method I've tried that would appear correct to me:

Remove tyre and wheel from car and lay on a flat horizontal surface.

Get a long rod/screwdriver that one can fit through the wheel stud holes.
Put the rod through the hole all the way to the ground and using a marking pen/pencil mark on the rod where the inside of the wheel would make contact with the hub.
Turn the wheel upside down repeat, marking the position where the inside of the wheel would make contact with the hub.
Measure the dist b/w the two marks on the rod and halve.
I come up with +31mm on a rim from the UC, +ve meaning the offset it towards the front surface of the wheel.
Comments on whether this is correct or better ways most welcome.

Edited by devilsadvocate, 14 April 2006 - 11:52 AM.

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#4 _CHOPPER_

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Posted 14 April 2006 - 12:04 PM

You could do it that way. With a steel ruler, lay it across the top of the wheel/tyre assembly. Using you eye, you can see where the sidewall bulge is top and bottom on the outside of the tyre. Place one edge of the ruler there. Do the same for the inside. You then have the overall width of the tyre. ( distance A ) Now measure the distance from the bolt up face of the rim to the inside edge of te tyre as described above. ( distance B ) Halve distance A. The difference between the two distances is your offset. If A is bigger than B, you have negative offset. If B is bigger than A, you have positive offset.

NB: If you have raised white lettering tyres, you may get an inaccurate result.

To the question in the original post:

13x5.5" Torana rims: +32 offset
13x6" Torana rims: + 25 offset.

99.99% of Commodore 15x6 rims: +43
VG ute 15x6 rims: +37
VP IRS 15x6 rims: +27

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#5 gtrboyy

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Posted 14 April 2006 - 08:56 PM

You have to work out what brakes you will use & what wheels.Vt have different offsets to vs when it comes to the alloy wheels.

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#6 _CHOPPER_

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Posted 14 April 2006 - 09:35 PM

There are a variety of offsets for factory GMH rims. But since they first came out on the VL turbo, the 15x6 steel rims have had a +43 offset as standard. I've seen some 7" VS SS rims with a +40 offset.

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#7 antelopeslr5000

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Posted 15 April 2006 - 11:31 AM

Thanks heaps for the information.

The front discs will be replaced with either CP5000-210/11G8 or DBA5046B discs. I also will be running FR17 X 7" Simmons on the front with 215/45 tyres. Still not 100% confident in my ability to obtain the correct offset for my setup. :huh:

Hopefully I'll be able to test try a few different offsets before I buy them.

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#8 makka

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Posted 15 April 2006 - 04:46 PM

so what brakes are you gonna run with those discs? AP? Brembo?
I have had some 17x8 wheels on my LH, they were +20. if your running 7s I would go a similar offset, this should give you enough clearence on the guards.
look here for some pics
http://www.gmh-toran...?showtopic=4439