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Location:
Hobart, Tas
Registered:
May 2002
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 "Ideal" offset (general question, and yes I do know what offset & backspace mean!)
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Sat, 02 October 2004 00:21
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When fitting different sized (i.e. wider) wheels, is the ideal to:
1) Maintain the same backspace - the inner wheel/strut clearance is exactly the same, but the offset is more -ve and the outside of the wheel extends further
2) Maintain the same offset - centreline of wheel stays exactly the same, and the wider wheel extends inwards and outwards by the same mount
I always assumed 2) so that there was not extra stress on wheel bearings etc, and the track & scrub radious etc remained the same.
BUT - the xA6x Celicas & Supras - with the exactly the same suspension geometry (think IRS Aus-market xA6x celica vs US GT-S, or MA6x vs Celica XX) came from the factory with either 7" rims with a +8 offset, or 5.5" or 6" rims with a ~+25 or ~+20 (IIRC) offset. This follows paradigm 1), and now I am confused.
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Registered:
July 2002
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Re: "Ideal" offset (general question, and yes I do know what offset & backspace mean!)
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Sat, 02 October 2004 00:51
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It all comes down to what room you have. If your 5.5 inch rim is nearing the strut then clearly changing to a 7 inch rim with the same offset is going to cause problems.....
Most cars (especially 60 series celicas  ) have the wheels tucked deep in the guards so you're really going to need and want a different offset when going wider anyway.
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Registered:
August 2002
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Re: "Ideal" offset (general question, and yes I do know what offset & backspace mean!)
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Sat, 02 October 2004 01:02
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celicas also didnt have flares.
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Location:
Hobart, Tas
Registered:
May 2002
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Re: "Ideal" offset (general question, and yes I do know what offset & backspace mean!)
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Sat, 02 October 2004 01:11
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| BlackSupra wrote on Sat, 02 October 2004 11:02 |
celicas also didnt have flares.
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Celicas in the US did, and they have the same suspension as those that don't.
If you just meant in Aus - umm, so what? I'm not talking aesthetics here.
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Registered:
August 2002
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Location:
Cabramatta, NSW
Registered:
May 2002
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Re: "Ideal" offset (general question, and yes I do know what offset & backspace mean!)
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Sat, 02 October 2004 02:27
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I think it's just a matter of track...
Whatever track you're aiming for (distance between the centres of the wheels) determines the offset that you want.
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Location:
Hobart, Tas
Registered:
May 2002
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Re: "Ideal" offset (general question, and yes I do know what offset & backspace mean!)
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Sat, 02 October 2004 04:50
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| BlackSupra wrote on Sat, 02 October 2004 11:25 |
your legally allowed to run wider wheels
how about you tell us the wheel width you want to run.
EDIT: its niether 1 nor 2.
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Thanks for the reply, BlackSupra, but legality, or whatever I may personally want are irrelevant to the question. xA6xs were just an example, perhaps a bad one [reason further down]
I feel like I'm talking another language here, and no one understands...
| Nark wrote |
I think it's just a matter of track...
Whatever track you're aiming for (distance between the centres of the wheels) determines the offset that you want.
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except perhaps Nark, except now we have to ask that is the best track to use to not adversely affect stress on wheel bearings, suspension geometry etc. If the answer to this is to maintain whatever is stock, then the offset has to remain static.
But what Toyota did with the 5.5"/7" rims doesn't follow this - if 7" in a +8 offset is 'correct' for the xA6x geometry, then surely the 5.5" rim should also have been made +8. The alternative is that 5.5" is 'correct' and to put 7" rims on some xA6x models & not have inner clearance issues, they had to increase the offset... which you would think would lead to bump steer etc issues - especially given that these cars also came stock with much wider rubber too.
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Location:
Brisbane
Registered:
May 2002
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Re: "Ideal" offset (general question, and yes I do know what offset & backspace mean!)
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Sat, 02 October 2004 12:16
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No-one's discussed legality yet. In most states (certainly in Qld) you're not allowed to change the track width for a given axle. I think there may be some leeway but it's not much. So that means you have to use wheels with the same offset as the factory wheels, regardless of their width.
In some cases this will place limits on how wide you can go without clearance issues, so a lot of people "cheat" by using different offsets. You probably won't get defected for it (unless it's very obviously wrong), but the risk is always there.
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Location:
Lost in the K hole
Registered:
May 2002
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Re: "Ideal" offset (general question, and yes I do know what offset & backspace mean!)
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Sat, 02 October 2004 12:20
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NSW legal increase in track (per side) is 12mm = 24mm total increase
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Registered:
August 2002
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Re: "Ideal" offset (general question, and yes I do know what offset & backspace mean!)
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Sat, 02 October 2004 12:24
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| ed_ma61 wrote on Sat, 02 October 2004 22:20 |
NSW legal increase in track (per side) is 12mm = 24mm total increase
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And the rim must stay inside the guard at all times.
This is the sort of thing i was aiming at above, but to no avail. IF you have a rim width, just figure the offset.
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Location:
Cabramatta, NSW
Registered:
May 2002
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Re: "Ideal" offset (general question, and yes I do know what offset & backspace mean!)
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Sat, 02 October 2004 13:39
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If you get pulled over, they won't be able to see if your track has increased.
It's only when your wheels are sticking out of the guards that they will book you.
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Location:
Hobart, Tas
Registered:
May 2002
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Re: "Ideal" offset (general question, and yes I do know what offset & backspace mean!)
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Sat, 02 October 2004 13:52
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| Norbie wrote on Sat, 02 October 2004 22:16 |
No-one's discussed legality yet. In most states (certainly in Qld) you're not allowed to change the track width for a given axle. I think there may be some leeway but it's not much. So that means you have to use wheels with the same offset as the factory wheels, regardless of their width.
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This is why I find the whole xA6x flared vs non-flared factory wheel thing so interesting. The track is different from the factory for cars with the same suspension.
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Location:
Adelaide
Registered:
September 2003
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Re: "Ideal" offset (general question, and yes I do know what offset & backspace mean!)
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Mon, 04 October 2004 21:26
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[quote title=Stefan wrote on Sat, 02 October 2004 23:52
This is why I find the whole xA6x flared vs non-flared factory wheel thing so interesting. The track is different from the factory for cars with the same suspension.
[/quote]
But do they ?
The best compromise is option 2, and it is always a compromise. Those that are astute will notice that most modern cars have very high offsets, regardless if they are RWD or not. This has to do with King pin inclination angle, scrub radius etc.
Except for F1, all suspension design is a compromise of some sort.
Stefan, what are you looking at specifically ?
Cheers
Michael B
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