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Discussion Starter · #1 ·
I'm considering new wheels - 1/2" wider (16x7") - for my 9000. Has anyone else done this size on their 9000? I'm not worried about running larger calipers, but am concerned about the offset and what would be the best for this width. I'm not sure if this should be posted on the 9000 board, but I reckon that there's a high probability that people who change the stock wheels would be more likely to hang-out at the 'Performance' area. The wheels that are being considered are mini-lite 'clones' (14-15 lbs) and have a 25 mm offset.
 

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I'm sure some here could work out precisely the correct offset, but Saab did do a 7" rim for the 9000 (only a 15"), but I don't know what offset they used.



Andrew
 

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Discussion Starter · #3 ·
Thanks Andrew, guess I'll have to go see the parts-guy at my local Saab dealer. He should be able to tell me the offset on those 5 spoke wheels. I'm pretty sure there's a bit of room to play with at the rear - there seems to be about 5/8" between the rear trailing arm and the stock rim/tire. I know that Abbott uses 30 mm w/7" rims, but I wonder what, if any, bad aspects would result with the 25 mm offset?
 

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I've test fitted some 7x17 inch wheels on my car. these rims I fitted had an offset of 35 mm, which caused rubbing on the inside of the wheel. after fitting spacers I'd say 30 is ok but 25 mm is perfect. The wheels I ordered are 7x17's with an ofset of 25 mm.
 

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Robert,

This has been done to death on the 9000 board- use the search facility above and the key words wheel offset for more detail.

However, in brief the correct wheel offsets for a 9000 are:

6.5" 37mm (stock)
7.0" 31mm
7.5" 25mm

The key point here, and this applies to any wheels (except those on large 4WD with -ve offset)) is that if you increase the width, you need to reduce the offest by half that amount in order to maintain the same effective distance between centres
 

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Discussion Starter · #6 ·
Mark, it may have been done to death, and I did do a search on wheel offsets, but I really wanted to hear from others what their experience was with 7" rim widths vs. offsets. Also, having been done to death, I'm a bit confused with what you've just posted: "The key point here, and this applies to any wheels (except those on large 4WD with -ve offset)) is that if you increase the width, you need to reduce the offest by half that amount in order to maintain the same effective distance between centres". I think there must be a mistake, either in the listed offsets you give or your 'theory'. My 6.5" Super Aeros are stamped as having a 27 mm offset, not 37. If Abbott uses 30 mm for 7" rims, then their 'theory' is to add 3 mm of offset to the 27 mm, not reduce. I know what offset means and how to determine it - what I'd really like to hear is peoples' experience with the offset they have with 7" rims. And, for Injecties response, it's greatly appreciated.
 

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Robert,

I'm not trying to belittle your enquiry. I'm simply alluding to the fact that I believe you can find the information you require on the board.

There is a huge amount of discussion that has taken place on the 9000 board about wheel sizes, including a diagram that I posted which very clearly indicates the relationship between offest and width. The Abbott combination of 30mm/7" is correct and agrees with my formula. I have answered your question on the ideal offset for 7" wheels.

I am, however, at a loss to explain the offest you report on your Super Aeros. Mine were 37mm .

Lastly, can I point you to the line in the AUP that says "Be nice to each other"
 

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Mark,

I am surprised by the 37mm offset on your 16" rims. I have run two different styles of the Saab 16" wheel (the grey centred Aeros and the cross spoked BBS style) and both of these had a 27mm offset.

With Saab rims, as the width is increased the offset is changed to keep the inner rim position the same. ie if going from a 5.5" wide rim to 6" one the outer rim moves out the complete 0.5".
 

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Ok we're getting a lot of oppinions here and I'm trying to visualize this.

Ideally you want the wheel to be centered over the axis of movement for the hub. So that when you step on the throttle the wheel is centered and doesn't produce any torque in any direction.

Poorly offset wheels produce strain on the steering componants.

I'm not sure how offset is measured though. I assume it's either

a) distance from axis of hub to mounting point, which would correspond to the distance from the mounting point on the wheel to the center of the wheel ...

or B) the distance from the outer edge of the wheel to the inner mounting point.

If it's (a) it shouldn't matter what the wheel size as the distance from mounting to axis on the hub would be constant, so I guess I can rule that out.

If it's (B) as the wheel size increased the offset would increase as well, rather than decrease, as the larger wheel's outer edge would be further away from the hub axis.

There MUST be something I'm missing, but I can't figure out why the offset would decrease. Could it be they just did that to keep it from rubbing? It *would* position the wheel futher out.

Yours Truly,
Dubbya
 

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Discussion Starter · #11 ·
Sorry Mark, I sometimes say things that are interpreted as being 'not-nice', but I really was puzzled by your 'theory' because I recognize you as being a very knowledgeable saab-o-phile
However, I recall others saying that the offset on the Aeros and Super Aeros were 27 mm. When I read your post, I immediately went out to my garage and removed the rear wheel (I had to check other dimensions for fitment, too) and it definitely was stamped as 27 mm. I think you'll agree that being 27 mm will change your calculation in determining the 'correct' formula for the offset with 7" wheels.

Alex, aren't those BBS cross-spoked 15 x 7"? I'm not sure about the UK, but here in the 'states Saab fitted these on Griffens - they had 20 spokes. If they're 7" rims, then they're using the same offset as the 6.5" .......hmmmm
 

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[edit] Sorry, Robert, I obviously misread your reply

OK, going with the facts first

For geometry purposes i.e. keeping the centre of the tyres in the same position, then it is correct to say that for a positive offset, for every 10mm increase in wheel width, you should reduce the offset by 5mm. Previous diagram below:

At the moment I am unable to locate the source of my long standing info for 37mm being correct for 6.5" rims. A quick check on the Rimstock website however indicates that it is indeed 33mm for 6" and 27mm for 6.5" Following that logic, for 7" it should be 21mm. However, I can say that running 7" with a 25mm offset and 215 tyres, I do have light rubbing on extreme lock on the inner wheel arches. If we extrapolate my results, then going back to a "stock" 205 tyre on 7" rims with 21mm would be the same distance from the inside wheel arch (bar 1mm) and also result in rubbing.

I guess it's therefore a compromise between rubbing on lock/rubbing on max suspension travel/keeping the geometry intact. I for example that ylee runs 235 on his 9000, without any probs on non stock wheels. When I ran 225/50R16 on my 9000 with Super Aeros, I had rubbing problems on the inside...
 

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It would appear from that diagram, Mark E, that it is indeed a compromise.

As for the rubbing, with the 25 mm offset your wheel would be further in, which is why it rubbed on 25, but shouldn't on 21. The greater the offset, the farther towards the fender well the center of the wheel is in relation to the hub. Obviously the hub doesn't change when you change the offset. (Unless of course you use spacers.) Add wider tires and you're realling rubbing. If you have large wheels and a large offset they're poking very far into your fenders indeed.

This might be why *sometimes* installing larger wheels doesn't improve handling. The offset might have to be changed so much that the akward position of the wheel negates the increase in grip area. It would move the center of the wheel well outside the center of the hub. This can also exacerbate torque steer.

Looks like this topic was worthing bringing up again.
It's not quite dead yet.

Cheers,
Dubbya
 

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Discussion Starter · #14 ·
Mark, this begs another question: what about Abbott using 30 mm offset? If your 215/50's rub the fenders with 25 mm, then at 30 mm the stainless moulding studs must be scraping like crazy - I, too, had problems with tires scraping on the studs that hold the moulding to the inner wheel arches, but that was on the CC body. I'm presently running 225/50's, on my CS, and haven't had any rubbing issues, at all - perhaps, this is due to variations in different tire brands. Anyway, this is all rather moot, to me, because I've gone ahead and placed the order for the 16 x 7's w/25 mm offset. Only bad thing is that they're out of stock and it'll take 8 weeks for a new order to come from Japan.
 

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Originally posted by Mark E:
[qb]....For geometry purposes i.e. keeping the centre of the tyres in the same position, then it is correct to say that for a positive offset, for every 10mm increase in wheel width, you should reduce the offset by 5mm.....  [/qb][/b]
Sorry, I don't agree with this. Since the offset is shown in the diagram as the distance between the mounting flange and the centre of the tyre, surely you should keep the offset the same whatever the wheel or tyre size in order to keep the centre of contact in the same place?

The calculation you show for recalculating offset with different width tyres will keep the outside edge of the tyre in the same place relative to the wing/fender.
 

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Robert, in the UK (at least) the 9000 Carlsson was available with a 16x6.5 with a BBS cross spoke style as well as the 3 spoke grey centred wheel.

My c900 is happily running 17x7 with a 35mm offset without rubbing problems. An offset that may cause problems at 15" diameter may not cause the same problem at 17" as the metal diameter has been moved outwards.

And yes, different tyre brands can have considerably different actual widths for the same given profiles. One of the UK 'performance' magazines ran a comparison a while back. For a stated 205 width, actual widths ranged from close to 195 up to 214mm over a range of brands!
 
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