Maximum Offset? 90 535i? ET30 okay? or No?

[Guelphguy]

Ok, I am sure this has been discussed, I just can't find exactly what I am looking for?

I know that 90 535I factory Rim offset I believe is 20MM, I have seen a lot of rims that are 15mm. I have a nice set of rims that I am looking at that the guy claims he had on his 5er and from the back he read ET30, of which I believe is 30mm offset...I thought that 3 series are 35MM + for offset? Would 30mm offset work? Is that better or worse than 20MM....
Any advise would be great...if it matters these rims are 7.5" wide...
Thanks...

[Guelphguy]

Also, see if I undestand this correct...would 30mm move the Rim 10mm more towards the outside of the car or the inside....assuming I think it is in towards the car and the factory rim is a 7" rim, this being 7.5" the net effect is a 8mm movement towards the center of the car? That would not be right...I assume?

[Bellicose Right Winger]

30mm offset moves rim 10mm towards center of the car.

Paul Shovestul

Also, see if I undestand this correct...would 30mm move the Rim 10mm more towards the outside of the car or the inside....assuming I think it is in towards the car and the factory rim is a 7" rim, this being 7.5" the net effect is a 8mm movement towards the center of the car? That would not be right...I assume?

[Guelphguy]

Which I assume that 20MM is the max for the e34? Is 30mm too much?

[Qsilver7]

Which I assume that 20MM is the max for the e34? Is 30mm too much?

...on the e34 with no problem except the e39 5 series which needs hub centric rings. The e39 is the odd ball with a 74.1mm wheel hub...whereas all the other 5/6/7/8 series have a 72.5mm wheel hub. The offsets of these wheels range between 10mm- 26mm. Going beyond 26mm you will need to look at buying wheel spacers. The wheel offset of the 3 series will not fit correctly and wheel spacers would be needed at the offsets they have.

I would suggest to steer clear of wheel offsets that high...but in the end...it's your call.

If you go to the online parts database http://www.realoem.com/bmw ... you can input generic data for a 5/6/7/8 series and click on the WHEEL (maingroup) to get the wheel offset and diameter etc. for the BMW OE wheels for those models.

[zygoteer]

I have read many posts about wheel offsets on here, and people sometimes say ok, sometimes not, but so far, I haven't read anyone really stating clear logical reasons why, only odd hints.

It is my understanding that only two fundamental criteria applies (if I'm wrong. I'm sure someone will correct me on this knowledgeable forum !) ... so not in any particular order ...

1.
The change in ET must not be such that the tyre fouls the suspension/steering gear or the body work.
(not just at the straight ahead/no suspension deflection position, but especially at steering extremes on full bump , which is more critical)
A caveat here may also be national vehicular legality to do with projecting beyond the bodywork, and is why some people add wheel arch flares; which also helps to contain spray when its raining !

2.
The change in ET combined with the usual change in rim width (the real reason to change rims, as the vast majority don't change rims for an identical size on a pure cosmetic level), should put the geometric centre of the tyre tread in the same place or very near to the original.
This would then mean the the steering geometry/handling is largely unchanged, and also avoiding excessive tyre scrub when cornering, as would be the centre of load remaining in the same place or very near the centre of the wheel hub bearings, to avoid excessive wear on the bearings.


Most also change the diameter, and use a lower profile tyre.
This has the advantage of stiffening the wheel/suspension combination for better road-holding ability.
As I see it (again correct if I'm missing something here), this really only gives an advantage on a smooth (track?) surface, not the normal pot-holed public roads where we have to drive around them to avoid risking rim/tyre damage.
The disadvantage is simply that the "spring" effect of the tyre is now smaller, thus resulting in a harsher ride which means you will feel smaller tarmac irregularities more through the steering and the 'seat of your pants' etc.

That said .. big wheels look great !

On a further note, I have noticed that the ratio of rim width to nominal tyre section width can vary enormously in what people say.
I was told many years ago (too many years) by a Lotus engineer that the ratio is about optimum at around 1.15 for track use, but can vary for road vehicles, depending on unsprung weight and ultimate cornering speed, up to 1.3 or even down to 0.95 !

Does anyone have any proper info on this aspect ?

[Dash01]

My '90 535ia has stock 15" basketweaves with 20mm offset. I tried to mount some stock 16" basketweaves from a '95 740il, which have 23mm offset, so there's only a measely ~3mm difference.

Now, the new 23mm offset wheels fit my car, but the bulge in the sidewall of the Michelin Energy tire is too much, so rubs against the front strut/spring perch. No go.

So, I'm now debating whether to try other tires on the 16"/23mm offset basketweaves, or sell the set and start with something else.

Bottom line: reach around your stock wheel/tire and do a careful measurement of the clearance between wheel/tire and strut. Maybe jam some putty in there, to get an exact clearance measurement.

[jplacson]

I'm running 18" with a 15ET. Would 5mm be considered a drastic change?

[Dash01]

I'm running 18" with a 15ET. Would 5mm be considered a drastic change?

Well, unless I'm calculating offset backwards, your 15 mm ET + 5 mm = 23 mm offset, which is exactly what the early E34 came from the factory with. So, unless your tire sidewalls bulge out too much and rub on the spring perchs, you should be good to go.

But, triple-check with with folks more knowledgeable on this topic than I.

[Dash01]

Well, unless I'm calculating offset backwards, your 15 mm ET + 5 mm = 23 mm offset, which is exactly what the early E34 came from the factory with. So, unless your tire sidewalls bulge out too much and rub on the spring perchs, you should be good to go.

But, triple-check with with folks more knowledgeable on this topic than I.

I messed up: MEANT to say 15 mm ET + 5 mm = 20 mm offset, which is exactly what early E34 came with.

Still, it may be the spring perch clearance that makes or breaks a given wheel/tire combination. Triple check.