Wheel offset

[DutchWestfield]

Hi,

I know Wheel offsets have been discussed many times before, but I am really puzzeled now, so time for a question.

I have been advised (by the Dutch Westfield representative) to use an offset ET20. I have been searching for offset ET20 wheels for a few weeks now, and concluded that these are hard to find.

To assure myself that I get things right i mounted the cycle wings this afternoon. The cyclewings are 250 mm wide. I hang a piece of string from the outer edge of the cycle wing. Then I measured the distance from the string to the face of the hub. This distance is 90 mm (car is level on axle stands, and on a level floor).

I think I can calculate the required ET value by doing this:

ET value = (250 / 2) - 90

250 / 2 gives me the centerline of the rim, substract 90 and you have the ET value.

Am I doing something wrong here, or do I indeed need an ET of 35 mm ?

Oh, car is a SEiW, delivered november last year....

Many thanks,

Bertram Bakker

http://www.planet.nl/~bertram.bakker

[Nick M]

Firstly, what width of wheel did he quote that offset figure for ?  And what size wheel are you wanting to fit ?

I think your measurement assumes the cycle wing sits with it's centre-line directly over the hub mounting face.  And I'm pretty sure it won't be.  And you're also assuming the cycle wing is as wide as the wheel, which I also doubt is the case.  

Basically, and not to put too fine a point on it, I don't think you can work out the offset from measuring from the outside edge of the cycle wings.  What if the distance from the inside edge of the wing to the hub face is different ??  Incidentally, you also need to check the rear wheel clearance too.

For a 6" wheel the width in mm (assuming I've picked the right conversion figure of 1" = 25.4mm) would be 152mm.  For a 7" wheel it would go up to 178mm (with a bit of rounding).

So the centre line of the 6" wheel would be only 76mm from the rim.  You also have to factor in the width of the tyre - probably a minimum of 15mm I would guess - when looking at clearance issues.

There should be plenty of wheels around with 19mm offsets (Peugeots and Citroens) but the centre bore is bigger than it is for Ford wheels (which is what the hubs are designed to take).  You may, therefore, need fit spigot rings.  There's a load of stuff relating to *this* side of things in the archives

[DutchWestfield]

Nick,

Thanks for your reply. I have been thinking about the offset a lot, and came to the conclusion that the width of the wheel doesn't matter for the offset (which does not mean that this is true   )

I want the front wheels to sit in the center of the cycle wing, and the offset value is measured from the center of the rim (right ??)

So what I want is that the center of the wing and the center of the wheel are in the same position. The offset value is the distance from the center of the wheel to the mounting face of the wheel.

Maybe a little drawing makes it clear ??

Does this make sense ? Or is it complete  

P.S. I understand that the cycle wing does not sit centrally over the mounting face of the hub, and hope that the wheel is less wide than the cycle wing. The ET20 I was quoted is for a 7 inch wide wheel, but as stated above, i think it doesn't matter. Noticed the difference in hub hole (63.7 vs 65) too, could be adapted by a ring indeed...

Many thanks,

Bertram

[ACW]

something in ET17 or ET19 should be fine with your car and 7 inch rims.

As said b4 you probably dont want the wheel centre of the front cycle wing, work instead from the outer edge of the cycle wing + a safe margin. Most cars will have more of a gap between wheel and wing on the inside edge rather than the outside edge and IMO this looks best.

Beware that with many manufacturers, larger width wheels will likely not be availiable direcly with this ofset and may only achieve this ofset with an included spacer. This is typically the case for wheels above 6.5 inch width. you may or may not be happy with the engineering of a wheel spacer, but obviously this would also require longer studs etc...

HTH,

ACW.

[neilwillis]

I beg to differ here, my 7" wheels, as advised by the factory are ET35 offsets.   They fit precisely in the cycle wings at the front, but need spacing out just a tad - perhaps 20mm under the rear arches.

I think you will find I have the same kit as you Dutch

I'd phone the factory, and ask them what you should have.

Neil

[markg]

i rang the factory twice, and then asked again at the parts counter and they would not give me a definative answer, the guy who ran the firm i bought the wheels from said that et15 would be best, this is a 2002 seiw v8 and they fit perfectly, without the need for spacers.

[Nick M]

Hi Bertram,

I think you need to reappraise why relatively specific offsets are quoted.

Offset is not just a cosmetic or clearance issue, it's handling one too, particularly with the front wheels as the offset describes the arc through which the front wheels move.  Different offsets can alter the way the steering feels, especially when you start using low offsets or even insets.

Offset also has a bearing on the leverage and loads placed on suspension components.  Smaller offsets mean more leverage for the wheel and potentially more stress on things like stub axles and wheel bearings.

So, as you can see, the width of the wheel and the offset are pretty much inexorably tied.  A 20mm offset with a 7" wheel will give you a whole different story to a 20mm offset with a 6" wheel.

Hopefully that's given you a little more food for thought.  I can see what you're trying to achieve, I just thought you ought to be aware of the other implications of playing around with offsets  

[ACW]

ooppps sorry big questions first, I just made some assumptions:

Kit age/type ?

Fixed or detachable rear arches ?

Normal or wide arches ?

My ET17 assumptions assumed:

newish SEiW, detach arches in normal width. if you have fixed rear arches then I think you would need more like ET30 ofset.

[DutchWestfield]

Hi,

First of all, everybody thanks for your help on this already enlessly discussed subject so far. The stuff you told me did learn me a lot though...

Nick:

So, as you can see, the width of the wheel and the offset are pretty much inexorably tied.  A 20mm offset with a 7" wheel will give you a whole different story to a 20mm offset with a 6" wheel.

I agree, but do you agree that the increase in width will be equal on both sides of the wheel is the offset is the same ??

Adrain:

Kit age/type ?

Fixed or detachable rear arches ?

Normal or wide arches ?

Kit age: delivered november 2002

Kit type: SEiW

Detachable arches in standard width

Very good assumptions I would say    

My conclusion: ET35 will sit centrally in the cycle wings. This might not be the best position; clearance of the cycle wing mounting bracket, and road holding characteristics might be better with the advised ET20. I'll speak to the Dutch Westfield representative again ...  

Thanks again,

Bertram

http://www.planet.nl/~bertram.bakker

[Buzz Billsberry]

I suppose the easy way is just to use the information on the Image Wheels site www.imagewheels.co.uk or www.image-wheels.com  or even look in their mag....  just a thought

Buzz

[Guest]

My 2 pence : I was at the factory about 2 weeks ago and discussing wheels and was told that for 15x7" I needed ET35 offset, front & rear (though the front wasn't so important since I haven't fitted the cycle wings yet).

- Dan.