Need expert advice about "offset"

[20ducks]

Here is the picture:

I have 41 offset rims.

My car needs: 18"rims with an offset of 47mm Front & 26mm Rear.

This "offset" business has always befuddled me for whatever reason. So do I read this correctly by saying that for the fronts I can use my existing set up (41 offset) as in in the front, but need a spacer for the rears? If I am correct, what size spacer do I buy?

 

[GP20]

You're correct. You need rear wheel spacers. 15mm would essentially make ET41 into ET26. Personally I wouldn't run more than 15mm anyway to avoid issues with straining hubs, wheels bearings, wheel bolts, etc.

 

[20ducks]

Thanks for the trusted response. I've never had a need for spacers, are they sold (made) in increments of 5mm or ...?

 

[GP20]

There are several common sizes you can find. For Rogue Engineering, this is what they say on their site:

http://www.rogueengineering.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=RE&Product_Code=WSPACER

Sizing
Rogue Engineering manufactures a few popular, most requested sizes. All of our wheel spacers have a hubcentric lip

which helps with the installation of wheels with the spacer in place. For this reason, we do not produce sizes smaller than 10mm. By making spacers to our design, we can produce unique sizes such as 12mm, originally designed for E46 M3s using Brembo big brake kits and OEM 18" wheels.

We produce the following sizes:

10mm
10mm Flat* (2 piece spacer)
12mm
15mm
18mm
All spacers fit BMW 5x120 bolt patterns with 72.5mm hub flanges (not E39, E70). We do not produce any 4x100 patterns (older 3-series BMWs).

 

[davidch]

You're correct. You need rear wheel spacers. 15mm would essentially make ET41 into ET26. Personally I wouldn't run more than 15mm anyway to avoid issues with straining hubs, wheels bearings, wheel bolts, etc.

Spot on

 

[Mr Whippy]

You're correct. You need rear wheel spacers. 15mm would essentially make ET41 into ET26. Personally I wouldn't run more than 15mm anyway to avoid issues with straining hubs, wheels bearings, wheel bolts, etc.

Spot on

I can see why the bolts will be strained a bit if they are just really long (ie, not the bolt on spacer that can use new bolts/new studs), but the hub and wheel bearings?

Shirley if the track width is consistent, the moment arm (torque) on the bearing/hub is the same?

Ie, the spacer is only replacing material that has been removed on the aftermarket wheel originally, giving it a higher offset?


Now, when you add spacers that push out the track width and then add wider wings etc, then I can see problems.

Dave