Ewrek

Haha...I know huh. How much you pay for you carbon fiber Hartge Lip?

NavarroOne

Some of you will want to snap at me but please forgive that I'm a bit of a wheel novice! I'm trying to cement my understanding of wheel offset and I'd appreciate your comments as to whether I got this summary right?

If the mounting plate of the wheel to the axle is dead centre of the width of the rim, then there is no offset. If however the mounting plate is closer to the outside edge of the wheel then the offset is positive; vice versa.

A positive offset will give a more narrow track width.

Conversely, a negative offset will give a wider track width.



In Germany, offset is called "einpresstiefe" and is abbreviated ET. It is typically given as a positive number (in millimeters) and thus listed as e.g. ET18

If your car is intended for a certain range of ET, say 18-20 like my E61 wagon, then it is wise to stay in that range, else you may experience scrubbing of the tyres against shocks, fender arch or inside fender wall. In Germany it isn?t road legal to choose a different size from that which the vehicle is pre-approved with, unless you obtain individual permits for your particular vehicle through TUV.

By adding a spacer to your axle, you may eliminate the effect of too large an offset. i.e. if you have a wheel with an offset of 35 and you have a spacer of 15mm then your wheel will fit just like a wheel with an ET20. Since the spacer is attached to the axle using the wheel bolts, you will need correspondingly longer wheel bolts, i.e. your regular set of wheel bolts will not fit but will need to be 15mm longer. Viz TUV you would still need approval regardless of the spacer ring. If on the other hand you have a wheel with a negative offset, there is no way to mitigate the effect.

All of the above pre-supposes that you use a wheel of the same width, say 8.5" which is the max width for my wagon. If you choose a 9.5" wide wheel, using a 15mm spacer may not alleviate the problem and you may still experience scrubbing. I don't actually know whether a 9.5" will fit on my wagon with sports suspension and if so, what the ET should be, but that's a seperate issue.

Anzafin

CORRECT.

NavarroOne

Thanks, appreciated. Found this German illustration which is quite good I think. It clearly shows how wheels with a negative offset stick out and how the regular (positive) offset places the wheel deeper inside the wheel opening.

NavarroOne

My E61 can handle ET from 18 to 20. I learned on velocitymotorcars.com that I can buy 5, 10, or 12mm spacers for my car only. (not 3 or 15 or 18). I calculate that I can fit wheels with ET 18-20, 23-25, 28-32 which opens up the range of wheels a bit.

I also found a nice illustration of how a spacer works:



This particular spacer has a very nice feature; a retainer screw as illustrated by item 3. Without it, it is hard to fit the loose spacer just right when you fit the wheel.

As to extended bolts, I learned that the wheel bolts must engage the wheel hub by 12mm or 8 full complete turns. In the case of a spacer of 5mm, the bolts must be 30mm (no more, no less) and for spacers of 10 or 12mm, they must be 37mm long.

I realize this is written to the lowest denominator but when you are unfamiliar with a subject and in my case are buying expensive used wheels via the internet 1.000 km away without seeing them up front; then sourcing an accessory elsewhere you've never used before and expecting it all to come together you get a little wary of putting a foot wrong so I'm S P E L L I N G it out. I'm hoping a kind soul will point out if there is anything in my summation that is incorrect.

NavarroOne

Oh, and for anyone in GERMANY, is a car street legal if it is certified for ET18-20 and gets a set of ET30 wheels installed with a 10mm spacer? Or will it require that the car is individually approved by TUV? (Einzelabnahme vom TÜV)?