Brett Jenkins

I need to pull my front wheels and have them repaired. I believe one or both are a bit bent and causing my road vibration. So, looking for something to mount temporarily.

Mark Anderson

We have 2 factory 7.5x18 wheels with 50 et

$200 each

Brett Jenkins

I'm not sure how the ET50 will work with my widebody. Since the current 3-piece wheels don't have ET stamped, how do I manually measure the ET?

The Forgotten On

^^ These rims fit under the factory body. I'm sure you wont have problems with a wide body.

Brett Jenkins

I have decided to replace these BBS E28 wheels with something else. I'll have them repaired/refinished and put them up for sale.
I have no idea what the offset is on these wheels. Since the car is a widebody with an extra 2.5" in each corner, I need some advice on how to determine the proper offset to get to make sure the wheels are flush with the fender lips.
The fronts are 18x8, the rears are 18x12. I'm contemplating a more deep dish type of rim for the rears, so I'll need to take that into account when calculating the optimal offset.
Is there a mathematical method to determining this, like measuring from the hub face to the fender lip and then using the rim width to determine the best offset?
I think I could build a rocket ship and fly myself to the moon before I totally understand offsets and such. :-)
Thanks for any and all assistance.

Adamant1971

Start by measuring the current rim width and distance from the inside lip to the hub surface on the inside of the wheel. Draw a template on paper, then measure in mm from the outer lip to the hub on your template, that will give you your ET. When you find possible options simply draw a template in the same way and over lay them. Keep in mind that tire brands can have different tread widths within the same size, they can very up to an inch between brands.

terry gt

Offset (out) and inset (in) is the distance from 0 offset { 0 offset is the rim to hub contact surfaces exactly in the middle of the rim }
for example a 8 inch rim with 0 offset will measure about 4.5 inches outside and 4.5 inches inside {rim lips usually add .5 on each side }
so a 56 mm offset adds that distance to the inside , and subtracts that distance from the outside
so your width of the rim effects the required offset

GregBBRD

Is it just me, or is having the width in inches and the offset in millimeters one of the dumbest things ever?

Rob Edwards

Ask BMW and Ferrari how their all metric TRX tires went over in the market.

Brett Jenkins

I pulled the rear wheel this weekend and measured as best as I could by laying a straight edge on the lip of each side. First of all, the tire width measured 14", as did measuring from outer edge of outside lip to outer edge of inside lip. Taking into account that most wheel lips add .5" to each side as stated above, does that make the actual wheel width 13"?

Measuring from the straight edge to the mating service on the back of the wheel center was 8.5" If the wheels are actually 13", then the difference is 4.5" Does that calculate to 114.3mm offset? If so, then is it safe to assume that my options will be limited to custom 2-piece or 3-piece wheels?

FredR

Brett.,

14 inches equates to 355mm and that should be the size stamped on your rear rubber. The optimal rim sizing for a given tyre section is obtained when the side walls are pretty much parallel to the rim outer edges but any rim has a degree of latitude as to acceptable tyre sizes to mount on it. In your case I would say there is a good chance your rear rims are 13 inch sections. On my rear rims they were sized for a 285 application, with such section fitted the sidewalls look more or less flush with the outer rims. My rear rims are 10 inch items, that is 255mm, add 15mm either side and you get 285 surprise surprise albeit 15mm is a tad bigger than half an inch but as you can see the principle seems to hold true give or take a little.

Your rear wheel offset calculation seems reasonable given the big size of the rims. The fronts are more the problem area for a 928. First of all the thing has to fit and as I am concerned, just as important is the steering geometry. Most folks seem to focus on whether the wheels will fit whereas I believe the focus should be on whether they work. Sticking wide fenders on the front permits more wheel rim size/offset combinations to fit the car but it does not make them work. My front rims are 9.5 inches wide, they are ET68 and they most certainly "work" when carrying a 265 section in a stock fender arrangement. This setup would possibly look silly if my front wings were extended 2 inches. The suspension concept is what is referred to as NSR [negative scrub radius] and this is an inherent characteristic controlled by offset. Reduce the offset and this characteristic of the superb suspension design is killed and that to me is unacceptable but others live with such corruption of the design. If you have front fender extensions and 8 inch rims and they look as though they were designed for the car then logic suggests you must have a very low offset as the stock setup can "fit" an 8 inch rim with a 225 section at ET50 [just]. If you have a similar combo fitted with extended fenders then you may well have a front ET of somewhere in the region of ET25 [that is a SWAG- a scientific wild *** guess]. ET 52 gives a NSR of zero mm on my model year and apparently this is the worst case scenario. In reading into the NSR concept one article I read suggested the steering would be better with a positive scrub radius as would happen with say ET40 but I have no experience of that.

Bottom line - if you are only interested in straight line performance the concept of NSR is probably not too important but if cornering performance is important then NSR is important.

Wheels can be straightened very quickly in the right hands.

Trust the above is helpful.