Maximum offset without fender modification?

[illmatic37]

(searched)
Does anyone know what the max offset can be on the rears? For a 16x8 wheel?

Here's my situation. I have a staggered set of RS's. 16x7 et 11 fronts, 16x8 et11 rears. The 7 has a 2in lip, the 8 has a 2.5 inch lip. Been thinking that since I want to refinish the lips (high polish), maybe I'll put the 8's on the front, and replace the 2in lip on the 7's with a 3in lip.
I did the calculations with a 3in lip and what I came out with was a 16x8 et -1.6 offset. Is this offset too aggressive? I do not want to pull/roll my fenders. My 635 will be on racing dynamics springs and bilsteins when the wheels go on if that makes a difference.

On a semi related side note, when searching, I've come across multiple examples of tire sizes for fellow 6ers running 16in staggered wheels. I noticed that the front tires have a higher "series" as compared to the rears. ie 205/55 fronts and 255/50 rears. I know that the sidewall height (series) is a ratio to the width and diameter of the tire, so the 55 series front tire doesn't have a taller sidewall "height" than the 50 series tire on the rear? (Coming over from the (fwd) Honda camp, we've always ran square setups with front and rear tires the same width and series. I've not encountered this type of setup before. )

[Taylor Marshall]

I know that the sidewall height (series) is a ratio to the width and diameter of the tire, so the 55 series front tire doesn't have a taller sidewall "height" than the 50 series tire on the rear?


I'm not sure if you are asking a question or making a statement of fact here but the answer is 'yes'. The usual goal when running a staggered set up is to ensure that the rolling diameters of the front and rear tires are as identical as possible.

As for your ET question have a read of Rob Anderson's excellent write up and do your sums and I think you'll find the correct answer. Bear in mind too that an ET by definition is a negative number so I'm not sure if you mean by ' et -1.6 offset' that there is a positive offset or a negative one and I'm too lazy to replicate your calculation :)

QUOTE

Wheels and Tires

Offset and how it relates to fitment
If you measured the width of the wheel, for example an 8 inch wheel. You then find the mid-point of that which would be 4 inches from the edge. The hub on the wheel, where the wheel bolts to the car, is 4 inches from both edges of the wheel you have a 0 offset. This means that you have 4 inches off of the hub, or towards the outside of the car, and 4 inches inside the hub, or towards the inside of the car.
If we look at American cars for a second, as the offset number increases, the further off the hub the wheel sits, on an AMERICAN CAR. BMWs are the opposite. We have what is considered to be negative offset. This is because as you increase the offset number value on a BMW, the further inside the hub the wheel sits. That is why our offset is measured in ET. That takes into account the negative.
Now for an example. We will use my Hartge wheels. In the rear I run 16x8.5 wheels. The offset is ET25. This means that the wheel sits 25mm further inside the hub than an offset of ET0. So, that means that instead of having 4.25 inches on either side of the hub, I have approx. 5.25 inches inside the hub and 3.25 outside the hub. Now on the front I run 16x7.5 wheels. The offset is ET15. This means that the wheels sits 15mm further insider the hub than an offset of ET0. So, instead of having 3.75 inches on either side of the wheel, I have approx. 4.25 inches inside the hub and 3.25 outside the hub. Now you ask how does this effect the fitment on the car.
Well on a BMW there is generally more room on the inside of the hub than on the outside. The fender well is a finite width, unless you modify it, and the hub sits a specific distance from the outside of the fender well and the inside. The higher offset number you have, the further towards the center of the car the wheel sits, so therefore the less chance of having the tire rub on the outside fender. But for example I tried putting my 16x8.5 wheels on the front of my car. The problem I found was that I cannot bolt the wheel to the hub because the strut tube hits the inside of the tire. So on the front there is only so much distance between the hub and the strut tube. This is what generally governs front offset. In the rear though, the clearance on the fender is what governs offset. Depending on the width of the wheel and the offset, you may or may not have to use a spacer. What a spacer does is change the offset number to what you want. So if I had a wheel with an ET35 I could use a 10mm spacer to get the wheel back to an ET25. But if you get a wheel with too low an ET number than you may have to mill the hub of the wheel down to get the correct offset.
Written by Rob Anderson '00

Will I Have to Roll My Fender Lips?
OK you say you have ET11, so your wheels stick pretty far off the hubs huh? Do you have a picture of the car with those wheels on it? Here is what I say, what tires are you running now? BMW used a 16x7 with an ET of 20, so you should have nothing to worry about with getting the 225s to clear the strut tubes. But you might have to severely roll the fender lips front and rear. ET11 means that the wheels are sitting quite a ways off the hubs. For example I am running 8.5s in the rear with an offset of ET25. They required rolling when I lowered the car. Therefore we will do some math.
I currently have 8.5s with an ET25 that means that my wheels are 215.9mm wide. Now to find the center line, or ET0 I divide by 2. 107.95 Now if I have an ET25 that means that the wheel sits 25mm further in towards the center of the car therefore making it so that I have 82.95mm from the hub to the outside of the rim. And I have 132.95 from the hub to the inside of the wheel. Since I had to roll my fender lips with the 8.5s we will do the math for your wheels and see if they will fit.
You say you have 7s with an offset of ET11. Now your wheel is 177.8mm wide. Therefore we divide by 2 to find ET0. 88.9mm Now you say you have ET11 so that means that you will have 99.9mm inside the hub, towards the center of the car. And you will have 77.9mm outside the hub. Ok so your wheel is actually further away from the fender lip than mine.
Now we will figure out if you can fit the 225s in the rear. I run 245s, which are exactly 29.1mm wider than my wheels. This means that they stick out on either side of my wheels by that much. So we divide by 2. 14.55 This is how much my rear tire sticks off of my rim on the outside. So if you measure the distance from the hub to the edge of my tire you will find that it is 97.5mm. Now with that width I had to roll the fender lips.
This is what you will have. Your 225s will stick 47.2mm outside of your wheels. Therefore on the outside they will stick out 23.6mm. So your distance from the hub to the outside of the tire is 101.5mm. Therefore you will have to roll your fender lips more than I have to. What this means is that your rear tires will sit 4mm further towards the outside of the car than mine. This may not seem a lot, but it will require some serious fender lip modification, especially on a lowered car. As for the fronts we will use my front Hartge's to compare to.
I have 7.5s on the front of my car with an ET15. This means that I have 110.25mm inside the front hubs and 80.25mm outside the front hubs. Now you are using the same wheels front and rear so I will copy and paste the previous calculations.
You say you have 7s with an offset of ET11. Now your wheel is 177.8mm wide. Therefore we divide by 2 to find ET0. 88.9mm Now you say you have ET11 so that means that you will have 99.9mm inside the hub, towards the center of the car. And you will have 77.9mm outside the hub. Ok once again your wheel is actually further away from the fender lip than mine.
Now we do the tire calculation again and we find that I run 225s on the front of my car. So the tire sticks off the rim a total of 34.5mm So the measurement from the hub to the outside of the tire is 97.5mm. Now I have not had to modify anything on the front of my car but I am also running 1.25 degrees of negative camber.
As per the previous calculations, you would have a distance from the hub to the outside of the tire of 101.5mm. Therefore again your wheels will sit further off the hubs and would require more rolling or may require rolling in the front. As for strut tube clearance, you are fine, but when you start talking about clearing the body panels, I don't think it will be very easy.
Written by Rob Anderson '00

[illmatic37]

Thanks Taylor. I pretty sure that if I relip the wheels I won't have enough clearance under the fender, esp. If I take the tire into account.

[ISavant01]

wow. wish i had found the "Wheel Information" article before i did my own research. luckily, i was correct in my final determination for my '89 E24. it took me a bit of research. but i ended up with one of the solutions listed in the article: 36112225518 Style S from E28 or E34 M5; 7 1/2 x 16 and 225/50-16 tyres.

one question about the info in the article about spacers. i had some front-end shaking going on during one of my 15" wheel experiments. does the admonition to "ALWAYS buy hub-centric spacers" apply in my case? my '89 has "only" 333,333 miles on it and i want it to last even longer. do i need spacers?

[RSheiman]

Hubcentric are a must. Cheapest thing you will buy for the car.

[e24mpwr]

wow. wish i had found the "Wheel Information" article before i did my own research. luckily, i was correct in my final determination for my '89 E24. it took me a bit of research. but i ended up with one of the solutions listed in the article: 36112225518 Style S from E28 or E34 M5; 7 1/2 x 16 and 225/50-16 tyres.

one question about the info in the article about spacers. i had some front-end shaking going on during one of my 15" wheel experiments. does the admonition to "ALWAYS buy hub-centric spacers" apply in my case? my '89 has "only" 333,333 miles on it and i want it to last even longer. do i need spacers?
I really appreciate you updating the old thread - makes it much easier for future searchers!



Hubcentric are a must. Cheapest thing you will buy for the car.

Several kinds of truth here.