Changing my offset?

[Topher91]

The problem with my wheels is that they are 20mm offset, which doesn't sit too well on a non-M E36. The problem is that I love my wheels and I do not want to sell them.

Could I ask a machine shop to shave a CM from the rear hub where it mounts so that I could have the wheels tuck in a little more? Right now they stick out more than i'd like, and I want a little bit off.

I think I have enough space to safely do this. I'd have the machine shop measure and check also, just to make sure that I don't sacrifice the integrity of the ride. But my question to you guys is:

Have you ever heard of anyone doing this? Is there anything i'm not seeing that you can point out to me?

PLEASE don't ask me to sell them and buy new. I already know that this is one of my options, but it's a huge hassle and i'd rather just keep these ones.

[carcrazed4life]

A machine shop will do anything for you, but I wouldn't trust my life on it. even 5mm off the back of the hub, can weaken its mouting point by upto 25%... Imagine the 15 you need to get back upto 35ish. Good luck.

[Daved]

Take them to a machine shop. You can also try with a *big* wheel shop that may know a little more about this.

[luv4myE36]

i was just about to ask the same thing. how bout 5mm to go from 35 offset to 40 that shouldnt be as bad rite?

[Ty Vil]

why do you need to increase it that little? How wide are your wheels.

[EEEEeeee36]

The problem with my wheels is that they are 20mm offset, which doesn't sit too well on a non-M E36. The problem is that I love my wheels and I do not want to sell them.

Could I ask a machine shop to shave a CM from the rear hub where it mounts so that I could have the wheels tuck in a little more? Right now they stick out more than i'd like, and I want a little bit off.

I think I have enough space to safely do this. I'd have the machine shop measure and check also, just to make sure that I don't sacrifice the integrity of the ride. But my question to you guys is:

Have you ever heard of anyone doing this? Is there anything i'm not seeing that you can point out to me?

PLEASE don't ask me to sell them and buy new. I already know that this is one of my options, but it's a huge hassle and i'd rather just keep these ones.
People need to know the size of your wheels before they can even begin to help you...

[Topher91]

The wheels are 17", the tires are 225/45/17

[EEEEeeee36]

The wheels are 17", the tires are 225/45/17
So your wheels are 17" in diameter, and infinitely wide or infinitely thin?

Your whole question is about offset and you didn't even state the width of your wheel.

[Topher91]

Troll much?

My question is about grinding the inner hub to change offset. It has nothing to do with the diameter or width of my wheel. These cannot be changed. Thanks for your "help".

[EEEEeeee36]

Troll much?

My question is about grinding the inner hub to change offset. It has nothing to do with the diameter or width of my wheel. These cannot be changed. Thanks for your "help".
Let's start again, shall we.

You choose a wheel that doesn't fit your car. You asked if you could grind the hub to make it fit...not a common fix, but do-able. So, you want to know how much you have to grind in order to make it fit...

In order to know how much you need to grind (how much back-spacing you need to create), you need to know how much it sticks out too far...

In order to know how much it sticks out too far, you need to know the wheels width..

Oh, wait...so the diameter and width of the wheel ARE important? Next time you ask a question and you don't know how to provide the information needed, don't flip out when people ask for it. I asked for your wheels specs so that I could tell you how much additional back-spacing you would need and you didn't even give all of the wheels specs. You still haven't. Look at the post before mine:


why do you need to increase it that little? How wide are your wheels.

Oh...so someone ELSE asked why you need to shave so little, and how wide your wheels are?

I guess we just don't know what we're talking about. :dunno

Thanks for playing.

[Topher91]

Fair enough, my apologies. The wheels are 17x7.5, 20mm offset.

[EEEEeeee36]

Fair enough, my apologies. The wheels are 17x7.5, 20mm offset.
Okay, you obviously won't have problems hitting the strut with such a low offset. The easiest way to remember how much room you have is by thinking about your backspacing. You also don't want to remove too much material.

That being said, the biggest wheels that will typically fit under a standard E36 is 9" with about a 42mm-45mm offset. A friend of mine just mounted 18x9 with ET 38mm on her E36 328iC and she is having to roll the fenders. Working backwards and knowing that there is 25.4mm/inch we can see how much material you need to remove to not rub. So, from 9" to 7.5" you have 1.5" difference, but that is distributed between each side, so you actually have .75" less width on the fender side. Follow? That is approximately 19mm (.75*25.4). That means you would be fine with 7.5" rims on an offset of ET26 (we'll take worst case ET45 - 19mm). So, really it looks like you only need to shave about 4-6mm for those to work within your fender wells.

What I would recommend is actually trying to mount them. See where they line up. Maybe you could get away with a fender lip roll. Quite honestly I would rather roll my fenders than have my wheels machined; like carcrazed4life mentioned you don't want to weaken the point at which the most stress is going to be put on the wheels.

Have you test mounted them yet?

[metale]

I agree with the answer being you to roll the fenders.

[luv4myE36]

why do you need to increase it that little? How wide are your wheels.

if that was for me... the rears are 18x9 et35. im going to roll the fenders but if my wheels were in just a little bit more i think they would fit perfectly

[Jim@tirerack]

I would not recommend to shave off the hub of the wheel. You will lighten the load capacity of the wheel and the structural integrity as well. Even if you like the wheel I would not say it is worth your life, Go for the wide body on the fenders if you want to keep the wheels.

[EEEEeeee36]

I would not recommend to shave off the hub of the wheel. You will lighten the load capacity of the wheel and the structural integrity as well. Even if you like the wheel I would not say it is worth your life, Go for the wide body on the fenders if you want to keep the wheels.
Jim I don't even think he would need to do that... if he's only running 7.5" rims then all he should need to do is a fender roll, and a light fender roll at that. :dunno. They might even fit fine with no roll on the rears...

[Jim@tirerack]

Actually you are correct. I just looked at the size and offset wrong. But you will need to stay real narrow on the tire. The 20mm offset does stick out toward the fender about 1" more than a 40mm offset.

[Topher91]

Im not sure I follow. If the 20mm offset sticks out towards the fender about an inch more than a 40mm offset, how will a small 7mm shave help?

[EEEEeeee36]

Im not sure I follow. If the 20mm offset sticks out towards the fender about an inch more than a 40mm offset, how will a small 7mm shave help?
Like mentioned before, you shouldn't be thinking about shaving. You should be thinking about rolling your fenders.

You have about an inch of play with 7.5" rims to begin with.

Let's start from stock size instead of aftermarket so I can better illustrate it.

Stock size is 15x7, ET47 (in fact here is a link so you can verify: http://realoem.com/bmw/showparts.do?model=CD43&mospid=47501&btnr=36_0208&hg=36&fg=15)

With those rims you have about 1.25" of play WITH a fender roll. 1.25" is 33mm.

Going from 7" to 7.5" you are adding only .25" to the outside/fender side of the rim (remember whenever you add width it gets added to both the inside and the outside). .25" is about 6mm. That leaves about 27mm of room left (38mm of play -6mm of increased width).

The difference between your offset and stock offset is 27mm (ET47 - ET20). If you take the difference in offset and you subtract it from the amount of space you have left you get ....0. 27mm left - 27mm less backspacing. So from that you can determine that all you need to do is roll your fenders a little and they should fit. These numbers are based off of your front fender too... your back fender has more room and probably doesn't need a roll at all.

Okay, enough talking now. Jack up the car tomorrow and test fit one of the wheels on the rear. :thumbup:

[ozbmw]

I think everyone here is forgetting one important thing: The Offset is not an imaginary number just to get the wheel under the fenders. Using a +20 wheel on a car designed for a +41 to +47 fitment will change the leverage the wheel places on the hub, the wheelbearings will also have abnormal loads placed on them. The car will tramline excessively.

These parameteres were set by engineers at BMW for a reason. The fact is that the E36 should not be fitted with +20 offset wheels. The wheels mounting faces should not be machined. Insurance companies would not cover the owner if his wheels were found to have been machined as described. Bite the bullet and get the correct wheels for your car.

[EEEEeeee36]

I think everyone here is forgetting one important thing: The Offset is not an imaginary number just to get the wheel under the fenders. Using a +20 wheel on a car designed for a +41 to +47 fitment will change the leverage the wheel places on the hub, the wheelbearings will also have abnormal loads placed on them. The car will tramline excessively.

These parameteres were set by engineers at BMW for a reason. The fact is that the E36 should not be fitted with +20 offset wheels. The wheels mounting faces should not be machined. Insurance companies would not cover the owner if his wheels were found to have been machined as described. Bite the bullet and get the correct wheels for your car.
Correct; tramlining of course is a whole other issue, but rightly addressed. It is arguable that if the wheel is wide enough that an offset that low would be adequate.. but you are right that with a wheel width that narrow there would be load carried more towards the edge of the hub.

Do you think that only an inch less of backspacing will really effect the wheel bearings that much? I mean the majority of the wheel is still behind the hub; it's not like he's going from almost 2" of positive offset to a negative offset.

[ozbmw]

As a rough guide, take the percentage change in position on the wheel in relation to the hub and use that percentage as the amount of extra wear and tear on the bearings. It won't wear out rapidly but it will not last as long as it should. The costs, in money outlaid, changes to handling and longevity aren't worth modifying these wheels.