Factory wheel offset

[Mbin903]

I have a 2011 35is with the factory 19” wheels. I have been thinking about getting something new. I want the same width and diameter. I like how mine fit in the wheel well and want to stay with the same thing.
I have looked all over the internet to try and find the offset and can’t find it. Does anyone know what it is?

[B21]

29mm and 42mm

https://www.wheel-size.com/size/bmw/z4/2009/

[Mbin903]

It’s almost impossible to find an aftermarket wheel with this offset

[Mbin903]

I found something close….
30mm front, 35mm rear. Will 5 mm make that much of a difference?

Also what’s the width of the factory 19”? Is it 8.5 and 9.5?

[ray7792]

Factory width is 8 and 9.
19x8 +29
19x9 +40

If you want same fitment as OEM then front 19x8.5 +35 and rear 19x9.5 +45 will give you basically same fitment as stock within like 1 or 2mm. Those sizes should be a lot more common.

If you want it to be more flush without rubbing...I believe a 19x8.5 +35 with a 12mm spacer in the front, and 19x9.5 +35 in the rear would fit very well. This will push out your wheels by +11mm and +10mm front and rear respectively so wheels will be closer to being flush with the fender without rubbing. Those sizes are very common as well.

[Mbin903]

Ray….
Thank you so much for that information.
I have seen a lot of talk in various places online of using the spacers. It sounds like a lot of guys run them. Are they safe to use?

[ray7792]

As long as you use hub-centric spacers, they're going to be fine 99.99999% of the time.
Hub-centric just means that it has a little lip sticking out for the center of the wheel to fit into.

Spacers that are too small, like less than 7mm, usually are not hub-centric as there isn't enough material for the wheel to sit on but for the most part any spacer larger than that will be fine.

One potential negative is that if you use a spacer that is too large, like larger than 20mm...it puts more stress onto your wheel bearing which can cause premature wear.

You'd also want to get longer lug bolts if using spacers as the OEM bolts wouldn't be long enough depending on the width of the spacer. But for the most part any good spacer you purchase will come with longer bolts to be used with it.

I've used 12mm spacers for years on my z4, never had any issue nor have I ever known anyone to have had issues with spacers with any car...as long as you don't use moronically large spacers, they are perfectly safe.

[Mbin903]

If I decide to go with wheels that are 1/2” wider than stock, won’t I need to go to a slightly wider tire for it to look right? So the tire doesn’t look like it’s being stretched

[ray7792]

It'll be fine, the stock tires are front 225mm and rear 255mm

A 8.5" wheel can take tires sizing from 225 to 255 without issue.
A 9.5" wheel range is 245 to 275.

I do recommend ditching the stock tires though cause they suck and you might as well size up to 235 and 265 front and rear respectively.

But either way, the actual appearance of them is nearly impossible to differentiate it's not being stretched by any means.

[Mbin903]

Yes I’m definitely getting rid of the RF. I’ve heard a regular tire does make a difference in the ride

[B21]

BMWs 437Ms which are 9j and 10j as the factory offsets ..need to be mated with 235/245 fronts and 275 rears…tried those…

I’m currently running Apex Arc-8 with 8.5j and 9.5j with 245 / 275 rear ..minor offset differences..

Tried various other sizes in 17/18/19 with various tyre combos..

Lots of options but as others have said any other tyre apart from the OE runflats is a good move

[Mbin903]

Ray
I have been looking at different wheels and think I found some. I was going to ask because I’m curious, how does that work out math wise with the size you suggested and with the spacers? I’m not understanding how you came to that.
And my stock wheels are 8” and 9”? For some reason I thought the 35is 19’s were 8.5 and 9.5, but honestly I don’t know.
Thank you again so much for all your help

[ray7792]

Yes, assuming you have the stock 35is wheel, the style 326, they are 8" and 9". Every 19" wheel for the e89 z4 has the same width and offset.

https://www.bmwoemwheels.com/en/rim-...heel-style-326

Front 19x8 offset +29
Rear 19x9 offset +40

Keep in mind that the lower the offset, the more the wheel is pushed outwards towards the fender. A higher offset means the wheel goes towards in towards the car more.
Example if you have a 19x8 +24 wheel, that will push the wheel outwards towards the fenders by 5mm compared to the stock 19x8 +29.


For example if you change your front wheel to a 19x8.5 offset +29 (same as stock offset) you will see the wheel go outward by roughly 6mm compared to where your front wheels seat right now.

You get to 6mm because the wheel width increases by 0.5" which about equals 12mm, divide that by 2 and you get 6mm.
Now if you get a wheel that is 19x8.5 offset +35, because the offset is higher by +6mm (+35 vs +29), it'll push the wheel inside more thus cancelling out the 6mm you got from the change in width

By adding a 12mm spacer that is the same thing basically as decreasing offset by -12mm. Which means Wheel will go outwards by 12mm.


For the rear you don't need a spacer if you get a wheel that is 19x9.5 +35:

OEM rear: 19x9 +40
New rear 19x9.5 +35
Difference in width 9-9.5 = -0.5" which is -12mm. -12mm / 2 = -6mm
Difference in offset 40-35 = -5mm
Total change in offset is roughly -6mm - 5mm = -11mm. Which means wheel will go outwards by 11mm.


I'm not using exact measurements here but it'll be pretty damn close.
The dividing by 2 to get the change in width is an estimate, if you wanted it to be exact you'd need to measure the center of the wheel barrel for stock and new wheel.

Post below does a pretty good job explaining, better than I can.

https://blog.edgeautosport.com/tire-...tting%20before.


Now you do need to worry about whether the wheels will hit the brake calipers but it will very extremely likely be fine as the brakes on these cars aren't that large and you have a lot of clearance.

[Mbin903]

Ray
Thank you so much for the informative and in depth reply.