Wheel offset
- Thread starter bluecs
- Start date
I'm not one that would be able to tell you if it will fit or not, but those that can will need to know the rim width also and probably what size tires you plan to run. Also useful would be to know if the car is anything other than stock ride height.
Look like 15x7 BBS RZs, they should fit just fine on your coupe
Gotta love a little instant gratification...good for you nosmonkey.
I guess I’ll be the counterpoint on this one. I think the rears will fit if the tires don’t interfere with your exhaust pipe. I think the front tires will rub the strut.
Firstly, you didn’t mention the wheel width but I’ll assume 15x7. An 8” ET20 puts the tire right up on the strut. A 7” wheel is 12mm further from the strut than an 8”, but 10mm more offset, meaning you have 2mm more room that the sometimes problematic 8” ET20.
I can say with confidence that my 16x8 ET23 rub the struts. Your proposed wheels have 10mm less width, and 7mm more offset. At the same time, your wheel lip is 12mm further down an angled strut. You may need a 3mm spacer. Either way, it isn’t the right offset for the car. Factory 7” wheels were ET11.
Firstly, you didn’t mention the wheel width but I’ll assume 15x7. An 8” ET20 puts the tire right up on the strut. A 7” wheel is 12mm further from the strut than an 8”, but 10mm more offset, meaning you have 2mm more room that the sometimes problematic 8” ET20.
I can say with confidence that my 16x8 ET23 rub the struts. Your proposed wheels have 10mm less width, and 7mm more offset. At the same time, your wheel lip is 12mm further down an angled strut. You may need a 3mm spacer. Either way, it isn’t the right offset for the car. Factory 7” wheels were ET11.
The picture is a bit fuzzy, but the rim is 7", stock suspension, and I would put 205 70 14 in front.
Not sure if I should go a bit wider in rear.
Not sure if I should go a bit wider in rear.
I have 15x7 BBS BRZs with 205/65/15 Michelins and stock European ride height up front in that my US spacers are removed. The tires don't rub the struts or hit the fenders if I am careful. Since you have 14 inch, my information may not be helpful. You can seem my wheels in the FAQ wheel thread.
Oops! It would be 205 65 15, not 205 70 14 that I would consider using with such wheels if I go this route.
Here is a pic of my strut vs. tire spacing. I am not sure of my offset but I don’t have any spacers. I didn’t measure it, but the clearance to the strut is over 1/4 inch. I suppose a large bump could compress the tire enough to rub the side of the strut but it hasn’t happened to me.
I love the detail of this answer but I still don't understand it 100%. If someone wants to draw some sort of diagram for me explaining, offset, width, lips etc I would gladly receive it
Simufly
Well-Known Member
Here you go
Timm's BMW Wheels and Tyres Page
Timm's BMW Wheels and Tyres Page explains how tyres and wheels are measured and what is compatible
www.meeknet.co.uk
perfect. Thank you Simon
Here is a site to compare offsets.
tiresize.com
An example on your size
tiresize.com
And here is one to find the correct tire size.
In your case 205/65/15 is too big comapred to the original size. You should use 205/60/15
Wheel Offset Calculator
Use our wheel offset calculator to visualize the new tire position when changing wheel and tire sizes. Convert wheel offset and backspacing to calculate the correct setup for your vehicle.
An example on your size
Wheel Offset Calculator
Use our wheel offset calculator to visualize the new tire position when changing wheel and tire sizes. Convert wheel offset and backspacing to calculate the correct setup for your vehicle.
And here is one to find the correct tire size.
In your case 205/65/15 is too big comapred to the original size. You should use 205/60/15
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I love the detail of this answer but I still don't understand it 100%. If someone wants to draw some sort of diagram for me explaining, offset, width, lips etc I would gladly receive it
Sure! Offset is the delta between the centerline
of the wheel and the mounting surface. So a CSL racecar with super deep wheels will
have a negative offset. An BMW e30 with mo
wheel lip has a positive offset.
Wheel diameter is irrelevant in the calculation,
but does play a role in fitment when you have struts, springs, and other bits in the way. It shouldn’t matter since the overall diameter of a tire stays the same, but in practice there can be clearance issues.
Wheel width is all relative. A 7” ET0 wheel is a perfectly centered wheel. So is an 8” ET0 wheel. So what is the difference? Well, and 8” wheel is 1” wider, or .5” wider on each side
of the center line. That is about 12.7mm.
What this means is that you can take your existing wheel, with a known offset and use
it as a baseline for your fitment.
If you have a 14x6 ET11 wheel, and you want to fit a 15x7 ET30 wheel, you can do the math. First, a 15x7 ET11 wheel would be 12.7mm closer to the strut, because the wheel is 1” wider. But you don’t want an ET11 wheel, you want ET30. So now add 19mm, which is the difference between ET11 and ET30. So 12.7mm + 19mm = 43.7mm.
Now go outside and crawl under your e9. Measure the distance between your whee lip and the strut. Do you have about 1 3/4”
or 43.7mm. If you don’t, your 15x7 ET30 wheels likely won’t fit.
Spacers:
Any narrow wheel (7” or less) with a
high offset will be spacer-friendly. Try the math again. A factory CSL wheel is 14x7 ET11. You know it fits. The 15x7 ET30 wheel is the same width, but 19mm closer to the strut due
to the ET30 offset. That means you can fit a 19mm spacer on the hub before the outer lip is back to a factory 14x7 ET11 distance from
the fender. This calc is easy because
the wheel widths are the same. If the width is different, just add or subtract the extra 12.7mm.
Style 5 came on a lot of cars with quite an ET range. If you have the wheels my point is moot but if you want that style and are looking...
| Series | Model | Except | Size | Use | ET | Kg |
|---|---|---|---|---|---|---|
| 3er E30 | M3 | 6,5x14 | ET 30 | 6,35 | ||
| 3er E30 | M3 | 7x15 | ET 24 | 7,38 | ||
| 3er E30 | 325ix | 6,5x14 | ET 45 | 6,92 | ||
| 3er E30 | 325ix | 7x15 | ET 41 | 7,68 | ||
| 3er E30 | M3 | 7x15 | ET 30 | 7,26 | ||
| 3er E30 | M3 | 7,5x16 | ET 27 | 8,22 | ||
| 3er E36 | Touring, M3 | 7,5x17 | ||||
| 5er E28 | 7x14 | ET 18 | ||||
| 5er E28 | M5 | 7,5x16 | ET 20 | |||
| 5er E34 | 7x15 | ET 20 | ||||
| 5er E34 | 7,5x16 | ET 20 | ||||
| 6er E24 | 7x14 | ET 18 | ||||
| 6er E24 | 7x15 | ET 20 | ||||
| 7er E23 | 7x14 | ET 18 | ||||
| 7er E32 | 7x15 | ET 20 | ||||
| Z1 | 7x15 **** |
@Norm!,
Your pictures help illustrate my point. Compare your wheels to the ones shown by @bluecs. They are apples and oranges, the same size but significantly different offset. I suspect that the ET30 wheels are from an E30M3, and yours are from some 5 series. There are many style 5's, but only a handful have spokes that extend all the way to the wheel lip. As seen on the M3, and the e28 M5, etc.
@Norm! only has about .25" of clearance from the tire to the strut, on a wheel with less offset. Both wheels are 15x7, but the wheels purchased by @bluecs will be quite close to the strut, if not against the strut. So essentially the same wheel, but that "dish" that you see is represented as a lower offset.
If you look at the wheel posted by @bluecs, the spoke ends at the lip with almost no dish:
The wheel on @Norm! 's car has at least .5" of dish.
On the subject - the way that you get that desirable "dish" without a really low (or negative) offset is to have a curved wheel face. This is how you can have 3" lips on an ET20 BBS Style 5. It is a bit of an illusion, but the wheel faces are in no way flat as seen on most Style 5's and BBS RS. The spokes go inward towards the strut increasing the offset to ET20. Then the wheel lip can be larger. So the 17x8 ET20 wheel looks more like an ET0, and that "dish" that people prefer is created.
RC090 (17" 2 piece Style 5) face - not the curvature:
Look at all that "Dish". Thanks @vince:
Your pictures help illustrate my point. Compare your wheels to the ones shown by @bluecs. They are apples and oranges, the same size but significantly different offset. I suspect that the ET30 wheels are from an E30M3, and yours are from some 5 series. There are many style 5's, but only a handful have spokes that extend all the way to the wheel lip. As seen on the M3, and the e28 M5, etc.
@Norm! only has about .25" of clearance from the tire to the strut, on a wheel with less offset. Both wheels are 15x7, but the wheels purchased by @bluecs will be quite close to the strut, if not against the strut. So essentially the same wheel, but that "dish" that you see is represented as a lower offset.
If you look at the wheel posted by @bluecs, the spoke ends at the lip with almost no dish:
The wheel on @Norm! 's car has at least .5" of dish.
On the subject - the way that you get that desirable "dish" without a really low (or negative) offset is to have a curved wheel face. This is how you can have 3" lips on an ET20 BBS Style 5. It is a bit of an illusion, but the wheel faces are in no way flat as seen on most Style 5's and BBS RS. The spokes go inward towards the strut increasing the offset to ET20. Then the wheel lip can be larger. So the 17x8 ET20 wheel looks more like an ET0, and that "dish" that people prefer is created.
RC090 (17" 2 piece Style 5) face - not the curvature:
Look at all that "Dish". Thanks @vince:
As usual your are correct and clear with your explanations. My wheels are actually aftermarket 1993 vintage BBS RZs and not from a BMW. The attached pic shows my wheel info. My rim dish is +- 1 1/8 inch so it is substantially more than the pic bluecs sent.
Ahh yes. Yours are ET18. These wheels are 12mm further from the strut than the wheels @bluecs wants to buy, and (ET30 - ET18 = 12mm). That just happens to be about .5”. You mentioned earlier that you have about .25” (or 6mm) of clearance from the strut. What that tells us is that the ET30 wheels will not clear the struts if indeed the free space is .25”. That would mean that you only have 6mm if clearance, he needs 12mm. A 6-10mm spacer would be required.
With that said, you mentioned: “OVER 1/4”. Looks more like .5”. If the clearance is .5”, it possible the wheels will fit. But again, they aren’t the right wheels for the car and the tire will be right up on the strut.
To add a little more precision to my over 1/4” glance last night, I just measured my 205/65/15 tire clearance and it is 8mm to the strut and the rim is 16 mm.
...then there is BACKSPACING
Offset and ET (einpress tiefe) are the same thing. They are the distance between the mounting surface and the geometric center of the wheel usually expressed in millimetres.
Backspacing is the distance between the wheel’s mounting surface and the outer lip of the wheel usually measured in inches.
Offset and ET (einpress tiefe) are the same thing. They are the distance between the mounting surface and the geometric center of the wheel usually expressed in millimetres.
Backspacing is the distance between the wheel’s mounting surface and the outer lip of the wheel usually measured in inches.