The 17 and 18 inch tires you are looking at have essentially the same
outside diameter/circumference, so they will fit the fender openings.
The thing that I do not know is the offset or backspacing, which governs
clearances relative to the suspension components on the inside. My worry is
that the shocks that the tire may rub against. I think the M cars get wider
fender openings than the mere-mortal versions of the 3 Series, so the tires
(18") from an E46 should not present any problems on that side of the tire.
Here's the answer to your question ...
If you current rims are 17x8.5, then you should be good with a new rim that
is 18x8.5. Since the overall diameter of both tire sizes is the same, and
you already have the width, then converting the rims should not present you
with any problems whatsoever, ASSUMING the backspacing (offset) are the
same. (Offset and backspacing are functional equivelents for one another.
They are different measurements, but a rim maker wouuld not use both figures
because they ultimately give you the same thing. I forget if BMW uses the
offset number or the backspacing number, but whichever they use, if it is
the same on both rims, then you arte good-to-go.)
Many thanks for that comprehensive reply Jeff. According to
the offset on the standard E36 is the same as the E46 but the M cars are
different. My wheels are ET47 so it seems they are not suitable for an M3.
(E46 M3 is also different from the standard car).
Offset and backspacing are different ways of saying how far the hub section
of the wheel is from the centerline of the wheel, or how far from the back
side of the wheel it is. If the rim was 8 inches wide, and the hub was in
the middle, then the backspacing and offset would be the same at 4". But, if
you took the rim and made it 9 inches wide, but retained the 4" backspacing,
then the offset would change (or vice versa).
I _think_ BMW uses the offset figure, which references the centerline, as a
wider wheel would have a different offset than a narrow wheel, but still
have the same back spacing.
I would suggest you shop on eBay to see if you can find your car's wheels
and the dimensions, then compare the numbers with those from the donor you
are considering. I suspect your M3 will take a set of wheels from an E46
withoug any problem. If your car takes a 17x8.0 on the front and a 17x8.5 on
the rear, then the same widths (8.0 and 8.5) from an E46 should fit your
car. Your issue is not the change from 17 to 18. The issue is the width. If
you get the same width you are already using, then you are in good shape.
Your car might not have staggered (different widths front and rear), but
they offered the E36 M Series cars with stagggered tires, so staggered tires
will fit your car.
I'm not suggest you actually buy anything on eBay, just shop there to search
for the specs you are interested in. I did a quick look on my first reply to
your inquiry, and I think you can easily do what you want to do.
I had a '94 E36 Sedan with the Sports Package. My car came from the factory
with 225/55x15s, and they were very costly to continue using. I found a set
(all 5) of 17" rims from a '95 M3, that were a direct fit to my car. This
car was hit by an old lady with blue hair and a double-knit polyester pants
suit, that pretty well destroyed the car. I bought a '94 E36 convertable
that came with a 205/60x15, and I swapped the tire package on my 4-door to
the convertible. The fitment was the same ... No muss, no fuss.
I think your plan to swap out a set of 17s for a set of 18s will give you
the same experience that I had -- your donor wheels will bolt directly to
your car without any modifications.
Probably you're trying to help but in this case I don't think you are.
*Why* do you think the E46 M3 has wider fenders? Yes, to fit the
wheels in! ..particularly on the rear which has a smaller offset and
bigger tyres. It'd be like putting 5 series wheels on. I dare say it
can be done but there will be problems. Because of this the problem
is not so much rubbign on the inside but on the fenders. It could be
that with the narrower tyres suggested it would work.
Go to m3forum.net and search there. I'm sure there are E36 owners who
want to put E46 M3 wheels on and I'm sure the topic would have been
done to death. In general the answer is to get two sets of fronts.
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