Plus size wheels on E30 325i

I am looking for wheels for my 89 325i and it seems I can either get 15" (+1) or 17" (+3) wheels. Tire sizes for the 17" are either
205/45/17 or 215/40/17 to remain close to the stock tire circumference. I am leaning towards the 17 but am concerned with the handling and ride changes to the car. Anyone have any experiance with this that could offer advice? Thanks in advance!!!
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15" wheels were standard on the M3 and the iX. 14" on most other RWD E30's.
14" stock size is 195/65/14 15" stock size is 205/55/15. Let's use this as our baseline
On my iX I did a +0, to 225/50/15. -0.1% circumference.
For a 16" wheel you could do: 205/50/16 = +0.8% circumference 215/45/16 = +1.1% circumference 225/45/16 = +0.4% circumference
in a 17" you could do 205/45/17 = +1.6% circumference 215/40/17 = +0.4% circumference 225/40/17 = +0.9% circumference
My "+0" of 225/50/15 gives improved grip and cornering, increased tramlining, stock ride, essentially no speedo error. This would be quite a change already from stock 195/65/14 size tires. I don't give up anything over stock except some tramlining, but I gained handling.
Every time you go up in wheel size, you go down in profile. So, you have a tire with shorter, stiffer sidewalls. This gives improved cornering due to sidewall flex control, and reduced ride quality because vibrations are transmitted with less dampening. As you head down into 45, 40 even 35 aspect ratio, your short sidewalls begin to expose your rims to damage from potholes, and your ride harshness increases.
When you go wider, you improve cornering and braking by changing the shape of the contact patch. Firmly inflated tires will still maintain a good sized contact patch and deform less than tall tires will, so more rubber stays in contact with the road. But the wider they get beyond stock, the more they want to follow the grooves in the road. As you move up in width eventually they will begin to rub the body or suspension, but I have fit 225's in my car with no rubs. You may need to roll your front fenders slightly.
Lastly, as you go down my chart above, you'll find that they line up almost perfectly in this: Farther down costs more. Both for wheels and for tires. Lower profile costs more within the same size also. Hop on tirerack.com, pick a tire type, and look at the prices across the size ranges. Pick out the sizes in the chart above, and compare prices. Do the same for wheels.
Many of the guys in the lists that wear 17" rubber aren't that pleased with it -- these are bimmer guys not ricers, and they don't like bending rims and rattling their kidneys. Also, larger rims weigh more, and unsprung weight is bad for autocrossing, so many of the guys autocross on 15" wheels. The 16" guys are mostly happy with a few grumbles here and there, and the 15" guys all seem happy. The 14" guys are envious of everyone. Except we pretty much all wear 14" tall skinny tires for winter if we have heavy snow to deal with. :-)
So, decide what your priorities are, and what your budget is, and have at it. All the sizes I listed above are truly minor variations on your speedo -- I wore the 205/60/15 for a while on my car that it came with, which are 3.4% too big in circumference, and it was no big deal for speedo error. Only under hard cornering (ie, 2 track days), they would deform enough to rub the shock towers, and they would also rub if I hit a bump at full lock in a parking lot. And they handled like crap, they were all-season. Yuck.
-Russ.
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Between the comments I got here and from talking to a few other people, it sounds like the 15's are the way to go. The car is already riding on Bavarian Autosport springs and Bilstein "sport" shocks and struts which not only lower the car a bit but make the ride a bit stiff. The price of the rims and tires didn't change much with the combo I was looking at in the two sizes but there is a greater choice of tire in the 15. Also, I'd like to have a set of wheels for a long time and not have to worry about being able to replace one a year from now...
Thanks for your comments!
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I run 205/55/15s and am very happy with them. 17s will ruin the ride on an E30 and it'll tramline all over the palce - avoid.
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I got some Alpina 7X16's for my 325 sport. I was so disappointed with 205/50R16's ride I now use 205/55R16. The tyre choice is everything. I used to have Yokohama A539 now using Continental sportcontact. Massive improvement in ride and noise and not much difference in handling.
David
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