[stevehecht]

This is for a 328d Sportline with DHP. I'll be getting some aftermarket wheels that are 19x8.5 with an offset of 30. I will be going four-square. Going by the magic <3% rule of diameter variance being "OK" compared with OEM size 225/40r19, if I want to upgrade my tire size I can go with either:

1) 245/35-r19--diameter variance = -1.28%

2) 245/40-r19--diameter variance = 2.41%

3) 255/40-r19--diameter variance = -0.23%

Using http://www.rimsntires.com/specs.jsp calculations, my only fitment challenge might be with the lateral extension of the wheel. In the front it is between 0.6-0.8" closer to the fender depending on the tire chosen. Will this be a problem with sharp turns and/or a drop of ~0.5"? In the rear the increased lateral extension toward the fender is 0.5" (OK by rim 'n tire) to 0.7". Is that acceptable? I would think it would look better.

I have a feeling the 255s will be bit much for the car at four-square, and even though the variance of the 245/40s is nearer the diameter limit, I like the fact that the sidewall height is .5" taller than the 235/35s thereby offering more protection to my expensive wheels. Also, the 245/40s will fill out the wheel well by an additonal 8mm in the front and 9mm in the rear.

(BTW, the reason I don't want to do a staggered set-up is increased tendency to understeer and no ability for tire rotation = increased cost.)

So right now I'm leaning to the 245/40s. Does that make sense? Opinions?

FYI, here is a pic of the wheel. Kelleners Sport Hamburg Titanium Grey

[shivaswrath]

Cool site!

I have 255's out back....outside of a decrease in mpg, it's been nice to handle on the track, very predictable.

With that said many have gone staggered 245's all around with little issue; my personally i would just slap on some 275's back there!

[.BMW.]

Originally Posted by stevehecht

This is for a 328d Sportline with DHP. I'll be getting some aftermarket wheels that are 19x8.5 with an offset of 30. I will be going four-square. Going by the magic <3% rule of diameter variance being "OK" compared with OEM size 225/40r19, if I want to upgrade my tire size I can go with either:

1) 245/35-r19--diameter variance = -1.28%

2) 245/40-r19--diameter variance = 2.41%

3) 255/40-r19--diameter variance = -0.23%

I would have chosen 245/40-19.

I'm afraid 255 up front with ET30 will be outside the fender, or at least very close.

[stevehecht]

Originally Posted by shivaswrath

Cool site!

I have 255's out back....outside of a decrease in mpg, it's been nice to handle on the track, very predictable.

With that said many have gone staggered 245's all around with little issue; my personally i would just slap on some 275's back there!

Yes, I just found out about rimnstires.com yesterday. Very cool site!

When you say you have 255s in the rear--do you have 245s in front? That wouldn't seem to make much of a difference.

You said, "many have gone staggered 245s all around"--that doesn't make any sense! Did you just mean 245s all around? If so, yes, that would be helpful information that many have gone that route and like it.

[shivaswrath]

Originally Posted by stevehecht

Yes, I just found out about rimnstires.com yesterday. Very cool site!

When you say you have 255s in the rear--do you have 245s in front? That wouldn't seem to make much of a difference.

You said, "many have gone staggered 245s all around"--that doesn't make any sense! Did you just mean 245s all around? If so, yes, that would be helpful information that many have gone that route and like it.

Yes, I meant non-staggered, 245s all around.
255's in rear, and 225's in the front....allows for a nice, gentle understeer.

[stevehecht]

Originally Posted by shivaswrath

Yes, I meant non-staggered, 245s all around.
255's in rear, and 225's in the front....allows for a nice, gentle understeer.

So the complaints I've heard about understeer--would that only take effect when you're running at track speed? I'm supposing that at street speeds the understeer would be gentle as you say, and not detrimental to handling.

[stevehecht]

Originally Posted by ss0803

I would have chosen 245/40-19.

I'm afraid 255 up front with ET30 will be outside the fender, or at least very close.

rimsntires.com calculation put the 255/35 up front at extending an additional 0.8" to the fender. So that might be close. I was thinking that 255s front would be a bit cumbersome weight-wise and affect turn-in.

[shivaswrath]

Originally Posted by stevehecht

So the complaints I've heard about understeer--would that only take effect when you're running at track speed? I'm supposing that at street speeds the understeer would be gentle as you say, and not detrimental to handling.

Yes, basically, and it's VERY manageable and quite fun.
Usually at speeds over 70-95, and since I have the M Performance Suspension, I was able to even "learn" to power slide through and use to my advantage...

[momo3605]

Originally Posted by stevehecht

rimsntires.com calculation put the 255/35 up front at extending an additional 0.8" to the fender. So that might be close. I was thinking that 255s front would be a bit cumbersome weight-wise and affect turn-in.

So I went square, but I wasn't sure about fitting 245's in the front, and I didn't want to reduce my rear's to 245 so I went 245/255. Basically square. It performed quite well at an autocross. I think 225/255 would be too much understeer for an autox, but it might work better for a track. Though I think if I had wider rear rims, I'd go 245/265. Like a stock e9x M3.

edit: Just saw you're getting 8.5's ET30. I have ET29, the fitment is so flush, you're gonna love it! I think 245 all around is a good option. Depends what kind of driving you're aiming for. If you want an easily tossable, tail-happy ride, 245s all around is good. For high speed tracking, stagger is probably better.

[stevehecht]

Originally Posted by momo3605

So I went square, but I wasn't sure about fitting 245's in the front, and I didn't want to reduce my rear's to 245 so I went 245/255. Basically square. It performed quite well at an autocross. I think 225/255 would be too much understeer for an autox, but it might work better for a track. Though I think if I had wider rear rims, I'd go 245/265. Like a stock e9x M3.

edit: Just saw you're getting 8.5's ET30. I have ET29, the fitment is so flush, you're gonna love it! I think 245 all around is a good option. Depends what kind of driving you're aiming for. If you want an easily tossable, tail-happy ride, 245s all around is good. For high speed tracking, stagger is probably better.

Excellent information, very helpful. Thanks much!