[addm]

Originally Posted by drob23

I agree with your general skepticism, you are correct that the most of the insight we have into the performance differences come from bench racer style hypothesizing. Most of these magazine comparisons are not done in a controlled manner (recent MotorTrend S4 vs 335i used AS tires on 3er), so ultimately all we have are anecdotal opinions. Marketing and sales pitches are the worst way to go, and many opinions we read on boards like this are biased based on preference (post-purchase rationalization?) or first hand knowledge of the wrong platform (b7 s4 vs b8 s4 are *completely* different for example).

With that said, it is a well known fact that the biggest performance barrier for an AWD car is understeer. The rear sports differential in the S4 and X6/MX5/MX6 is a pretty cool way to combat this. Does it turn the S4 into an M3 sans V8? No way, it's still an AWD car.

It really all comes down to personal preference. I live in the snow belt and need AWD because I can't afford a DD and weekend toy. The BMW IMO should be driven in the RWD variant, so I ultimately went with the S4. If I was still in college down in SoCal (ugg do I miss the SB beach), I'd probably be driving a 335i. Was this based on scientific fact, of course not, just how I felt about it. Now this doesn't mean that I don't enjoy the after the fact debate , it's fun learning about this and doing the research - just wish there was better information out there.

Well said.

[seis-speed]

Originally Posted by 300hp

Get the Dynamic Handling Package with the xdrive

More please, can you or anyone else elaborate on how this helps.

This will be manual only, I am leaning S4 with Stasis.

Again I should have stated in the OP this is a XDrive vs S4 debate.

[BruceOmega]

Originally Posted by 335BBS

Unfortunately the xi isnt offered with sport suspension. It sits higher on softer suspension than the S4. As mentioned earlier, xi was originally developed as a foul weather aid. I'mm really surprised they didnt address this with new model.

I was asking a slightly different question. Putting aside for the moment the S4 and the non-availability of a sport suspension with AWD-

Given the 335i RWD with a sport suspension has a slightly lower ride height than the 335i AWD, does the AWD have a lower center of gravity?

Thanks
Bruce

[DarkTrigger]

Originally Posted by seis-speed

More please, can you or anyone else elaborate on how this helps.

Tis will be manual only, I am leaning S4 with Stasis.

Again I should have stated in the OP this is a XDrive vs S4 debate.

That's easy then, S4 if you want performance. 335xi if you want everything else.

[DesertSmokeBBQ]

Originally Posted by 335BBS

Until something blows up .......no warranty. Sound of 4cyl takes a while to get used to.

and THAT's why i'm neither doing anything extreme NOR on the cheap. everything i'm doing is from EXTREMELY reputable vendors.

[335BBS]

Originally Posted by BruceOmega

I was asking a slightly different question. Putting aside for the moment the S4 and the non-availability of a sport suspension with AWD-

Given the 335i RWD with a sport suspension has a slightly lower ride height than the 335i AWD, does the AWD have a lower center of gravity?

Thanks
Bruce

I'm confused Bruce. Awd is higher therefore I assume its cog is higher.

[drob23]

Originally Posted by BruceOmega

I was asking a slightly different question. Putting aside for the moment the S4 and the non-availability of a sport suspension with AWD-

Given the 335i RWD with a sport suspension has a slightly lower ride height than the 335i AWD, does the AWD have a lower center of gravity?

Thanks
Bruce

The sport suspension does not come on the 3 series xdrive in either sport or m-sport lines (I assume you are referring to this), which I understand is due to clearance issues with the extra underbody hardware. The sport suspension includes a 10mm drop, so the xdrive variant will have a higher COM, I doubt the 150lbs underneath is enough to offset this.

If you only consider the non-sport 3 series lines, then yes, the COM would be marginally lower. The larger effect on the dynamics involve the pitch and yaw moments of inertia. This calculation is proportional to distance squared, so sticking a lot of mass in the front of the vehicle will throw off the natural balance of the car more so than you'd think. I know driving dynamics are more complex than this, but the 50-50 balance of the BMW is what gives the legendary handling...

As mentioned, you can still get the DHP package on xdrive, which allows you to stiffen things up.

[drob23]

Originally Posted by seis-speed

More please, can you or anyone else elaborate on how this helps.

Tis will be manual only, I am leaning S4 with Stasis.

Again I should have stated in the OP this is a XDrive vs S4 debate.

A Stasis tuned S4 is kinda in a whole other world performance wise at 12k for the B8. I think they are close to releasing a tune for the B8.5. From the dyno sheets I've seen, the real change to the performance is within the upper rev limits, where the stock loses steam.

But that stasis suspension, brake, exhaust and engine tune probably bring the S4 into M3 territory (well stock M3 of course), comparing it to a 335ix is at that point laughable. Sweet rims too...

[335BBS]

Originally Posted by drob23

A Stasis tuned S4 is kinda in a whole other world performance wise at 12k for the B8. I think they are close to releasing a tune for the B8.5. From the dyno sheets I've seen, the real change to the performance is within the upper rev limits, where the stock loses steam.

But that stasis suspension, brake, exhaust and engine tune probably bring the S4 into M3 territory (well stock M3 of course), comparing it to a 335ix is at that point laughable. Sweet rims too...

$1700 gets you Stasis ecu tune.....just over 400hp.

[seis-speed]

Originally Posted by 335BBS

The differences are so small that most here wouldn't be able to notice. Having said that, in the hands of a Pro the S4 is superior to 335xi....even with staggered set up. The awd systems are very different and built for different purposes. I'm really surprised that BMW didn't offer a different awd system and or lower firmer sport suspension on new xi to compete wit it's main competitor.

I agree, I really think BMW should I offer a sport suspension in the XDrive as an option. If that were the case I would not be looking toward jumping to the competition. I will always own 1 BMW, IMO the X5D is the best machine on the road for the money and versatility.

[seis-speed]

Originally Posted by drob23

A Stasis tuned S4 is kinda in a whole other world performance wise at 12k for the B8. I think they are close to releasing a tune for the B8.5. From the dyno sheets I've seen, the real change to the performance is within the upper rev limits, where the stock loses steam.

But that stasis suspension, brake, exhaust and engine tune probably bring the S4 into M3 territory (well stock M3 of course), comparing it to a 335ix is at that point laughable. Sweet rims too...

$1800 is what I will be paying.
Although I am intrigue by APR's pulley system.

[drob23]

Originally Posted by seis-speed

$1800 is what I will be paying.
Although I am intrigue by APR's pulley system.

Oh OK, for some reason when you said an "S4 with Stasis" I assumed you meant the full on package - touring or challenge - which are both lots of $$$. There are some ECU tunes for the 3 series, check out Dinan for example. Stasis doesn't have a B8.5 ECU tune (assuming you're shopping for a 2013) yet, but it's expected any day now.

[BruceOmega]

Originally Posted by drob23

..... The sport suspension includes a 10mm drop, so the xdrive variant will have a higher COM, I doubt the 150lbs underneath is enough to offset this .....

Yes, this is what I was asking. Interesting, my technical intuition would have said the COM on AWD is lower since 10 mm drop is such a small amount, less than 1/2 ".

Thanks
Bruce

[drob23]

Originally Posted by BruceOmega

Yes, this is what I was asking. Interesting, my technical intuition would have said the COM on AWD is lower since 10 mm drop is such a small amount, less than 1/2 ".

Thanks
Bruce

If you solve the equation to determine the displacement necessary (assuming lump sum) for the xdrive to lower the CM by 10 mm for 328ix you get

(x * 135/2.2 + 0 * 3461/2.2)/(3596/2.2) >= .01m

implies

x >= .256m

So if the xdrive hardware is .256m = 10 in lower than the current CM, you would be correct. I'll check out carsim at work tomorrow and might be able to get a rough guess of where a nominal vehicle's CM is. My guess is it will be quite low and probably less than 10 in above the drivetrain - based on nothing at all but my best guess

Of course the 335 is heavier and thus CM is less affected by xdrive...

[drob23]

FWIW - the default CarSim D-Class sedan has the sprung center of mass .54 m above the ground. The wheel center is .335 m above ground, which should be *at least* lower than the driveshaft + xdrive hardware. Thus the difference is .205 m which is not enough to lower the CM of a 328ix as compared to sport suspension 328i using my calculation above.

The GT model in carsim (supposed to be a Porsche) has the CM .39m above ground and wheel center .325m above ground. So for a sports car with low CM the xdrive would do nothing to the CM.

[BruceOmega]

Originally Posted by drob23

FWIW - the default CarSim D-Class sedan has the sprung center of mass .54 m above the ground. The wheel center is .335 m above ground, which should be *at least* lower than the driveshaft + xdrive hardware. Thus the difference is .205 m which is not enough to lower the CM of a 328ix as compared to sport suspension 328i using my calculation above.

The GT model in carsim (supposed to be a Porsche) has the CM .39m above ground and wheel center .325m above ground. So for a sports car with low CM the xdrive would do nothing to the CM.

Interesting. I appreciate an engineering approach, but am having trouble following the above example for the D-Class sedan.

From looking at the drawing of xDrive for the 335i sedan on the BMW website, the extra hardware of xDrive looks like it is roughly in the same plane as the driveshaft, which is roughly in the same plane as the wheel centers.

According to the example above, the sedan's wheel centers are .205m / 8" below the COM, so that would put the extra weight of xDrive lower than the COM. If so, that should have the effect of lowering the vehicle's COM with xDrive.

I'm also having trouble following the effect of the 10mm lowered ride height for RWD with sport suspension. In terms of meters as the unit of measurement used in the example, that 10mm is only 0.01m.

Am I missing something?

Thanks
Bruce

[drob23]

Originally Posted by BruceOmega

Interesting. I appreciate an engineering approach, but am having trouble following the above example for the D-Class sedan.

From looking at the drawing of xDrive for the 335i sedan on the BMW website, the extra hardware of xDrive looks like it is roughly in the same plane as the driveshaft, which is roughly in the same plane as the wheel centers.

According to the example above, the sedan's wheel centers are .205m / 8" below the COM, so that would put the extra weight of xDrive lower than the COM. If so, that should have the effect of lowering the vehicle's COM with xDrive.

I'm also having trouble following the effect of the 10mm lowered ride height for RWD with sport suspension. In terms of meters as the unit of measurement used in the example, that 10mm is only 0.01m.

Am I missing something?

Thanks
Bruce

According to the calculation in post 168 - the CM of the 328ix will be lower than 328i w 10mm drop if and only if the xdrive hardware is more than .26m below the nominal CM. Since it's only .205 m, the 328ix CM is higher than the 328i w/ sport suspension (the d class sedan is meant to represent a midsize sedan like the Fusion or Malibu).

edit - I attached the data for you to see.

[335BBS]

Originally Posted by BruceOmega

Interesting. I appreciate an engineering approach, but am having trouble following the above example for the D-Class sedan.

From looking at the drawing of xDrive for the 335i sedan on the BMW website, the extra hardware of xDrive looks like it is roughly in the same plane as the driveshaft, which is roughly in the same plane as the wheel centers.

According to the example above, the sedan's wheel centers are .205m / 8" below the COM, so that would put the extra weight of xDrive lower than the COM. If so, that should have the effect of lowering the vehicle's COM with xDrive.

I'm also having trouble following the effect of the 10mm lowered ride height for RWD with sport suspension. In terms of meters as the unit of measurement used in the example, that 10mm is only 0.01m.

Am I missing something?

Thanks
Bruce

This is a street driven 3. Why so curious?

[mtgswede]

I did, I wanted to like the S4 so much but after driving it, I could really tell the front wheel bias. Never owned an Audi so the difference was pretty apparant to me. I also was really dissappointed in the dated interior. Just doesn't hold a candle to the F30. Now if I had to choose between an E90 and the Audi, I would have taken the Audi just on the basis of how horrid the E90 interior was.

[335BBS]

Originally Posted by mtgswede

I did, I wanted to like the S4 so much but after driving it, I could really tell the front wheel bias. Never owned an Audi so the difference was pretty apparant to me. I also was really dissappointed in the dated interior. Just doesn't hold a candle to the F30. Now if I had to choose between an E90 and the Audi, I would have taken the Audi just on the basis of how horrid the E90 interior was.

Very funny. My Audi oversteers. I can do donuts in the snow without rear diff option. I think you fell victim to preconceived ideas from reading biased posts here. I steered one around an on ramp with right foot. That f30 int looks pretty mixed up to me. What's with the Mimi screen? Afterthought?

[shivaswrath]

Originally Posted by 335BBS

Very funny. My Audi oversteers. I can do donuts in the snow without rear diff option. I think you fell victim to preconceived ideas from reading biased posts here. I steered one around an on ramp with right foot. That f30 int looks pretty mixed up to me. What's with the Mimi screen? Afterthought?

I can do donuts without a rear diff too.

[buildbright]

Originally Posted by 335BBS

Very funny. My Audi oversteers. I can do donuts in the snow without rear diff option. I think you fell victim to preconceived ideas from reading biased posts here. I steered one around an on ramp with right foot. That f30 int looks pretty mixed up to me. What's with the Mimi screen? Afterthought?

I can do donuts on dry payment. No Audi Oversteers Unless It's Wet or Snowing.