Style 132 19" - Anybody running other than 255/50 ?

[TurnAround]

TireRack calls for 255/50. Anybody running any different widths for their 19's? If so, do you have pics? I'd like to see the side wall and whether it "rounds" to the outside (for wider sizing), or leans in (for narrower sizing).

[motordavid]

T/A...staggered or, the rare unstaggered?
I have pics coming outta my ears of staggered, with the 255/50 front,
but the wider 285/45 rear tire...
BR,mD

[TurnAround]

Originally Posted by motordavid

T/A...staggered or, the rare unstaggered?
I have pics coming outta my ears of staggered, with the 255/50 front,
but the wider 285/45 rear tire...
BR,mD

Decided to buy (4) fronts from the Style 132 for all around. This.. to save centrifical spin up weight for my 3.0i engine.

But something just occurred to me; I could use one tire size on the front and another on the rear, for the same rim width.

Anyway.. I'm just exploring tire side wall looks for the 19x9 rim. On the coupe, BMW used a stock tire sizing that is narrower than any of us would have calculated. I've yet to find out why. But this narrow width puuullls the tire out in order to mount it. The result is a leaned in way cool looking tire side wall, but... the tire is literally deformed from this stretch and the center of the tread Cups downward, putting much more pressure on the outer edges. With all the negative camber of BMW's, this leads to extremely fast tire wear. Like... 8,000 miles and they are technically shot, but we all push them to 12,000.

Since I'm about to replace the rims entirely and go to a new tie size, I have no context or historical frame of reference for what BMW has selected for a tire width on a 9" rim. I started to order the tires when I realized.. whoa.. who knows what they look like and if they're stretched to fit or not?

[motordavid]

T/A...I don't get the concern over the cent. spin up weight. I have a
3.0 also, as do several on the Board with 132s or even, 87s. We aren't
doing wet track burn outs and hot starts too often.

Also not sure of your concern over the sidewall "look" or the perceived
stretch...yes, most of us have inner tread wear on the rears, espc. in
the 285/45 size. These aren't long haul 200k mile/yr 18 wheelers, so
I don't sweat the small stuff. The staggered 132s look Titz imo, only
outdone by the 87s.

I pasted several pics of my front 132, 255/50 and one of my rear 285/45 staggered, for your perusal.

It seems like a lot of hand wringing to me.
GL,mD

[dkl]

T/A, most of us that have 19s are using the staggered setup...so you're not going to see much of us, if any at all using other sizes. Since tire choices are already limited in the OE sizes, factor in the staggered combo and it's nearly impossible to find the proper sizes (if one wants to veered off the OE sizes).

I'm also running the 132s OEM staggered 19 setup on my little 3.0i (step). You will definitely feel the heft of the 19s compared to the 17s, but as mD meantioned, the little 3.0i won't have trouble with it. I'm not too sure about your concern about the centrifical spin up weight, though. If you're going to move up to 19s, it's not going to make much of a difference whether you have 19x9 on all corners versus staggered. The 19x10 wheel/tire combo is only about 2 lb heavier than the 19x9 wheel/tire combo. Will that extra 2 lb difference be all that significant? Plus, some of that 2 lb savings will be erased if you're adding spacers to the rear. Unless tire rotations and more tire choices are your main reasons for using all 19x9s, I would recommend just sticking with the staggered setup.

[TurnAround]

This is good feedback guys. Thanks.

MD's pics definitely finalize the one concern, which is that the OEM sizing does not pull or stretch the tire in any particular direction (in .. or out). Take a look at a Z3 ( or M) sometime and you'll see what I mean on the rear tires. Better yet, take a look at a stock M3 sport. The tires are significantly narrower than the rims. The tires look wickedly cool this way, and of course the car has maximum cornering acceleration due to the very rigid tire sidewall from the match up. But this arrangement provides a harsher ride and burns through tires.

As far as the added weight of the wider rears. I so badly want the wider wheels in back. But centrifical spin up weight is an important topic. The Coupe and Roadster guys watch this closely. You can definitely feel even one more pound of weight cutting into power.. when that weight is at the outer diameter of the wheel / tire. I don't have the ratio off hand, but centrifical spin up weight is something like 6 or 7 times more significant than static weight. The weight of the wheel spacers, for example, would go undetected. Its right at the center of the wheel. It's like chucking your gym bag in the X. Nuffin. But adding pounds to the outside of the wheel is substantial. This is the very reason why guys remove their stock BMW/BBS wheels and put on super "light weight" after market racing wheels.. even at the risk of bending them on holes. These rims will typically only save 3 to 4 pounds, but the difference to the performance of the car is significant.

You both have an excellent point that the weight of the X5's wheels (even the 17's) is already so much heavier than a sports car, we're all deep into the "engine has already lost about as much power as it is going to lose" territory. But it is still a topic of interest to watch, I think.

You're saying 2 pounds. That's not bad. I'm curious whether it is more though. The extra 1" of rim section in aluminum I would guess is probably a pound or 1.5. But then the tire is wider, right at its thickest section. Rubber and steel belts are very heavy. Yeah.. ok, maybe that would only be about 2 pounds.

My dealer agreed to order one wheel of each width so that I could weigh them. I'd already decided to just go with the four fronts all around. But you guys are making me re-think this! THanks.

[dkl]

Originally Posted by TurnAround

You can definitely feel even one more pound of weight cutting into power.. when that weight is at the outer diameter of the wheel / tire. I don't have the ratio off hand, but centrifical spin up weight is something like 6 or 7 times more significant than static weight. The weight of the wheel spacers, for example, would go undetected. Its right at the center of the wheel. It's like chucking your gym bag in the X. Nuffin. But adding pounds to the outside of the wheel is substantial.

To stir things up some more...It's true that the weight of the wheel spacers themselves may not be significant, but the point I'm trying to make is that if you add spacers to push out the 19x9 rears, you are essentially increasing your centrifical spin up weight anyway. Therefore, the difference in centrifical spin up weight between the pushed out 19x9s may be very close to the 19x10s. Besides, the weight of the 19x10s (half of the increase are moved inside/half are outside) are probably better distributed than the pushed out 19x9s, where all the increases are on the outside corners.

FYI...the 285 tires sit very close to the rear wells. There's only about 15mm to 20mm of clearance between the tire sidewall and the well.

...just food for thoughts

[TurnAround]

Originally Posted by dkl

if you add spacers to push out the 19x9 rears, you are essentially increasing your centrifical spin up weight anyway.

Centrifical weight refers to the negative resistance effect placed on the drive shafts, and ultimately the motor, from the majority of the weight of the wheel being far out on the diameter of the wheel rather than close in to the hub... and the motor having to "spin up" this weight initially from a dead stop.

There's a formula for it, but I can't remember what it is off hand. But it is an exponential increase in resistance. There are two variables that play into the formula. The farther out the weight is, the worse the effect (increase the diameter of the wheel). The second, which is less damaging, is increasing the weight near the outer edges of the wheel, without increasing its diameter.

In this case, we're talking about the latter. In other wheel mod scenarios, some guys are actually looking at the former (i.e., going from a 245/40 to a 255/40 on the rear wheels of a Coupe increases the weight (tire width), and more damaging, the diameter of the tire increases.

The centrifical spin up problem still exists at 50mph, say in a corner, and then trying to punch it up to 75 coming out of the corner. But the ratio of resistance is considerably smaller at 50mph. From 0 to 40 the ratio is much higher, and that's where the main concern is.

Moving the wheel further in or further out from its previous axis would have no effect on the centrifical spin up formula. This is why adding weight in the form of spacer material, near the very center of the wheel, would not have an effect.

Bicycle racers are very aware of centrifical spin up. The lighter the wheels you can build, the faster you can sprint. I took it the next step and went after the more significant variable of diameter. I had a local custom bike maker create me a specially designed hill climbing bike that uses 650c wheels (much smaller diameter) instead of the standard 700c wheels (larger). The bike is substantially easier to climb hills on. Its quite shocking, the difference, actually.


Not trying to be argumentative. Actually, this kind of stuff is super interesting I think.

So what we're really talking about here is; There is no question but that the impact to performance on a light weight 2,900 pound Coupe, with the same M54 3.0i engine is immediately apparent. The question is, with the X5 being so heavy, and already having heavy wheels (One 18" X5 wheel weighs as much as two of my coupe wheels), is the same engine already "bogged down" to a point where.. somehow.. perhaps.. one pound of extra outside weight on an X is not noticeable, compared to one pound extra on the Coupe, which is very noticeable??

You guys are saying... it is not noticeable. That is encouraging.

I definitely noticed the difference of loss in power from the 17's to the 18's. I know the 19's will take a hit as well. Just wondering if the extra inch of aluminum and rubber in back would then make a 4th decrease.

[motordavid]

TurnAround,
I don't want to arm wrestle but in 46+ years of hanging around/working on/bs'ing about cars and performance, I must admit I have never worried about "centrifical spin up weight",(sic), in a street car.

So, I GOOG'd it and came up with very little; a couple posts wondering if they put 25" or 26" wheels on their car what happens to the trans overcoming the dreaded 'csuw', etc. The response was yes, it wil take more torque to overcome inertia/the added weight of the wheels to get moving from a dead start, but once moving...blah, blah, blah.

I have an old friend that still races ProStock on one of the drag circuits; I called him to run this term by him.
He wondered if I was sneaking an early afternoon G&Tonic...he knew about the term and how it affects drag
starts, based on tire grip, wheel size, (esp circumference & weight), etc.

He wondered if I was getting into drag racing again after 45 years away from it. He also wondered why anyone
driving a streetable car in normal situs with "reasonably sized wheels & tires" would wonder or worry about that potential effect/determent.

I musta been sleeping in car class but I just don't get your concern over the 19" rear staggered vs. a 19" even
all around set, as it pertains to 'csuw' in real world, every day driving situs.

If one likes the look of non-staggereds, I get it...otherwise, I'm not convinced there is a problem or reason
for concern. But, diff'n strokes.
BR,mD

[TurnAround]

Centrifical weight is my term. I'm sure there's a more accurate term.

Also keep in mind that this concept is one of the many on forums like the Coupe board, etc.. that is not stated... as everyone is aware of it. They will talk about wheel weights for different wheels being considered, but won't take the bandwidth to define its effect because they're assuming the others know about it. But these lighter wheels they're after.. it's not to save 20 pounds total on a 2,900 pound car. Its only for two reasons.. spin up, and reducing unsprung weight.

Even on this board or the old X5 board you can find posts where guys come on and say, "Something's wrong with my X. I upgraded my stock 18's to 21" and now the car drive like ____". These folks are not aware of the spin up reality.