Crown

Some info I got from BMW and 6speed Turbo forum, note the weights (!!):

19"x12, offset 50 (FI012); weight: 8.9 kg
Cost 1200 euro (US $ 1700 - unconfirmed) per wheel.

If what I read is correct, then the BBS Fi wheel is designed by BBS Motorsport Division in Germany, and manufactured in Germany, unlike other consumer level BBS (made in Japan).  The famous Manthey itself is made by BBS and is a product of the same division. But... I prefer the Fi because it's made of aluminum alloy, versus magnesium of the Manthey, and the Manthey is a lot more expensive.

Although I don't like the design (and hate the chrome finish in the enclosed picture), all things considered, this has got to be the best wheel on the market now for Porsche 911 because of the weight and the "pedigree." There was a US company called AMT that made light aluminum wheel also, but AMT has unfortunately ceased existing as a legit company, and it ain't BBS Germany.
If I were to order a new Turbo now, there is no way I would get the Spyder over this BBS.

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http://www.bbs.com/en/company/news/fi_en.html

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Regards,
Can
997 Turbo + Bilstein Damptronic "Stage 2" ( Review ) + GIAC ECU Tune ( Fast as a torpedo & reversible to stock - Review ) + Cargraphic Exhaust ( Oh heavenly noise! )

From the website I saw that you can also order a matt silver or even better a silver/black option, which I think looks great!

Personally, I don't think that this BBS wheel matches the 911 too well but I guess it is a matter of taste.  

Weight isn't always everything, the whole chassis setup is important and changing weight at the wheel doesn't always improve things.

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RC (Germany) - Rennteam Editor 997 Turbo, BMW X5 M (on the ship), BMW M3 Cab DKG, Mini Cooper S JCW

Not sure how suited it is to the 997, but this is a gorgeous wheel...

RC:

Personally, I don't think that this BBS wheel matches the 911 too well but I guess it is a matter of taste.  

Weight isn't always everything, the whole chassis setup is important and changing weight at the wheel doesn't always improve things.

Since we are not downhill bobsledding here , I am sure you must have a good reason for stating unsprung weight is good in motorsports? (Not sarcastic at all, I *know* you have some explanation.)

I remember, vaguely, reading some comments, maybe from Ruf, stating that heavier wheel is good at high speed?? If so, what about getting to that high speed? I thought the REAL reason is because their wheels are among the heaviest around?

As far as suspension matching, sure. Obviously the suspension is not designed to work with 0 weight. But... we also know that PCCB cuts 35 lbs/4 or so from each wheel, and that there is no change in suspension from PCCB to non PCCB cars. Meaning, there is a range.

Agreed with you on the styling. This is a mesh/fork design, with 5 forks. And although it's a matter of personal prefrerence, and I think it's necessary for less weight, mesh wheel with less than 7 forks ALWAYS looks weird to my eyes.

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Regards,
Can
997 Turbo + Bilstein Damptronic "Stage 2" ( Review ) + GIAC ECU Tune ( Fast as a torpedo & reversible to stock - Review ) + Cargraphic Exhaust ( Oh heavenly noise! )

 A GT3 RS at Scuderia Hanseat had these BBS wheels. Looked pretty nice real life.

987 Boxster S, Arctic Silver with 'Martini Racing' Livery, H&R Monotube Coil-Overs, H&R Anti Roll Bars, Strut Brace, FVD ECU, BMC Air Filter, Sachs Racing Clutch, Single-Mass Flywheel, Recaro Racing Shells, PSE.

997 Carrera 4S, Guards Red, Bilstein PSS10 Damptronic, H&R Anti Roll Bars, IPD Plenum, Dension Gateway 500, PSE.

bluelines:

 A GT3 RS at Scuderia Hanseat had these BBS wheels. Looked pretty nice real life.

we discussed months ago about and to me are fab these wheels on the RS

SciFrog:

Not sure how suited it is to the 997, but this is a gorgeous wheel...

Well said.

The secret of life is to admire without desiring.

I, also, have been looking into these wheels... The most informative site I have found is on the following website (need to copy and paste the link, the "Insert/ Edit Link" edit tool did not allow me to post the entire length of the link):
www.oclbrorssons.se/6249_SE.67EA239344e193626da5d17d43ce4a94b16ff6a0?webbid=5&webdid=416&webban=1
On the right hand side of the page, clink on:
"TEKNISK INFORMATION" for details on various sizes, offset, weight, etc.
"BILDER" for quite a few photos of the wheel.

RC, could you share with us more on why less unsprung weight is not always a good thing?  The review of the 997.2 TT on Excellence also stated something similar (I suppose): "The Turbo center-lock wheels weigh more than thee GT3 rims because the Turbo is heavier than the GT3" (December 2009 issue, page 79). 

Not trying to set any flames here... just trying to understand the topic more before I dive into my next mod, potentially the BBS Fi...

I lIke these BBS wheels also, they look great on that white RS 

If it turns out we can't get the Dymags refurbished (mine are looking pretty tatty now, with the laquer flaking off through heat (I guess) ) since noone has the tools to take them apart / rebuild them, then I would definately consider these BBS......

The ONLY reason heavier wheels are beneficial is strength in all other respects lighter is always better - as GT says Dymags which are ultra light courtesy of the outer rotating rim being CF and they make a huge difference compared to standard.

With the 1987 onwards CTR Ruf would say that the heavy wheels made the car stable at the very high speeds in a straight line due to a gyroscopic effect - if this is true (which seems to make sense) then I guess by definition the gryoscopic effect would make the heavier wheels a hinderance when the wheels are turned for a corner......

I had a set of the CTR wheels on a 3.2 Carrera back in ~1989 and whilst they looked awesome they felt bloody heavy and one could feel them through the unassisted steering. The CTR wearing the same wheels for some reason didn't feel quite as heavy but that may be down to the user being more focused onthe ballistic performance and how the car was going to get around the next curve at the huge velocities it reached, rather than detecting the nuances of the subtlety or otherwise of the steering feel and handling  

2009 997 GT2 659PS/827NM DIN

^^^^Thanks. The gyroscopic explanation makes sense, or rather "some" sense. And I wouldn't have the temerity  to question an observation by Ruf anyhow.  ( http://en.wikipedia.org/wiki/Gyroscope ....This orientation changes much less in response to a given external torque than it would without the large angular momentum associated with the gyroscope's high rate of spin...)

OTOH,  there are multiple parameters to consider that bring more questions to this "observation." What speed does it matter, what percentage of drivers who would venture to such speed, it's not an on/off phenomenon so who decides what weight is the sweet spot, what is the sweet spot, what trade-off one is willing to give up to achieve this stability, how applicable it is to our modern 997 cars, etc.

In addition to your counter points of hindrance to handling and steering feel from using heavier wheels, I think should be added ride, braking, and acceleration as well. I haven't done my "web research" ;-) but have to believe that less rotational mass allows both braking and accelerating to be more efficient (less mass to spin, less momentum to stop).
In addition, all else being equal, AFAIK, a lighter weight wheel allows better tracking of road irregularities and therefore better traction and ride. The example I remember reading: When one hits a bump, the larger mass, hence linear momentum, of a heavier wheel causes it to want to go further up, compressing spring more, with higher chance of unweighting that particular corner. Anyone please feels free to correct me as needed; I think I should be pretty close though.

Back to the BBS Fi (i, not 1), one thing about this wheel: the reaction to pictures so far seems to be that people either love it or hate it (the design). I do think that there is something "dissonant," or "unsettling" about the design, unlike the pretty Dymag for example, which gets near unanimous positive response.
But, look is a matter of personal taste; if one likes the look, this has got to be the number wheel on the market right now, all things considered.

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Regards,
Can
997 Turbo + Bilstein Damptronic "Stage 2" ( Review ) + GIAC ECU Tune ( Fast as a torpedo & reversible to stock - Review ) + Cargraphic Exhaust ( Oh heavenly noise! )

BTW discussing the gyroscopic effect makes me think about those "flybrid" (flywheel hybrid) Porsche race car -- the one with the internal flywheel that rotates at several thousand rpm's. What do those flywheels do to the car's balance when you enter a banking curve? Will a "flybrid" car steer like a motorcycle?   See animation below.

"The behaviour of a gyroscope can be most easily appreciated by consideration of the front wheel of a bicycle. If the wheel is leaned away from the vertical so that the top of the wheel moves to the left, the forward rim of the wheel also turns to the left. In other words, rotation on one axis of the turning wheel produces rotation of the third axis."

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http://en.wikipedia.org/wiki/Gyroscope
A gyroscope is a device for measuring or maintaining orientation, based on the principles of conservation of angular momentum.^[1] A mechanical gyroscope is essentially a spinning wheel or disk whose axle is free to take any orientation. This orientation changes much less in response to a given external torque than it would without the large angular momentum associated with the gyroscope's high rate of spin. Since external torque is minimized by mounting the device in gimbals, its orientation remains nearly fixed, regardless of any motion of the platform on which it is mounted. Solid state devices also exist, such as the ring laser gyroscope.

Applications of gyroscopes include navigation (INS) when magnetic compasses do not work (as in the Hubble telescope) or are not precise enough (as in ICBMs) or for the stabilization of flying vehicles like Radio-controlled helicopters or UAVs. Due to higher precision, gyroscopes are also used to maintain direction in tunnel mining [1].

Description and diagram

Diagram of a gyro wheel. Reaction arrows about the output axis (blue) correspond to forces applied about the input axis (green), and vice versa.

Within mechanical systems or devices, a conventional gyroscope is a mechanism comprising a rotor journaled to spin about one axis, the journals of the rotor being mounted in an inner gimbal or ring, the inner gimbal being journaled for oscillation in an outer gimbal which in turn is journaled for oscillation relative to a support. The outer gimbal or ring is mounted so as to pivot about an axis in its own plane determined by the support. The outer gimbal possesses one degree of rotational freedom and its axis possesses none. The inner gimbal is mounted in the outer gimbal so as to pivot about an axis in its own plane that is always perpendicular to the pivotal axis of the outer gimbal.

The axle of the spinning wheel defines the spin axis. The inner gimbal possesses two degrees of rotational freedom and its axis possesses one. The rotor is journaled to spin about an axis which is always perpendicular to the axis of the inner gimbal. So, the rotor possesses three degrees of rotational freedom and its axis possesses two. The wheel responds to a force applied about the input axis by a reaction force about the output axis.

The behaviour of a gyroscope can be most easily appreciated by consideration of the front wheel of a bicycle. If the wheel is leaned away from the vertical so that the top of the wheel moves to the left, the forward rim of the wheel also turns to the left. In other words, rotation on one axis of the turning wheel produces rotation of the third axis.

A gyroscope flywheel will roll or resist about the output axis depending upon whether the output gimbals are of a free- or fixed- configuration. Examples of some free-output-gimbal devices would be the attitude reference gyroscopes used to sense or measure the pitch, roll and yaw attitude angles in a spacecraft or aircraft.

Animation of a gyro wheel in action

The center of gravity of the rotor can be in a fixed position. The rotor simultaneously spins about one axis and is capable of oscillating about the two other axes, and thus, except for its inherent resistance due to rotor spin, it is free to turn in any direction about the fixed point. Some gyroscopes have mechanical equivalents substituted for one or more of the elements, e.g., the spinning rotor may be suspended in a fluid, instead of being pivotally mounted in gimbals. A control moment gyroscope (CMG) is an example of a fixed-output-gimbal device that is used on spacecraft to hold or maintain a desired attitude angle or pointing direction using the gyroscopic resistance force.

In some special cases, the outer gimbal (or its equivalent) may be omitted so that the rotor has only two degrees of freedom. In other cases, the center of gravity of the rotor may be offset from the axis of oscillation, and thus the center of gravity of the rotor and the center of suspension of the rotor may not coincide.

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Regards,
Can
997 Turbo + Bilstein Damptronic "Stage 2" ( Review ) + GIAC ECU Tune ( Fast as a torpedo & reversible to stock - Review ) + Cargraphic Exhaust ( Oh heavenly noise! )

Did this thread lose all the audience with the gyroscope article above?   Good thing I didn't post the one on conservation of angular momentum? That read goes well with extra strength aspirin -- and it still may not make any sense. LOL

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http://en.wikipedia.org/wiki/Angular_momentum

Angular momentum simplified using the centre of mass

It is very often convenient to consider the angular momentum of a collection of particles about their centre of mass, since this simplifies the mathematics considerably. The angular momentum of a collection of particles is the sum of the angular momentum of each particle:

where R_i is the distance of particle i from the reference point, m_i is its mass, and V_i is its velocity. The center of mass is defined by:

where the total mass of all particles is given by

It follows that the velocity of the centre of mass is

If we define as the displacement of particle i from the centre of mass, and as the velocity of particle i with respect to the centre of mass, then we have

   and   

and also

   and   

so that the total angular momentum with respect to the center is

 
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Regards,
Can
997 Turbo + Bilstein Damptronic "Stage 2" ( Review ) + GIAC ECU Tune ( Fast as a torpedo & reversible to stock - Review ) + Cargraphic Exhaust ( Oh heavenly noise! )

Now you are really scaring them away....

"Bad" joke on my part. I merely was quoting the section with the most squiggles.

Back to the wheel: Confirmed to be TPMS compatible. Someone in Germany got a set for his GT2; hopefully we'll have more pictures of side profile of the wheel.

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Regards,
Can
997 Turbo + Bilstein Damptronic "Stage 2" ( Review ) + GIAC ECU Tune ( Fast as a torpedo & reversible to stock - Review ) + Cargraphic Exhaust ( Oh heavenly noise! )

cannga:

"Bad" joke on my part. I merely was quoting the section with the most squiggles.

Back to the wheel: Confirmed to be TPMS compatible. Someone in Germany got a set for his GT2; hopefully we'll have more pictures of side profile of the wheel.

 

 

 a GT2 should look great with those wheels. 

Very interesting (please note I didn't say right, or wrong, just interesting ) exchange on light versus heavy wheel and gyroscopic effect. The guys there don't post here and vice versa, so let me provide the quote.

Originally Posted by Tech1_Mike

Originally Posted by cannga

 

So... are you saying:
1. Yes gyroscopic effect is a problem, but the heavier wheel is not at an advantage because:
2. With road irregularities, the force on the heavier wheel is larger, and therefore it suffers just as much from precession?

 

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Originally Posted by Tech1_Mike

The short version is that the rotational inertia of the wheels and the resulting gyroscopic effect do NOT contribute to stability. Quite the opposite.
The vertical forces of road irregularities cause the "gyroscopes" to precess at right angles, even with tiny inputs. The faster the wheel is turning and the greater the moment of inertia, the worse the precession. Thus, the heavier wheels add nothing on perfectly smooth roads and cause a left to right oscillation on rougher roads.
The gyroscopic theory regarding vehicle stability is very interesting to think about and quite logical, but has no foundation in science. Gyroscopes are actually used primarily to provide "error" signals to control surfaces that in turn create stability in aircraft, spacecraft and marine vehicles. They are positioned in a known attitude, spin at a known rate, and have a fixed moment of inertia. Therefore tiny inputs of force cause the Gyro to precess, acting on an electronic circuit that creates a corrective input to a control surface. The Gyro then senses the correction and neutralizes the control surface. This happens very quickly and reliably, stabilizing the vehicle.
However, the gyro itself doesn't directly stabilize anything, only indirectly.

Fun subject.

BTW, #2 is actually correct.

Regards,
Can
997 Turbo + Bilstein Damptronic "Stage 2" ( Review ) + GIAC ECU Tune ( Fast as a torpedo & reversible to stock - Review ) + Cargraphic Exhaust ( Oh heavenly noise! )

I was quoting what Ruf was saying back 1988. The CTR Yellowbird ran at 213mph and journalists were impressed by its stability at these speeds, it was in response to questions about why it was so stable that Alois spouted about the wheels and their gyoscopic effect. He has since used this line again but probably only because his wheels have always been so heavy with the obvious but often overlooked trade off in strength....

I am with the above that the weight/gyro effect does nothing for stability and weight is always bad as Mike says.

As far as light wheels effecting stability at high speed ? at 200mph on the Autobahn my Dymags were rock solid - the guy with the instability + light wheels has other (probably aero related) issues.....

2009 997 GT2 659PS/827NM DIN

^^^And that quote has led to a very interesting discussion.

Forgot, here is the url for anyone interested: http://www.6speedonline.com/forums/997-turbo-gt2/206016-five-lightest-wheels-997-turbo-5.html . The thread is a good read, with the pro's weighing in with their opinions. Anyway, some more data:

Champion RS 98: 19x8.5 (8.2 kg), 19x11.5 (9.06 kg)

Dymags: front (7.62kg), rear (9.30kg) (Seem high?? They are actual measured weights by imcarnuts.)

Tech1-110: 19x8.5 (7.53Kg) , 19x11.5 (8.93 Kg)

BBS Fi: 19x8.75 (7.4 kg ), 19x12 (8.9 kg)

I haven't looked up the costs (lazy), but note that there are large differences between the wheels: Dymag 10k? >BBS Fi 7k?>Champion 5.5k?>Tech1 4k? (Please correct me as needed.)

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Regards,
Can
997 Turbo + Bilstein Damptronic "Stage 2" ( Review ) + GIAC ECU Tune ( Fast as a torpedo & reversible to stock - Review ) + Cargraphic Exhaust ( Oh heavenly noise! )

 dymags are between 5.5kg and 5.8kgs. I have them on my car

GT:

 dymags are between 5.5kg and 5.8kgs. I have them on my car

GT, the 7.6 kg and 9.3 kg Dymag weights I posted are actual measured weights by owner (who used to post here I think). See pic below of the front wheel, 16.8 lb = 7.6 kg. These relatively big numbers so surprised me that I tried to see if anyone else put them on the scale. I saw another example of an 18x10 Dymag for BMW that weighs 8.4 kg.

Very light (and pretty) as they are, I do not think that they are below 7kg, let alone 6. Was there an official spec sheet from Dymag?

Regards,
Can
997 Turbo + Bilstein Damptronic "Stage 2" ( Review ) + GIAC ECU Tune ( Fast as a torpedo & reversible to stock - Review ) + Cargraphic Exhaust ( Oh heavenly noise! )

 I ll measure mine again soon then.  Mine are the magnilium version (pic above is magnesium that was replaced as it had leakage issues).

I ll measure wheel without wheel nuts and report back.

GT:

 I ll measure mine again soon then.  Mine are the magnilium version (pic above is magnesium that was replaced as it had leakage issues).

I ll measure wheel without wheel nuts and report back.

How are yours fairing ? Mine are getting pretty tatty now, the lacquer has come off everywhere and I noticed that some of the alloy (magnalium) spokes are begining to show the first sign of corrosion (bubbling).

Phil at Tech 9 was trying to get hold of the spanner/socket to be able to dismantle them for refurb but he says it is proving impossible. He says if I send mine to him he will get a socket made, find out all the correct torque specs and get them sorted - they do a new darker finish now which doesn't go yellowy like mine have.....

I think the Dymag weights cannot really be compared to other wheels since the lightest part, the carbon is outermost and will benefit the handling more since it is the fastest rotating etc - I don't know the physics but its all pretty obvious one would want the fastest rotating bit to be lightest...... One has to drive with Dymags to appreciate how they change the handling.

2009 997 GT2 659PS/827NM DIN

 Agreed. Toby mine are still ok. But regarding the lacquer you might not have to actually send them to dymag. I have re-lacquered mine for minor dents and it is fine. Unless you have leaks or sth I dont think you need to disassemble really.

Regarding the colour change I know exactly what you mean and I am in touch with the ex MD of dymag who gave me all specs and instructions on how to do it. I intend to have a go at an extra set of fronts i have to colour match.

Also I hear that dymag product will be available again soon through another company as they bought new equipment to make carbon wheels. PM me for more detail.

TB993tt:

I think the Dymag weights cannot really be compared to other wheels since the lightest part, the carbon is outermost and will benefit the handling more since it is the fastest rotating etc -

Absolutely -- very good and important point. But... with a slight modification: I believe it's not primarily the handling that is affected by inner vs. outer weight distribution of any particular wheel. It's the braking and acceleration.

There are two types of wheel movement: rotational (wheel rolling) and linear (movement up and down when wheel hits a bump on the road).
I believe decreased "rotational/angular" momentum (aka angular mass or moment of inertia) improves primarily rotation related parameters such as acceleration, braking, steering. OTOH, decreased "linear" momentum improves coilover related parameters such as ride and handling.

For example, given 2 wheels a & b, with wheel a has lighter rim/barrel (and therefore heavier center disc/spoke), I think that while both a and b will have similar ride and handling, wheel a will have the advantage in acceleration, braking, and steering (rotation related parameters). Fascinating subject and anyone please corrects me as needed.

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Regards,
Can
997 Turbo + Bilstein Damptronic "Stage 2" ( Review ) + GIAC ECU Tune ( Fast as a torpedo & reversible to stock - Review ) + Cargraphic Exhaust ( Oh heavenly noise! )

Can

I saw the discussion you are having on Bling about the BBS FI being specified by BBS as for "road use".....

I think some people have the wrong end of the stick here: Being specified as suitable for road use means the wheels are considered by BBS as STRONGER than their race wheels, contrary to what some people are saying on your Bling thread, "road" use is considered much harsher than "race" use. I ran BBS E88s race wheels on the road on my 993tt (aluminium not mag) and they are not recommended for road use by BBS and AFAIK have not been put through the road use TUV tests..... this is what I understand

2009 997 GT2 659PS/827NM DIN

TB993tt:

Can

I saw the discussion you are having on Bling about the BBS FI being specified by BBS as for "road use".....

I think some people have the wrong end of the stick here: Being specified as suitable for road use means the wheels are considered by BBS as STRONGER than their race wheels, contrary to what some people are saying on your Bling thread, "road" use is considered much harsher than "race" use. I ran BBS E88s race wheels on the road on my 993tt (aluminium not mag) and they are not recommended for road use by BBS and AFAIK have not been put through the road use TUV tests..... this is what I understand

Toby, pardon the temerity to discuss the intricacy of the Queen's English with an English man? (Kidding)

a. Road wheel, ok for racing.
b. The wheel is not for racing purposes but for road use.
a would be what you are talking about (interesting point btw). But b. is what is being discussed in that thread. Looking at the statement, I could see why the question was raised.

But bottom line, I agree with you in the sense that the concern about the Fi being not strong enough for amateur-level racing is un-justified; this is BBS Motorsports Germany we are talking about. Most likely, I think BBS are just protecting themselves against any possible future claims, such as when people damage the wheels at the track, from accidents. I do think that all these super light wheels are more prone to bending with accidental hits, but this risk is not limited to just the Fi.
BTW... the look of the Fi -- I can't stand it. Something unsettling about the design to my eyes. Aesthetically, it is no Dymag.

For anyone interested, the thread that Toby refers to is a GREAT thread on wheel's technology; check out  the posts by Tech1_Mike, in particular the latter ones in response to my questions. Very interesting. http://www.6speedonline.com/forums/997-turbo-gt2/206016-five-lightest-wheels-997-turbo-6.html

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Regards,
Can
997 Turbo + Bilstein Damptronic "Stage 2" ( Review ) + GIAC ECU Tune ( Fast as a torpedo & reversible to stock - Review ) + Cargraphic Exhaust ( Oh heavenly noise! )

cannga:
Very interesting (please note I didn't say right, or wrong, just interesting ) exchange (on 6speedonline.com) on light versus heavy wheel and gyroscopic effect. The guys there don't post here and vice versa, so let me provide the quote.

>>>>>>>>>>>>>>>>>>>>>

Originally Posted by Tech1_Mike

I have the utmost respect for the entire Ruf organization.
Alois Ruf is an innovator par excellence!
That said, I disagree that the gyroscopic effect contributes to stability. No road surface is smooth enough to escape all the effects of gyroscopic precession. Every force applied to a rotating body causes the "gyroscope" to precess in a direction 90 degrees from the applied force. This is one reason why heavy wheels resist turning. (The other is kinetic energy).
Unfortunately, every bump or irregularity in the road, regardless how small, causes these forces to be applied and this precession reaction to occur. The heavier the wheel, the greater the force and the greater the reaction. In addition, the heavier the wheel, the more the impact force is transmitted to the suspension and to the car itself. It's physics. And it is inescapable...

If you were, like me , wondering what on earth PRECESSION is, take a couple aspirins (doctor's order LOL) and follow the article below.
BTW, I am **still** wondering about the 40,000 rpm flywheel in the GT3 R hybrid and whether its gyroscopic effect affects handling, for example when the car is banking at an oval track. Does it have to be near the center of rotation of the car in all planes, so that it sees minimal yaw/pitch/roll angles?

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http://en.wikipedia.org/wiki/Precession
 

Precession of a gyroscope

Precession is a change in the orientation of the rotation axis of a rotating body. It can be defined as a change in direction of the rotation axis in which the second Euler angle (nutation) is constant. In physics, there are two types of precession: torque-free and torque-induced.

In astronomy, "precession" refers to any of several slow changes in an astronomical body's rotational or orbital parameters, and especially to the Earth's precession of the equinoxes. See Precession (astronomy).

..................

Torque-induced

Torque-induced precession (gyroscopic precession) is the phenomenon in which the axis of a spinning object (e.g. a part of a gyroscope) "wobbles" when a torque is applied to it. The phenomenon is commonly seen in a spinning toy top, but all rotating objects can undergo precession. If the speed of the rotation and the magnitude of the torque are constant the axis will describe a cone, its movement at any instant being at right angles to the direction of the torque. In the case of a toy top, if the axis is not perfectly vertical the torque is applied by the force of gravity tending to tip it over.

The response of a rotating system to an applied torque. When the device swivels, and some roll is added, the wheel tends to pitch.

The device depicted on the right here is gimbal mounted. From inside to outside there are three axes of rotation: the hub of the wheel, the gimbal axis and the vertical pivot.

To distinguish between the two horizontal axes, rotation around the wheel hub will be called 'spinning', and rotation around the gimbal axis will be called 'pitching.' Rotation around the vertical pivot axis is called 'rotation'.

First, imagine that the entire device is rotating around the (vertical) pivot axis. Then, spinning of the wheel (around the wheelhub) is added. Imagine the gimbal axis to be locked, so that the wheel cannot pitch. The gimbal axis has sensors, that measure whether there is a torque around the gimbal axis.

In the picture, a section of the wheel has been named dm₁. At the depicted moment in time, section dm₁ is at the perimeter of the rotating motion around the (vertical) pivot axis. Section dm₁ therefore has a lot of angular rotating velocity with respect to the rotation around the pivot axis, and as dm₁ is forced closer to the pivot axis of the rotation (by the wheel spinning further), due to the Coriolis effect dm₁ tends to move in the direction of the top-left arrow in the diagram (shown at 45°) in the direction of rotation around the pivot axis. Section dm₂ of the wheel starts out at the vertical pivot axis, and thus initially has zero angular rotating velocity with respect to the rotation around the pivot axis, before the wheel spins further. A force (again, a Coriolis force) would be required to increase section dm₂'s velocity up to the angular rotating velocity at the perimeter of the rotating motion around the pivot axis. If that force is not provided, then section dm₂'s inertia will make it move in the direction of the top-right arrow. Note that both arrows point in the same direction.

The same reasoning applies for the bottom half of the wheel, but there the arrows point in the opposite direction to that of the top arrows. Combined over the entire wheel, there is a torque around the gimbal axis when some spinning is added to rotation around a vertical axis.

It is important to note that the torque around the gimbal axis arises without any delay; the response is instantaneous.

In the discussion above, the setup was kept unchanging by preventing pitching around the gimbal axis. In the case of a spinning toy top, when the spinning top starts tilting, gravity exerts a torque. However, instead of rolling over, the spinning top just pitches a little. This pitching motion reorients the spinning top with respect to the torque that is being exerted. The result is that the torque exerted by gravity - via the pitching motion - elicits gyroscopic precession (which in turn yields a counter torque against the gravity torque) rather than causing the spinning top to fall to its side.

Precession or gyroscopic considerations have an effect on bicycle performance at high speed. Precession is also the mechanism behind gyrocompasses.

Gyroscopic precession also plays a large role in the flight controls on helicopters. Since the driving force behind helicopters is the rotor disk (which rotates), gyroscopic precession comes into play. If the rotor disk is to be tilted forward (to gain forward velocity), its rotation requires that the downward net force on the blade be applied roughly 90 degrees (depending on blade configuration) before, or when the blade is to one side of the pilot and rotating forward.

To ensure the pilot's inputs are correct, the aircraft has corrective linkages which vary the blade pitch in advance of the blade's position relative to the swashplate. Although the swashplate moves in the intuitively correct direction, the blade pitch links are arranged to transmit the pitch in advance of the blade's position.

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Regards,
Can
997 Turbo + Bilstein Damptronic "Stage 2" ( Review ) + GIAC ECU Tune ( Fast as a torpedo & reversible to stock - Review ) + Cargraphic Exhaust ( Oh heavenly noise! )

So look at who's using the BBS FI to set a Nurburgring record?  I guess BBS should clarify..."The wheel is not for racing purposes but for road use...like roads through the Green Hell."