Spring rates....450 fronts and 275 rear?
06-30-2011, 12:59 AM
#61
i had no experience prior to ordering my setup and after reading i decided to go with a rear sway bar for several reasons:
-lower spring rate for improved ride "comfort"
-lower spring rate may not stress upper mount as bad (if it is even an issue)
-MO30 sway bar and KLA drop links allow for some simple adjustment
jim, you sound like a guy i should meet and learn from. what are the chances you are in the twin cities area?
-lower spring rate for improved ride "comfort"
-lower spring rate may not stress upper mount as bad (if it is even an issue)
-MO30 sway bar and KLA drop links allow for some simple adjustment
jim, you sound like a guy i should meet and learn from. what are the chances you are in the twin cities area?
06-30-2011, 06:53 PM
#62
on an unrelated note, I read that whole McLaren article, and they do have "swaybars" they're a really sweet hydraulic system that connects the dampers and is completely adjustable electronically so they can modify the rates at turn in, apex, and track out.
06-30-2011, 08:49 PM
#63
Three Wheelin'
First, for a street 944, daily driver type, most of this does not matter.
You can drive around w/ no swaybars. Really doesn't matter what the
spring rates are, doesn't matter what shocks you have, or condition. The
car will still do its job, getting from point A to B.
When setting up a car for competitive high performance driving, whether
for auto-x, or high speed road course DE/Racing, then of course all of
that does matter.
Swaybars are not a band aide, only used to compensate for low spring rates when
trying to improve street ride quality. They increase the roll
stiffness/resistance of the front and rear of the car, which is somewhat
of a different function than springs alone accomplish. Bar size/rates
should be balanced with the overall suspension setup.
Only time I have seen swaybars taken off 944s, are when auto-xing a track
car setup for a road course. Need to get the rear to rotate more in tight
turns, so taking off the front swaybar will help to get the car to turn.
That is a band aide fix, because the spring rates were not balanced/setup
for that type of use.
The use of Z-bars on late 60's VW bugs and Karmann Ghias probably is not
directly applicable to a 944 suspension setup. Nor is the McLaren, as
the design and technology of the suspension differ greatly. Maybe an
interesting theoretical automotive suspension design discussion, but not
immediately applicable to our chassis.
Very seldom will you ever see a 944 pickup an inside tire on a road
course. It will never be a rear, only an inside front. So no reason to
remove the rear bar to avoid this anomaly. And generally will only occur
due to track surface variation at trackout (so may only ever happen at one
corner of one track, and no where else). Older 911s more commonly lift
the front inside, much due to suspension travel limits of very stiff
torsion bars, a huge rear weight bias, and yes stiff front sway bars. The
front wheel drive, front engine cars are the ones chronically prone to
lifting inside rears, especially on auto-x courses.
The Bilstein turbo cup suspension was developed w/ Porsche for the turbo
cup cars. The Cup suspension was designed using 30mm front bars and 21mm
rear bars. No way that the bilstein suspension was intended to be used w/
smaller or no sway bars.
Also, Porsche used koni dbl adjustable 8742 struts and 8242 rear coilovers
on the US Escort/Cups and the Firehawk Clubsports, w/ the same springs and
same swaybars as used on the Bilstein equipped Euro & Canadian Cups. The
konis are actually valved to handle at least equal if not somewhat higher spring rates than the bilsteins.
Tires pressures are not directly used to tune handling. Incorrect tire
pressure will affect handling because it may cause the tire to operate
outside of its designed temperature range. The optimum tire pressures are
based on the brand/model (sidewall construction and rubber compound) of
the tire, not on the brand of shock.
I would recommend that others, before spending money based on any specific
advice from this thread (or any forum thread), look at how 944s have been
setup to auto-x and race by competitive individuals and shops (for
amateur and pro race series) over the years.
The factory Turbo Cup/Escort cars, the IMSA Firehawk S2s, any current club
series where 944s are present in numbers and competitive - PCA Club
racing, NASA, SCCA spec series in North America, or equivalent series
elsewhere. As allowed by rules, you will always find higher spring rates,
higher damping rates, and larger front & rear sway bars.
And look at more modern dedicated factory race cars - 997 Cups and RSRs
use front and rear sway bars, and all P-factory production based race cars
always have. No comfort or band aid compromises on those cars. Even 962s
used sway bars, and it wasn't to compensate for inadequate spring rates.
You can drive around w/ no swaybars. Really doesn't matter what the
spring rates are, doesn't matter what shocks you have, or condition. The
car will still do its job, getting from point A to B.
When setting up a car for competitive high performance driving, whether
for auto-x, or high speed road course DE/Racing, then of course all of
that does matter.
Swaybars are not a band aide, only used to compensate for low spring rates when
trying to improve street ride quality. They increase the roll
stiffness/resistance of the front and rear of the car, which is somewhat
of a different function than springs alone accomplish. Bar size/rates
should be balanced with the overall suspension setup.
Only time I have seen swaybars taken off 944s, are when auto-xing a track
car setup for a road course. Need to get the rear to rotate more in tight
turns, so taking off the front swaybar will help to get the car to turn.
That is a band aide fix, because the spring rates were not balanced/setup
for that type of use.
The use of Z-bars on late 60's VW bugs and Karmann Ghias probably is not
directly applicable to a 944 suspension setup. Nor is the McLaren, as
the design and technology of the suspension differ greatly. Maybe an
interesting theoretical automotive suspension design discussion, but not
immediately applicable to our chassis.
Very seldom will you ever see a 944 pickup an inside tire on a road
course. It will never be a rear, only an inside front. So no reason to
remove the rear bar to avoid this anomaly. And generally will only occur
due to track surface variation at trackout (so may only ever happen at one
corner of one track, and no where else). Older 911s more commonly lift
the front inside, much due to suspension travel limits of very stiff
torsion bars, a huge rear weight bias, and yes stiff front sway bars. The
front wheel drive, front engine cars are the ones chronically prone to
lifting inside rears, especially on auto-x courses.
The Bilstein turbo cup suspension was developed w/ Porsche for the turbo
cup cars. The Cup suspension was designed using 30mm front bars and 21mm
rear bars. No way that the bilstein suspension was intended to be used w/
smaller or no sway bars.
Also, Porsche used koni dbl adjustable 8742 struts and 8242 rear coilovers
on the US Escort/Cups and the Firehawk Clubsports, w/ the same springs and
same swaybars as used on the Bilstein equipped Euro & Canadian Cups. The
konis are actually valved to handle at least equal if not somewhat higher spring rates than the bilsteins.
Tires pressures are not directly used to tune handling. Incorrect tire
pressure will affect handling because it may cause the tire to operate
outside of its designed temperature range. The optimum tire pressures are
based on the brand/model (sidewall construction and rubber compound) of
the tire, not on the brand of shock.
I would recommend that others, before spending money based on any specific
advice from this thread (or any forum thread), look at how 944s have been
setup to auto-x and race by competitive individuals and shops (for
amateur and pro race series) over the years.
The factory Turbo Cup/Escort cars, the IMSA Firehawk S2s, any current club
series where 944s are present in numbers and competitive - PCA Club
racing, NASA, SCCA spec series in North America, or equivalent series
elsewhere. As allowed by rules, you will always find higher spring rates,
higher damping rates, and larger front & rear sway bars.
And look at more modern dedicated factory race cars - 997 Cups and RSRs
use front and rear sway bars, and all P-factory production based race cars
always have. No comfort or band aid compromises on those cars. Even 962s
used sway bars, and it wasn't to compensate for inadequate spring rates.
My examples were to illustrate concepts, not specific cases. The Bilstein comment was not Porsche-specific.
Tyres are spring/mass/damper systems just like shocks and springs, and have interaction with the suspension response.
The frequency-dependent response crossover point between a GENERALISED Bilstein shock/spring arrangement and the tyre's own spring/damping/mass frequency-dependent response is GENERALLY at a different point to a koni setup and OFTEN requires SOME lowering of the tyre pressure to obtain best PERFORMANCE.
I am not talking about tuning handling here.
VW Beetle suspension is CONCEPTUALLY similar to ours in that the front camber curve is COMPARATIVELY shallow and the rear camber curve is COMPARATIVELY steep. The front roll centre is RELATIVELY low and the front roll centre is RELATIVELY high.
Therefore the CONCEPT of increasing the front roll stiffness/heave stiffness ratio and reducing the rear roll stiffness/heave stiffness ratio is relevant.
Once you think through these CONCEPTS, they agree with all of your examples. Good examples too. Most of my suspension work has been with vehicles that have far more extreme envelope requirements than the examples you mention, so I tend to think more conceptually rather than iteratively.
A car is only there to get the tyres around the track as quickly as possible!
Cheers,
Mike
06-30-2011, 10:04 PM
#64
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Don't forget that Porsche put in a stiffer torsion bar and NO rear sway bar in a few early 944's. How do I know? My 83 had no rear swaybar and 23.5mm torsion bar (I took it appart to replace the bushings and found out it was larger than the stock 23mm)
07-02-2011, 10:13 PM
#65
Three Wheelin'
A lot of the current interest in interconnected suspension comes from a seminal artical in Racecar Engineering about 10 years ago. It suggested a mechanism for creating practical "warp-soft" suspensions by interconnecting diagonally opposite suspension elements. Usually only practical with hydraulics but I built a prototype using pullrods and cables. Cool but not relevant to 944's!
Another of the biggest conceptual/inspirational suspension developments of recent history is the inerter. Doh!
Cheers,
Mike
Another of the biggest conceptual/inspirational suspension developments of recent history is the inerter. Doh!
Cheers,
Mike
07-02-2011, 10:43 PM
#66
Rennlist Member
Seriously? If that were the case, we would all be driving Kias around. Don't forget we are on a Porsche board and we are talking about suspension on a 944.
I honestly did not read the rest of your drabble, because you have yet to post any logic or evidence behind your findings. It's all been hearsay and pulling from the rear. Just stop already and let us big boys try and fix the current issue with the lack of knowledge towards this subject.
I honestly did not read the rest of your drabble, because you have yet to post any logic or evidence behind your findings. It's all been hearsay and pulling from the rear. Just stop already and let us big boys try and fix the current issue with the lack of knowledge towards this subject.
07-03-2011, 12:41 PM
#67
Race Car
Seriously? If that were the case, we would all be driving Kias around. Don't forget we are on a Porsche board and we are talking about suspension on a 944.
I honestly did not read the rest of your drabble, because you have yet to post any logic or evidence behind your findings. It's all been hearsay and pulling from the rear. Just stop already and let us big boys try and fix the current issue with the lack of knowledge towards this subject.
I honestly did not read the rest of your drabble, because you have yet to post any logic or evidence behind your findings. It's all been hearsay and pulling from the rear. Just stop already and let us big boys try and fix the current issue with the lack of knowledge towards this subject.
Since you mention needing to touch up, I'd recommend a book by Allan Staniforth over Carroll Smith. It is called "Competition Car Suspension: A Practical Handbook." However, if you are a fan of Carroll Smith, if you'll turn to page 210 of "Engineer to Win," and read teh paragraph under "Load Transfer and teh antiroll bar as history," about 2/3 of the way down, you will see the sentence: "EVERY self-respecting racing car has featured an anti-roll bar at each end for decades now...."
Now, I know the point you are making, and again, theories abound, but that is what Carroll Smith's observations about the prominence of bars in racing applicaions are. He goes on to say.....".....and, in the interest of tightened response and reduced understeer, most self-respecting passenger cars have had added a rea bar to the front one that they have had forever. The passenger car people use them to limit body roll. WE also use them to limit body roll -- BUT we also use them as a quick adjustment to the basic understeer/oversteer balance of the racing car, AND as a crutch." That is how it is written in the book, teh emphasis is his, not mine.
I've been under a multiple time 944 Super Cup Championship winning car. He uses a rear bar. I've been under plenty of other 944 race cars, and every one I've seen uses a rear bar. There is one exception. Folks will tend to disconnect it when it rains. But that has been the only time I've seen 944's run with no bars.
07-03-2011, 02:42 PM
#68
Drifting
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Seriously? If that were the case, we would all be driving Kias around. Don't forget we are on a Porsche board and we are talking about suspension on a 944.
I honestly did not read the rest of your drabble, because you have yet to post any logic or evidence behind your findings. It's all been hearsay and pulling from the rear. Just stop already and let us big boys try and fix the current issue with the lack of knowledge towards this subject.
I honestly did not read the rest of your drabble, because you have yet to post any logic or evidence behind your findings. It's all been hearsay and pulling from the rear. Just stop already and let us big boys try and fix the current issue with the lack of knowledge towards this subject.
With regards to sway bars, yes you can say well I'd rather have more spring and no sway bar because of the jacking effect. Well hey if you can dial in your suspension by reading a board and taking a guess then by all means go for it. But can your damper handle all that spring? Unless it's a $2K plus system for shocks alone, chances are it can't.
Do you think you are smarter than Porsche (or ANY manufacturer for that matter), for years and years, with millions & millions in R&D? Hell if it was as simple as increasing spring rates & removing sway bars to go faster then 95% of us are doing it wrong.
and my contribution to this thread is, with Bilstein Firehawk front struts & Escort Cup rears I ran 400/200 with 968 M030 bars (rear set to middle), with a straight up alignment, and the car handled like it was on rails. With a 225/50 R-Compound tire the street driving was nice and firm, not too harsh.
07-03-2011, 07:30 PM
#69
Three Wheelin'
Since you mention needing to touch up, I'd recommend a book by Allan Staniforth over Carroll Smith. It is called "Competition Car Suspension: A Practical Handbook." However, if you are a fan of Carroll Smith, if you'll turn to page 210 of "Engineer to Win," and read teh paragraph under "Load Transfer and teh antiroll bar as history," about 2/3 of the way down, you will see the sentence: "EVERY self-respecting racing car has featured an anti-roll bar at each end for decades now...."
Cheers,
Mike
07-06-2011, 12:41 PM
#70
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I was going from memory! Motion ratio of 0.94 seems about right. That would imply zero offset and a 20 degree strut inclination.
The 1:1 ratio is modified by roll centre effects and sway bars. I run much less negative rake than most people which has a notable effect on front/rear relative roll stiffness. I'm also running 235/265 tires.
And of course, on our RHD cars the battery is in the boot!
The 1:1 ratio is modified by roll centre effects and sway bars. I run much less negative rake than most people which has a notable effect on front/rear relative roll stiffness. I'm also running 235/265 tires.
And of course, on our RHD cars the battery is in the boot!
07-06-2011, 02:08 PM
#71
Race Car
and my contribution to this thread is, with Bilstein Firehawk front struts & Escort Cup rears I ran 400/200 with 968 M030 bars (rear set to middle), with a straight up alignment, and the car handled like it was on rails. With a 225/50 R-Compound tire the street driving was nice and firm, not too harsh.
Setup #2. Same, but moved up to 245's (17's - Hoosier Cups, very similar to R6) at all four corners. Changed rear bar to a 16mm to compensate. Remained incredibly well balanced, but leaned WAY too much.
Setup #3. Same, but moved up to 968 M030 bars (30mm front, 19mm adjustable rear). Set rear bar to middle position. A bit of understeer, mostly at mid corner. Added another 1/2 degree of negative camber. Very well balaned.
Setup #4. Put on my 18" wheels - 245 front, 285 rear, Hoosier R6. Moved rear bar to full stiff. Bad understeer at mid corner, most pronounced in the esses and sweeping turns when I added throttle. I was pretty convinced at this point that my problem was that I needed stiffer springs in the rear.
So after talking with Karl at Racer's Edge, I ordered some 850# springs for the rear. We benchmarked the front/rear balance from his car, which runs the same tires. However, my sway bars are VERY different from his. I assume he doesn't want that advertised, so I won't do that. But I am fully anticipating softening my rear bar before I take it out next month.
07-06-2011, 08:08 PM
#72
Three Wheelin'
