Open minded suspension guru
Discussion
Does anyone know a suspension specialist that could offer objective opinion based on theory rather than known and tested 911 set-ups already on the market. I want to try something a little different where all my searches appear to show nobody has been down this road before. I can see in principle my idea should work as the S1 Elise, for instance, has the front axle set-up similar to what I am trying to achieve. McLaren also have a Kinetic anti-roll suspension system, that in principle could work, but the development costs for implementation into a 911 would be prohibitively expensive.
Spoke to Gordon. He is a treasure 
It looks like I have a potential solution. One question though, does anyone know the stock spring rate on a 996 C2 in N/mm for both stock and M030? I have found the data for a GT3:
FRONT: 996.1 GT3
PART NUMBER: 996 343 531 91
SPRING RATE: 35N/mm
Basically my issue is I want to remove the front ARB due to the inherent forces you need to overcome when approaching full lock (not noticeable on a stock car; I have removed PAS). Now OEM manufacturers fit ARB's in order to run as soft a spring as possible to improve compliance...
My thinking is a stock C2 probably has a 25-30N/mm spring rate (as the GT3 is running 35N/mm on the front). With my Ohlins I'm now running 60N/mm on the front also combined with a 18% total mass reduction (260kg). My current set up is to run the rebound adjusters at the mid setting (10 clicks of the possible 20, both front and rear).
My gut feeling is with the higher 60N/mm spring rate, lower mass and running max rebound (20clicks) on the front (keeping the rear at 10clicks), ditching the front ARB should be no problem. Gordon at Proflex agrees and says give it a try. BMW M3's when running serious spring rates get away with removing the ARB's.
Getting TUV approval is another hurdle but I'll face that when the time comes in a few months.
What says the good fellows PH???
It looks like I have a potential solution. One question though, does anyone know the stock spring rate on a 996 C2 in N/mm for both stock and M030? I have found the data for a GT3:
FRONT: 996.1 GT3
PART NUMBER: 996 343 531 91
SPRING RATE: 35N/mm
Basically my issue is I want to remove the front ARB due to the inherent forces you need to overcome when approaching full lock (not noticeable on a stock car; I have removed PAS). Now OEM manufacturers fit ARB's in order to run as soft a spring as possible to improve compliance...
My thinking is a stock C2 probably has a 25-30N/mm spring rate (as the GT3 is running 35N/mm on the front). With my Ohlins I'm now running 60N/mm on the front also combined with a 18% total mass reduction (260kg). My current set up is to run the rebound adjusters at the mid setting (10 clicks of the possible 20, both front and rear).
My gut feeling is with the higher 60N/mm spring rate, lower mass and running max rebound (20clicks) on the front (keeping the rear at 10clicks), ditching the front ARB should be no problem. Gordon at Proflex agrees and says give it a try. BMW M3's when running serious spring rates get away with removing the ARB's.
Getting TUV approval is another hurdle but I'll face that when the time comes in a few months.
What says the good fellows PH???
Thank you Henry, so if I assume the sports springs are around about equivalent of M030 (could be X74 or similar), then going from the 29N/mm spring rate to 60N/mm spring rate, with the lower mass, should mean I can get away without the front ARB.
Besides the pre-load and height adjustment, the only other adjustment is for rebound. No remote reservoirs or the like.
You also throw another spanner into the works by raising the question as to whether the rear ARB could also be removed. Not something I had even considered, as my primary concern was steering input forces rather than the handling. You may be onto something here though. It could potentially give better balance and there is also the additional 2.5kg or so that would be removed.
To give you an idea how they look, here they are with my custom CLR top mounts ready to fit:
Yellow491 said:
Does your dampers have remotes that you can adjust the pressure in,instead of a stiffer spring.
You could try with the rear bar off also
Hi Y491, the Ohlin damper/spring combo is really well judged/balanced. I did consider custom valving or different springs but with the big weight reduction they really do work well with the car. You could try with the rear bar off also
Besides the pre-load and height adjustment, the only other adjustment is for rebound. No remote reservoirs or the like.
You also throw another spanner into the works by raising the question as to whether the rear ARB could also be removed. Not something I had even considered, as my primary concern was steering input forces rather than the handling. You may be onto something here though. It could potentially give better balance and there is also the additional 2.5kg or so that would be removed.
To give you an idea how they look, here they are with my custom CLR top mounts ready to fit:
Steve Rance said:
Rich. How much does the PAS system weigh?
Hi Steve, it is not particularly heavy by itself (pump, reservoir, 1.5l fluid, some light alloy pipes) probably only 5kg or so. I did the PAS&A/C delete together and recorded 21.2kg removed.The reason for the PAS delete was more about reduction in parasitic drag on the engine and achieving the ultimate in feel akin to the good old days of the 964RS or earlier. Removing around 50kg from the engine total has also added many other benefits such as: less heat soak, greater air circulation, simplified servicing, improved weight distribution, more reliable (as less systems)...
Thank you very much gents, I will get back to some of the points made in due course, when i get a few minutes but just to pick up on this:
If I jack up the front axle then apply full lock you can feel that quite a force is required to overcome the ARB. If I disconnect the ARB and do the same thing, there is virtually no effort required to go from full lock to full lock.
Gustavo said:
Does the overall effect on the steering forces, from removing the front ARB, depend on the caster angle of the geometry?
Yes and no is the answer. The castor angle will have an effect but you are kind of limited in what you can do here by the wheel arch. Also high castor angle has a minimal effect when compared with the ARB issue. If I jack up the front axle then apply full lock you can feel that quite a force is required to overcome the ARB. If I disconnect the ARB and do the same thing, there is virtually no effort required to go from full lock to full lock.
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