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.
I'd be interested in hearing more... I'd have thought someone like Pilbeam would be a good shout for suspension design theory/ kinematics etc?
A few of those small race car constructors ought to know their onions. Maybe look at a list of chassis being used in hill climb?
Ok, not road focussed but probably pretty clued up on theory and simulation etc.
A few of those small race car constructors ought to know their onions. Maybe look at a list of chassis being used in hill climb?
Ok, not road focussed but probably pretty clued up on theory and simulation etc.
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???
CarreraLightweightRacing said:
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???
Afternoon Richie 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???
Spring rates for ROW and US cars here in post 6. Factory ROW front sport springs work out at 29n/mm (but no M030 info) :
https://rennlist.com/forums/996-forum/339648-sprin...
Lots of info on the 996 C2 suspension and factory sport options here :
http://www.neuralblog.com/_content/Porsche/996-Sta...
Though rather annoyingly the table mentioned in the article doesn't feature anywhere ...
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:
My understanding is that it's safer to have a softer front end (higher roll-rate) than the rear, as it makes the car more prone to understeer. So I would go front-disconnected only, initially.
However, if it's got too much understeer, disconnect the rear one, too.
Downside of disconnecting both would be ultimately less cornering grip, but that makes it more fun :-)
However, if it's got too much understeer, disconnect the rear one, too.
Downside of disconnecting both would be ultimately less cornering grip, but that makes it more fun :-)
I get your dampers,its worth trying with out the rear on,corner weight and rake of the car can make a good differance on front end grip and turn in.Also your running very good modern dampers and springs,way better than standard factory parts.
I always used to suffer with understeer on a 911,now never worry about the rear being lively as it aids turn in with a good set up that keeps the car controlable,and never with power steering.
In the wet on full wet tyres,i normaly run the rear disconnected and the front on softest roll bars,some times front off also.
Hillclimbing my little monster, front and back bars are on the softest setting for best results,and when really wet both disconected,its worth trying.I also run some of the very best dampers and springs .
I always used to suffer with understeer on a 911,now never worry about the rear being lively as it aids turn in with a good set up that keeps the car controlable,and never with power steering.
In the wet on full wet tyres,i normaly run the rear disconnected and the front on softest roll bars,some times front off also.
Hillclimbing my little monster, front and back bars are on the softest setting for best results,and when really wet both disconected,its worth trying.I also run some of the very best dampers and springs .
EGTE said:
My understanding is that it's safer to have a softer front end (higher roll-rate) than the rear, as it makes the car more prone to understeer. So I would go front-disconnected only, initially.
However, if it's got too much understeer, disconnect the rear one, too.
Downside of disconnecting both would be ultimately less cornering grip, but that makes it more fun :-)
On my GT3 and 968 we did it the other way around. Softening front ARB normally reduces understeer (although disconnecting it completely will increase roll and may increase it again). And softening rear reduces oversteer. Safer to run softer rear ARB for inexperienced 911 driver. On wet track days / sprints I used to soften both to get quicker laps / times. However, if it's got too much understeer, disconnect the rear one, too.
Downside of disconnecting both would be ultimately less cornering grip, but that makes it more fun :-)
More experienced drivers can run any permutation I suppose
Give Simon Roberts at Cornering Force a call, what he doesn’t know about suspension and vehicle dynamics isn’t worth knowing.
www.corneringforce.com
www.corneringforce.com
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)...
Understood Rich. Looking at the risk/time v reward element of this aspect of the project. The anti roll bar is a fundamental element of the adjustability of the 911 chassis and to a large extent the set up of the front end is critical to the performance and bLance of the car. I see what you are trying to achieve and I applaud your ambition but I’m questioning the benefit when compared to what could be a journey to re invent the wheel (pardon the pun). What makes it harder is that in my experience the 911 has one of the toughest chassis to set up anyway.
I don’t want to p*** on your fire - I love this project - i’m Just worried that the path that this element of it may take you could be never ending.
I don’t want to p*** on your fire - I love this project - i’m Just worried that the path that this element of it may take you could be never ending.
I would say carry on,good effort,a 911 chassis is not difficult, especially later ones are a lot easier to tune the chassis unlike the early models.The important part i am sure you know is getting it right ,when you get it wrong or push the car over its limit,thats when you find out how good the car and weight is.
I have always found unless you can get a min of a 100kg out of the car,it wont make much difference.
Dampers with remotes are great once you get your head around them,you can get the dampers to carry more weight of the car with out increasing the spring,you can start off with a softer spring.
I cant give to much away at the moment,but been involved with a 3 year project on a 996 which now looks like a gt3r,but aiming below 1100kg,engine has no drag,as in its a 3.8 rsr aircooled engine on a quaffe sequential with a tilton tripple plate,revs like a bike engine.
Just working on roll bars at the moment.
Junked all that water stuff!
I have always found unless you can get a min of a 100kg out of the car,it wont make much difference.
Dampers with remotes are great once you get your head around them,you can get the dampers to carry more weight of the car with out increasing the spring,you can start off with a softer spring.
I cant give to much away at the moment,but been involved with a 3 year project on a 996 which now looks like a gt3r,but aiming below 1100kg,engine has no drag,as in its a 3.8 rsr aircooled engine on a quaffe sequential with a tilton tripple plate,revs like a bike engine.
Just working on roll bars at the moment.
Junked all that water stuff!
Does the overall effect on the steering forces, from removing the front ARB, depend on the caster angle of the geometry? If the BMW M3 mentioned in an earlier post achieves a noticeable reduction in steering effort then it might be worth comparing the caster angles and kinematic trail on an M3 versus the 996. If I understand the problem correctly, an increased caster angle gives higher suspension jacking forces which react through the ARB drop-links and increase the steering torque required. I guess there's always the risk that while stiffer springs will compensate for a missing ARB they won't actually reduce the steering effort that much.
Retaining the rear ARB will still allow some roll balance adjustment too; also, would stiffening the rear springs to compensate for removing a rear ARB potentially hurt traction?
I do like the idea though, even if heave and roll of the suspension become coupled at the front, although I can't get my head around the damping requirements - presumably the job of the dampers is made more challenging when the springs are (much) stiffer and the suspension travel is drastically reduced?
Retaining the rear ARB will still allow some roll balance adjustment too; also, would stiffening the rear springs to compensate for removing a rear ARB potentially hurt traction?
I do like the idea though, even if heave and roll of the suspension become coupled at the front, although I can't get my head around the damping requirements - presumably the job of the dampers is made more challenging when the springs are (much) stiffer and the suspension travel is drastically reduced?
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