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YOUR RESEARCH996 Underchassis Braces?
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deciding factor
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Reported cause · Original poster
It was the deciding factor for me when I bought a 993 back in the late 90s.
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Suggestion · Original poster
Once we get the suspension from Elephant, we will start to test the car.
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Suggestion
If I'm off-base here, it'd be extremely informative for everyone if you make your brace, bolt the cage in and do an A/B test on-and off-road, with and without stiffeners.
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Suggestion
If I'm off-base here, it'd be extremely informative for everyone if you make your brace, bolt the cage in and do an A/B test on-and off-road, with and without stiffeners.
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We are working on our
996RR Road Rallye
build and my friend, Steve, who races 911s and had suggested I look at ways to stiffen the chassis. He felt the 996/997s could use some help. I've searched on the forum and internet and not able to find any solutions.
I don't think a half cage is practical for many so looked under the car and saw an opportunity for improvement. We decided to fabricate a brace to see what might be possible.
Has this been addressed by anyone?
You can integrate bracing into an underbody aero solution, but the bottom of a C2 is quite flat so you end up reducing ground clearance quite a bit for that marginal gain.
IMO you do not need to stiffen a 996 coupe until you're into race tires + aero territory. It's already much stiffer than many competitive BMW's and will happily support unwise spring rates. Overly stiff makes the car feel sharp and responsive but you lose absolute grip because you're making the tires and dampers do more work, rather than tuning the whole car as a holistic system.
Love the build idea and look forward what you end up doing. To your comment on a half cage not being practical, there is nothing you are attempting to do with this build that is practical. Easiest and cheapest thing you can do to stiffen up the chassis is the half cage.
Thx for the feedback.
A stiffer chassis allows the suspension to work without any chassis flex clouding the suspension's response. I do agree that stickier tires/aero/heavier springs can all make a stock chassis twist more. We created
a brace for the Lotus Elise
that makes a difference with stock tires. Hence my curiosity with the 996 as the rear subframe seems ripe.
We will certainly consider the ground clearance issue with a brace as I also don't like to lose it. This car has bottom out quite a bit and the oil pan is ground away pretty good (bad
)
I guess that depends on how you define practical.
We are making the car work better on rough CA roads and streets - so I think it will be more practical as it will have more ground clearance and suspension compliance. I don't want to lose the rear seats as it is one of the best features of the car for folks with kids. It was the deciding factor for me when I bought a 993 back in the late 90s.
We have some good ideas on a brace that will be more practical than a half cage and not as permanent - in fact the current design is bolt on and off. Porsche felt bracing was important in the rear so created some simple solutions that are practical for factory line assembly and service. You can see them in the picture above. We removed them and installed a more comprehensive solution that should reduce possible flex in that area even more than the stock braces.
Once we get the suspension from Elephant, we will start to test the car. I will get my Ride & Handling Engineer friend to test it vs the stock brace to see if he can tell the difference on the street.
That's not how it works. The chassis is an undamped spring that is part of the entire system of a car, including the damped springs, tire flex and to an extent even wheel flex. Yes, a stiffer chassis will sharpen response, but blindly reducing compliance just removes a tool from your arsenal to reduce load fluctuations at the tire (this is what gives the feeling of confidence and predictability) when you're going over not perfectly even surfaces. The chassis responds faster than the dampers because it is undamped - of course if it's too floppy that will also cause more fluctuations, but the 996 is literally as stiff stock as a caged E36. You have enough already, is my point.
When grip is high you need a stiffer chassis so that the higher loads from the tires don't bully the chassis too much; when it's low, you actually want less so the chassis can help the dampers keep the rubber planted. It's a well studied tuning tool in off-road racing circles and I've built TA winning cars deliberately skipping the cage. If I'm off-base here, it'd be extremely informative for everyone if you make your brace, bolt the cage in and do an A/B test on-and off-road, with and without stiffeners.
We can agree to disagree.
R&H Engineers ask for the stiffest chassis so their suspension tuning is cleaner and not masked by an undamped spring. Manufacturers have switched to stiffer and stiffer chassis for a reason - now CF tubs make these steel or Al unibody seem flexy.
Having worked with several OEM Ride & Handling Engineers, I too have spent time dialing in suspensions. Ultimately we are tuning this car with a set-up that others have not. I want to take chassis flex out, as much as reasonably possible. Yes, I will be recruiting one or two of my Ride & Handling Engineers who have raced 911s to get our set up dialed in. I will test with and without. I am willing to admit that a brace may NOT make a difference. My professional experience suggests that this is a R&D bet worth taking...
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