Hello all, tried searching but didn't come up with much. It seems like the only rear diffusers available are made of carbon fiber, which unless the car is 100% track, I feel like is overkill as the use of carbon is mostly about weight savings. I've been thinking about a rear diffuser to help with stability at highway speeds (70-85mph)(or the occasional high speed blast, let's be honest). I was thinking maybe a diffuser would help, but I can't justify $1,600+ for a carbon piece. Anyone make one out of fiberglass, urethane, etc?

 

What car are you putting it on?

 

What car are you putting it on?

 

No matter what Porsche you're driving, if you're having stability problems at 70-85 miles per hour, lack of a diffuser is not you problem. Before you spend money on aerodynamics, check you tires, alignment and suspension.

 

None of what OP wrote make any sense.

 

Thanks for the tip. My PSS's were installed last month and an alignment was performed at that time. To be clear, it's more when I'm above 85..... Sooo, "shouldn't" be an issue on the street, but if I have a clear highway and want to open it up a bit....

 

How can I make it more clear? I'll try to elaborate better.

 

06 Cayman S. New PSS's with about 7,000 miles. Recently remounted and balanced after winter. Recent alignment performed.

 

Your 2006 Cayman S is designed to have a top speed of 171 mph. If you need more stability at 85mph on the street, there's something wrong with your Cayman that needs to be diagnosed.

What are the list of mods you've done to the car? Simply adding a diffuser won't do much, as aero is a combination of front + rear lift/drag.

 

OP... Here's the long answer:

As already stated above, assuming no strong crosswinds or weird pavement conditions, you should not be experiencing stability issues in your Cayman at the speeds you stated. Have you actually experienced instability above 85 MPH or are you merely anticipating such a condition?

If you have actually experienced instability at high speed, I still think it would be a good idea to revisit your alignment settings. Find an alignment shop with a strong reputation for Porsche alignments, talk to them about the issues you are experiencing, then let them look at your current alignment and make suggestions for an alignment that might make you more comfortable. Be aware, however, that the stability that comes with more aggressive alignment settings may also come with increased or uneven tire wear.

If, on the other hand, you are anticipating instability but haven't yet experienced it, then you may profit from spending some time exploring the upper limits of your car's performance, preferably on track with an instructor. A couple of days of DE with a competent instructor will do wonders for your comfort level both on road and track.

With regard to the issue of a diffuser, take care to use a balanced approach to aero modifications on your car. If you increase the drag on the rear of your car without taking a similar approach on the front, you'll end up with lift on the front which will increase, rather than decrease, instability at higher speeds.

 

Thanks for the comments. @ekam The car is stock. @TMc993 To be honest, I'm feeling the steering get light above 90 and going around a corner. I'm assuming this is early onset lift.

 

What's your alignment setting?

 

 

Come to think of it, these may be the before settings. I don't remember, but I don't have any other photos. From what I remember, the rear camber cannot be adjusted any more and was throwing the rear toe/thrust angle off. Nothing bent in the suspension.

 

I would start by getting a set of GT3 LCA and set the front camber to -1.5 at the minimum. The factory front camber setting suck for sports driving.