The time/distance from A to B is only part of the story, as the two entry lines are different in the approach as well- you're going to be able to stay on throttle longer and brake later for the tight line, and will spent a lot more time than 2 seconds in the longer sweeper- probably more than 4 seconds total. You'd also have to account for the time spent tracking out to get to the wide entry point, and then tracking back in after exit. To do this properly, the calculation really needs to start at the previous element and end at the next, and compare the complete time spent between the two points.

I found the notes I made of a sweeper we had an an autocross in 2010 that I took the time to do very detailed calculations on- in my case I modeled the exit as restricted (feeding a chigago box) but the entry was wide open and I was very curious how best to take it. I ran three scenarios using 1g cornering, 1g braking and 0.5g acceleration. The two wider entries start slightly back compared to the tight line due to having to drive out wide to get there.

Tight (green): 8.395 sec
Late apex (blue): 8.404 sec
Geometric apex (magenta): 8.533 sec

Qbr8V2d.png

Note the brake points prior to entry into the chicago box: it's counter-intuitive, but the wide geometric line, despite having the highest cornering speed, resulted in the slowest speed of the 3 lines in the transition zone, because both the tight radius and late apex finished up sooner and allowed greater acceleration- thus the green and blue lines reached 36.3 and 36.9mph respectively and had to get on the brakes earlier than the magenta line which was only at 34.1mph when it hit that brake zone. What surprised me was the tiny different between the tight & late apex lines; if this had been a longer straightaway, the late apex would likely have been the fastest line.

Something to chew on

I'm really intersted in pivot cones, too, but it's extremely difficult to mathematically model tight corners as the front tires are operating at much higher slip angles than the rear and you're not going to be able to hold as many gs in a tight corner as a more open corner.

 

Ok. Got the car. The build is in progress....albeit slightly limited right now.

I have XRR spec wheels with Bridgestones. Going to start with 255 front and 275 rear.

Front bar will be here tomorrow. Going to start at middle setting but based upon my experience will likely go to 2 of 5.

Question: Are wheel studs legal in street? Ugh, I hate wheel bolts or whatever the call the porsche setup.

Alignment will be Saturday. Going to start with max front camber, rear camber to match. Front toe = zero, rear camber = .1 per side or was that .1 total?

So far the car is amazing. It has been a struggle to find the limits of lateral grip. I will say that roll on the throttle versus an aggressive stab results in better rotation than inner wheel spin, can't wait for the bar.

First event is likely this weekend in Knoxville and then Wilmington the following weekend.

 

Bummed I'll be missing the Wilmington Champ. Watched Junior and Daddio duke it out in AS this weekend at the Pro, was quite a sight.

 

Really good!

You proved Taruffi correct when he wrote (I paraphrase) "connected curves should be taken in the most direct way" I.e. On a mutual tangent.

If the inner radius is constrained,as by your road (or cones set in a circle) I agree it does no good to go wide. You have driven in the wrong direction only to end up on the same path at the same velocity.
But, if you can flatten the arc, as in my example, there are gains to be had by going wide.
I think whoever designed the moultrie course had some understanding of this complexity. One 180 (my example) was open, open, open (entry, path, exit) the next was open, closed, closed. The last was closed, open, closed. Tricky SOB!

 

Yes, they're legal in SCCA Street classes. (And in probably every other SCCA class as well.)

You can also convert centerlock attachment systems (like on the GT3) to stud/nut or bolt systems.

 

Got a chance to weigh the stock wheels and OZ wheels today. Tires are also on the wheels.

Stock 19" Carrera S Wheels with stock sized rubber.

Front - 45.2 lbs
Rear - 53.0 lbs

18" OZ XRR spec wheels, w/255 front and 275 rear tires
Front - 43.1
Rear - 47.7

So thats a total unsprung weight savings of 14.8lbs total. Not huge, but it is something.

 

I'm still guessing the XRR setup is legal on the narrow body 996 too. Sure would help with the 315 Rivals I have coming, although a 315 A6 was fine. When I used to run 245/40 BFG R1s up front in A Stock, they rubbed the spring perch and wheel well, so instead of getting the 245/40/18 Rival-S, I am going to get 255/35/18 Bridgestones for the front. Hopefully bridgestone will come out with some better-sized rear tires in 18" in the future.

 

Porsche Exclusive
- I have been reading and it appears there is a LSD for the 987.1 listed.

How can I get documentation on this? Is it as easy as just going to the Porsche dealer and asking? I also assume they are the only place I can get the A street legal diff (if its legal) to have it put in?

 

There's a guy in Memphis who can install and set it up for you, if it's legal.
(I doubt that it is.)

 

I guess you know that XRR for the 911 is not the same as XRR for the Cayman.

 

Yeah, thats the mission right now. Getting someone who actually knows is the difficult part. I will stop by the local dealer tomorrow.

 

I set up and installed my own diff, but I'm equal parts ballsy and stupid.

On mobile right now, I'll dig up a link I followed when I get to a desktop.

EDIT:
Here's the post I found that convinced me I could do it myself.
And here's how I did mine.

A Boxster should be the same with the exception that your drivetrain is 180° wrong. The two things you have to get right are the overall width, as that controls how much tension is on the carrier bearings, and the lateral position as that controls your gear mesh.

The official Porsche procedure, at least for the old cars, is very involved. There's special tools, pinion depth, all that jazz, the kind of nightmare you'd expect. BUT that's for setting up a brand new R&P. If you have something that was already set up properly, and works fine, you should be able to swap a diff and set it back the exact same and it should still be correct. At least that was my theory. I've put maybe 5,000 miles on the car since, and the gears aren't any louder than before I did it, so I know at least I didn't completely do it wrong.

 

It doesn't sound too hard. Documenting if it is legal or not appears to be more difficult.

 

I am aware that it is different, however it is the same in that it is more better than the standard wheels. For whatever reason, I've only seen XRR 996s when they are wide body.

 

Ah, gotcha. According to this '06 brochure, XRR was an option but 220 was not. This 07 Cayman brochure shows the same.