ProCoach

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fleadh

Tahoelife,

Does the car not have ABS?

If you have the brake bias completely turned in either direction, your system probably isn't optimal. Here's the g-traces from a lap in my GT3 Cup a few months ago at Laguna-- obviously apples to oranges comparison and ignore the absolute values, but compare the slopes/overlaps.



To me it sounds like you don't have the brake bias setup properly. I'd make sure that's squared away before you sweat the data or lap time to much...

-mike

Veloce Raptor

Yeah, I'd agree with fleadh here. If you have adjustable bias, you have turned the 964 from an OEM car with ABS into a manual dual master cylinder brake car? if so, clearly there is too much rear bias.

Randy, if you'd like another set of eyes on your data, feel free to email to me as well. Generally, Peter & I will likely see the same things, but it cannot hurt...

KaiB

Let's be careful here guys.

The OP does not have a dual M/C setup. The car has 3 channel ABS and the bias adj is installed on the single line to the rear brakes. (I don't know if the OP has an ABS interrupt switch like I do).

The adjustable bias is necessary for a car with his brake rig: The original front 964 calipers were moved to the rear and will over power the fronts in many situations unless some means of control for the bias is installed.

This is the reason I questioned the location of the adj lever (full rear vs. full front), as the OP indicated he was locking up the fronts...certainly not possible if the lever is set full open (or closed if installed backwards).

This is the very same setup I run and it performs very well indeed when set up properly.

tahoelife

@ Mike thank you I will study your data for sure realizing that the cars are way different, @Kai VR Pro Coach and MaTT my car has the same setup brake wise as Kai minus I do not have any ABS the ABS system was not working when I got the car the other bit of info is my car was a C4 at birth and Previous owner did the convert so the rear calipers are the original c4 fronts with 36/40 pistons, I now have 993 big reds up front with giro disc rotors. I am having to learn the expensive way with no abs and have flat spotted a few set of fronts now. From what Kai and Mike are saying I think the next step is to sort out the braking system and why the rears are not working. I am going to try and dig in tonight now that family duties from Tday weekend have been met

@ Mike we have met I am the Registrar for GGR look foreword to seeing you run with us again !

Heath

Charles Freeborn

Hope you don't mind a novice chiming in....
I'm gearing up for my 2nd season of HPDE - can't wait to get started. I'm at the point where I'm beginning to fathom how much I don't know.
This year my focus is going to be on consistency ( turn in points, hitting apexes, etc) and smooth inputs. I nearly swapped ends last year by lifting off too quickly in an off camber sweeper.
Car is a bare bones '74 - nicely refurbished suspension with upgrades to SC brakes and sway bars. Engine is stock in all it's 175 hp glory. I'm not at all worried about being fast, just safe and smooth.
Any other suggestions for stepping up to the next level?
Many thanks,
-C

Veloce Raptor

Get as much in-car instruction as you can! And remember to smile! A day at the track sure beats a day at work!!

ProCoach

Fantastic post! Good luck on your sophomore season!

I will say that you can't know if you don't measure... Something as simple as an AiM Solo, Traqmate Basic or VBOX Sport would really allow you to see how consistent you are in braking points, minimum and maximum speeds, cleanliness of throttle-to-brake and brake-release-to-throttle transitions and even where you are beginning, apexing and ending your cornering "arcs."

Overlay several laps using speed, then set aside the areas on track that you are doing the same thing (as evidenced by overlays that are nearly identical) and FOCUS on coming up with a better plan and executing with precision and consistency the areas that look like you did one or more turns ten different ways in ten different laps!

If you don't want to look at a few squiggly lines every now an then, buy an "intelligent video" camera, one that overlays speeds, g's and other information over top of the video, so you can see HOW consistent you are, before you bump it up to the next level in terms of speed, risk and effort.

You would be SHOCKED to see how different things were in the car than how you remember them. The key to accuracy is to know where it can be improved.

It's never been so easy to get good information. The data is not a tattletale, it's a tool, one used by any really good coach or instructor in a variety of ways.

When, and I stress when, you hear several different ways to "skin a cat" from a variety of different, ostensibly experienced instructors, MEASURE and FIND OUT, instead of guessing...

Most of all, have fun! You've got a great car and a great attitude...

Charles Freeborn

Many thanks! Yes, this has been a long time coming - I've had the 911 for going on 15 years - 8 of which it was mothballed. Only last year things settled down enough for me to get it safe to drive at speed. Here's the work done so far on the front suspension:
http://forums.pelicanparts.com/porsc...-re-build.html
I'm collecting parts now for the rear and will have re-furbed SC trailing arms & sway bars done by the start of this season.
The onboard analytical system is enticing. I'll look into that. Meanwhile, I'm incredibly fortunate to have as friends some very experienced (pro) drivers and teachers. I'm scheming ways to get as much input from them as I can. At my age (56) I have no expectations of setting any track records, but I've spent enough time sideways in cars and on motorcycles to fully understand the physics - so it should be fun to say the least...
Home track for me is Portland International Raceway, which is as they say "easy to learn - hard to master". Even after one season I've only got a couple of corners that still confuse (1 & 7), but I'm already seeing how the turns all feed into the next and it's a multi-step dance - understanding and managing inertia sure seems to be the trick.
I'll get at least some in car video and report back when I have more questions. Many thanks again for your input. This forum is a huge resource for us beginners, even if much of it is over our heads.
-C

RickBetterley

Changing from a 993 to a Cayman platform - its going to be different. Can you share your thoughts on how so?
Both cars have race suspensions but the Cayman is more developed. It also has a lot more aero.
Thanks!

ProCoach

More competent, stable and effective. Should not require as much steering input, and much less correction, when required...

Spencer will (and has) hook(ed) you up!

Veloce Raptor

Also, it will have much higher limits and will take rotation much more easily...although once it really starts to spin, it might be more difficult to rein in...

RickBetterley

Thanks, Pete and Dave. This is going to be really different - with a really good run from turn 1 into bus stop braking zone at Watkins Glen, I might touch 130. Shortened gears, of course.
With the Cayman? I'll be approaching at a much higher rate of speed.
That's going to take some getting used to!
This is going to be a blast.

winders

High polar moment cars don't want to turn as easily as low polar moment cars...the flip side is that low polar moment cars spin much easier and are harder to drive at the limit.

From one of Mark Oritz's newsletters:

Within limits, yaw inertia can be coped with by driving technique. In some situations, it can even make the car faster. Overall, though, less yaw inertia is better, particularly when the course demands high yaw accelerations, as when negotiating chicanes or street-circuit turns that come in quick succession. But steady-state handling and ability to put power down are more important. A rear-drive car with only 45% rear weight and a powerful engine is seriously traction-challenged, especially when exiting turns. Any further reduction would not be good.

With more front percentage, you will actually have to stiffen the rear suspension, at least in roll, with respect to the front. Otherwise, you will be adding understeer. The inside rear will then be extremely light when cornering. It probably is now.

One situation where yaw inertia can make a car faster is where the car may unexpectedly encounter a slippery spot in the middle of a turn. If the slippery patch is short enough so the front and rear of the car hit it separately, the car will experience understeer and then oversteer in very quick succession: it will do a wiggle. If it has little yaw inertia, it will do a big wiggle. If it is close to the limit, it may spin. If the driver wants to allow a margin of safety to increase the chances of catching the wiggle before it becomes a spin, for a given level of risk the driver must stay further from the limit in a car with little yaw inertia.

P.S. "Speed" is a rate so "rate of speed" is redundant.

RickBetterley

Thank you for correcting me; you are of course right that I used 3 words when I could and should have used 1.
Much like with cars, in writing less is so often better than more.