Autocross updates: tires, approach ...
07-16-2002, 04:29 PM
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Autocross updates: tires, approach ...
I was hoping to get some updates from your various autocross campaigns. I've done my 3rd event with the local PCA, so I'm still learning. I've closed the gap between the street-tire leaders from 2 to 1 second, so now I'm within striking distance (watch out, Mike!).
I've been working on both the car and my driving. I tried something last weekend which seemed to work. With plenty of gas in the tank, I dropped my front pressure to 36 psi and left the rears at 44 (I started at 40/44). Well, I turned in my best time with that set up.
Unfortunately, I can't confirm that that was the key ingredient since my times varied a bit(3-second range) and, of course, the best time occurred during my last run. At the very least, it didn't hurt me and the front definitely felt softer in the tight turns.
Jim Michaels, I got under my car to see if I could unhook the sway bar, but my mechanic must've welded it on (no doubt, to keep me out of trouble). I'll definitely work it loose for next time.
But it always seems to comes back to driving. Knowing the track and your car's capabilities are key. The leaders know how to attack the course while I'm still learning it; their actions are deliberate while I'm being tentative. And as soon as I hesitated--I knew--it was all over. Next time, I'll walk it a couple times and take a pad of paper.
Any thoughts on the setup or approach? Anyone try a near-empty tank? Anyone have success with adjustable shocks?
I've been working on both the car and my driving. I tried something last weekend which seemed to work. With plenty of gas in the tank, I dropped my front pressure to 36 psi and left the rears at 44 (I started at 40/44). Well, I turned in my best time with that set up.
Unfortunately, I can't confirm that that was the key ingredient since my times varied a bit(3-second range) and, of course, the best time occurred during my last run. At the very least, it didn't hurt me and the front definitely felt softer in the tight turns.
Jim Michaels, I got under my car to see if I could unhook the sway bar, but my mechanic must've welded it on (no doubt, to keep me out of trouble). I'll definitely work it loose for next time.
But it always seems to comes back to driving. Knowing the track and your car's capabilities are key. The leaders know how to attack the course while I'm still learning it; their actions are deliberate while I'm being tentative. And as soon as I hesitated--I knew--it was all over. Next time, I'll walk it a couple times and take a pad of paper.
Any thoughts on the setup or approach? Anyone try a near-empty tank? Anyone have success with adjustable shocks?
07-16-2002, 06:16 PM
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Messr. Donuts,
You have a habit of starting threads that are intersting to me.
At the risk of giving away trade secrets.....
IMHO, you are on the right track WRT tire pressures. I am running Victoracers (225/50-16, 245/45-16), and set them to 30F/40R cold (cold being defined as whatever the ambient temp is in my garage at the time).
My second event in the car was an SCCA National event (at Jack Murphy Stadium, which as far as autocross goes, is a pretty open course) with hardly any gas in the tank (on the second day/last lap, I got some fuel starvation), and no spare, tools, etc.
While I admittedly was still getting my feet wet with the C2, I got the distinct impression that the front wheels wanted to lift at the slightest application of throttle. It just flat out did not allow ANY meaningful use of power without massive understeer unless the front wheels were pointed DEAD NUTS straight ahead. Slaloms are no fun when you can't really feed in any power.
I spoke to a top shelf SCCA/PCA driver at the event mentioned above. This guy has actually won a Speedvision Cup race on TV, and was my instructor at a Evolution Autocross School. He is also a contract Kumho driver. He has experience with Porsche 911s. He told me that the key to setting the pressures in a 911 is as follows:
1. Lower the front pressure as much as required so that the tires start to roll over onto the shoulder. Reason being is that you need to soften the front.
2. Raise the rear presuures as much as needed to STOP the rears from rolling over too much. Reason being that you need to stiffen the rear.
Experimentation with this approach has lead me to 30/40.
The following may not directly apply to you since I think you have swapped springs, but my bone-stock C2 with the front perches bottomed out still looks silly (way too high!) with no gas in the tank and no weight in the front.
So, to distill that down to "What do I do?", I run a full tank, and leave the spare in. The ride height in front drops significantly, and thus improves camber.
The courses I have been running with PCA are pretty wide open (we run on either real race tracks, or psuedo race tracks that are used by local law inforcement for driver training).
At my current state of knowledge about the car, I would say its pretty damn nuetral, with a slight bias toward oversteer (I actually prefer that. I HATE a car that plows). I can dial up oversteer or understeer on command with my right foot and steering wheel.
Of course, if you find yourself on a tight-*** autocross where you are needing 1st gear, pack up and go home. She's going to PLOW (or take the advice of those who suggest lossening the front sway bar). I personally strive to avoid those courses.
As I said in a different thread, if your times are varying by 3 seconds, you are still on the steep part of the learning curve, and any changes to the car will be masked by what you are doing or not doing behind the wheel. When you can run times that are consistent, thats the time to tweak the car. And BTW, only change ONE THING AT A TIME, or you will be lost!
I ran a PCA event last weekend at a Police Training track. I got to take eight laps. My first 5 laps were within a couple tenths of each other. My 6th was a throw away (almost looped it), my 7th and 8th I improved, but the point is my best time was only about 1/2 second quicker then my worst.
At this point, a change in line, or a change to the car should be fairly noticeble.
OK, thats my contribution to this thread. If these things work for you, you owe me a beer someday. If they don't, my name is Jack <img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" /> .
Reagrds,
Brian
<img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" />
You have a habit of starting threads that are intersting to me.
At the risk of giving away trade secrets.....
IMHO, you are on the right track WRT tire pressures. I am running Victoracers (225/50-16, 245/45-16), and set them to 30F/40R cold (cold being defined as whatever the ambient temp is in my garage at the time).
My second event in the car was an SCCA National event (at Jack Murphy Stadium, which as far as autocross goes, is a pretty open course) with hardly any gas in the tank (on the second day/last lap, I got some fuel starvation), and no spare, tools, etc.
While I admittedly was still getting my feet wet with the C2, I got the distinct impression that the front wheels wanted to lift at the slightest application of throttle. It just flat out did not allow ANY meaningful use of power without massive understeer unless the front wheels were pointed DEAD NUTS straight ahead. Slaloms are no fun when you can't really feed in any power.
I spoke to a top shelf SCCA/PCA driver at the event mentioned above. This guy has actually won a Speedvision Cup race on TV, and was my instructor at a Evolution Autocross School. He is also a contract Kumho driver. He has experience with Porsche 911s. He told me that the key to setting the pressures in a 911 is as follows:
1. Lower the front pressure as much as required so that the tires start to roll over onto the shoulder. Reason being is that you need to soften the front.
2. Raise the rear presuures as much as needed to STOP the rears from rolling over too much. Reason being that you need to stiffen the rear.
Experimentation with this approach has lead me to 30/40.
The following may not directly apply to you since I think you have swapped springs, but my bone-stock C2 with the front perches bottomed out still looks silly (way too high!) with no gas in the tank and no weight in the front.
So, to distill that down to "What do I do?", I run a full tank, and leave the spare in. The ride height in front drops significantly, and thus improves camber.
The courses I have been running with PCA are pretty wide open (we run on either real race tracks, or psuedo race tracks that are used by local law inforcement for driver training).
At my current state of knowledge about the car, I would say its pretty damn nuetral, with a slight bias toward oversteer (I actually prefer that. I HATE a car that plows). I can dial up oversteer or understeer on command with my right foot and steering wheel.
Of course, if you find yourself on a tight-*** autocross where you are needing 1st gear, pack up and go home. She's going to PLOW (or take the advice of those who suggest lossening the front sway bar). I personally strive to avoid those courses.
As I said in a different thread, if your times are varying by 3 seconds, you are still on the steep part of the learning curve, and any changes to the car will be masked by what you are doing or not doing behind the wheel. When you can run times that are consistent, thats the time to tweak the car. And BTW, only change ONE THING AT A TIME, or you will be lost!
I ran a PCA event last weekend at a Police Training track. I got to take eight laps. My first 5 laps were within a couple tenths of each other. My 6th was a throw away (almost looped it), my 7th and 8th I improved, but the point is my best time was only about 1/2 second quicker then my worst.
At this point, a change in line, or a change to the car should be fairly noticeble.
OK, thats my contribution to this thread. If these things work for you, you owe me a beer someday. If they don't, my name is Jack <img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" /> .
Reagrds,
Brian
<img src="graemlins/drink.gif" border="0" alt="[cherrsagai]" />
07-16-2002, 06:41 PM
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Joey:
Some of my competitors used to run with about a quarter tank of fuel. Sometimes got fuel starvation in hard turns. I run with tank over half full. Some also remove the spare tire, but I leave it in. I've seen a 911 driver add a sack of sand in front trunk for autox. I was told that Don Kravig (Precision Motion, Riverside, CA, now deceased) used to do that. Hope you hear from someone who lightens the front.
I think it might be pretty hard to weld the sway bar link that one would remove for autox. Maybe he welded a sway bar bracket, which are known to crack. There is a swivel joint in the link that needs to be able to move around.
The link is about 7" long with a bolt, washer, and lock nut at each end. To remove the link, jack up both sides about the same amount (in gear, hand brake on, and rear wheels chocked). Remove the wheel on the side you want to remove the link from (I remove from the passenger side). Look for the down link from the sway bar on the other side of the rotor. The bolt is on the far side of the bottom connection and on the near side of the top connection. You can use a socket wrench (17 mm) on the lower connection, but mine won't fit in the tight space for the upper connection (a ratchet wrench will, if you can find a 17 mm). You may need a very thin 16 mm wrench (found at bike shops) to hold the bolt on the other side of the joint as you loosen the lock nut. After removing the lock nuts at each end, just push and pull a little on the link to remove it. It shouldn't be hard, unless you forgot to jack up the other side of the car, of course. Now paint a big "B" on the bottom of the link so you'll know which end goes on the bottom when you replace it.
The above description seems longer than needed for such a simple job (at least it will eventually come to be simple), but I did this for the first time with only the description "remove the down-link on one side." It took me over an hour to learn everything else from direct personal experience. I try to learn as much as possible from other peoples' experiences.
Some of my competitors used to run with about a quarter tank of fuel. Sometimes got fuel starvation in hard turns. I run with tank over half full. Some also remove the spare tire, but I leave it in. I've seen a 911 driver add a sack of sand in front trunk for autox. I was told that Don Kravig (Precision Motion, Riverside, CA, now deceased) used to do that. Hope you hear from someone who lightens the front.
I think it might be pretty hard to weld the sway bar link that one would remove for autox. Maybe he welded a sway bar bracket, which are known to crack. There is a swivel joint in the link that needs to be able to move around.
The link is about 7" long with a bolt, washer, and lock nut at each end. To remove the link, jack up both sides about the same amount (in gear, hand brake on, and rear wheels chocked). Remove the wheel on the side you want to remove the link from (I remove from the passenger side). Look for the down link from the sway bar on the other side of the rotor. The bolt is on the far side of the bottom connection and on the near side of the top connection. You can use a socket wrench (17 mm) on the lower connection, but mine won't fit in the tight space for the upper connection (a ratchet wrench will, if you can find a 17 mm). You may need a very thin 16 mm wrench (found at bike shops) to hold the bolt on the other side of the joint as you loosen the lock nut. After removing the lock nuts at each end, just push and pull a little on the link to remove it. It shouldn't be hard, unless you forgot to jack up the other side of the car, of course. Now paint a big "B" on the bottom of the link so you'll know which end goes on the bottom when you replace it.
The above description seems longer than needed for such a simple job (at least it will eventually come to be simple), but I did this for the first time with only the description "remove the down-link on one side." It took me over an hour to learn everything else from direct personal experience. I try to learn as much as possible from other peoples' experiences.
07-16-2002, 07:53 PM
#4
Burning Brakes
Brian, great info. Coincidentally, I just switched to Victoracers in the EXACT same sizes you are using. I've only run one event on them and used 40 psi cold front and rear. Your comments about softening up the front make sense. At my next event, I'm going to try my first run with the fronts at 40 psi, then drop them to 36, then to 32 (if I don't have too much rollover at 36). I'll report back if I notice a difference.
Drew
92 C2
Drew
92 C2
07-16-2002, 08:35 PM
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Drew,
You may want to do your first 2 runs at the higher pressure, then drop.
The reason is that you will want the tires to get some heat in them before making your evaluations.
You also will need to learn the course. My 1st lap is usually used to see if my perceptions made when walking the course match up with the reality of driving it!
BL
You may want to do your first 2 runs at the higher pressure, then drop.
The reason is that you will want the tires to get some heat in them before making your evaluations.
You also will need to learn the course. My 1st lap is usually used to see if my perceptions made when walking the course match up with the reality of driving it!
BL
07-16-2002, 11:44 PM
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Thanks, Brian, for the pointers. Unfortunately, my PCA Region has a preference for slow and tight layouts. 1st gear came out a couple times after I realized I was coming out of the esses way too low in the torque band. That shaved two seconds off my times. The good news is that all the others in my class, 993's primarily, suffer from the same handicap so it all evens out in the end.
Curious, though, what are your WARM pressures? You can send it off line if it's proprietary.
Jim, I was just kidding about the welding. I tried to adjust the rear bar and it appeared my mechanic used an impact wrench because those bolts wouldn't budge. I'll leave those alone and focus on the fronts. Bill Gregory's pics on the John Miles website will help me figure things out along with your marvelous instructions. Yes, I definitely enjoy making the most of other's experiences, like yourself.
One last comment. The fellow who usually takes FTD in our club ended up sharing a car since his ride was in the shop. He'd never driven this SC before and it ran on Yokohama AVS's. Well, believe it or not, he still managed the second best time of the day! We've got every kind of Porsche you can imagine at these outings and they're plenty with R compounds and turbochargers and he still managed to walk in cold and put up a low time. Now THAT was impressive!
And no, the SC's owner didn't take FTD. He was back in the pack with the other mortals.
Curious, though, what are your WARM pressures? You can send it off line if it's proprietary.
Jim, I was just kidding about the welding. I tried to adjust the rear bar and it appeared my mechanic used an impact wrench because those bolts wouldn't budge. I'll leave those alone and focus on the fronts. Bill Gregory's pics on the John Miles website will help me figure things out along with your marvelous instructions. Yes, I definitely enjoy making the most of other's experiences, like yourself.
One last comment. The fellow who usually takes FTD in our club ended up sharing a car since his ride was in the shop. He'd never driven this SC before and it ran on Yokohama AVS's. Well, believe it or not, he still managed the second best time of the day! We've got every kind of Porsche you can imagine at these outings and they're plenty with R compounds and turbochargers and he still managed to walk in cold and put up a low time. Now THAT was impressive!
And no, the SC's owner didn't take FTD. He was back in the pack with the other mortals.
07-17-2002, 05:29 AM
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Joey, Everyone
May I break in, please, and ask a similar question to Joey.
While I am only just beginning down this path, and therefore read your posts with much interest and humility ('cos half the time I honestly struggle to 'get it'
), I am trying to get myself acquainted and familiar with all the variables involved.
I know that the best thing I can do now is simply learn the technique of race driving. To that end I am reading (High Speed Performance Handbook by Elford, Going Faster by Skip Barber) and practising as much as possible.
However, tyre pressure is one thing I am very green on. I have a 91 C2 Turbo, it has SO2s on it, and std 17' wheels. Any suggestions for a novice when taking the car out on track? I plan to go out this weekend again.
Thanks muchly
May I break in, please, and ask a similar question to Joey.
While I am only just beginning down this path, and therefore read your posts with much interest and humility ('cos half the time I honestly struggle to 'get it'
), I am trying to get myself acquainted and familiar with all the variables involved.I know that the best thing I can do now is simply learn the technique of race driving. To that end I am reading (High Speed Performance Handbook by Elford, Going Faster by Skip Barber) and practising as much as possible.
However, tyre pressure is one thing I am very green on. I have a 91 C2 Turbo, it has SO2s on it, and std 17' wheels. Any suggestions for a novice when taking the car out on track? I plan to go out this weekend again.
Thanks muchly
