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Old 05-31-2010, 06:18 PM   #1
Pat
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This weekend was my first time with the Boxster at the track.

The Boxster was bulletproof, which is a big relief with a new (to me) car. The only thing I can complain about it the understeer. I was shocked at how much there was, regardless of tire pressures. That took a bit of fun out of things, but it did encourage me to try trail braking. That didn't go over so well, though. =X Scared myself a couple times, but managed to keep in (mostly) on the track, and pointed (pretty much) in the right direction. My braking skills could use some work.
The car can only go up to one degree of camber without aftermarket parts. Hopefully I can figure out how to adjust that without screwing up the other alignment settings and make it faster for the next event at PPIR in a month.
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Old 05-31-2010, 07:08 PM   #2
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Here are your options to go more than 1 degree negative camber:
a) camber plates
b) GT3 control arms
c) lower the car with (stiffer) lowering springs, this changes the whole geometry of the front (and rear) axle so that you can get more negative camber. I did this and got -1.75 degree
d) you can also go balls out and install adjustable front and rear sway bars and now can dial in any kind of over and understeer

but wait, there's also e): go wider on the front tires (example from 205 to 225), this increases the patch area in the front and dials out some of the understeer
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Old 05-31-2010, 07:11 PM   #3
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Thanks, Chris. At this point I'd like to get as much out of the car as possible without buying parts. I just learned the camber is adjusted on the top of the shock tower. I'll check that out this week to see how much room is left to play with. I'd like to see plenty of room to spare, but am keeping my fingers crossed.
Thanks again.
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Old 05-31-2010, 08:24 PM   #4
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what tires and what sizes are you running by the way? and if possible what rim sizes
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Old 06-01-2010, 03:20 AM   #5
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The car should not be understeering like that... your best bet is to go and have it aligned by a shop that specializes in setting these cars up for the track. Better to spend a few hundred bucks and get it done right rather then waste a few track days with a car that isn't handling correctly.

The other thing to look at, and I say this with respect, is the driver. It is possible to induce understeer in these cars very easily if your transitions off the brake are not smooth... it might also be helpful to have an experienced driver take a lap or so to make sure it is the car that is causing the problems.
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Old 06-01-2010, 04:14 AM   #6
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Quote:
Originally Posted by Lobo1186
what tires and what sizes are you running by the way? and if possible what rim sizes
The wheels are stock 18" Turbo Twists. The tires are stock sized RE050As, which I was very impressed with.
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Old 06-01-2010, 04:19 AM   #7
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Quote:
Originally Posted by mdex
The car should not be understeering like that... your best bet is to go and have it aligned by a shop that specializes in setting these cars up for the track. Better to spend a few hundred bucks and get it done right rather then waste a few track days with a car that isn't handling correctly.

The other thing to look at, and I say this with respect, is the driver. It is possible to induce understeer in these cars very easily if your transitions off the brake are not smooth... it might also be helpful to have an experienced driver take a lap or so to make sure it is the car that is causing the problems.
Yeah, I know this is the LAST car that should understeer like that. That's what makes the whole thing so frustrating. I think your alignment advice is right on track.
While I am far from a great driver, I do have some experience and understand how hammering the gas too early can induce understeer. That is not what's going on. The car understeers even when leaving the it in gear and letting off the gas 100% with the engine around 6K RPM while entering a turn. In other words, even with the front tires loaded significantly more than they are just by the weight of the car, it understeers. Very frustrating. The ONLY way I could get the back out was to trail brake, and it wasn't like I was just tapping the brake pedal a little bit to make it happen. I had to get on it a bit before the back end would come around. And yes, I know that has a lot to do with the amount of steering input at the same time, too.
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Old 06-01-2010, 05:46 AM   #8
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I drove a friends boxster a few years ago that he had just gotten from the dealer, and it huge understeer issues. Even though the dealer had just aligned it, we had it re-done by a local speciality shop and the understeer was dialled right out.

I normally have my alignment re-done at the start of every track season, and checked once or twice during the track season just to be sure nothing has moved... one of the simplest things you can do to be sure you are getting the most out of the car (until you start to slip down the modification slope that is)
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Old 06-01-2010, 05:48 AM   #9
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Quote:
Originally Posted by mdex
I drove a friends boxster a few years ago that he had just gotten from the dealer, and it huge understeer issues. Even though the dealer had just aligned it, we had it re-done by a local speciality shop and the understeer was dialled right out.

I normally have my alignment re-done at the start of every track season, and checked once or twice during the track season just to be sure nothing has moved... one of the simplest things you can do to be sure you are getting the most out of the car (until you start to slip down the modification slope that is)
Hey mdex, thank you VERY much for posting this. I felt like I was the only one on the planet with this issue. Your post gives me great hope.
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Old 06-01-2010, 08:21 AM   #10
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It could be possible that you are turning in too fast, and quickly breaking the grip of the front tires. It sounds like your turn entry speeds are just a bit too high. Enter the corner slower so you can get back on the gas earliers, and that will get you around the track faster than reducing your braking. I've never had a problem understeering at the track.

BTW, what tire pressures were you using? I don't go with stock pressures at the track. IIRC, I use somewhere around 32-34 cold all the way around.
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Old 06-01-2010, 08:44 AM   #11
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Quote:
Originally Posted by Mike_Yi
It could be possible that you are turning in too fast, and quickly breaking the grip of the front tires. It sounds like your turn entry speeds are just a bit too high. Enter the corner slower so you can get back on the gas earliers, and that will get you around the track faster than reducing your braking. I've never had a problem understeering at the track.

BTW, what tire pressures were you using? I don't go with stock pressures at the track. IIRC, I use somewhere around 32-34 cold all the way around.
Thanks for the response, Mike. While it is possible I'm turning in too fast, I think it is unlikely. I tried many different driving styles, and the only thing that seemed to work was trail braking. While I have a lot to learn, I do know the basics. This year I am instructing with NASA.
I tried a wide variety of tire pressures. As little as 23 cold (!) to 36 cold. All four tires would go up 8 psi when hot. Pressure differentials from front to rear were anywhere from 2 to 9 psi.
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Old 06-01-2010, 09:58 AM   #12
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understeer really is a big issue on these cars w/ stock settings. it took me awhile to get my car dialed in so it would rotate instead of plow.

you mentioned trying to change the camber settings without messing up any other alignment settings. FYI, not possible. changing the camber on this car will change the toe. you will need to do a full alignment.

you should be able to get around -1.6 deg up front without camber plates or longer control arms. this is actually plenty for street tires. try -1.2 up front and -1.8 in back. zero out the toe front and rear. finally, run HIGHER tire pressures up front than in back (trust me on this). the RE050A is a decent tire; try 34F / 30R for cold pressures.

if you do all of this, understeer should not be much of an issue.

IMO, those who haven't had understeer issues w/ a stock boxster at the track are not driving fast enough. understeer quickly becomes the barrier to going faster, and is therefore a problem. reducing the understeer = faster lap times.
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Old 06-01-2010, 11:00 AM   #13
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What is the reasoning for the higher pressures up front? With my car with an aggressive alignment tends to work best when all the hot pressures are even. It does depend on the track of course, but most times the cold pressures end up within around 1psi of each other.
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Old 06-01-2010, 11:08 AM   #14
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Originally Posted by mdex
What is the reasoning for the higher pressures up front? With my car with an aggressive alignment tends to work best when all the hot pressures are even. It does depend on the track of course, but most times the cold pressures end up within around 1psi of each other.
depends on a lot of factors. i personally prefer a car that is VERY neutral (most would think it oversteers); this is faster for me because the car is most 'neutral' when i'm fully on throttle (rather than an understeering car that is most neutral when you lift a bit).

to cure the understeer, we want a bit more grip up front. we do this IN THIS CASE by adding pressure to the front tires.

i say IN THIS CASE because people will argue that increasing the pressure will DECREASE grip & that lowering the pressure will increase the size of the contact patch & add grip. tires are funny things. above & below a certain range, lowering the pressure WILL increase grip. however, within a specific range, adding air actually increases the efficiency of the tire & adds grip.

at any rate, i know from experience with THIS tire and THIS car that 34F/30R helps to neutralize understeer. give it a shot.
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Old 06-01-2010, 12:22 PM   #15
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Fantastic! Thank you VERY much for the info. It's nice to have technical resources available here in addition to the common problems/mods people discuss. I'll let you guys know how things turn out.
If anyone else has something to add I'd love to hear it.
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Old 06-01-2010, 12:48 PM   #16
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Would these pressures be adviseable on the street? I'd like to reduce the understeer, though some is due to the rear weight bias, which gives great rear grip. In tight turns (on the street), I tend to hit the throttle to soon, causing power-on understeer.

I also think Porsche did TOO good of a job in eliminating trailing throttle oversteer. I'd like the car to rotate more with a throttle lift, for mid-corner corrections. I've never driven a car so stable off the gas and trail-braking, even with the PSM off. (MY06) I find the PSM very intrusive if I'm trying to have fun, it kicks in way too early. But, it's great for joe blow, or if you're not paying attention, you couldn't spin the car if you tried!

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Old 06-01-2010, 01:33 PM   #17
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depends on a lot of factors. i personally prefer a car that is VERY neutral (most would think it oversteers); this is faster for me because the car is most 'neutral' when i'm fully on throttle (rather than an understeering car that is most neutral when you lift a bit).

to cure the understeer, we want a bit more grip up front. we do this IN THIS CASE by adding pressure to the front tires.

i say IN THIS CASE because people will argue that increasing the pressure will DECREASE grip & that lowering the pressure will increase the size of the contact patch & add grip. tires are funny things. above & below a certain range, lowering the pressure WILL increase grip. however, within a specific range, adding air actually increases the efficiency of the tire & adds grip.

at any rate, i know from experience with THIS tire and THIS car that 34F/30R helps to neutralize understeer. give it a shot.
I never have issues with front end grip, it is mostly about balancing it with the rear with my set up so getting more front end grip isn't normally my concern. I tried running larger tires up front (actually due to stock sizing not being available in time for the next track day) and the extra grip in the front slowed things down as I wasn't able to get on the gas as early coming out of high speed corners.

What tires / sizes are you running?

I find that a 26psi to 28psi cold temp all the way around gives a dead neutral car on most "R" tires with my setup. I guess alignment and other issues have a big part in our tire pressure balance front to rear and car to car.
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Old 06-01-2010, 01:36 PM   #18
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Originally Posted by stephen wilson
Would these pressures be adviseable on the street? I'd like to reduce the understeer, though some is due to the rear weight bias, which gives great rear grip. In tight turns (on the street), I tend to hit the throttle to soon, causing power-on understeer.
yes this will also work on the street. the understeer is due more to factory setup than to the rear weight bias.


Quote:
Originally Posted by stephen wilson
I also think Porsche did TOO good of a job in eliminating trailing throttle oversteer. I'd like the car to rotate more with a throttle lift, for mid-corner corrections. I've never driven a car so stable off the gas and trail-braking, even with the PSM off. (MY06) I find the PSM very intrusive if I'm trying to have fun, it kicks in way too early. But, it's great for joe blow, or if you're not paying attention, you couldn't spin the car if you tried!
again, this is due to a large extent to porsche's OEM setup. understeer is SAFE for road cars because, to the untrained driver, it is a self-correcting phenomenon. the instinct is to lift off the gas & this solves the problem. oversteer, on the other hand, requires a trained response. porsche spent a long time trying to engineer turn-in on throttle lift for road cars. we can, of course, add this feature with a few mods. by FAR the most bang for the buck here is a rear sway bar upgrade. simply swapping to the BASE model's M030 sway bar makes a HUGE difference.

with the right setup, a mid-engined car will rotate like a top; all the mass from the motor/tranny is right at the center of the car. this means VERY short polar moments of inertia. this can be a blessing.....and a curse.

another reason the car is tough to rotate with power ON is because it lacks a limited slip diff. right about the time the car is putting down enough power to cause power-on OS, the inside tire will spin.

i have experimented EXTENSIVELY with various isolated & incremental mods to the 986. if anyone has questions about how different things WILL effect handling (NOT are likely to, WILL) on this car, fire away. i have tried all KINDS of stuff, street & track. i have logged data to back a lot of it up.
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Old 06-01-2010, 01:38 PM   #19
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Originally Posted by mdex
I never have issues with front end grip, it is mostly about balancing it with the rear with my set up so getting more front end grip isn't normally my concern. I tried running larger tires up front (actually due to stock sizing not being available in time for the next track day) and the extra grip in the front slowed things down as I wasn't able to get on the gas as early coming out of high speed corners.

What tires / sizes are you running?

I find that a 26psi to 28psi cold temp all the way around gives a dead neutral car on most "R" tires with my setup. I guess alignment and other issues have a big part in our tire pressure balance front to rear and car to car.
mdex - keep in mind you're running r-comp & the OP is running street tires. also, his car is stock. if you're on r-comp, i'm guessing you have a few other bits installed that help neutralize the handling.
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Old 06-01-2010, 01:49 PM   #20
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mdex - keep in mind you're running r-comp & the OP is running street tires. also, his car is stock. if you're on r-comp, i'm guessing you have a few other bits installed that help neutralize the handling.
True that... but driving stock cars as well (and even on street tires!) I still have found that most understeer can be dialed out (or at least back to the point that most people don't notice it) with alignment.... which gets us back to the original posters question as well, not that I am not enjoying our discussion on set up overall with our cars.
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