stout

From the "What did you do to your GT4 today?" thread, an alignment spec I'm trying out on my GT4, which is a daily driver. I was asked to share it, but wanted to request permission to do so—as you could say the spec is "hard won," and was sent to me by someone I admire...who knows his stuff but would like to remain anonymous. Try it at your own risk.

My first impressions are quite positive, but I need to put more time and miles on this setup. The car was aligned by Gunther and Ron at Fremont Porsche (yes, I paid for the alignment—so this is no paid endorsement), and had a great experience there. My car was very close to spec right from the factory, even after 7,000 miles. The drive home from Fremont was all traffic on the freeways, so I took to the hills of Berkeley—the same roads I used to run eight nights a week in a 914 in high school, so I know them very well. While it was more of a "light fun" kind of drive, I was VERY impressed. My GT4 felt like a new and keener car—more alive and more stable...two handling characteristics that are usually opposed to one another unless you've got rear wheel steering. So, his spec follows:






If you’d like to try something different, here is an idea:

Ride height:

• Fuel tank at least 3/4 full, driver or additional weight inside
• Lowest front ride height + 1/8 inch higher (for ground clearance reasons)
• Lowest rear ride height +1/4 inch for roll center reasons
• Have a good look on the wheel loads—don’t let them differ too much. You don’t need to get perfect cross weight distribution front to rear, but left/right +/- 20lbs is a target the alignment shop might reach for the front and the rear.

Camber:

• I wouldn’t go crazy on the camber, since this affects your braking performance significantly.
• I would keep it well above -2° at the front and -1.8° at the rear.

Toe settings:

• Slight toe out at the front (-2’ each wheel)
• Slight toe in at the rear (+5’ each wheel)

Anti-roll bars:

• Front middle
• Rear hard

The idea is, to reduce lateral forces at the rear tire—which causes understeer—and let the car rotate a bit. If you decrease the static angle on each of the outer wheels, you increase their dynamic capabilities—basically, you have a “slip angle reserve” at the wheel. Turn-in is slightly lazier (or as I would like to call it, less aggressive), but the balance is more neutral due to less toe in and the stabilizer setting at the rear. Also, the maximum grip is a bit higher.

While this setup is meant for spirited driving on back roads, it does have roots in a race car and thus has its flaws:

• Car will wander around a bit more in straight line driving (freeway)
• For track driving, you need a bit more camber
• Cross weight balance is not prioritized, since this is not a track setup
• Ride height is factory spec min tolerance at the front and max tolerance at the rear to get the roll center down at the front and high at the rear. In combination with the hard anti-roll bar setting at the rear, this should be the main reason for the agility you experienced, while the “slip angle reserve” at the wheel gives you stability.

One more thing to play with now could be tire pressures. A bit higher (3-4psi) improves response but slightly lowers grip at the limit. This is valid for both ends, front and rear.[/FONT]

Leuz

definitely sub, want to know more about these settings and what they do

Beantown Kman

Pete, do you know roughly how much this will lower the car in front and back?

stout

Not much—and it may raise some cars.

I skipped the recommendation to raise the front by 1/8 inch for added ground clearance, as I'm still on the same front lip after 7,000 miles and it still looks near-new. We tweaked my rear slightly, but the car looks better than it did to these eyes. Of course it would look better still if we had lowered it, but my front end is maxed out on the minimum spec and I wanted to try optimal dynamic rather than visual settings.

Car looks good to me. Drives even better.

bk_911

Would this be a good road + occasional track spec? I like tracking but I'm not looking to maximize lap times.

I did 7 days last year and a total of 5500 miles on my car. The tires are still the original cup2 only recently showing signs of needing replacement recently.

I like the description!

stout

I suspect yes, since the setup has roots in a GT4 Clubsport race setup but gives up quite a bit of negative camber for street use. Your use sounds like what I was after: Good for street use without killing tires, fun on back roads, ready for occasional track work.

JSF101

Pete,

thanks for sharing!

and especially thankful for keeping things on an even keel, respectful, professional

cheers,
jsf

jmartpr

This setup is very similar to mine which is mostly street driven and feels great.
All measurements were taken with full tank of gas and me on the driver seat:


Front -2.3 deg, zero toe
Rear -2.0 deg, 1 mm toe IN


This was done using the TPC rear toe links and shims...also have the DSC.
Bars were left in stock position for now.
Tom from TPC also recommended the front, toe out for track duty but will wander a bit.
Car improved a lot with this setup....will probably add more front camber for a total of -2.5 for next event.

stout

Great to have other feedback on a near/related setup.

I have had my eyes on the TPC links and/or DSC—Levitas is one of the few true geniuses I've encountered in North America when it comes to road-car suspension—but want to keep everything factory for now to see how well the GT4 can be set up without parts. I've hot-rodded every Porsche I've owned, so it's kinda nice to have one that was hot-rodded by the factory and very close to how I would have done it. Of course, if this GT4 sticks around long enough…

trebien

As the owner of a stock GT4 with many dancing track days under her garter... therein lies the danger.

I'm at the knife-edge of leave-her-be versus all-in... while enjoying every minute on track, nonetheless.

KOTYKB

OP - Do you mind posting pictures of the stance of the car now?

mrd_spy

I am

-2.2 front
-1.8 rear

zero toe front
a tad toe in rear, forget off hand.

ARB middle/middle

imo that's a faster better road spec car than the OP's

My set up is based on pyro testing on the tyres inc track work.
you don't want toe out either on a road car imho it's a pain in the ****.

Imo you don't want to adjust tyre pressure up 4psi either, again my set up is pyro tested, not guessed.

If I put 4psi extra in my tyres I would get the middle of the tyre hotter than either edge and thus less grip as the contact patch will not be correct.

My geo also works ok on track and is very well balanced, again on the limit the rear ARB on full stiff is not that stable. Tried it and was nice to begin with but when pushed to 100% not a stable set up.

was ok on the road with stock geo, but with a more focused geo ARB works best in the middle imo.

The car did need rear toe links, but the front is ok at -2.2 and caster is fine.

I do think people over do the rear camber looking at peoples set up's.

jmartpr

I agree with you on the ARB setup.....I do have the DSC added but found the car neutral and easy to push with this setup. Your alignments setups are almost identical to mine and works fine on track and road.....I stopped at zero toe up front because of the problems for road use (wandering) and I hate doing alignments before and after track days....I may try it someday for a single track day to see how it feels on the track.

mrd_spy

how do you like the DSC ? I keep going to press buy and keep changing my mind !

Alan C.

My settings are:

Front -2.5 deg on camber and toe is .1mm (I like a bit of toe out for the track but really don't like it on the street)

Rear -2.0 deg on camber and total toe is 2mm

Added shims both front and rear to get the camber.

Bars full soft front and medium rear. ( I take the time/laps to get the tires up to pressure)

I am using TPC rear toe links and their DSC system.

First time on track with this setup will be at the Smokies event next month.