taly911

Can the 964 C4 understeer be adjusted? What kind of modifications are needed.

Thank you Tal

joey bagadonuts

From John Miles's wonderful 964 website (www.porsche964.co.uk), there's a reprint of a 1992 Excellence article entitled Wringing Out the Carrera 4 which contains good recommendations and background regarding this issue. A thicker rear sway bar and wider front tires are a good start but to gain a better understanding of this subject, I highly recommend giving this article a good read.

Bill Gregory

Tal,

Here are the things that can be done that will yield more oversteer, hence reduced understeer:

* Lighter front spring rate
* Heavier rear spring rate
* Thinner front sway bar or adjust to lengthen the arm
* Thicker rear sway bar or adjust to shorten arm
* Softer front shocks
* Harder rear shocks
* More negative front wheel camber
* More positive rear wheel camber
* Wider front tires
* Thinner rear tires
* Lower front tire air pressure
* Higher rear tire air pressure
* Wider front track
* Narrower rear track
* Larger front spoiler
* Smaller rear spoiler

Now, given that laundry list, what's typically done? Going to 225 tires in front is one item, and installing adjustable sway bars is another, especially with a larger, ie 21mm and greater, bar in back . You can certainly play with the suspension, too. Hopefully some of our C4 owners will chime in with what they've done in the track environment to reduce the inherant 964 understeer. Joey?

joey bagadonuts

On it, chief!

On my car, the 25/22 front and rear sway bars (both set at the middle) along with wider front tires (225 f and 255 r) provide some very neutral handling. If I wanted a really "loose" car, I'd probably soften the front bar or keep it stock.

However, a neutral setup is exactly what I wanted for high-speed track events. When you're shooting out of the corners at 60-70 mph, hanging the tail out isn't exactly the "attitude" I was looking for.

Finally, I'd suggest you practice trail braking--in a safe environment. As the Excellence article pointed out, the C4 will rotate nicely when the brakes are applied on turn in. Get on the gas too early and the "locked" rear differential will encourage your car to push; nail the line, and you're rewarded with a very satisfying four-wheel drift.
Good luck and be safe.

taly911

Thank you,
Tal

Adrian

Guys,
If you read taly911's post you will see he has something called a 965 C4 TT.
I do not know if this is a 964 Turbo that has been fitted with a 993 AWD system or a 964 C4 with a twin turbo engine modification.
However regardless of this the information provided applies to standard C4s.
More information is required on what the beastie in question is first because by reducing understeer one increases oversteer and TTs have enough of that all on their lonesome.
As I said also what kind of AWD system is fitted? Very important.
So Tal first thing please,
What is your 911 made up from? Please provide exact details.
Ciao,
Adrian
964C4

Bill Gregory

However, he asked about a 964 C4...he may be helping his cousin

Adrian

Yes or his brother
but lets wait and see what he replies with.
Ciao,
Adrian
964C4

taly911

Hi guys,
I'm helping myself, my car is a 964 C4 wide body with 500-550HP 993TT engine, the AWD is the original C4 system.

Tal

RSAErick

Uff da!

pzull

Bill,
I always thought to reduce understeer one should reduce front tire pressure and/or increase rear tire pressure. At least that's what I learnt from karting days. Is it different for AWD 964s?

Adrian

Dear Tal,
I will be quite honest. I think the set up neds to be inspected by an expert to determine what components you already have on the car.
I would advise a 21 mm or 22 mm rear sway bar to start with if not already done. Front strut brace would be useful to reduce body torque from the rather powerful engine at the rear.
You have a widebody and clearly the rear track is wider than the front track which is not good for the understeer.
You will need to be really careful with the power as well. You actually reduce understeer by increasing oversteer. Under heavy acceleration that could mean rear end trying to overtake front end.
Your 964 is so highly modified I do not know what the weight distribution is and that greatly affects things as well.
This is a job in my opinion for somebody who has the 964 in their view and can drive it and inspect it and advise accordingly.
I would be interested to know what model year this originally was. The VIN would be helpful.
Ciao,
Adrian
964C4

taly911

Hi Adrian
This is 1990 C4, I've widen the body, all genuine Porsche parts.
Tal

Adrian

Dear Tal,
Okay. However still need to have a complete breakdown of all the changes you have made before any genuine advice can be offered. It is often a good idea to try and find a cause for the understeer first.
Need to know wheel sizes, tyre sizes, spacers if used, plus all supension changes etc. The weight change would also be useful.
Ciao,
Adrian
964C4

Bill Gregory

You're absolutely correct - good catch, original post corrected.