jack.pe

Since the main culprit for understeer on the c4 Is the rear diff locking up on the limit, has anyone tried to stop it happening by eliminating the locking function in the rear diff? I believe it is activated hydraulically so potentially the hose could be disconnected. Has anyone ever tried this?

Makmov

I think its the 300 lbs in the front.

In any event, you can tune the understeer out with a rear bar, suspension package, and an alignment.

jack.pe

I've been told by others in the forum and by my mechanic (cliff from Project 9) that the culprit is definitely the rear diff and how it is set up to lock. Would rather attend to the cause if this is it, rather than try to mask it with geometry changes. And if anything the extra weight at the front should help eliminate understeer not make it worse?

ras62

I thought the diff lock simply locked front and rear together? I dont think you have a lsd on the rear so the opposing wheels will always be locked. Geo and roll bars is the acknowledged way of reducing under steer on a C4.

Derek Pedersen

Just turn it off when you don't want it. Hold the PDAS **** over until it beeps at you (takes more than 10 seconds) and it will be defeated until you restart the car. Works like a charm.

koenig_roland

My C4 has no understeer. H&R coils and H&R sways with an aggressive set-up. It drives "like on rails" (a german proverb) through the corners... I never used the pdas **** yet.

Strega(UK)

I dialled out the understeer on my C4 by simply fitting the rear anti-roll bar off a C2 with some poly bushes.
I think messing with the 4WD PDAS system is a waste of time/money and could be dangerous as it is there to stop you doing anything too silly!!

ras62

Great overview of PDAS is available, google 964 PDAS or here http://www.adrianstreather.com/.../P...0overviewR2.pd...

It does talk about massive understeer if either diff locks are activated. Tapping the brake will disengage the system. Front / back locks are operated through separate solenoids.

I take it no warning lights are showing?

jack.pe

Thanks for you post Utah, read your PDAS thread and it seems really interesting.

https://rennlist.com/forums/964-foru...uestion-2.html

jack.pe

Hi,

I currently have red H&R springs and the geo has just been set up to RS spec. The car still understeers, though admittedly much less than before. The rear anti roll bar may be a way forward... I'll see how it goes. But this PDAS thimg also sound pretty interesting. See the link in the post above from another Rennlist discussion.

Strega(UK)

Mine has KW V3 suspension set to RS geo and still understeered until I recently fitted the bigger anti-role bar.

Goughary

+1 on turning it off. I would like to re-program the thing to always be off and to have a switch to turn it on if I want to drive in the snow...

Makmov

I haven't even done the bar on mine yet, just H&Rs and Bilsteins and most of the understeer went away. The little bit that is left I cannot imagine would not tune out.

FeralComprehension

I took the front bar off instead of going stiffer at the rear. No real report yet- still sorting the geo.

Porsche964FP

I second Scott's motion.

If you look through the past threads here you will see the universally recognised solution is a thicker anti roll bar.

I have KW V3 coil-overs and heavy duty H&R anti roll bars.

What eliminates under steer is the thicker rear roll bar.

It's worth also taking into consideration that it is only at the limit that these cars will under steer. This limit is unlikely in my mind to be truly exploited on public roads. A point that Adrian Crawford had expressed in his 964 book.

I would say that if you are experiencing understeer on the road I would suggest two options:
Have the alignment checked or spend more time learning the characteristics of your car. 911s require a very specific approach to driving. Driver training on track is an amazing way to discover you and your car.

I have only ever experienced understeer on track and am confident in saying that it was due to my driving.

All cars will understeer if incorrectly driven. 911s aren't easy to drive well.

Either way if you do decide non the less to pursue, I would suggest going the tried and tested root before exploring alternative options.

Best of luck.

Cheers,,