C2 vs C4 Understeer?

In my quest to narrow down the preferences for my purchase of a 996, I have been test driving and comparing the feel of the C2 vs C4S. I have driven 2 C2 MKII's which I liked the feel of but when I drove a 2003 C4S, I felt a lot more understeer than the C2 in the corners. I realize this could be affected by incorrect tire pressures but I can't help wonder if this is inherent in the design with the wider stance of the 4S. Can anyone shed some light on this? All cars I drove were completely stock with stock wheels. Thanks, Scott

Where and how hard did you drive the cars? It's very difficult to get to the limits of these cars on roads, unless you're really a daredevil. On the street at least, I can't get my C4S to induce understeer. On the track, the stock C4s did exhibit some. It was subtle however, nothing that's going to make you say "wow, this thing is a pig." More like a safety net for when you get near the limit. I haven't driven a C2 on track so I can't really comment on it. Also, the optimal lines through a corner for an awd and a rwd car are going to be different. If you're trying to drive the 4 & 4S like you are the C2, chances are you're not getting to tap the full potential of the car. I've since done some weight reduction on my car, and removing weight off the rear end has really helped to cure the understeer. Now I can get the car to rotate pretty easily on demand.

I have not driven a C4 but my Quattro's have a considerable amount of understeer vs my C2. Obviously the weight distribution is different in a Audi vs. Porsche

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I have owned a B6 S4. It was the most understeering car that I have ever driven. The C4S does not in any way drive like that car.

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I believe it, there is so much weight forward of the front wheels...

Piece of cake, here's how: in a reasonably tight turn--90 or tighter--second gear corner, overbrake before the corner. Then before turn-in, get on the throttle and haul the wheel over while the weight's transferring to the rear. Front will push wide well before the back breaks loose. It's just like every 911, ever, just at somewhat higher limits. Unless you stand it on its nose going in, you'll be understeering first.

Yup. That'd do it! Even better, if you're standing still and turn the wheel, the car doesn't turn at all! No matter how much weight I reduce, I can't seem to fix this problem.

Thanks for the feedback on this. The C4 was the first AWD car I have driven so from some of your posts I am gathering, these cars push a little more than rear drivers. I was able to eliminate most of this underrsteer in my BMW 330Ci by changing the wheel and tire sizes to a non staggered set up which is why I was sensitive to this when comparing the C2 vs the C4. BTW, the owner of the C4 was sitting next to me during the test drive and told me to go for it on my favorite highway entrance ramps. I still think the tire pressure were a bit off though.

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I'd bet that the 4WD system has way more to do with it than the wide stance. My C4 understeers, just like most of them. You might be able to tune a little bit of it out, but a 4WD 911 is almost always going to do it.

The 996 R/awd front VC coupling mode is normally always so flaccid that I really doubt that any of this effect is the result of drive coupling to the front. The VC drive coupling remains flaccid, <10%, except under sustained F/R tire slippage.

I just had an interesting experience going from a completely ideal handling car (perfect performance alignment) to a complete pig just by changing tyre sizes. To be honest I was shocked by just how much difference it made by going to 285s in the rear instead of 265s. The details are on my web page but the point is that if the setup (pressures/tyres/alignment etc) aren't optimised then the handling results can vary widely in a 911 with all that weight over the rear.

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After reading your web page and understanding your suspension and tyre set up, its clear you created more understeer. Perhaps not intentionally. I have an 01C4 with the X74 suspension with Michelin Pilot sports as track tires (235F and 285R) starting with tire pressures below 30lbs cold, to an optimal 34-35 psa hot. These tyres will behave very poorly when over-inflated, thus creating the sense of less traction when in fact you should be incresing grip with a soft compound r-tyre. Although the tyre size makes a difference, the biggest difference here was incorrect tire pressures. These 996's are extremely versatile, with the correct suspension and tyre set up you can achive a great balance. Remeber the car is set up with understeer by design from the factory for safety. hope this helps

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I get that most manufacturers do this but I was trying to determine if the C4's have more understeer than the C2's. I'm not sure anyone was able to answer this directly other than saying that most AWD understeer more in general which doesn't address the 911's directly. I guess I'll know for sure when I test drive another C4S. Thanks

The C4 and C4S will understeer more than a C2, that's just a fact. C4's carry some additional weight up front plus feed power to the front wheels mean that you are simply asking the front tires to do more. I had the opportunity to drive a C2 and a C4 on an autocross course and a slalom at a dealer event several years ago and I'd say the difference was pronounced under those conditions. In every day street driving, not so much. That being said I would not say the C4 understeers badly from the factory, in fact in my experience it has less understeer (stock) than a RWD E46 M3 (stock). As others have said there are steps you can take to dial some of the understeer out of both the C2 and the C4 if you so desire.

With that in mind a larger front tire to back tire ratio would reduce understeer given the other parameters are held constant, correct?

As long as you stay at less than 2% difference between front and rear.. Much more and the coupling will die.. The viscous coupling behaviour can vary depending on age and mileage,, The coupling limits the amount of power that can get to the front. Based my std C4 cab, I've noticed the front end doesn't come to the game really until your pushing pretty hard.. And the traction and stability control will throttle you back if the rear wheels spin.. Mine seems to want classic 911 inputs,, Break before the turn and be on the throttle through the turn.

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I�ve had the traction control kick in twice in the couple months I�ve owned my C4S. Both times during �spirited� twisty drives. Comes in pretty abruptly when it cuts the power. Didn�t think I was really pushing the car that hard either. My 99 C2 def felt more nimble and I was more aware of the pendulum effect of being rear engined. No traction control but never felt it needed it.

So far I've never got in to full traction control on the street in the dry,, My car has both it and stability control,,, the combo inspires.. The TC only kicks in for me on Wet or Icy pavement,, I have noticed on "dirty" roads that If I gas it hard enough in a turn I'll feel just a tick of understeer then it pulls through the turn.. I'm assuming that's the Viscous coupler "locking" up to push power forward. They don't work instantly in my experience unless its an electrically enhanced coupling.

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Are you running 40mm wider stagger in the back, 225/265?

I'm still running the stock 18" C4 setup,, 5 spokes with,, 225/40R18 Front 285/30R18 Rear Michelin Sport Pilots.. PS2's

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A 285 should result in more understeer in comparison to a 265 oh, is that correct? No significant effect on your Driving Experience?

If the original specification was 265 35 then increasing to 285 30 would help decrease oversteer. I would like to do the same if it does not exaggerate understeer. it does satisfy the 2% difference requirement.

The driving dynamics of my C4 changed dramatically when I did the "RWD conversion." Regardless of whether power is going through the viscous coupling, the front wheels are still connected via the front differential when the front-drive hardware is installed. I was not satisfied with how my C4 "pushed" through corners in ways I did not expect/want. It also seemed to me that there was far more PSM intervention in corners that didn't seem to warrant it when the front diff was installed. After removing the FWD components, my 996 behaves much more predictably with no other suspension/tire size/etc. changes.

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Agreed. PSM seems to step in very easily.

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I agree on PSM. But I would have thought that alignment settings would have a greater effect on handling than 4 vs 2-wheel drive. So the pushing was due to the diff and/or PSM, or was it something else? Also, is there a sway bar in the rear on the C4 versus the C2? As I understand it, if we want to stiffen up or loosen up the front end, we�d want to adjust the rear sway bar, correct?

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I didn't change anything else - the only change at that time was removing the front drive unit and "converting" the front CV assemblies into stub axles. In hindsight, I probably should have just purchased stub axles, but I was eager to prove my indie wrong (at the time, he was convinced that what I was doing would wreck the ABS encoders and render PSM permanently confused). It could also be that my CV joints were working less efficiently than they should have been. Both joints felt smooth, and the boots were intact and full of clean grease (before I wrecked 'em).

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Good to know.

My new-to-me 996.2 C2 is far less nosey at turn-inn than my 996TT is. The Turbo has Ohlins and GT2 alignment. I�m so enthralled with the C2. A RWD narrowbody feels very light on its feet, quick, and is notably more eager to turn in than most modern 911s I�ve driven recently.

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What size are your front tires/wheels on both?

I've owned a C4 and C2, but haven't pushed either to the limit, so can't comment on understeeriness. I don't think it's been mentioned, but it seems relevant to the discussion to take note the weight differences. The C4 weighs 131 lbs more than an identically equipped C2 and I'd guess that the vast majority of that weight is in the front of the car. The C4S weighs 281 lbs more than an identically equipped C2 (presumably only about half of that weight (the AWD and middle radiator?) is biased towards the front of the car).