rezzer

Hi Gurus

I've been sweeping through forums on finding a possible solution for my light/loose steering feel at higher speed on my 997.2 but seem to have many pointing to either
1. Bad alignment
2. Mixmatched rear spoiler and front bumper/splitter thus causing too much downforce at the back
3. It's just how a 911 is since the engine is at the back. (I'm not accepting this as this is real dangerous free play/loose feel at high speed). Can't be how a Porsche reacts. I've driven 2 other Porsches and they felt much more planted.

Details of my car:
997.2 c2 manual
Aftermarket BBS LM 19 inch on Ps4s
OHLINS coilovers

Presto

Petza914

Your alignment settings look fine and even achieved a total thrust angle of 0 which means the car is going down the road with the front and rear perfectly aligned.

What are the width and offsets of your wheels and are you running front spacers at all. I ask because my car has always been rock solid at any speed I was willing to drive it, even up to 125 mph and beyond. I put a new set of wheels on that were 19x8.5 et 42 with normal 235/35 tires and aside from not looking great with too much poke past the fender, with the same tires I had been running and am still running, and without any alignment changes, the car became very twitchy and unstable even at speeds as low as 90 mph. Sold that setup off immediately and installed some custom Forgelines in a 19x8.5 et 50 (which is the perfect front offset for our cars by the way) and it was back to rock solid. You wouldn't think that 8mm further out per side could make such a huge difference, but it was the only variable in that "experiment" with the brand, model, and size of F&R tires being exactly the same on all 3 sets of wheels - offset on set one was et53, on set two et42, and on set three (current) et50.

Complete specs on the 3 sets are:

Champion RS171 Wheel Specs
Front - 19" x 8.5" with 53mm offset
Rear - 19" x 11.5" with 62mm
​
ADV1 Wheels
Model ADV05 Mv1 SL (forged 1 piece lightweight)
19x8.5 with 42mm offset
19x11 with 52mm offset
Finish: Brushed & cleared

Forgeline SC1 Forged Monobloc
Finish: Brushed & Cleared
Front - 19" x 8.5" et 50mm
Rear - 19" x 12" et 74mm

For comparison, my wife's car has these GT3 Wheels, which I based some of my measurements off for my custom Forgelines)
Front - 19" x 8.5" with 53mm offset
Rear - 19" x 12" with 68mm offset

All these sets except the ADV1s drove perfectly and all are hugh-quality, forged, lightweight wheels. The Champions are currently for sale if anyone is interested.

rezzer

Hi Petza914,
Thanks for the reply. No I am not running spacers. Here are my specs
Michelin PS4S Tires
Front - 19" x 8.5 ET50 235/35 Tires
Rear - 19" x 11 ET50 305/30 Tires

The offset for the front is 50mm like yours, but my rears are also 50s. With wider tires.

Petza914

That's the same size tire I run on the back of both my 997s, but you have WB offset rears on your NB C2S car, which is why your wheel widths are also narrower, which can tend to round out the tread section of the tire instead of letting it sit flat as intended, but I doubt that's the cause of the instability at speed. I could be a downforce isse as there's a reason the active aero wings I have on my cars deploy in the 75-77 MPH range. I didn't see a pic of what your rear wing setup looks like compared to the front, but if the rear is aggressive, like an Aero kit or GT type fixed wing, maybe you need to add some front downforce either with a different front bumper (GT3 / Aerokit style) or some diveplanes, or something.

rezzer

Yes my car has a Techart Type-4 Spoiler. For my front, I have a Turbo Bumper (with an OEM Lip). Would the Turbo Bumper not generate enough downforce in this case?

voiceprint1

Drive another same year and model but bone stock to compare if you can, you also might check your tire pressure, it might be too high, which can lead to the car feeling twitchy.

I know that there are much more informed people on here, but I would start with swapping your rims to stock and if the coils overs have adjustments move onto that, just a suggestion, since it sounds like you did not do the work and therefore did not dial it in.

Ben Z

When you feel the steering twitchy, dig into the gas and note what happens to steering feel. If the steering settles down while accelerating, everything is normal for one of these cars. I also thought I had a problem until I spoke with my indie who has a team of these cars and races them.

rezzer

Thanks. Tried that, still the same. Actually the freeplay/looseness is even present driving straight. And when i slow down to about 70mph or so, steering feels tight and all feels planted.

rezzer

Yeah am planning to send it to another round of adjustments to the coils and alignment. Do you think it has anything to do with Rims?

Petza914

Great looking car. I would think that setup would be pretty well balanced aero-wise. Might be time to start looking at worn suspension components, bushings, or something not torqued properly.

rezzer

Thanks. Will definitely do that on my next visit while I get the coils adjustment done and alignment.

Speaking of Aero, as my car has a retrofitted Turbo Bumper, the standard C2 doesn't have an intercooler upfront like the Turbo. This then leaves the center of the bumper "empty". Stock c2 bumper has the center piece covered up but the Turbo is open (technically having the intercooler there to suck in air)

Curiously, I was thinking that could it be that air gets into the Turbo bumper front hole/gap (no intercooler blocking) and probably finds a way underneath the car more thus causing lift?

Sample of stock c2 front bumper:

Petza914

That's a good thought. You could add the c2S center radiator kit which would actually add cooling capacity and fill the opening in the turbo bumper, which might be a win-win for you.

voiceprint1

I would say that maybe a combination of factors might be throwing the car off, which is why driving a comparable car at the same speed will give you some clues. The tire tread depth or wear has an influence on road feel for sure, if you just put fresh tires vs older. I just put on the C4S tires on my car, a base, and you could take your hands off the wheel at over 100, no wandering or light feeling, but it did take some adjusting of pressure to feel more planted, and some time wearing in the tires.

Changing rims might affect ride as well, again I am no expert, but aftermarket rims tend to differ from factory specs in many ways.

nwGTS

What's the rake on the car? Should be slightly lower in front. Flat or too high will lift the front at speed. Nothing inherently wrong with it but it's gonna be hard to dial this in if it's aero since you have a mishmash of aero bits.
PS... awesome color.. car looks great