I notice that my 02 Z06 feels very susceptable to front end lift and loss of steering feel under acceleration - I kind of feel like I'm going tippy toed on the front at WOT. I'd much prefer that the car settled down at speed/acceleration than the way it currently feels slightly out of control. :U

Any ideas on how I can dial this out?

Thanks,
Graham

 

Now that you're the proud owner a very quick car your imagination has begun to run wild. Next time close your eyes and try the same maneuver for an even more thrilling experience. ;)
:lol: :lol: :lol: :lol:

 

Oh Yeah! 0-60 in 4.0 sec. will do that... :D

 

Believe me, you don't know what front end lift is until you drive a C2 coupe at 150 MPH. Know what a 767 feels like just before lifeoff? ;) If you've ever seen the many photos of Grand Sports under maximum power, you get the idea.

Pitching is a natural vehicle behavior under acceleration (and braking), and the greater the acceleration, the more the nose will pitch up. There are suspension layout stategies to counteract pitch and the C5 incorporates some anti-pitch features, but experience has shown that some pitch should be allowed eventhough you can layout the suspension for 100 percent anti pitch under both acceleration and braking. In general designing for "50 percent anti-pitch" is a good compromise.

It's just something you have to get used to. The Z06 is really quite stable under almost any condition. You have to allow the car to move around a little bit, or it would just be a 3100 pound go-kart.

Duke

 

Graham, This is due to shock valving. The only way to dial this out is to increse the rebound in the front shocks. You can do this by revalving the shocks or purchasing adjustable shocks. :yesnod:

 

Shocks are velocity senstive devices. They won't change steady state pitch (or steady state roll angle during cornering, contrary to popular myth), but more front rebound damping will reduce the RATE of pitch. You'd have to have way more rebound damping to slow the rate of front lift enough to perceive less pitch angle, and this much would make for an awfully stiff ride. The pitch we perceive under acceleration is a combination of front lift and rear squat.

Conversely, under braking the front will dive and the rear will lift, so both jounce and rebound damping are at issue, but the primary controlling factors are the amount of anti-squat/lift you design into the rear suspension geometry, and how much anti-dive/lift you design into the front geometry.

I remember the McLaren M8s as they exited the corner coming off the back straight up to the Corvette bridge at Road America circa 1970. They practically lifted the front wheels off the ground. At the time I didn't understand why they didn't have more pitch control built into the basic suspension geometry, but I later learned that 100 percent anti dive and squat can lead to chattering (like axle hop) under braking and acceleration, so most high performance cars' suspension geometry are only set up for about 50 percent anti-squat/lift and anti-dive/lift.

Those McLarens had a wet race weight of about 2000 pounds and with 750 lb-ft of torque and 750 HP from the 465-510 CID aluminum big blocks, they really reacted to WOT in second gear.

Modern open wheel cars have more pitch control derived from both suspension geometry and extremely high ride rates (i.e. stiff springs), but on a bumpy course the cars can vibrate so bad the driver's vision can literally blur, and such a ride would be very unsuitable for a street driven car.

Duke

 

I kind of LIKE it!!!!!!!!!! :D :D
When the horsies start pumpin', and the window washer starts peein'...........and the front kinda L-I-F-T-S-U-P..............good to go!!!!!!!!
Whats disconcerting is driving something that WON'T come up at all.......... :cry


[Modified by ZO6LS6, 3:32 AM 11/13/2001]

 

Modern open wheel cars have more pitch control derived from both suspension geometry and extremely high ride rates (i.e. stiff springs), but on a bumpy course the cars can vibrate so bad the driver's vision can literally blur, and such a ride would be very unsuitable for a street driven car.

Hmm, I guess I'll live with it then! :reddevil

For reference, I didn't used to get this type of lift with my 380hp Ferrari F1 GTS and neither do I get it with my Porsche which is laying down somewhere near 340hp. (I'd expect this to be more pronounced that the Z06!!). So, I did wonder whether someone had countered this without necessarily making the rear end undrivable. :reddevil :reddevil

Thanks anyway!!

Graham

 

Remember that both the F355 and Porsche are relatively torque shy compared to a Corvette, and even if the Porsche is a Turbo, the lag will take a second or two to build full torque. When you goose the throttle on a Corvette, you INSTANTLY deliver at least 300 lb-ft of torque, and there is a corresponding near instantaneous pitch reaction.

Earlier 911s with the semi-trailing arm suspension had poor rear squat control, but on the later models with the multilink rear suspension, it's much better.

Duke

 

The trick with the F355 is that Ferrari got real serious with the center of gravity. The CG of an F355 is about 1.7" lower than the CG of a C5. So with an equal amount of acceleration from each vehicle (4.5+/- 0-60) there is a lot less weight transfer on a F355 than on a C5. You end up with less pitch and squat.

Another phenomonom is that the lower the center of gravity, the less your head is thrown back under acceleration. Although the forceful shove on you back remains high in both cases, you head is not (ahem) pitched backwards and thereby, you mind doesn't preceive the acceleration as being as great (even when it is). Racing cars with dry sumped engines and high spring rates also confuse the acceleration versus head pitch with similar effects.

So, I disagree with the previous assertion that it is the 350 lb-ft that causes acceleration. I assert that is the engine-TQ *times* transmission-ratio *times* differential-ratio /divided by/ roling-radius-of-rear-tires that produces thrust (the force which accelerate vehicles). So if you have a puny 175 lb-ft from an engine but give it twice the gears of a 350 lb-ft monster engine, equal weight cars will accelerate equally (for the duration of that gear).