C7Kevin

I have a 2015 Z51 and have noticed, consistently, that when I really nail the throttle, the front end of the car lifts noticeably.

I'm not saying that the car pops a wheelie or anything close, but it is somewhat annoying on a car that otherwise handles beautifully.

Has anyone experienced this symptom and/or has anyone wondered if this behavior is due to inadequate rebound damping from the front shocks/dampers?

I know that coilovers are a popular conversion that many have adopted and wondered if any of this move to convert is due to front rebound inadequacy.

Any feedback would be appreciated.

AUTO_X_AL

Is it an MR car?

I will say that any of the non Z07 Z06's under hard throttle appear to be damn near pulling a wheelie. My MR Z51 has a lot of body movement but it's still quite fast.

AUTO_X_AL

This is a great shot of the car static and under load on a hard takeoff. The car has RE71R's on it too which yield a ton more longitudinal grip than the stock tires. The car barely spins if you launch it right.

I don't think that this is excessive although it may seem like it from the cockpit. The car turns in well and transitions good too.

juanvaldez

Under hard acceleration weight is transferred to the rear wheels. With enough traction and horsepower all the weight is transferred to the rear wheels and you have a wheelie. With no rebound damping the front suspension would just extend to maximum travel. With maximum rebound damping the front suspension wouldn't move down much. Rebound damping has little to do with the attitude of the car under hard acceleration.

Too much rebound damping and the suspension will pack down, won't full extend after jounce and will gradually have less and less suspension travel under repeated bumps. Too little and the car will pogo or top out.

I autocross my '16 Z51 M7 coupe some. It is non-magride and seems to be very planted, near neutral since I replaced rear swaybar with Z06/magride rear bar.

axr6

Like juanvaldez stated it has to do with the weight transfer to the rear. The rear spings on the Stingray are relatively soft, allowing such weight transfer, which in turn, helps with rear tire traction under hard accelearation. I personally like it, I was always in the camp that used relativelty low rate rear springs exactly to allow that weight transfer and its resultant increase in traction for both street and race driving.

\Boost Monkey/

Well said.

meyerweb

Exactly. Front-end rise on acceleration has more to do with rear spring rates than front damping. One could stiffen the rear to minimize it, but not without other effects on ride and handling.

C7Kevin

thank you all for your comments.
I well understand that weight is transferred to the rear from the front under hard acceleration. No question about that.

However, all of my experience to date, with decades of race car(road racing) suspension analysis and tuning, leads me to understand that rebound damping, if inadequate, can also contribute to nose lift.

That said, I also understand that too much rebound damping can cause the suspension to gradually, over several bumps, cause the suspension/damper to "jack down" with the result that damper travel available can be diminished to the point where a tire can lose contact with the ground under extreme combinations of roll and rebound damping. Not very common at all, but still possible.

I would like to hear from anyone who believes that the C7 Z51 with MSRC has inadequate rebound damping.

C7Kevin

Sorry, but your statement "Rebound damping has little to do with the attitude of the car under hard acceleration." contradicts another statement in your post. Taking a worst case, as you say, a front damper with no rebound damping would allow the front of the car to rise to that point at which the damper is fully extended(assuming nothing else limits damper travel.

What I described in my original post is not as extreme as full damper extension, but enough extension that I can easily feel the front of the car rise under hard acceleration. I find this annoying but not worrisome. I have to wonder if increased rebound damping would relieve this issue.

I have not owned or driven any other cars as highly powered as a C7 Stingray, so I don't know how prevalent this problem is under hard acceleration. If the rebound damping was adjustable on my car, I would certainly try increasing it to see if the front end rise would be significantly reduced or not.

I can't help but wonder if C7 owners who have converted to coilovers end up running more rebound damping than is built into the stock dampers. Do any coilover folks know about this?

juanvaldez

Let's take two extreme cases, no rebound damping and infinite rebound damping. In the first case, under hard acceleration the front end would come up taking all or most of the weight off the front wheels. The front suspension would drop to maximum travel. The rear suspension would squat under the roughly doubling of the weight (no weight on front wheels).

With infinite rebound damping the same thing would happen under hard acceleration except that the front suspension would stay in mid-travel (where is normally is when half the weight is on the front end).

Drag cars used to (and maybe still do) run 90/10 (almost no rebound damping/heavy compression damping) shocks that let the suspension drop to full travel and basically kept it there to shift the center of gravity rearward

C7Kevin

Juan,
I understood your point in your earlier posting, in spite of the contradiction, just as I understand all of what you have said in this reply to my post. You have said nothing at all to contradict my point that, IF the C7's front rebound damping is inadequate, the front of the car could rise, perceptibly, under hard acceleration. I was out driving the car today and verified, to my satisfaction, that the front of the car DOES rise under hard acceleration. As I said in my original post, the car in no way approached a wheelie, but it does rise enough that a perceptive driver feels/sees it(and may be annoyed by it....as I am.

That said, I am in no way criticizing the suspension designers who came up with the C7 Z51's front rebound damping rate. I am merely asking the obvious questions...1) does anyone know, factually, if the front rebound damping rate is low enough that it alone allows the front of the car to rise OR 2) is there some other factor at play other than rebound damping?

I ask because there are a few folks on this forum who quote figures that are not known to the average C7 owner and these same folks seem to have the benefit of inside(or deliberately hidden) figures as relates to spring rates and such.

Just honest questions, that's all.

4GS7

IIRC, the MSRC is actually programmed to stiffen the rear and soften the front under hard acceleration for better traction both off the line and out of a corner. Remember, with MSRC, the valving is fixed and the changes are made in the fluid viscosity. If the front rebound valving was too soft, the front of the car would wallow on bad highways as well, where you get those big wheel/body motions.

juanvaldez

You really need to be on a motorcycle with 3lbs/hp to see how suspension works. There is no way to keep the front end from rising under hard acceleration without altering the laws of physics.

C7Kevin

You make a good point, Irv.
I know about MSRC and how it uses changes in fluid viscosity rather than valving to alter damping characteristics.
That's why I always used the word "damping" rather than "valving" in my posts.
My car has MSRC, so it would not have to suffer from the wallowing you describe since with MSRC the damping could be different for hard acceleration and normal driving.
How is it that you know about MSRC programming?
I have not YET come across any information regarding that subject.
What is the source of your information on this subject?
Thanks.

meyerweb

More rebound damping on the front, I think, would only slow the rise of the front end, not limit it. If the car makes enough power, and has enough traction, to fully extend the front suspension, more damping (except for infinite damping, as discussed above) won't prevent that from happening.

ageshelin

None of us are answering the Op's question. Also the full picture has not been explained here, either.

Under acceleration, there are 3 factors affecting the attitude of the car and the speed of weight transfer from font to back:

Things that affect amount of weight transfer:

1. Center of gravity.
2. Wheel base. This with (1) create a kind of fulcrum.
3. Weight of car.
4. Power applied.
5. Front and rear wheel (spring rates).
6. Anti-squat geometry built into the car. This is the angle of the rear a-arms with respect to the horizontal plane. This angel will affect the force vector generated by 1 through 5. C4's had a lot of anti-squat built-in, for example. This is the a very important point that everyone missed!... or appears to have missed. The other similar angle on the front a-arms can reduce the amount of dive that the car experiences under braking.

The speed at which the weight will be transferred from the front to the rear:

7. Front shock rebound dampening and rear shock compression dampening will decrease the speed at which the weight will be transferred. Assuming a constant acceleration effect, the car's nose will still end-up in the same attitude after a longer or shorter period of time. However, it takes a lot of power to maintain constant acceleration rate for a long time. Eventually the acceleration decreases and the nose of the car settles down. Hence, the visual effect of higher shock rates may seem like it is helping the car to settle down.

Some anti-dive and anti-squat maybe OK. In road racing cars, there is none. The driver is left to control the weight transfer and optimize the balance between cornering and acceleration. This is not to say that the suspension tuning, including shock dampening curves does not help. Also, note that the wheelbase of modern race cars is increasing, including the Corvette, from 96" in the C4 to 106" in the C7. One of the effects is less weight transfer without anti-dive or anti-squat.

Therefore, based on this it would appear that anti-squat has been tuned out of C7 suspension.

Does anyone have a C7 suspension co-ordinates or a CAD file to confirm?

Anton