I want to expand a bit on PatK's statement about the rebound setting and its relation to grip at initial turn in.

I believe increasing rebound can help at turn in but it is predicated on some variables. Firstly, how much rebound is already dialed in before the change is made and secondly is this a trail-braking corner or not. Dialing in more rebound will keep the spring from releasing, as rapidly, the energy it produced and stored during the braking phase. If rebound were set more lightly it would allow the spring to elongate from its compressed position at a more rapid rate. If no trail braking is occurring, there will be a period of time from the release of brakes until turn in that the spring will dissipate some energy by elongation. By increasing rebound this process can be slowed, thus retaining more spring energy and increased pressure on the contact patch.
This is my understanding of how it works but I would love to hear from others with opposing opinions.

 

Ok, here's my opposing opinion.

When you release the brakes, you get weight transfer off of the front. Upon initial rise in the front due to this transfer, the front tires will have less weight (or force) on them, hence less pressure. How quickly they lose this pressure depends on how tightly the rebound is set. The tighter (or stiffer) the rebound, the slower the suspension will expand, which is what keeps pressure on the front tires. So when you increase the rebound, you lose grip faster.

 

I think this is a matter of difference in thinking that the suspension using the wheels to pull the car down instead of thinking of it as the suspension using (less or moreso) the car (chassy) to pull the wheels up.

Al's point made sense to me until I read Larry's. But you would want less rebound so it takes longer for the car to relieve the added weight and grip on the front tires by allowing the suspension to expand. More rebound will make that process faster and relieve pressure on the front wheels faster. At least I think so.

 

Let me clear up confusion that seems to be happening with my terminology. My Motons have 16 clicks of rebound settiing. At the 0 setting the rebound is at full soft and at 16 it is full hard. When someone says to me add some rebound or increase rebound, it is shorthand for add some rebound control as in increase the number on the ****, as in make it stiffer and more resistant to change per unit of time. In my statement I said "if rebound were set more lightly..." this means if it were set more towards the full soft or 0 position. Sorry if my statement was misleading to some.

As many of you already know, the rebound adjuster is found on top of the piston rod. There are several orifices drilled below the piston. At the 0 position all the orifices are open and the damper will transfer oil as quickly as possible within the confines of how the shocks were valved to begin with. As the rebound **** is clicked to higher numbers, these orifices close off progressively to lessen the amount of oil transfer per unit of time.

 

This is pretty much how I took your terminology to be when I read your postings.

I haven't read all of the books that some others here have (maybe I should), and can't calculate all of the physics behind this stuff, but I do have a lot of experience and I have learned a lot of this empirically over many years. I understand things by visualizing what is happening and draw knowledge from that. I also change things to see what happens, and try to determine the reasons that produced the results.

One factor here that seems to be glossed over is what the body of the car is doing, and how it affects the "pressure" of the tire against ther road; i.e. grip. The car is the major mass here and acceleration, cornering and braking forces will act on it. The car will then compress or unload the suspension as the spring and dampening rates allow. You can't produce grip by "clamping" the car down. If forces act to lift the body, the suspension will unload, period. The springs and dampening will only serve to control how long this takes, and how far the car actually moves.

 

I will say this: if it weren't for Larry's knowledge on this subject, I would have had a LOT harder time sorting my car out when I equipped it with Moton CS dampers. He knows his ****, and explains it (at least to me) in my language.

 

I do understand that "if forces act to lift the body, the suspension will unload, period. I agree 100%. What I seek to understand is whether the increased rebound damping, as opposed to zero damping, will cause a momentary (albeit only a portion of a second) sustaining of the weight of the L or R front contact patch (from energy stored in the spring) in the short period between releasing the binders and starting the turn-in. I know the ultimate result but what is the instantaneous result? I'm new to all this and enjoy the opinions of those of you with much more experience (and histograms) than I.

 

Thanks, Dave. Check's in the mail.

I see what you are asking. Think about what is happening here. The spring and shock are not "holding the body down" on the tires. Gravity is holding the body down on the springs, and the shocks inhibit the movement of the springs. When you release the brakes, the weight WILL immediately shift backwards. How fast the body moves (and therefore how quickly the suspension is unloaded) is another story.

You asked about what happens instantaneously. Consider what happens the moment you get off of the brakes. If you had no rebound dampening at all in the front, as soon as the weight shifts, the front would start to rise. The springs would begin to push the nose up and the pressure on the tires would slowly begin to drop. If you had a high amount of rebound dampening, when the nose begins to rise, the springs would not be able to expand as quickly; their "energy" would be bound up by the shock. As that happens, the weight on the front tires drops more quickly, because the springs cannot expand to keep up. Here shock is actually removing the pressure that the springs are trying to exert on the tires because the shock is inhibiting the expansion of the springs.

Remember that shocks affect spring movement over time. The stiffer the setting, the longer it takes the springs to compress or expand.

 

Thanks Larry, that last response helped me understand the instantaneous reaction. Just like adding bump will cause quicker weight transfer to the front patches under braking (via the shock and not the spring component), adding rebound will cause quicker unloading when the brakes are released.

 

Thanks Larry,

for explaining these actions in ways that we experience when driving the car.

We've all experienced the front-end lift coming off "hard braking", the stiffer shock setting in rebound... slows down that effect.

 

Too complicated. makes my head hurt. Im thankful I dont have the funds to buy triple adjustable new shocks. I wouldnt know where to start. Ive got my two way koni's maxed out and havent touched them in 10 years.

I like what Karl said here:

It is very clear if you analyze the graphs and there is no room for debate on this. But I do like your Carroll Smith quote "Sometimes I think that I would have enjoyed racing more in the days of the friction shock. Since you couldn't do anything much to them or with them, I would have spend a lot less time being confused."
__________________
Karl Poeltl
Racer's Edge Inc.

I truely think that if i got a "real " suspension, it would take me a season to get it as good as what I have by near chance today, and another year to make it work better.

mk

 

I always thought the proper english blokes calling shocks dampners helped people to understand this a little better.

 

All you guys are valuable resources (except the one we all know who argues with everyone)

I called Lex at Moton (super nice and really knows his ****) and he gave me settings for the tracks i run on. I used them as a starting point and then handcuffed Stanton to the steering wheel and had him go through a fresh (repeat fresh) set of tires before i released him. (I find out later that Craig gave the settings to Lex) The car is a dream and 5 sec (avg) then when I tried to set it up myself.)

My point is in the absence of a shaker rig and datalogging and an engineer (or even with) practical experience is the key. No matter how well we know the theory, the pro guys have countless hours of seat time testing set up.

My .02$

 

cough cough This is why people hire folks like Larry & Chris & Viking & Seth & me. cough cough

 

Excellent discussion and input that helps put these concepts into descriptions that I can visualize, which help to explain what I have learned through experience (trail and error) over many years. Where the hell were you guys when I was attending the School of Hard Knocks, where the tuition is very high but the lessons are well learned and remembered?