Shock School 101
08-18-2007, 09:54 AM
#1
Melting Slicks
Thread Starter
Shock School 101
Shock school 101.
The first race(s) after I bought and installed my new 3-way adjustable Motons was just awful to be honest. I knew nothing about them. During the weekend, the adjustments I made were wrong and the car did not handle well at all.
Even before buying them though, I searched the web but could not find any quick reference charts or CLEAR explanations of how shocks worked and what to do to improve the handling under different circumstances.
Now that I’ve had a while to experiment with them, I have a much better “handle” (pun intended) on how they work and what you can do to improve the car. Since I couldn’t find a quick-reference chart, I decided to make one of my own…but I’ll get to that in a minute.
First, to understand the chart, you must understand some basic characteristics of adjustable shocks and exactly what they do. If you forget everything I’m about to tell you, but remember these 3 words: “Facilitate Weight Transfer”, then you’ll be OK. That’s what shocks do…other than just dampen the springs when you hit a pothole.
In the world of race cars and shocks, you’ll primarily hear the words bump and rebound. To keep things simple, I’ll just work with those terms. When you’re talking about bump, that’s referring to when the shaft of the shock is compressing, or going into, the body of the shock. Rebound is when the shaft is coming out of the shock body. When you hit a bump, the shaft of the shock goes into the body of the shock and then the car’s spring tries to pull the shaft back out (and put the car’s tire back on the street). Depending on how stiff each of those settings are will determine the rate at which the shaft compresses or releases from the shock body.
Now let’s look at how a shock helps the handling of the car. Bump: When you hit the brakes, weight transfers to the front tires (or tries to) which allows the tires to grip more and brake harder. This phase of handling is primarily dealing with the bump settings on the front. If the front shocks are really stiff, the weight won’t transfer as well and braking performance is reduced. If the bump settings are too soft, you’ll get lots of weight transfer and the back end will dance around. Get it?
Rebound: In this braking phase, rebound of the rear shocks is also critical. The rear spring is attempting to keep the rear tires on the pavement. The shock shaft is lengthening…coming out of the shock body. If the rebound is nice and soft, the shaft comes out of the body easily and the spring keeps the rear tires planted. If the rebound is too stiff, the spring can’t push the tires down to the pavement fast enough and the car seems to dance and is unstable.
This leads directly into the first of 3 primary phases of a corner – corner entry. For the purposes of this discussion, think about turn 1 at Road Atlanta or Roebling Road – they are right hand turns. During this phase, weight is on the front tires. The bump settings on the front end (specifically the LF) is the one primarily affected. As you turn the wheel, weight tries to transfer to the LF. If it transfers easily, the LF will have good contact (traction). If weight doesn’t transfer easily, the bump is too stiff and the car will most likely push on corner entry.
Conversely, when the front end grips very well, the car will probably be loose. Since the weight is still on the front tires, it’s imperative that the rear rebound still be soft enough to allow the spring to push the tire to the ground.
So, in short, if the car pushes on corner entry, it’s best to soften the front bump. If it’s loose, soften the rear rebound. Starting to get it yet? Stay with me…
The second phase of handling is mid corner – right around the apex area where the car is under maintenance throttle and you can really tell if the car is balanced or not. The outside tires are loaded while the inside tires are just there for decoration.
Think of Roebling Road’s turn 7 and 8. Since weight has transferred to the outside tires, we’d like the car to behave well – not oversteering or understeering – equal weight transfer. However, if the bump settings on the front are too stiff, more weight will be transferring to the back and giving those tires grip, which will result in understeer. Conversely if the rear bump settings are too stiff, more weight will be on the front tires and you’ll be loose (oversteer).
So, in short, if the car pushes during mid corner, softening the bump on the front should help the problem. If it’s loose, soften the rear bump.
Rebound during this phase is a bit trickier. Since the throttle is the primary means of steering the car in phase 2, what you’re doing is essentially just adjusting how much weight transfers to the front and back. If you lift throttle a bit, more weight transfers to the front (and off the back) helping the car to rotate and turn better. If you get on the gas, you transfer weight to the back helping the rear tires grip. If you notice the car pushing badly as you roll down on the throttle, the front rebound may be too stiff. The spring is trying to push the front tires to the ground to get traction, but is not able to. Softening the front rebound allows the spring to do this so you’ll get a bit more grip in the front.
Conversely, if the car is really loose during those times when you lift off the throttle a bit, the rear springs are not able to keep the rear tires firmly planted, so softening the rear rebound may help.
So, in short, if the car pushes during mid corner, you can try softening the front rebound. If it’s loose, soften the rear rebound.
The third phase of the corner is while you’re applying power, unwinding the wheel, tracking out and exiting. Think about Roebling Road’s turn 2 and Road Atlanta turn 7. Weight is transferring from the front to the back. The front shocks are primarily rebounding while the rear shocks are under compression (bump). Softening the rear bump will allow weight to transfer faster to the rear tires giving them more grip. Too much weight transfer will cause the rear to grip too much and the car will understeer. Not enough weight transfer and the rear tires will lose traction – loose/oversteer.
While the weight is transferring to the back, the front shocks are rebounding and the front spring is trying to push the tires to the pavement. If the rebound is too stiff, the tires will essentially be suspended in mid air and the car will push/understeer. If the rebound is too soft, the spring will push the tires to the pavement easily and will get excellent grip…so much so that the car will now be loose.
As you can see, all of this is a balancing act. If you “give” the front end more grip, the rear will not have as much traction and vice-versa.
And as a general rule, to increase grip, simply soften the end of the car that is sliding too much. If the car understeers, soften the bump and/or rebound on the front; if it oversteers, soften the bump or rebound on the back.
Check out the chart I’ve attached and you can see how everything is labeled. “+” means stiffer, while “-” means softer. B is bump and R is rebound.
http://forums.corvetteforum.com/atta...7&d=1187479758
Again, just keep those 3 words in your mind while adjusting the handling of your car: Facilitate Weight Transfer! I hope this helps!!
Chris
The first race(s) after I bought and installed my new 3-way adjustable Motons was just awful to be honest. I knew nothing about them. During the weekend, the adjustments I made were wrong and the car did not handle well at all.
Even before buying them though, I searched the web but could not find any quick reference charts or CLEAR explanations of how shocks worked and what to do to improve the handling under different circumstances.
Now that I’ve had a while to experiment with them, I have a much better “handle” (pun intended) on how they work and what you can do to improve the car. Since I couldn’t find a quick-reference chart, I decided to make one of my own…but I’ll get to that in a minute.
First, to understand the chart, you must understand some basic characteristics of adjustable shocks and exactly what they do. If you forget everything I’m about to tell you, but remember these 3 words: “Facilitate Weight Transfer”, then you’ll be OK. That’s what shocks do…other than just dampen the springs when you hit a pothole.
In the world of race cars and shocks, you’ll primarily hear the words bump and rebound. To keep things simple, I’ll just work with those terms. When you’re talking about bump, that’s referring to when the shaft of the shock is compressing, or going into, the body of the shock. Rebound is when the shaft is coming out of the shock body. When you hit a bump, the shaft of the shock goes into the body of the shock and then the car’s spring tries to pull the shaft back out (and put the car’s tire back on the street). Depending on how stiff each of those settings are will determine the rate at which the shaft compresses or releases from the shock body.
Now let’s look at how a shock helps the handling of the car. Bump: When you hit the brakes, weight transfers to the front tires (or tries to) which allows the tires to grip more and brake harder. This phase of handling is primarily dealing with the bump settings on the front. If the front shocks are really stiff, the weight won’t transfer as well and braking performance is reduced. If the bump settings are too soft, you’ll get lots of weight transfer and the back end will dance around. Get it?
Rebound: In this braking phase, rebound of the rear shocks is also critical. The rear spring is attempting to keep the rear tires on the pavement. The shock shaft is lengthening…coming out of the shock body. If the rebound is nice and soft, the shaft comes out of the body easily and the spring keeps the rear tires planted. If the rebound is too stiff, the spring can’t push the tires down to the pavement fast enough and the car seems to dance and is unstable.
This leads directly into the first of 3 primary phases of a corner – corner entry. For the purposes of this discussion, think about turn 1 at Road Atlanta or Roebling Road – they are right hand turns. During this phase, weight is on the front tires. The bump settings on the front end (specifically the LF) is the one primarily affected. As you turn the wheel, weight tries to transfer to the LF. If it transfers easily, the LF will have good contact (traction). If weight doesn’t transfer easily, the bump is too stiff and the car will most likely push on corner entry.
Conversely, when the front end grips very well, the car will probably be loose. Since the weight is still on the front tires, it’s imperative that the rear rebound still be soft enough to allow the spring to push the tire to the ground.
So, in short, if the car pushes on corner entry, it’s best to soften the front bump. If it’s loose, soften the rear rebound. Starting to get it yet? Stay with me…
The second phase of handling is mid corner – right around the apex area where the car is under maintenance throttle and you can really tell if the car is balanced or not. The outside tires are loaded while the inside tires are just there for decoration.
Think of Roebling Road’s turn 7 and 8. Since weight has transferred to the outside tires, we’d like the car to behave well – not oversteering or understeering – equal weight transfer. However, if the bump settings on the front are too stiff, more weight will be transferring to the back and giving those tires grip, which will result in understeer. Conversely if the rear bump settings are too stiff, more weight will be on the front tires and you’ll be loose (oversteer). So, in short, if the car pushes during mid corner, softening the bump on the front should help the problem. If it’s loose, soften the rear bump.
Rebound during this phase is a bit trickier. Since the throttle is the primary means of steering the car in phase 2, what you’re doing is essentially just adjusting how much weight transfers to the front and back. If you lift throttle a bit, more weight transfers to the front (and off the back) helping the car to rotate and turn better. If you get on the gas, you transfer weight to the back helping the rear tires grip. If you notice the car pushing badly as you roll down on the throttle, the front rebound may be too stiff. The spring is trying to push the front tires to the ground to get traction, but is not able to. Softening the front rebound allows the spring to do this so you’ll get a bit more grip in the front.
Conversely, if the car is really loose during those times when you lift off the throttle a bit, the rear springs are not able to keep the rear tires firmly planted, so softening the rear rebound may help.
So, in short, if the car pushes during mid corner, you can try softening the front rebound. If it’s loose, soften the rear rebound.
The third phase of the corner is while you’re applying power, unwinding the wheel, tracking out and exiting. Think about Roebling Road’s turn 2 and Road Atlanta turn 7. Weight is transferring from the front to the back. The front shocks are primarily rebounding while the rear shocks are under compression (bump). Softening the rear bump will allow weight to transfer faster to the rear tires giving them more grip. Too much weight transfer will cause the rear to grip too much and the car will understeer. Not enough weight transfer and the rear tires will lose traction – loose/oversteer.
While the weight is transferring to the back, the front shocks are rebounding and the front spring is trying to push the tires to the pavement. If the rebound is too stiff, the tires will essentially be suspended in mid air and the car will push/understeer. If the rebound is too soft, the spring will push the tires to the pavement easily and will get excellent grip…so much so that the car will now be loose.
As you can see, all of this is a balancing act. If you “give” the front end more grip, the rear will not have as much traction and vice-versa.
And as a general rule, to increase grip, simply soften the end of the car that is sliding too much. If the car understeers, soften the bump and/or rebound on the front; if it oversteers, soften the bump or rebound on the back.
Check out the chart I’ve attached and you can see how everything is labeled. “+” means stiffer, while “-” means softer. B is bump and R is rebound.
http://forums.corvetteforum.com/atta...7&d=1187479758
Again, just keep those 3 words in your mind while adjusting the handling of your car: Facilitate Weight Transfer! I hope this helps!!
Chris
Last edited by wtknght1; 08-19-2007 at 10:52 AM.
08-18-2007, 10:30 AM
#2
Melting Slicks
Member Since: Nov 2006
Location: Santa Barbara, CA
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Great write up. Best post I've seen on this board. There are some general guidlines to add to what you have written in this Penske manual.
http://hardbarusa.com/PenskeManual.pdf
So do you mind sharing about where you ended up on those settings? How many clicks away from full stiff? I just got some double adjustables and I'll be going through the same process. Triple seems even harder. I can't really see any time at the track you'd want a stiff fast bump. That way you are stable over the curbing.
FLB Front left bump
FLC Front left compression
etc
I was also surprised to read that when you lessen the weight transfer on braking it makes braking less effective. I thought if you slowed down the pitch you'd have more grip on the rear tires and not overloading the fronts. Can you explain this a little bit further?
http://hardbarusa.com/PenskeManual.pdf
So do you mind sharing about where you ended up on those settings? How many clicks away from full stiff? I just got some double adjustables and I'll be going through the same process. Triple seems even harder. I can't really see any time at the track you'd want a stiff fast bump. That way you are stable over the curbing.
FLB Front left bump
FLC Front left compression
etc
I was also surprised to read that when you lessen the weight transfer on braking it makes braking less effective. I thought if you slowed down the pitch you'd have more grip on the rear tires and not overloading the fronts. Can you explain this a little bit further?
Last edited by bowmanized; 08-18-2007 at 10:32 AM.
08-18-2007, 10:53 AM
#3
Melting Slicks
Thread Starter
The moderator hasn't posted my chart yet, but hopefully he'll get it soon.
As far as settings, my settings probably wouldn't do you much good. The original settings (mid range) were too stiff, so I kept softening until I basically ran out of adjustments. I sent them back to Moton for revalving - softening even more. I haven't tested the new settings yet.
As far as braking and weight transfer - traction is all about getting weight on that tire (or tires) that you want to grip. The front tires (and brakes) do 70-80% of the actually stopping anyway (on a Vette), so that's where you want the weight transfer. If that doesn't happen, the tires won't grip and you can't stop as well. There is a sweet spot though - for you, the tires, the pads, calipers, rotors, springs, etc. Now you have to find it with adjustments.
As far as settings, my settings probably wouldn't do you much good. The original settings (mid range) were too stiff, so I kept softening until I basically ran out of adjustments. I sent them back to Moton for revalving - softening even more. I haven't tested the new settings yet.
As far as braking and weight transfer - traction is all about getting weight on that tire (or tires) that you want to grip. The front tires (and brakes) do 70-80% of the actually stopping anyway (on a Vette), so that's where you want the weight transfer. If that doesn't happen, the tires won't grip and you can't stop as well. There is a sweet spot though - for you, the tires, the pads, calipers, rotors, springs, etc. Now you have to find it with adjustments.
08-18-2007, 02:11 PM
#4
Race Director
Weight transfer is even a bit more complicated than Chris explains. This becomes the case when changing corner weights, or Wedge. In this case, shifting weight to the UNLOADED tires increases grip.
If you have a car that is pushing, you can often jack static weight out of the ouside tire and into the inside tire. This relieves some of the loading on the overstressed tire, and forces the inside (unloaded) tire to do more of the work. So by decreasing 5% of the load off of the outside tire, you may increase the load on on the inside tire by 10% (since the outside tire was doing half the work before, it is larger percentage-wise).
Shocks are just as tricky, as Chris explains. You are trying to control motion, both my increasing and decreasing when and where it happens. I personally think 3-way shocks are overkill for most non-Pro applications, as the time it takes to ever dial them in is extensive. It certainly can be rewarding, if you've got the time to work through them.
Chris, that really sucks that they mis-valved the shocks wrong the first time. Granted a T1 car is significantly heavier than most of their customers' cars, but Moton should have no problem working that out.
Anyway, glad it's coming together.
If you have a car that is pushing, you can often jack static weight out of the ouside tire and into the inside tire. This relieves some of the loading on the overstressed tire, and forces the inside (unloaded) tire to do more of the work. So by decreasing 5% of the load off of the outside tire, you may increase the load on on the inside tire by 10% (since the outside tire was doing half the work before, it is larger percentage-wise).
Shocks are just as tricky, as Chris explains. You are trying to control motion, both my increasing and decreasing when and where it happens. I personally think 3-way shocks are overkill for most non-Pro applications, as the time it takes to ever dial them in is extensive. It certainly can be rewarding, if you've got the time to work through them.
Chris, that really sucks that they mis-valved the shocks wrong the first time. Granted a T1 car is significantly heavier than most of their customers' cars, but Moton should have no problem working that out.
Anyway, glad it's coming together.
08-18-2007, 02:35 PM
#5
Melting Slicks
Thread Starter
It may be more of a case where I just have to keep adjusting to find that "sweet spot" that works for me. You or somebody else could get in my car with the old settings and it would be perfect, but for me, it was just too stiff. We'll see how it goes.
08-19-2007, 12:27 PM
#8
Instructor
Member Since: Jan 2004
Location: laguna niguel ca
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Chris
Very nice write up. I met Lex at PRI last year and he is very knowledgeable and probably the funniest guy I have ever met. Unfortunately the Motons are "huge" money especially for those of us who already invested in the T1 legal single adjustable Penskes. Oh well, I will just have to add that to my Christmas wish list.
Good luck at the runoffs
Roy
Very nice write up. I met Lex at PRI last year and he is very knowledgeable and probably the funniest guy I have ever met. Unfortunately the Motons are "huge" money especially for those of us who already invested in the T1 legal single adjustable Penskes. Oh well, I will just have to add that to my Christmas wish list.
Good luck at the runoffs
Roy