Stock class shock valving
12-12-2005, 12:59 PM
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Stock class shock valving
Shaggy said he would post his experiences on stock class shock valving. Also, if anyone can explain what characteristics we're looking for when it comes to AutoX shocks that would be great. I currently run re-valved Koni's spec'd by T.C. Kline. I know I can ride the limit better than I could before during slaloms, but I can't tell you what changed from the re-valve.
I would also like to know what the road-race guys look for in shock valving as well.
-ukfinance
*edited to be more specific. I had a blown shock that was making slaloms near impossible. The re-valve solved the problem.
I would also like to know what the road-race guys look for in shock valving as well.
-ukfinance
*edited to be more specific. I had a blown shock that was making slaloms near impossible. The re-valve solved the problem.
12-12-2005, 01:31 PM
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On the Penske's, I've always been worried about going beyond about 2.5 turns out on the rebound as I was told that at anything beyond three turns the adjustment comes apart and you have to take ths shock apart to have it reconnected.
I have a MY 2000 with a Saner bar that has been modified to be even stiffer than the regular Saner bar. I have been working for the last several months just getting the car balanced again (i.e., getting rid of understeer). Dave McCombs has made some suggestions that have helped enormously, but the car is not near dialed in yet. The good thing is that I get absolutely NO wheel spin in corners.
Anyway, any guidance on how to make the car more comfortable on the street without sacrificing too on the auto-x course would be great.
First question - are there any good books that describe handling characteristics, corrections, etc.?
I have a MY 2000 with a Saner bar that has been modified to be even stiffer than the regular Saner bar. I have been working for the last several months just getting the car balanced again (i.e., getting rid of understeer). Dave McCombs has made some suggestions that have helped enormously, but the car is not near dialed in yet. The good thing is that I get absolutely NO wheel spin in corners.
Anyway, any guidance on how to make the car more comfortable on the street without sacrificing too on the auto-x course would be great.
First question - are there any good books that describe handling characteristics, corrections, etc.?
12-12-2005, 03:18 PM
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Originally Posted by silvershadow,Dec 12 2005, 05:31 PM
First question - are there any good books that describe handling characteristics, corrections, etc.?
12-12-2005, 05:02 PM
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OK, I'm home now, so here goes... longwinded blowhard warning 
In stock class you have only two tools at your disposal for changing roll resistance: The front sway bar and the dampers. There are other tuning tools, but these are the only ones that affect roll resistance.
As any good tuner knows, one of the fundamental characteristics of a car's balance (oversteer or understeer) is the relative roll resistance of the front of the car versus the rear of the car. If a car oversteers too much, the ratio is biased towards the rear more than it should (rear is too stiff or front is too soft). Convsersely, if a car understeers too much, the bias is too much towards the front of the car (front too stiff, rear too soft). Having said that, there is more than one type of roll stiffness: transient roll stiffness (dampers) and static roll stiffness (springs and bars). Note that the allowable modifications give you one tool for static roll stiffness (front bar) and one tool for transient roll stiffness (dampers).
As many of you know, S2000 guys use huge front bars to keep the rear of the car on the pavement and stop wheelspin. This dictates the minimum bar size that is acceptable to use. Larger bars may be used effectively to calm static (steady state, or mid-corner) oversteer. Now, on to the dampers themselves.
Dampers are most effective when the wheels are moving relative to the chassis. In other words, they don't do squat in mid-corner when the car is fully leaned over. The have a huge effect, however, in a slalom where the car is never settled. Basically, the faster the piston in a damper moves, the higher the force trying to stop the movement of the piston. But technology gives us many options when building the piston and shim stack set in each damper.
What type of movements do dampers feel? Anything that makes a wheel move relative to the chassis will invoke a damper force. How large that force is depends on the speed of the piston movement and the internal configuration of the damper. To correctly determine the internal build of a damper, the tuner must adequately determine the operating velocities of the piston in various situations and determine the desired damping force at each velocity. Doing this will create a graph of force versus velocity, or a damping curve. Or more specifically, damping curves... one for compression of the damper and one for rebound or extension of the damper.
Three types of wheel movement are seen in autocross situations: very slow, slow to moderate, and fast. Very slow speeds are seen during corner entry and corner exit, as longitudinal and lateral g-forces are increased and decreased. Slow to moderate speeds are seen in slalom elements. Fast piston speeds are seen going over bumps. This generates 3 zones of a damping curve to specify.
Where do you start? You start with what you know. Have your shocks put on a shock dyno to generate a damping chart. If you have adjustable shocks, make several dyno runs - one at each of the settings you commonly use. Then, for each zone of the damping curve, ponder what you want your car to do differently - in each of the following specific situations: turning and braking, turning and accelerating and even throttle turning. Adjust the curves in each zone as follows: braking engages front compression and rear rebound, acceleration engages front rebound and rear compression and neutral throttle is the sum of the compression and rebound at each end of the car.
What this led me to do to solve my problem (on throttle oversteer) was to increase the very low speed front rebound. I was also interested in making the dampers more appropriate for street driving so I reduced high speed damping in both rebound and compression at all four corners.
OK... corrections from anyone? Questions? More specifics? Help me out here!
Andy
PS - if you can change springs and bars at both ends of the car, do this long before you get whacko with the shocks like we do in stock class!
In stock class you have only two tools at your disposal for changing roll resistance: The front sway bar and the dampers. There are other tuning tools, but these are the only ones that affect roll resistance.
As any good tuner knows, one of the fundamental characteristics of a car's balance (oversteer or understeer) is the relative roll resistance of the front of the car versus the rear of the car. If a car oversteers too much, the ratio is biased towards the rear more than it should (rear is too stiff or front is too soft). Convsersely, if a car understeers too much, the bias is too much towards the front of the car (front too stiff, rear too soft). Having said that, there is more than one type of roll stiffness: transient roll stiffness (dampers) and static roll stiffness (springs and bars). Note that the allowable modifications give you one tool for static roll stiffness (front bar) and one tool for transient roll stiffness (dampers).
As many of you know, S2000 guys use huge front bars to keep the rear of the car on the pavement and stop wheelspin. This dictates the minimum bar size that is acceptable to use. Larger bars may be used effectively to calm static (steady state, or mid-corner) oversteer. Now, on to the dampers themselves.
Dampers are most effective when the wheels are moving relative to the chassis. In other words, they don't do squat in mid-corner when the car is fully leaned over. The have a huge effect, however, in a slalom where the car is never settled. Basically, the faster the piston in a damper moves, the higher the force trying to stop the movement of the piston. But technology gives us many options when building the piston and shim stack set in each damper.
What type of movements do dampers feel? Anything that makes a wheel move relative to the chassis will invoke a damper force. How large that force is depends on the speed of the piston movement and the internal configuration of the damper. To correctly determine the internal build of a damper, the tuner must adequately determine the operating velocities of the piston in various situations and determine the desired damping force at each velocity. Doing this will create a graph of force versus velocity, or a damping curve. Or more specifically, damping curves... one for compression of the damper and one for rebound or extension of the damper.
Three types of wheel movement are seen in autocross situations: very slow, slow to moderate, and fast. Very slow speeds are seen during corner entry and corner exit, as longitudinal and lateral g-forces are increased and decreased. Slow to moderate speeds are seen in slalom elements. Fast piston speeds are seen going over bumps. This generates 3 zones of a damping curve to specify.
Where do you start? You start with what you know. Have your shocks put on a shock dyno to generate a damping chart. If you have adjustable shocks, make several dyno runs - one at each of the settings you commonly use. Then, for each zone of the damping curve, ponder what you want your car to do differently - in each of the following specific situations: turning and braking, turning and accelerating and even throttle turning. Adjust the curves in each zone as follows: braking engages front compression and rear rebound, acceleration engages front rebound and rear compression and neutral throttle is the sum of the compression and rebound at each end of the car.
What this led me to do to solve my problem (on throttle oversteer) was to increase the very low speed front rebound. I was also interested in making the dampers more appropriate for street driving so I reduced high speed damping in both rebound and compression at all four corners.
OK... corrections from anyone? Questions? More specifics? Help me out here!
Andy
PS - if you can change springs and bars at both ends of the car, do this long before you get whacko with the shocks like we do in stock class!
12-12-2005, 06:39 PM
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I know a lot of the big dogs use Motons or Penskes, what are the fundamental differences (if any) between the shocks or does it all come down to valving? If it's all in the valving, could a set of Koni yellows properly valved be more effective than the big $$ Motons?
Thanks for taking time to respond Andy, great reply.
Thanks for taking time to respond Andy, great reply.
12-12-2005, 07:10 PM
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To answer the question... Yes. A Koni Yellow could theoretically be more effective than the Motons.
The biggest differences between Motons, Penskes, JRZ's and the "lesser" shocks is adjustability and rebuildability. OK, and weight. My Penske's (now Orthonormal's) were aluminum bodied and very light. Think JDM wheels vs. OEM wheels. But back to valving and adjustability.
With the high end dampers comes significantly more adjustability, both internal and external. In the Penske line, for example, they have about a dozen different piston designs that all create radically different damping curves. They name them based on the type of curve they produce:
Linear / linear
Linear / digressive
Digressive / digressive
VDP / linear
etc.
All of these pistons have different shaped passeges that the damping fluid must pass through when the piston moves. Once you select a piston, you can tweak the curves by building different stacks of shims on each side (compression shims on one face, rebound on the other). The shim game is the same across all shocks, but I suspect the piston game is unique to the high-end shock.
Another plus of the high end shock is that they were made to be rebuilt and revalved regularly. I don't mean that they wear out quickly and you have to do it, I mean that if you have the tools, you can do it yourself. The last revalve on my front shocks took one hour, total. Including running both shocks on the dyno. If you have the right friends or technical help, you could do a revalve overnight - from installed to installed.
Finally, the adjustability of the high end shocks is remarkable. Now on a 8100 series Penske, the compression adjustment is not all that effective for tuning, but the rebound adjustment on my shocks was everything. I could change the rebound damping from (assumed scale) a stiffness of 150 to a stiffness of 450 between runs if I needed to. So, my internal build doesn't have to be very close for me to be able to make the car work well. Also, I can move from Hoosiers to Kumhos and ashpalt to concrete (also wet to dry!) without having to internally revalve the shocks. For more money, I could get the same type of adjustment out of the compression side of my Penskes... its called the 8760 series canister.
Is the high end shock starting to make more sense for the big dogs? If you never race in the rain and always run the same lot (Wendover anyone?) a set of Koni Yellows could be made to suit you. But if you travel, the high end stuff is likely to make you more competitive at every site.
Andy H.
The biggest differences between Motons, Penskes, JRZ's and the "lesser" shocks is adjustability and rebuildability. OK, and weight. My Penske's (now Orthonormal's) were aluminum bodied and very light. Think JDM wheels vs. OEM wheels. But back to valving and adjustability.
With the high end dampers comes significantly more adjustability, both internal and external. In the Penske line, for example, they have about a dozen different piston designs that all create radically different damping curves. They name them based on the type of curve they produce:
Linear / linear
Linear / digressive
Digressive / digressive
VDP / linear
etc.
All of these pistons have different shaped passeges that the damping fluid must pass through when the piston moves. Once you select a piston, you can tweak the curves by building different stacks of shims on each side (compression shims on one face, rebound on the other). The shim game is the same across all shocks, but I suspect the piston game is unique to the high-end shock.
Another plus of the high end shock is that they were made to be rebuilt and revalved regularly. I don't mean that they wear out quickly and you have to do it, I mean that if you have the tools, you can do it yourself. The last revalve on my front shocks took one hour, total. Including running both shocks on the dyno. If you have the right friends or technical help, you could do a revalve overnight - from installed to installed.
Finally, the adjustability of the high end shocks is remarkable. Now on a 8100 series Penske, the compression adjustment is not all that effective for tuning, but the rebound adjustment on my shocks was everything. I could change the rebound damping from (assumed scale) a stiffness of 150 to a stiffness of 450 between runs if I needed to. So, my internal build doesn't have to be very close for me to be able to make the car work well. Also, I can move from Hoosiers to Kumhos and ashpalt to concrete (also wet to dry!) without having to internally revalve the shocks. For more money, I could get the same type of adjustment out of the compression side of my Penskes... its called the 8760 series canister.
Is the high end shock starting to make more sense for the big dogs? If you never race in the rain and always run the same lot (Wendover anyone?) a set of Koni Yellows could be made to suit you. But if you travel, the high end stuff is likely to make you more competitive at every site.
Andy H.
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12-13-2005, 07:29 PM
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I agree that rebound damping rates are more important tuning tools, but for a different reason: High compression damping rates make the car skip over bumps.
As a general rule, dampers do not change the rate of weight transfer front to rear or left to right. So, in essence, only the "across axle" entries are appropriate.
Only absolute accelerations on the car will determine the forces at any given instant. Roll resistance biases are important for determining the dynamic cross weight of the car, not front vs. rear or left vs. right. Dampers determine the rate at which the ultimate dynamic cross weight is reached, modifying the traction available at each wheel for a brief period of time. Springs and bars determine the ultimate dynamic cross weight and thus determine steady state grip levels at each wheel.
Agree / disagree?
As a general rule, dampers do not change the rate of weight transfer front to rear or left to right. So, in essence, only the "across axle" entries are appropriate.
Only absolute accelerations on the car will determine the forces at any given instant. Roll resistance biases are important for determining the dynamic cross weight of the car, not front vs. rear or left vs. right. Dampers determine the rate at which the ultimate dynamic cross weight is reached, modifying the traction available at each wheel for a brief period of time. Springs and bars determine the ultimate dynamic cross weight and thus determine steady state grip levels at each wheel.
Agree / disagree?
12-13-2005, 07:46 PM
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Originally Posted by shaggy,Dec 13 2005, 08:29 PM
Agree / disagree?
Increasing the front compression damping has the same effect under braking as making the springs very stiff at the moment you hit the brakes and then slowly making them less and less stiff. I guess what I am trying to say is that I think any characteristic of the car that is affected by the spring rate can also be affected by the dampers.