High Speed vs Low Speed
Updated: Apr 6
This is mainly for 12 and 13 Series Valving.
When understanding valve numbers, the first thing we need to know is, are we looking at high speed numbers or low speed numbers or maybe even zero points. Today we are going to look at low speed and high speed. Until recently most valve charts were high speed, like 30/30 or 3-3 were numbers giving to a high-speed number of a certain poundage. When the shock was dynode at 10 inches per second it created a number like 160 pounds and that was given a rating of 3. If you study the chart, you will see those numbers and how they represent the valve number they were given. Early on not much concern was given to the bleed circuit or the amount of bleed that a shock had in it and the whole shock was based off the high-speed number. Today this is not the case, and low speed is highly important to how the car is going to work on the racetrack, this is why we now have low speed numbers, and we need to learn how to read them.
Here is a chart to show the representation of a valve number to the poundage number and it compares Bilstein (old) to BSB so you can get a better idea of what you r are looking at.
Now, let’s look at how to understand the low speed and high-speed call outs and how they affect the shock.
30/30: Rebound/ Compression and this is the same as a 3-3. When looking at a standard scale used by Bilstein back in the day a 30 valve was 160 pounds of pressure at 10 inch per second of speed at the shock. That means the shaft was moving 10 ips and making a force of 160 ponds. Unlike other companies Bilstein did the same thing on both side of the shock, meaning that a 30/30 would make 160/160 pound of force. When we build a shock like this (30/30) we do it with a 4-bleed full bleed shim on both side and allow for 20 pound of tolerance at 10 ips.
160/160: Still Rebound/Compression and still a 30/30 but on a tighter tolerance, this with just 10 pounds of tolerance. This shock is still built on a 4-bleed full system and has a minimally value at low speed.
RF1-50/130: This is where we start building low speed car control in the shock. Frist is the location call out like the RF or LF followed by the 1 which indicates that the low speed has been modified (bleed system). The 50 is the 1-inch number in pounds when dynoing the shock at 10 ips. As this number increases the low and high speed rebound also increase, the high speed at this point is there to build strength for the low speed and is not as important so it is not added to the call out. The (/) forward slash separates the rebound from compression and the 130 is the high speed compression number. Depending on how the shock is built will depend on how we look at the compression number on the dyno. This shock is built on a smaller bleed system than the first 2 shock and also on a ring shim which adds preload to the shim stack increasing the power of the stack. Valving a shock this way will allow a ton of room to work in the valving range and could provide all the builds necessary to build a small body shock. Range runs from 30 to 100 which is a very good range to work in while allowing the shock to have bleed which will allow grip. Bleed in the shock is decreases as the number goes higher but still allows for spring return in the car.