Left Rear Shocks

Updated: Jul 28, 2021

I am trying to update this every time I post it so it has new info in it and you can learn more about the left rear. In this update we will cover the 4 thing that make up a left rear shock. See 7-8-21 below

Lets look at why we build some of the stuff we do and then what we build, this is probably true for other builders too.

· Stiff LR to hold the car up on entry.

· To make more drive.

· I ran one that a friend had, and it worked well.

· I am spinning the tire on exit.

· It frees the car up to much.

What ever you reason is the left rear shock will do so much for a car and that is it and it is somewhat different on a 4 bar car than a 3 link car depending on where it is located.

Here are some of the shocks we build and their functions:

· LR1-40-330@150 psi: This is a very good starting point and good for a car in moisture.

· LR1-40-350@150 psi: This is basically the same thing and is something we do for many classes.

· LR1-40-400@175 psi: Moving up the scale this is a great shock for a mod, sport mod or stock car.

· LR1-40-550@275 psi: This shock is going to really hold the car on the bar, has a lot of rod force.

· LR1-50-350@150 psi:

· LR1-50-400@175 psi:

· LR1-50-550@275 psi:

· LR1-60-350@150 psi:

· LR1-60-400@225 psi:

· LR1-75-550@275 psi:

This is a list of some of the left rears we build, and this list can go on for a while with different combination of low speed and high speed. When going down this list from one shock to the next the jump is not that great, so if you have a LR1-40-350 the next step would not be a LR1-40-400 because they are close to each other. This is not a complete list of what we do just some of them and it don't include things like base valve, bypass or SRT piston.

The 4 things that make up a left rear shock are compression, gas pressure, bleed and zero point. How you affect these will determine the outcome of your shock and they are going to come in effect by what you are looking for vs. your track conditions. A lot of issues can come out of your left rear shock and I feel like a lot of them get overlooked when diagnosing the problem of the race car and mainly because we don’t understand the effect that the left rear has good or bad on our car. We need to understand the pros and cons of each of the 4 factors of the left rear shock and the outcome to the car and what would be a good way to combat them. (SRT, Base valve, different locations)

One thing you must understand is that the stiffer the left rear the less traction it makes, now a lot of people are going to argue with this statement, and it is different in different cars, 3 link or 4 bars. So, the two thing it comes down to most of the time is this, holding the car up a ton or making a ton of traction and this will take 2 different shocks.

When buying a BSB this will be determined in the evaluation we do of your car/driver interview and we will cover more or go in depth in later update or in the members only guide. Left rear shocks good or bad you are going to need one until it falls off and you think it is better without. (this is where you ask why)


Update 5-16-2020:

Types of LR Shocks we build:

Gas shock: This is a standard gas shock built in any valving that you like, we normally do it with low speed nose and try to maintain the lowest gas we can in order to make traction. This shock gas pressure is based on the amount of compression that the shock has.

Gas Shock High Gas: This shock is built in any valving you want but has a higher gas pressure than normal as to increase the rod force to increase its ability to hold the car up. (300 psi)

Base Valve: This shock can be built in any valving and also can be built in low or high gas version depending on the desired outcome. The base valve is very good at making traction on a 4 bar car.

SRT: This is a piston design that allows bypass in the piston so when the car hits a bump or a hole on the track oil is processed through the SRT valve instead of the main shim stack. This allows the tire to stay in contact with the ground more increasing the cars traction.

Air Shock: Not to be confused with a gas shock an air shock has both an oil column and a air column, when in the oil the shock will build very good traction because of the lower gas pressure applied to the shock, but is the air column the rod force will increase to a level that hold the car in position through the corner.

Bypass: Bypass can be done in one of two ways, in the tube or by a T3 style shock. Either way oil is being bypassed around the piston allowing the tire to stay in contact with the ground. This shock can be configured in many ways and the mind is your playground.

COB: Compression only Bypass is what COB stands for, now it is being used in different ways and some of those may or may not work as good as we would like. As a standard I like it on the left rear for a shock that produces a very low rebound and a very high low speed (nose) compression shock. Some people have used this shock in the flip condition to produce rebound, but I feel as if there are problems with doing this, looks super good on the dyno and sometimes lack performance on the racetrack. This is a piston with a built-in check valve, and it works very well.

How to understand our shock valving:

We will stay with the left rear on this, but when dealing with a BSB shock we mark what is important to the shock. RF, LF and RR are mark in rebound low speed and LR is mark in compression low speed and high speed. Well here is how it works:

LR1-40-400 SRT@225 psi (2-8)

  • · LR: is the position of the shock.

  • · 1: Means the low speed has been increased from standard.

  • · -40: Is the low speed at 1” on the dyno on the average chart, this is higher than a standard bleed system, or when you have a hole in a piston that you can’t make any smaller.

  • · -400: Is the high speed at 10” per second, this is also where the generic valve number comes from. This number is not the same for two shock companies or two shock builders.

  • · SRT: This is where it will tell you if there is anything special about the shock. SRT, COB, Base Valve or Schrader valve is being added to the shock.

  • · @ 225 psi: This is the amount of gas that is being added the shock.

  • · 2-8: The 2 is rebound and the 8 is compression.

Now we can build any type of left rear you like as far as valving is concerned, we can also vary the zero point and gas pressure too. What we need and what we want sometimes are different and what we want doesn’t always make traction. Just let us know what we can do to help.


Updated: 7-8-21

The 4 thing that make up the left rear.

The 4 things that make up a left rear shock are, compression, gas pressure, bleed and zero point. Now what is the most important of the four, not for sure and they all work together to make the left rear shock. A better way to look at it maybe which one hurts me the most for our track conditions.

Compression: This is made up of both high speed and low speed and will effect bleed and zero point when messing with it. High speed is a 10-inch number we often use to call out the number that we think the shock is such as a 10 valve. It is the overall compression in the shock and the bigger it gets the stronger the shock is. We can add high speed to the shock and get a stronger shock for the left rear with out changing low speed much. There are some builds where you can achieve a lot of high-speed number on a big bleed and have a cool shock for the left rear, but you do not see it being used that much. This is something we should study a little more because it can have a good place in the market, because it allows the car to get through the rougher parts of the track without upsetting the car as much. Same as an SRT piston would but in a different fashion.

Bleed: Low speed is directly effected by the amount of bleed the shock is going to have on both side of the piston, remember that bleed is what lets you push a shock in and out. Bleed is so important to the overall effects of the car and how it will handle the track surface to the tire. It is also the main effect in how fast the car will settle back down when you get of the gas. Let us clear up something hear about that, the car is going to fall off the bars when you get off the gas, the shock is not going to hold it very long by itself. The compression high and low speed will only assist in helping the cars attitude, you must stay in the gas for it to stay on the bars.

Low speed bleed will change the nose of the shock and will determine how much traction the left rear will make on corner exit. What helps on one side often hurts on the other side of the corner, and low speed bleed can look good on the dyno but run bad on the car. You need to tell your shock builder the conditions of the racetrack on both entry and exit more than he needs to know how much help you need in hold up the car on entry.

Gas Pressure: I see this so much and do not understand it at all but get what the thinking is when it is done, and that is gas pressures. Understand this gas pressure is a direct relationship to compression high speed, the more-high speed the more gas. This is true in all gas shocks but not in a base valve shock and is not what we are talking about here. When the high-speed compression increases the gas pressure must also. High gas pressure left rear in not good for forward traction on a 4-bar car when the shock is in front of the axle but allowing the shock to struggle due to low gas pressure to increase traction on that corner will not work out all that well either. Sounds like a great deal but if you shock guy is giving you a shock that is 400 lbs of 10” number and says it has 75 psi in it take it back because it won’t work on the racetrack.

A couple of tricks for gas pressure, 1st you need the correct amount of gas to control the oil column on the compression side of the shock. 2nd if the head of the shock is collecting dust after a race it maybe the gas pressure is too low and is allowing the shock to cavitate and leak oil out the seal head. 3rd gas pressure on a 3-link car or a stock car may work in your advantage to increase wheel load when car is on the bars. 4th if you are using Schrader valve you will need to check the gas pressure all the time as they leak and that is just how it is.

Zero Point: This is the often overlooked when building a shock and is harder to control because a lot of people do not understand what makes it work. Zero point is often increased when bleed leaves get to low, there are other factors in this that will change zero point, but we will not cover at this time. Often a shock builder will sell a left rear shock base on zero being high as a good thing because it has become something he cannot control or a by product of what he is doing in the shock. Zero point can help in making the shock stiffer but often will decrease traction off corner in the slick and or rough conditions.

This is an update to left rear shocks as of 7-8-21 to help understand the 4 thing that make a left rear shock work, if you have ideas or knowledge on this subject please commit below, we are here to build a better piece to race on.

Next time lets discuss how a base valve shock will improve traction on a 4 bar car but not on a 3 bar car. Commit below if you want to know more about the left rear base valve shock.


BSB SRT piston

Understanding a Base Valve shock

Low gas shocks



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