February 17

Sim-Racing Brake Pedal Mods

I get questions all the time about brake pedal mods to Logitech and Thrustmaster pedals. There is lots of information and mis-information about the subject here on the internet. This article is not about determining which one is better, but more about giving you information to determine which one is best for you.

There are two main types. The more economical option is the harder spring or bushing option. These have existed for a long time and there are many variations of it. There is the GTeye style progressive spring, the Nixim style rubber insert and the shock absorber style dampener. All of these fall into the same main category type because all of these remain being distance based pedals. The pedals that host these mods are originally created to use a potentiometer for a sensor. For those that are unfamiliar with this device, it is similar to the guts of a volume knob. The pedal is attached to this and as the pedal is pressed downward the potentiometer turns. Rather than turning up the volume, it signals the game to apply more brakes.

This is perfectly adequate if it weren’t for the pedal being so darn soft. This becomes an issue when you are approaching a turn and you know that you need to apply 18mm of input on the brake pedal to slow the car to the right speed. Well, trying to measure 18mm with your foot without looking and doing it quickly proves to be a very difficult task.

A simple way to solve this is to make the pedal harder. This increases the amount of muscle needed to move the pedal. Many erroneously call this using “muscle memory.” While the term is wrong, the concept is valid. The principle is that you are better able to control muscle strength easier than muscle movement, so making the pedal harder places more of the pedal input on strength and less on movement.

So now that we have the basic principle out of the way, let’s look at how these modifications translate muscle input to brake input. The progressive spring is a type of spring that become progressively harder the more it is squeezed. While a linear spring on the other hand becomes steadily stiffer as it is compressed. Here is an example. A linear spring compresses 10mm for 1kg of load then it will compress 20mm under 2kg of load and 30mm under 3kg of load. The compression distance is linear. A progressive spring may compress the same 10mm under 1 kg of load but only 15mm under 2 kg of load and perhaps only 17mm under 3 kg of load. As you can see the compression distance is reduced as the load increases. When this type of spring is put into a pedal it makes the pedal feel more realistic since brake pedals in real cars get harder and move less as they are pushed down further. However, the sim- pedal retains its distance based pedal. As you can see, the pedal needs to move to register braking input but a progressive spring makes the pedal harder and harder to move.

In the end, the harder pedal does give more control over the braking input, but the progressive lack of movement hinders its full potential.

Rubber bushings such as the Nixim mod and the Conical brake mod that ships with Thrustmaster pedals have a similar effect as the progressive spring. In these applications, a linear spring remains, but a small stiffer rubber stopper makes the pedal harder as some point mid travel. The result is similar to a progressive spring since the pedal is soft then gets harder. Once again, the pedal needs to move to register braking input but a rubber insert makes the pedal harder and harder to move.

The dampener is typically taken from RC model cars. It is usually in the form of a coil-over shock absorber. When a mod like this is added to the brake pedal the springs make the pedal feel firmer and are usually linear and not progressive so it improves the experience. However, when it comes to the dampener aspect of the mod, the performance starts to be affected greatly. The dampener is intended to slow down the movement of the device it is attached to, so why would you want to slow down the movement of a distance based sensor. After all, if it takes longer to get the pedal to the required braking amount, would that make your lap times take longer?

There is another mod circling around intended for Logitech G25/27/29 pedals that involves installing an O-ring on the spring housing in order so slow down its movement. Again, slowing down the movement of the pedal means slowing down your lap times.

The second type of brake pedal modification is the load sensor. A load sensor comes in many varieties but the ones that are typically use for sim pedals measure weight applied to them directly or they measure fluid pressure applied to them indirectly. The load cell is commonly used in scales, from inexpensive food scales for home use to high-precision medical grade scales. It all comes down to precision.

There are several variations of the load cell brake mod, but they all work on a similar principle, they measure the force applied to the pedal rather than the distance the pedal moves. The kits use some form of resistance media such as springs, rubber, foam and even air cylinders to give the pedal the correct feel and then use a load cell to get the correct reading. The benefits are huge as now the pedal will not only feel like a real brake pedal but it can also react like a real brake pedal since a real brake pedal reacts to the force applied to it rather than the amount of distance it moves. This employs the use of “muscle memory” by using muscle strength rather than muscle movement. Additionally, many load cell upgrade kits will increase the amount of force required to brake, which employs the use of even more “muscle memory” Which increases braking accuracy even further.

Another lesser benefit of using a load cell is that braking input remains the same regardless of pedal “softening” over time. As with most things, the springs and bushings in a load cell kit may wear over time and become softer, but since the pedal reads force applied rather than movement, your braking accuracy will remain the same.

I certainly hope this article sheds some light on some of the myths that exist in the sim-racing community about brake pedal modification. My intention is to provide some insight about the science behind the mod. Don’t get me wrong, all the mods I talk about here will be an improvement and I am not claiming they will hurt your lap times. I am simply showing why these mods provide different levels of gain.

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Posted February 17, 2016 by Frank in category Technical Articles

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