# Is a heat vs Mu chart Misleading? What factors into Mu? (brake pads)

• A1337STI
In summary, the conversation discusses the concept of Mu charts for brake pads in cars and the assumptions surrounding them. It is mentioned that Mu is a calculated constant used to compare friction between two materials and that it does not change with speed. However, it is also noted that Mu is more sensitive to changes in temperature than speed. Additionally, it is mentioned that the clamping force may affect Mu to some extent. Overall, a chart showing Mu vs temperature can be used to compare the performance of different brake pads.
A1337STI
So I was trying to understand some Mu charts of Brake pads for cars.

I thought that Mu was basically a "calculated, or measured constant " which could be used to compare friction between 2 materials. like a solid iron Rotor, and a brake pad. I was thinking that a simple chart that shows Mu throughout the operating temperature range was sufficient.

My assumptions are that 1) Mu does not change with speed. whether a car is going 100 mph or 10 mph is irrelevant (rotor speed of 1333 RPM or 133 RPM) the Mu is the Mu .. Or am i wrong?

total friction generated per minute would obviously go up, and heat would go up as a result which might push the pad/rotor combination into a hotter part of the chart, but the Mu would fall in line with its established value .
Or does the mu change with speed ?

2) assumption , Clamping force doesn't change Mu, as you clamp down harder, the total friction would go up, but not the actual Mu .

If those assumptions are both correct, then someone Could look at a chart that shows Mu vs temperature and get a good idea of if brake pad A would perform better than brake pad B

something that looks like this :

Hopefully I'm not completely ignorant on this. i never took physics past high school, despite having a strong interest in it.

But I want to know the correct answer. thanks in advance. :)

Coefficients of friction are more sensitive to temperature than to speed.

The idea that coefficient of friction is completely independent of speed is only approximate. Brake pads might have their frictional coefficient vary 10-20% over their speed range. In contrast, the variation with temperature is much larger.

The idea that mu is perfectly independent of clamping force is also an approximation.

Gotcha.

was hoping for a yes/no kind of situation but that makes a lot of sense.

## What is a heat vs Mu chart?

A heat vs Mu chart is a graphical representation of the relationship between the temperature of a brake pad and its coefficient of friction, also known as the Mu value. It is used to show how a brake pad performs at different temperatures.

## Why is a heat vs Mu chart misleading?

A heat vs Mu chart can be misleading because it only shows the relationship between temperature and Mu for a specific brake pad under controlled conditions. It may not accurately reflect real-world performance, as other factors can influence Mu and the actual temperature of the brake pad during use.

## What factors influence Mu?

Several factors can influence the Mu of a brake pad, including temperature, pressure, speed, and the type of material used in the pad. Other factors can also play a role, such as the condition of the braking surface, the design of the brake system, and the presence of any contaminants.

## How is Mu measured?

Mu is typically measured by conducting a series of tests where the brake pad is pressed against a rotating surface at various temperatures and pressures. The resulting friction force is divided by the applied force to determine the Mu value. However, the exact method of measurement may vary depending on the manufacturer or testing organization.

## Can Mu be improved?

Yes, Mu can be improved by selecting a brake pad with a higher Mu value, using proper brake pad bedding procedures, and maintaining the brake system and braking surfaces in good condition. Other factors, such as the type of driving and braking habits, can also affect the performance of Mu and should be taken into consideration.

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