Mountain Road Survival Guide for CVT Motorbike Rider​

A continuously variable transmission (CVT) is an automatic transmission that can change seamlessly through a continuous range of gear ratios. This contrasts with other transmissions that provide a limited number of gear ratios in fixed steps. The flexibility of a CVT with suitable control may allow the engine to operate at a constant RPM while the vehicle moves at varying speeds.

Brake Fluid Standards

Brake fluid is one of the most important components in motorcycle operation. The chemical composition of the brake fluid should be of the highest quality, since the operation of the entire brake system depends on it.

Brake fluid is manufactured in all countries of the world according to international standards:

1. FMVSS #116. This standard was created by the United States Department of Transportation (USDOT). According to this standard, brake fluid is divided into classes from DOT-1 to DOT-5.

2. SAE J1703 and SAE J1704. These standards were created by the Society of Automotive Engineers (SAE).

In most cases, the American DOT3 and DOT4 standards are used in the production of brake fluid for private vehicles. Their composition differs in chemical additives that affect the boiling point of the brake fluid when it heats up during braking.

Why Disc Brake Fails?

During braking (when the brake lever is pulled), the caliper pistons are pushed out and the brake discs are compressed by the brake pads. As the brake pads make contact with the brake disc, heat is generated and transferred to the brake fluid. If the brake fluid is in good condition and the brakes are used correctly, the brake fluid will not boil and the braking system will work properly.

If a cyclist uses the brakes improperly and thoughtlessly, especially on long uphill slopes, it can cause the brake fluid to get very hot and then boil over. In turn, since brake fluid is hygroscopic and absorbs moisture during use and contains 0.5-3% water, when the brake fluid boils, the water it contains also boils.

When the brake fluid boils, air bubbles begin to appear in the brake fluid. Gradually their number increases, they increase in size. This is the vapor arising and releasing from the molecules of boiling water.

Since air has the physical property of being compressed, the brake fluid also becomes compressible once it begins to boil. As a result, when the brake lever is pulled, the air in the brake fluid is compressed, but the brakes do not work because the compressed air cannot push down on the brake caliper to give it the force necessary to stop the spinning wheel and brake disc.

This is the reason why disc brakes fail when improperly handled by CVT motorcycles on mountain slopes.

How It Works in Our Company

In order to avoid problems with the braking system, motor bike manufacturers recommend following a number of simple rules:

  1. It is necessary to periodically check the level of the brake fluid in the expansion tank and promptly replace it. The brake fluid must be changed every two years, or when the moisture content of the brake fluid reaches 3% (the higher the moisture content, the worse). In our company, we replace the brake fluid when the moisture content reaches 2.5%, but at least once a year.
  2. Motorcycle manufacturers recommend using DOT3 brake fluid, which has a dry/wet boiling point of 205°C/140°C (the lower the boiling point, the worse). Our company uses DOT4+ brake fluid with a dry/wet boiling point of 300°C/180°C.
  3. Manufacturers do not recommend using brake fluid from a package that has been opened for more than 6 months. In our company, the maximum shelf life of an open package is 3 months.

Thus, we not only follow the recommendations of the motorbike manufacturers, but also do it a little better.

By following these simple rules, we avoid serious problems that threaten the safety of your traffic:

  • brake failure due to excessive moisture content in the brake fluid;
  • brake operation with delay due to high viscosity at low temperatures;
  • wear of parts of the brake system;
  • corrosion of ferrous metals and aluminum alloys in brake system modules;
  • violation of the tightness of the brake system

What’s more, you’ll never find an automatic motorcycle with two disc brakes in our fleet. Our CVT motorcycles always have disc + drum brakes.

Because if you’re heading into the mountains and suddenly, due to lack of experience driving an automatic motorcycle on mountain roads, your disc brake fails, you can always use the drum brake to stop the bike completely.

If You Have Never Owned a Motorbike With a CVT

If this article is read by experienced riders who have never used a motorcycle with CVT and do not quite understand the problem of overheating disc brakes, just remember that on a motorcycle with a manual gearbox on mountain slopes, you can put in a lower gear, thereby slowing the motorcycle without using the brakes.

But motorcycles with a CVT do not have a manual transmission and a downshift. A motorcycle with a CVT without using the brakes on a long slope accelerates as fast as possible. Therefore, the motorcyclist is forced to use the brakes at all times. And if the brakes are used inappropriately, this can cause the brake fluid to overheat and boil over, followed by disc brake failure.


What to Do if Disc Brake Fails on a Mountain Slope?

What should you do if your disc brake fails on a downhill run?

  1. Don’t worry. Use the rear drum brake to come to a complete stop.
  2. After stopping, wait 20 to 25 minutes, allowing the brake disc and brake fluid to cool. Then continue downhill again.
  3. As you continue downhill, do not pull on the disk brake lever all the time. Push – release, push – release. The time to use the brake should be 3-5 times less than the break time between uses. For example, if you press the disc brake lever for 2-3 seconds, it should take 6-15 seconds before you press it again.
  4. After you return to the hotel, notify us of the problem so that we can run additional diagnostics and take corrective action if necessary.

If you haven’t read our travel guides to Northern Thailand yet, be sure to do so! You can find our motorcycle rental rates and conditions here.

See you at our office!


Cat Motors Team