The Short Answer is:
Modern freestyle BMX bikes have smaller front sprockets for faster acceleration and increased frame-to-ground clearance. Smaller sprockets are also more symmetrical, making the bike more stable and less likely to fall. Additionally, small sprockets are lighter and provide higher ground clearance which is necessary for certain tricks.
BMX bike sprockets are essential components of the drivetrain, connecting two chain wheels to transmit power or change torque.
They come in various sizes and materials such as 7075 alloy, 6061 heat-treated alloys, 4130 Chromoly and more, with different gear ratios available for different types of riding.
Sprocket guards can also be used to protect the sprocket while grinding or doing stalls. When purchasing a new sprocket it is important to consider the width of the teeth on the chain wheel and whether it has a bolt drive (one attaching hole) or spline drive (three holes).
Additionally, riders should look at how much weight they want to move around their bike when selecting a sprocket size.
Table of Contents
The History of Small Sprockets on BMX Bikes
Small sprockets on BMX bikes are used to facilitate pedaling and provide increased frame-to-ground clearance for tricks.
U-style rear brakes mounted to the top of the frame chain stay require a very small sprocket.
Tree Bicycle Co. have been known for their detailed and original designs, including their BMX sprockets.
Additionally, small BMX bikes are beneficial for performing tricks, protecting the bike from damage, reducing weight, and promoting maneuverability.
The Benefits of Small Sprockets on BMX Bikes
Small sprockets on BMX bikes provide faster acceleration and increased frame-to-ground clearance.
They also bend less easily than large sprockets when in contact with an object, providing more leverage force.
Smaller sprockets also facilitate pedaling considerably, lowering the chain to the extent of it getting into direct contact with the top of the tire.
The Connection Between Sprocket Size and Gear Rati
The connection between sprocket size and gear ratio is determined by dividing the number of teeth on the rear sprocket by the number of teeth on the countershaft sprocket.
This calculation gives a numerical value that represents the gear ratio, with a larger number correlating to shorter gearing and a lower number representing taller gearing.
The size of the sprockets also matters since they must have similar sized teeth in order for the gear ratio to be accurate.
Choosing the Right Sprocket Size for Your BMX Bike
The most common sprocket size for BMX bikes is 25T or 28T with 23.7mm, as it provides a comfortable pedalling pressure and clearance for grinding.
A larger front sprocket can provide more torque, while a smaller one can provide more speed.
Intermediate and advanced BMX bikes usually have a 25T/9T or 28T/9T ratio.
How to Calculate the Gear Ratio for Your BMX Bike
To calculate the gear ratio for a BMX bike, divide the number of teeth on the chainring by the number of teeth on the freewheel.
This will give you your gear ratio. The most popular gear ratios are close to 55 gear inches, which is derived from a formula that divides the number of teeth in the front sprocket or freewheel by the number of teeth in the rear sprocket and multiplies it by wheel size.
Gear inches can also be calculated using this formula. The example listed is a 44/16 combination, which has 55 gear inches.
The Role of the Chain in the BMX Bike Sprocket System
The chain plays an important role in the bmx bike sprocket system, connecting the sprocket to the crank arm or spindle.
The type of chain used can vary, with full-link chains being traditional and featuring a sequence of outer and inner links, while half-link chains are becoming increasingly popular.
As the chain and sprocket wear together, the teeth become sloped at the back and the rollers ride up on them until they reach a certain radius.
Different types of sprockets are available, such as bolt drive and spline drive, which are attached to the crank arm or spindle respectively.
Types of BMX Bike Sprockets: Materials and Shapes
BMX bike sprockets come in two types: bolt drive and spline drive. They are typically ½ inch in size and made from 7075-76 Alloy, though other materials such as aluminium may also be used.
Popular shapes include Profile Imperial, Tom Dugan, Profile Galaxy Spline, and Merritt Ackerman.
Maintaining Your BMX Bike Sprocket System
To maintain your BMX bike sprocket system, it is important to keep the chain clean and lubricated.
Regular cleaning and lubrication will help ensure the chain runs smoothly and lasts longer.
Additionally, you should check for dents, wear and tear, and loose nuts. When selecting a sprocket, consider factors such as size (e.g. 48T) and whether you need a guard to protect the chain.
Cleaning products such as sprays, brushes, soaps, and polish can be used to keep your bike looking its best.
Frequently Asked Questions about BMX Bike Sprockets
What size sprocket should I use for BMX racing?
The most common sprocket size for BMX racing is 25 teeth, although 28 teeth is also popular. 44 teeth was the standard size in the past, but it is no longer commonly used.
The gear size can be calculated by multiplying the gear ratio by 20 for 20-inch wheels or 24 for 24-inch wheels.
How do small sprockets improve BMX bike performance?
Small sprockets on BMX bikes improve performance by providing faster acceleration and increased frame-to-ground clearance.
They also facilitate pedaling, as they lower the chain and reduce leverage force when contact is made with an object.
Smaller sprockets also limit BMX bikes when it comes to speed, as a lower gear ratio results in a lower top speed.
How does the sprocket size affect the BMX bike’s top speed?
Increasing the number of teeth on the front sprocket or decreasing the number of teeth on the rear sprocket will result in a higher gear ratio, making it harder to pedal on take off but allowing for a higher overall speed.
A larger sprocket size exerts less force on the chain, increasing top speed, while a smaller sprocket size increases acceleration.
BMX bikes typically have small sprockets to increase acceleration and maneuverability.
Can I use a large sprocket on my BMX bike instead of a small one?
Yes, you can use a larger sprocket on your BMX bike instead of a small one. However, it is important to consider the gear ratio when making this decision as it affects acceleration and frame-to-ground clearance.
Can I change my BMX bike’s gear ratio by changing the sprocket size?
Yes, you can change the gear ratio of your BMX bike by changing the sprocket size. The gear ratio is determined by dividing the number of teeth on the front sprocket by the number on the rear sprocket.
Increasing or decreasing either of these numbers will result in a higher or lower gear ratio respectively. The chainring is also part of the drivetrain and can be altered to affect the gear ratio.
In conclusion, BMX bikes have small sprockets because they offer several advantages over larger ones. Small sprockets make the bike more nimble and easier to maneuver, which is important for performing tricks.
Additionally, smaller sprockets are more durable and less likely to break under stress. While larger sprockets exert less force on the chain, they are not as well-suited for the demands of BMX riding. Ultimately, the choice between a big or small sprocket depends on personal preference and riding style.