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BMX Frame Buyer’s Guide
The frame is one of the most important decisions a rider has to make when building a new bike. It is crucial to pick a frame that will compliment your style and be able to withstand the stresses of everyday riding. This article outlines some of the different variations in frame types, geometry, materials, and more.
Racing Frames – Racing frames are designed with speed, performance, and minimal weight in mind. Because they use lighter materials, they are unable to withstand the more stressful forms of riding like street, park, and sometime trails.
Freestyle Frames – Because most street, park, and trails (dirt jumping) frames are built the same way, and use the same materials and sizes, we have grouped them into the “freestyle” category. These frames are built to take abuse - whether from grinding, jumping, or dropping, they are made to last.
Cruiser Frames – Cruiser frames are larger than typical BMX frames. They are designed to use 24” wheels. These frames can be made for racing or freestyle use.
It is important to understand the different geometries and styles of a frame before making a purchase. The diagram below outlines the main geometries and frame components.
Head Tube Angle – The angle of a frame’s head tube affects how the bike responds in terms of both steering and the rider’s position over the bike. See the diagram below to get a grasp of how it is measured.
A “steeper” head tube angle (higher numbers; those in the 75-75.5 degree range) generally positions a rider over the front end of their bike, while also sweeping the bottom of the fork inward towards the frame. This makes tech tricks and nose manuals easier. Bikes with steep head angles also have shorter wheelbases.
A “shallower” head tube angle (lower numbers; those in the 74-74.5 degree range) make the frame feel more stable at speed and in turns, which is why trails and dirt jumping frames generally have a shallower head tube angles.
Seat Tube Angle – This is the angle that the frame’s seat tube sweeps back, away from the back end of the bike. This angle affects the position of your seat and the length of the frame’s top tube. A shallower angle means the seat tube sits further back and the top tube’s length increases. Frames are made with seat tube angles ranging from 69-71.5 degrees, with 69 degrees being the shallower option.
With exception to aluminum and carbon fiber race frames, BMX frames are most commonly made from chromoly. While many companies call their chromoly tubing by different names, most of the chromoly used can be grouped into the 4130 and 4140 families. These types of steel offer a very high strength to weight ratio, making them ideal for use in BMX frames.
Chromoly frames that are heat-treated have gone through a process that hardens the metal. Frames that are heat-treated are often more resistant to bending and cracking. This is a great option for strengthening a frame without adding weight.
Aluminum frames and carbon fiber frames are intended for racing only. If you’re a lighter rider that needs weight savings for better performance, and do not intend to ride the bike anywhere but the racetrack, these materials may be the ideal choice for you.
The head tube is the portion of a frame that the fork’s steerer tube passes through. There are several variations of head tubes available in BMX frames today. They can be broken down into three categories depending on the bearing systems they use.
Integrated Head Tubes – Integrated head tubes use sealed cartridge bearings that are pressed directly into the headtube of the frame without the need for additional bearing cups or shims. This system is the most widely used style of headset in aftermarket BMX frames.
Internal Head Tubes – Internal head tubes, also sometimes referred to as “semi-integrated head tubes,” use a press-fit system that functions similar to an integrated headset design. The difference is that internal headset bearings do not rest directly inside the frame, but instead use an additional shim or bearing cup inside the headtube to position the bearings.
Standard Head Tubes – Standard head tubes are found in older frames and complete bikes. This head tube uses bearing cups that are pressed into the top and bottom of the frame, and the bearings rest outside of the headtube.
For more information on head tubes and headsets, see our Headset Buyer’s Guide Article.
The bottom bracket, commonly referred to as the “BB,” is located inside the portion of a frame that the crankset’s spindle passes through. This portion of the frame is called a bottom bracket shell, and it’s size determines the type of bottom bracket the frame will use. There are several variations of bottom brackets that use different bearing styles. These can be broken down into four groups: American, Mid, Spanish, and Euro.
American Bottom Brackets – American bottom brackets were more common in the early days of BMX. They use a bearing set that rests inside cups that are then pressed into the frame. The downside to American bottom brackets is that they are large and contain unnecessary weight. They also take a considerable amount of force to press the cups into the frame. They are often found on bikes with one-piece cranks.
Mid Bottom Brackets – Mid bottom brackets use the same bearings that American bottom brackets use, however the cups are completely removed from the equation. The bearings are pressed directly into the frame, allowing for a less complicated setup and a reduced weight. Because the bearings are the same size as an American bottom bracket, there is no difference in strength between the two styles. This style of bottom bracket is the most common.
Spanish Bottom Brackets – Spanish bottom brackets also use bearings that press directly into the frame. Spanish bottom brackets use a bearing with a smaller diameter than a Mid bottom bracket, which means a smaller bottom bracket shell and less weight.
European Bottom Brackets – European bottom brackets are only common to race frames. European bottom brackets use smaller bearings that sit inside a cup that is threaded directly into the frame.
The dropout is the portion of the frame that the rear wheel’s axle slides into. Dropouts come in several sizes and styles that affect the strength and stiffness of a bike.
14mm – 14mm dropouts use a thick axle that is designed to withstand the most stress and abuse. It is recommended that people that ride park, dirt, or street run 14mm back axles in order to take the force that comes with these styles of riding.
3/8” (10mm) – 3/8” dropouts are designed for the smaller, 3/8” axles. Frames that use this size are generally designed for racing and trails riding. A 3/8” axle is more prone to bending, which should be considered before purchasing this style of frame.
Closed (Female) – Like the name suggests, closed dropouts are designed so that the end of the dropout is closed off, creating a hole instead of a slot. This style of dropout requires the use of a female rear hub (a bolt that threads into the hub shell).
Most companies manufacture frames with removable brake mounts (also known as brake bosses), allowing a rider to decide if they want to run brakes or not. This is a great option should you ever decide to put on or take off your brakes. The removable mounts will allow you to do this without purchasing a new frame.
Sizing generally comes down to personal preference. It’s commonly understood that a taller rider should ride a longer frame, and vice versa for a shorter rider. A frame’s length effects how your bike responds when it’s ridden. Short frames can be better for technical riders that grind and stall a lot, because shorter frames are generally more responsive and snappy, making it better for technical tricks. Longer frames can be better for riders that want speed and stability, because shorter frames often feel twitchy and cramped when moving at high speeds. Riders that ride trails or want to move faster on a bike generally ride longer frames.
There are two sections of a frame’s geometry that will affect overall length - the top tube, which is the front portion of the frame spanning from the seat tube to the headtube, and the chainstay, which is the portion of a frame spanning from the seat tube back to the dropouts.
If you are unsure of which frame size would work best for your riding, use the guidelines below.
|Rider Height||4’ - 4’4”||4’5” - 4’9”||4’10” - 5’2”||5’3” - 5’8”||5’9” - 6’1”|
|Top Tube Length||15”- 16”||16.5” - 17.5”||18”- 19”||19.5“ - 20.5”||21” - 22”|
The best way to figure out what frame size fits you best is to go to a bike shop and test ride bikes with different top tube and chainstay lengths. If your friends ride different sized setups, the next time you’re out riding ask if you can try their bikes. Finding the right sized frame can make a world of difference in how your bike feels.
How Much To Spend
It is always important to remember the saying, “you get what you pay for” when purchasing new bike components. When you spend more, you are paying for higher quality materials and better construction.
Plan to spend between $150 and $500 on a frame. The less expensive range of $150-$250 frames use heavier materials, are offered in fewer size options, and are rarely heat-treated. While it is possible to get a strong frame in this price range, it will generally weigh more than more expensive frames. The $250-$400 range consists of standard aftermarket frames. These frames are strong, use high-end materials, may feature machining in key areas, and are designed with serious riding in mind. Frames in this range are available in many size options and colors. $400-$500 frames are considered to be “high-end” specialty frames. These frames use the highest quality materials matched with the best manufacturing, paint, and heat-treatment processes. You can expect frames in this category to last a long time.
What To Look For
The first thing to consider when shopping for a frame is your body size and style of riding. This will reflect on the size of frame you choose and the material the frame is made of. The most common sizes are in the 20.5-inch to 21-inch top tube range. These frames are long enough to not feel cramped, and are still quite responsive which suits them to technical riding as well. Frames in the sub 20-inch range do exist, so if you’re a shorter rider or simply want super short setup, there are options available. The same goes for riders wanting longer bikes with top tubes up to 22-inches long.
Some frames feature additional machining to remove material from areas that see less stress. While this can be an effective way to reduce weight, it can also decrease the overall strength and lifespan of a frame. If you are a lightweight and smooth rider, these frames might be a good option for you. If you put more stress on a bike, then a slightly heavier frame may be a better option.
Most importantly, you want a frame that feels good and will last. When purchasing a frame, remember that it is the most important piece of your bike, so it makes sense to invest in something that will last you a long time.
Before buying a frame, be sure to do your research and read product reviews. Reviews are a great way to find out specifics about a particular model, user impressions, and things to watch out for. After you’ve purchased a frame and had enough time to thoroughly test it, we encourage you to leave a review for other people to see when they are researching frames on the web.
We hope you’ve found this information to be helpful. If you have a question that isn’t answered in this guide, our BMX forums are a great place to get advice from knowledgeable riders. Your local bike shop is also a great resource.
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