Oversize BB & oversize BB+ is used on Asama new sporty bike. This is a new technique about bottom bracket that is adapted in order to maximize loading efficiency and the durability of the frame.
Technologic signs:
Oversize BB Technique
Standard bottom bracket – 68mm
Firstly, we can realize that on the basic frame, the bottom bracket has short dimension, length: 68mm, cartridge bottom bracket, thin thickness and heavy weight.
A little gap will be seen, when adapting cartridge bottom bracket on frame. If you only use bike to go around the urban or ride on paved trail, it will be not a problem. Contrarily, if you ride through rough terrain, the sand will stuck on this gap. It causes of fiction, which need the extra effort of pedaling. Moreover, it also reduces the load – carry capacity when being under strong effect.
Cartridge bottom bracket has a low price and can get it at bike shop easily.
Oversize cartridge BB – 73mm
While sporty bikes are usually used with vigorous activities, its frames will be under strong force. Hence, the adjusting of Oversize BB technique brings a lot of benefits.
The length is 73mm, extra 5mm comparable to basic frame. Frame is equipped with Hollowtech bottom bracket having light, durable weight and good waterproof. It is also close to crank arms, so removing ones to clean easily.
Frame shell is manufactured from Oversize BB technique, which is thicker and harder.
Bottom bracket is a part that bears the gravity of rider and is position that connects frame tubes together, so all forces are sent to BB. Besides, the biker also affects to BB powerfully. Especially is sporty bikes, the force of rider and ground surface is higher. So BB of sporty bike is made thicker and larger to operate more stably during riding time.
Hollowtech BB has quite high price and has many size for different crank arms, so you must have knowledge about BB types to find suitable one. There are two basic Hollowtech bottom brackets: threaded BB and press fit BB. Threaded BB assembles and removes easier than press fit BB. Most of Asama frames is equipped with threaded BB tech.
Oversize BB+ technique
Oversize BB+ is a technique that increases contact area between seat tube and frame shell as well as the maximum of durability for frame.
The width of BB is 73mm. This creates the stability while riding. The surface of tubes connecting with BB increases more, which allow you to choose bigger ones. It even makes the frame harder.
The left frame shell is a standard kind, which does not apply Oversize BB+ tech. So, when a collision appears, a seat tube will lean and then lead to crack a weld between the seat tube and frame shell.
The right frame shell is designed Oversize BB+ tech. The seat tube gets bigger to frame shell, which increases the contact area with BB. It creates a triangular prism, which helps frame shell to fit with BB.
With Oversize BB+ tech, however a bike usually runs, its frame still keeps stable, lightweight and increases performance. You do not need to worry about performance, specially, when a bike is under high pressure and intensity.