Theory American Bottom Bracket cups

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This Theory bikes American Bottom bracket parts to mid BB cup is made for any frame that has an American bottom bracket and installing cranks with a 19mm, 22mm or 24mm spindle. The mid bearing pops in these aluminum cups and allows you to run a 19mm, 22mm, or 24mm sealed bearings. Most American BB frames have unsealed bearings and 1 piece cranks. So for anyone who is upgrading from the 1 to 3 piece cranks, this is the perfect starting point. Just be sure you get some bearings that match your spindle size and you'll be all set. 

Product Description

The Theory American to Mid Cups are the perfect solution for BMX riders looking to convert an American bottom bracket frame to fit Mid BMX bottom bracket bearings. Designed for freestyle BMX bikes, these American to Mid conversion cups help riders upgrade older BMX frames with modern Mid bottom bracket setups for improved performance, smoother spinning cranks, and better compatibility with modern BMX parts.

Whether you are restoring an old school BMX bike, upgrading a custom BMX build, or replacing worn out adapter cups, the Theory American to Mid Cups provide a secure fit and dependable durability for street, park, dirt, and big BMX riding.

Built for riders who want to modernize their BMX setup without replacing their frame, these BMX bottom bracket conversion cups are an affordable and effective upgrade for smoother riding and stronger crank performance.

Features & Benefits

• Converts American BB frames to Mid BMX bottom brackets
• Allows use of modern Mid BMX bearings
• Durable construction for freestyle BMX riding
• Helps improve crank alignment and smoothness
• Great for old school BMX restorations and modern upgrades
• Compatible with many freestyle BMX crank setups
• Easy BMX bottom bracket conversion solution
• Perfect for custom BMX bike builds

Product Use

The Theory American to Mid Cups are designed for:

• Converting American BMX bottom brackets to Mid BB setups
• Old school BMX restorations
• Freestyle BMX bike upgrades
• Street BMX riding
• Park BMX riding
• Big BMX bike custom builds
• BMX crank upgrades
• Riders wanting modern Mid BB compatibility

Theory word:
TBA

Why BMX Riders Use American to Mid Cups

BMX riders use American to Mid bottom bracket cups because many older BMX frames came with larger American bottom bracket shells that are not compatible with modern Mid BMX bearings. These conversion cups allow riders to install lighter, smoother, and more modern Mid bottom bracket systems without needing to buy a new frame.

They are especially popular with:

• Old school BMX collectors
• Custom BMX builders
• Riders upgrading vintage BMX bikes
• BMX riders wanting smoother crank performance
• Big BMX and wheelie bike riders modernizing older frames

5 Problems Riders Run Into Using Other American to Mid Bottom Bracket Cups

• Poor fitment causing movement inside the frame
• Cheap materials wearing out quickly
• Misalignment leading to crank wobble
• Weak cups cracking during heavy riding
• Bearings fitting too loose or too tight

5 Reasons Theory American to Mid Cups Are Better

• Designed specifically for BMX bottom bracket conversions
• Durable construction for freestyle BMX abuse
• Helps create a more secure bearing fit
• Makes older BMX frames compatible with modern Mid BB setups
• Affordable BMX upgrade for custom bike builds

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