PF30a vs PF30 – How to Tell the Difference Before You Buy a Bottom Bracket
- Bike Bearing Store Team
- Aug 19
- 3 min read
Updated: Sep 13
If you’ve ever tried to replace a bottom bracket and found yourself drowning in acronyms like PF30, PF30a, BB30 and BB30a, you’re not alone. The world of bottom bracket standards can be a confusing maze – even experienced cyclists and mechanics sometimes get caught out.
Recently, we had a customer who ordered a PF30 SRAM DUB bottom bracket for his Cannondale SuperSix Evo Hi-Mod (2017). Everything looked right at first – same press-fit frame shell inner diameter (46mm), same shell width (73 mm) – but when the customer installed it, the crank spindle was too short. The reason? The bike actually had a PF30a shell, not PF30.
So, how can you tell the difference before you buy?
1. Understanding the Basics
PF30 = PressFit 30, Symmetric shell
PF30a = PressFit 30 Asymmetric, Cannondale’s version with the non-drive side 5 mm wider than standard PF30
Standard | Shell Width | Shell Diameter | Symmetry | Common Brands / Models |
PF30 | 68 mm (road) / 73 mm (MTB) | 46 mm | Symmetric | Various brands |
PF30a | 73 mm (road) | 46 mm | Asymmetric – extra width on non-drive side | Cannondale SuperSix, Synapse, etc. |
2. The Quick Visual Check for PF30a Bottom Bracket
The easiest way to identify PF30a is to look at your frame shell from the bottom:
If the drive side and non-drive side look the same, you have PF30.
If the non-drive side sticks out slightly more than the drive side (about 5 mm extra), you have PF30a.
3. Common Pitfall – PF30 SRAM DUB vs PF30a SRAM DUB
SRAM’s DUB system adds another twist. A PF30 SRAM DUB bottom bracket is designed for a symmetric PF30 shell. If you try to fit it into a PF30a shell, the crank spindle won’t reach far enough, no matter how much you tighten.
For PF30a shells, you must use a PF30a SRAM DUB bottom bracket, which has cups designed to compensate for the extra width on one side.
4. Pro Tip Before You Order
Step 1: Check your bike’s manufacturer specifications; the model year matters as standards can change between versions.
Step 2: Visually inspect the bottom bracket shell. Both PF30 and PF30a can have a 73 mm width, but the difference is:
PF30 = Symmetric (both sides look the same)
PF30a = Asymmetric (non-drive side extends ~5 mm wider)
Step 3: Still unsure? Take a quick photo of your bottom bracket shell and send it to us. We’ll help confirm the standard so you get the right part the first time.
Bottom bracket standards are tricky, but with a little know-how, you can avoid costly mistakes. PF30 and PF30a may look almost identical, but the asymmetric shell of PF30a makes all the difference when it comes to compatibility.
BB30 vs BB30a: You can use all the information above to identify them. The key difference is that BB30/BB30a shells have a 42 mm diameter, whereas PF30/PF30a shells have a 46 mm diameter.
For your convenience, we’ve listed all the bottom bracket options compatible with BB30a and PF30a frames below:
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