What is an Offset Rim Bed?
Almost all bicycle rims are symetrical. The right and left sides look identical. While there are times this is needed, there are times where the right and left side of the wheel has different forces. This is where an offset rim bed has a major advantage.
The Offset rim will have the nipples sitting away from the center of the rim. This helps balance out the spoke tension between the right and left side. Your offset will face away from the rotor on the front wheel and towards the rotor on the rear wheel.
Keep reading to find out why.
Your spoke tension is dictated by the flange spacing. On a symmetrical rim there is a large difference in spoke tension between drive and non-drive side.
Lower non-drive side spoke tension means the nipples can more easily loosen, resulting in more wheel truing. Low spoke tension can also lead to broken spokes as the tension is constantly changing as the wheel rotates.
The bracing angle (angle at which the spoke enters the rim) is important for wheel stiffness. A larger bracing angle makes a stiffer wheel. By increasing the bracing angle of the drive side, the wheel increases stiffness and becomes more balanced between right and left sides.
Overall this makes a better responding wheel that stays true and will not break spokes. Stand up and sprint and you'll notice the response immediately!
FAQs
All the disc brake rims (road, gravel, and mountain) feature an offset rim bed. You will notice the offset always faces AWAY from the higher tension spoke.
On deeper rims the "flat" side needs to be reinforced a little more. This will add approximately 10-15 grams due to the extra layer of carbon fiber. Well worth it in our opinion.
Typically on a symmetrical rim you have about 50-55% of the drive side tension on the non-drive side spokes. This means if your drive side is at 120kgf, your non-drive side will be at 60-66kgf.
For an offset rim bed you will see about 65-70% of the drive side tension on the non-drive. This means if your drive side is at 120kgf, your non-drive side will be at 78-84kgf.
Every time your wheel makes a revolution your spokes go through a change in tension (depending on if the spoke is above or below the hub). Higher tension spokes do not change in tension as much as lower tension spokes (which is why it's rare to break a drive side spoke).
The non-drive side spokes are at lower tension, meaning the tension is constantly going through high/low changes. This constantly changing tension is what can fatigue the spoke and cause it to break.
By having a higher tension on the non-drive side, broken spokes are prevented.