Frame Stiffness (RA Rating)
The RA stiffness rating measures how much a racquet frame flexes at impact. It affects power, comfort, arm safety, and feel in ways that are often counterintuitive.
Frame stiffness is one of the most contested specifications in racquet design. Manufacturers, coaches, and players have strong (and often contradictory) opinions about it. Understanding what RA actually measures clears up most of the confusion.
The RA Rating
RA is measured on a Babolat RDC by clamping the racquet at the handle and deflecting the head with a known force. The resistance to deflection gives the RA number.
| RA | Classification | Examples | |---|---|---| | < 55 | Very flexible | Wilson Pro Staff RF97 (58), some classic frames | | 55–62 | Flexible | Head Prestige Pro, Yonex VCORE Pro | | 62–67 | Medium | Babolat Pure Strike, Wilson Clash | | 67–72 | Stiff | Babolat Pure Aero, Head Speed | | > 72 | Very stiff | Some power racquets, game-improvement frames |
RA ranges vary by measuring device. Values from Babolat RDC are the industry standard.
How Stiffness Affects Power
The relationship between stiffness and power is not linear and depends on swing speed:
- Stiff frame + slow swing: The frame barely deflects, and energy isn't stored and returned — the ball just bounces off with whatever energy the swing provided. Higher RA helps here.
- Stiff frame + fast swing: The string bed does most of the energy storage, not the frame. Stiffness has less effect.
- Flexible frame + any swing: The frame absorbs some energy during deflection and returns it slightly out of phase. This can mean slightly less power but a more "cushioned" feel.
Info: For most recreational players (swing speed below ~80 mph), a stiffer frame tends to produce more power because the strings do the deflecting. Advanced players with fast swings often prefer flexible frames for feel and control.
Stiffness and Arm Health
This is where stiffness has its most important practical effect. At the moment of ball contact, vibrations travel through the string bed into the frame and up the arm. A stiffer frame transmits vibrations more abruptly and with higher peak forces.
Research consistently shows that players with tennis elbow, golfer's elbow, or shoulder issues benefit from:
- Lower RA (more flexible frame)
- More elastic strings (natural gut or multifilament)
- Lower string tension
- Heavier racquets (more mass absorbs more energy)
Warning: If you have arm problems, RA is the first spec to address. Switching from a 72 RA frame to a 60 RA frame often provides more relief than any string or tension change alone.
Stiffness and Feel
Flexible frames (RA < 62): More "dwell time" — the ball stays on the string bed fractionally longer. Players report a "pocketing" sensation, more feedback, and better touch on drop shots and slice. Preferred by advanced players who value feel over power.
Stiff frames (RA > 67): Crisper, more immediate response. Less vibration dampening. More powerful for moderate swing speeds. Less feel and feedback for touch shots.
Measuring Your Frame
RA varies across the frame — the throat is always stiffer than the head, for example. The single RA number from an RDC is a standardised measure of the shaft/throat area and is useful for comparison even though it doesn't capture the full stiffness profile.
Some players also measure groundstroke stiffness (clamped differently to simulate a groundstroke) which gives a different number. When Arcus and most specs databases refer to RA, they mean the standard Babolat RDC measurement.