RA / Stiffness
Also known as: racquet stiffness, flex rating
RA is a racquet's stiffness measured by how much the frame deflects under load. Higher RA (66+) means a stiffer, more powerful but harsher frame; lower RA (under 58) flexes more for feel and arm comfort.
RA, or Racquet Advisor stiffness, is measured by clamping the racquet at the throat. A load is then applied at the tip while the deflection is measured in millimeters. A stiffer frame deflects less; a more flexible frame deflects more. The resulting number describes the frame's resistance to bending through the ball at contact. The measurement is taken on the frame alone, not with strings installed. That means published RA numbers represent the bare frame. String choice and tension modify the effective stiffness felt at contact.
Stiffer frames (RA 66 and above) return more energy to the ball on contact because less energy is lost to frame deformation. The practical result is more power: the ball comes off faster. But more shock is also transmitted to the hand, wrist, and elbow, because the frame absorbs less vibration. For players with clean mechanics and good timing who reliably hit the sweet spot, the power gain is real and the shock is manageable. For players with off-center contact, late timing, or existing arm issues, a stiff frame amplifies the problem. Every mistimed or mis-hit ball sends more vibration up the arm than a flexible frame would. Flexible frames (RA below 58) absorb more energy at contact, which reduces both shock and power. Players who describe a racquet as "arm-friendly" or having "good feel" are often describing a lower-RA frame. Such a frame dampens vibration and gives more tactile feedback rather than transmitting it as shock.
RA does not exist in isolation — it interacts significantly with string choice and swingweight. A stiff polyester string in a high-RA frame produces a very board-like, shock-transmitting setup that many recreational players find uncomfortable. The same frame strung with natural gut or a multi-filament synthetic string is noticeably more comfortable. That is because the string absorbs some of the energy the frame refuses to. Conversely, a flexible frame strung with polyester regains some of the power the frame surrenders in flex. This interaction means that players optimizing arm comfort should consider frame RA and string type as a system, not as independent choices. The same logic applies to swingweight. A high swingweight paired with a high RA frame creates a powerful but demanding setup. A lower swingweight with a more flexible frame creates a forgiving, arm-friendly combination. That combination suits players prioritizing feel and longevity over raw power.
Tips by skill level
If you are choosing a first or replacement racquet and are unsure about stiffness, err toward a mid-flex frame in the 60–65 RA range. It will be more forgiving of off-center contact and give you time to develop consistent mechanics before deciding whether more stiffness would benefit your game.
When optimizing arm comfort while keeping power, change the string type before changing the frame. Moving from a stiff polyester string at high tension to a softer multi-filament or natural gut in the same frame can reduce effective stiffness significantly — often enough to resolve arm discomfort without the cost of a new racquet. If string change is insufficient, then a frame swap to lower RA is warranted.
Example
A player with elbow soreness drops from a 69 RA frame to a 62 RA one to reduce shock without losing much control.
Why it matters
RA is one of the most important spec numbers for long-term arm health. Getting this wrong is a common contributor to tennis elbow in recreational players who do not reliably hit the sweet spot. That is especially so in the direction of too stiff.
How it shows up on video
RA stiffness is not directly visible in video. But its effects can be seen in player behavior: wincing after off-center hits, shortening the swing to reduce contact force, or shaking out the arm between points can all be signs of a frame that is too stiff for the player's mechanics. Impact feel and vibration, not swing path, are the observable consequences of RA.
Common mistakes
- Choosing a stiff frame for power without accounting for mechanics — off-center hits with a 68+ RA frame produce disproportionately high shock that damages the arm over time.
- Assuming a stiffer frame will cure power loss — if the loss stems from swing speed or contact point rather than energy return, a stiffer frame adds arm stress without solving the problem.
- Pairing a high-RA frame with stiff polyester strings — this compounds the stiffness at contact, a combination many coaches steer players with arm discomfort away from.
- Never considering RA when experimenting with lead tape — adding mass at the hoop raises swingweight and increases contact forces. This amplifies any existing RA-related arm stress.
In SwingVantage Motion Lab
Motion Lab does not measure RA or frame stiffness. It can flag a short follow-through, and its traced path can show a shrinking swing arc. If you also feel arm discomfort, these may point to equipment-fit issues, including frame stiffness, so have the racquet setup checked.
Frequently asked questions
What RA range should I look for if I have tennis elbow?
Many coaches suggest a more flexible frame (a lower RA) and a softer string at lower tension for players with tennis elbow. As a result, less shock reaches the arm. Frames below 55 RA exist but are rare and can feel hard to predict, because the flex is large enough to affect timing. Persistent elbow pain should be checked by a medical professional; equipment alone is not a treatment.
How does string tension interact with RA?
Higher string tension makes the effective playing stiffness feel greater regardless of frame RA — the tighter strings transmit more shock. Lower tension makes the system feel softer. As a rough rule, every 5 lbs of tension reduction produces a noticeable difference in shock and feel. Players with arm issues who cannot change their frame should try dropping string tension by 5–10 lbs as a first step before investing in a new racquet.
Related terms
- SwingweightSwingweight measures how heavy a racquet feels when swung, accounting for where its mass is distributed. Higher swingweight gives more plow-through and power but is harder to maneuver.
- String TensionString tension is how tightly a racquet is strung, in pounds or kilograms. It shapes the string bed's trampoline effect, control, and power.
- String GaugeString gauge is the thickness of a tennis string measured in millimetres or gauge numbers, with thinner strings providing more spin and feel and thicker strings offering greater durability.
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