King Radspeed XB Junior Driver: Sizing, Fit and Buying Guide for Parents

A King Radspeed XB junior driver is a graphite-shafted, oversized-head driver built for young golfers who are moving past plastic or cut-down adult clubs. This guide walks you through how to tell whether this model fits your child, which measurements matter most, and how to avoid the common sizing errors that make a driver feel harder to hit than it should. By the end, you will have a clear checklist for deciding between a fitting, a new size, or a different club entirely.

What the King Radspeed XB Junior Driver Is Designed For

The Radspeed XB line is part of the King junior range, which is aimed at kids roughly in the early-to-middle elementary years through their early teens, depending on height and strength. The head is large and forgiving, the shaft is lightweight, and the overall design prioritizes launch and consistency over workability. Manufacturers typically organize junior drivers by height bands and age, but those bands are starting points, not rules. Two children of the same age can differ enough in height and swing speed that one needs a longer or more flexible shaft than the other.

Before you measure anything, confirm which model variant you are looking at. Junior driver lines often come in several lengths and flex options, and the specification sheet will list the shaft length, flex, and loft for each version. Write those numbers down. They are the baseline you will compare against your child’s measurements.

Step 1: Measure Your Child for Club Length

Length is the single most important sizing factor. A driver that is too long forces a child to stand too far from the ball and reach, which causes early extension, rounded shoulders, and inconsistent contact. A driver that is too short cramps the posture and makes it hard to get the arms extended through impact.

The standard method is a simple wrist-to-floor measurement, but it works best when combined with a height check:

1. Have your child stand barefoot in a relaxed golf posture, with feet about shoulder-width apart.
2. Let the arms hang naturally, then measure from the crease of the wrist (with the wrist straight) down to the floor.
3. Compare that number to the length chart on the manufacturer’s sizing guide for the Radspeed XB line.
4. Check the result against overall height. If the wrist measurement and the height chart point to different club lengths, favor the one that matches your child’s typical swing setup in a short test swing.

Golf fitters often recommend that the grip end of the club reach about the child’s wrist crease when the child is in a proper address position. If the grip sits well below the wrist, the club is probably too long. If the child has to hunch to reach the grip, the club is probably too short.

Step 2: Check Lie Angle and Posture

Lie angle is the angle between the shaft and the ground when the club sole sits flat. If the lie is too upright, the toe of the club will point at the sky and the ball will tend to go left. If it is too flat, the heel will point up and shots will drift right. Most junior drivers are set to a general standard, but the correct lie depends on posture and height.

A quick check you can do at home:

• Place a sheet of carbon paper or a thin layer of foot powder on the sole of the club.
• Have your child take a normal address position over a ball on a mat.
• Look at the mark left on the sole. Even marking across the sole means the lie is close. Heavy toe marking means the lie is too upright. Heavy heel marking means it is too flat.

If the mark is consistently off, a club fitter or a qualified golf professional can adjust the lie. Do not bend a graphite shaft yourself, since this can weaken it or crack the hosel.

Step 3: Choose the Right Flex

Flex describes how much the shaft bends during the swing. Junior shafts are typically labeled with flex categories that roughly correspond to swing speed. Using a shaft that is too stiff makes it hard to load and release the club, so the ball flies low and to the right. Using a shaft that is too flexible can cause the face to close too quickly, producing hooks and a loss of distance.

The practical test is to watch the ball flight and feel. If your child consistently hits low, weak shots with little height, the shaft may be too stiff. If the ball balloons high and drifts left with a lot of spin, the shaft may be too whippy. Swing speed measurement from a launch monitor or a driving range with radar is the most reliable way to decide, but a golf professional can often make a good call after a few swings.

Step 4: Confirm Grip Size

A grip that is too large makes it hard to release the hands and tends to produce a slice. A grip that is too small encourages a overly tight grip and can cause a hook. Junior grips are usually thinner than adult grips, but many kids transition to standard sizes faster than parents expect.

Have your child hold the club in their normal grip. There should be a small gap between the fingers of the trailing hand and the palm of the lead hand when the hands are properly placed. If the fingers wrap all the way around with no room, or if the grip feels bulky and hard to close, consider a smaller size.

Step 5: Use a Simple Sizing Table

The table below summarizes the factors to check and what each result usually means. Use it alongside the manufacturer’s chart rather than in place of it.

Factor	How to Check	If Too Long or Stiff	If Too Short or Flexible
Length	Wrist-to-floor measurement	Reaches too far, early extension	Cramped posture, hard to extend
Lie angle	Sole marking test	Heel-heavy marks, shots drift right	Toe-heavy marks, shots drift left
Flex	Ball flight and swing speed	Low, weak shots, right miss	High, ballooning shots, left miss
Grip size	Finger gap check	Bulky feel, hands cannot release	Tight grip, hook tendency

When to Upgrade Instead of Adjusting

Some clubs are simply outgrown. If your child has gained noticeable height since the purchase, or if their swing speed has risen to the point that the shaft no longer loads properly, adjusting the existing club may not be enough. Signs that an upgrade is due include persistent difficulty making solid contact even after a fitting, a driver that feels like a stick instead of a tool, and a child who asks for a longer or stiffer option.

Timing matters. Many families wait until the end of a season or the start of spring, when golf equipment tends to be reviewed. Buying one size up in advance is sometimes tempting, but a driver that is too long can teach poor posture that takes months to correct. Fit to current measurements first.

Common Mistakes

• Buying for growth. A club sized for a child who is two inches taller will hinder swing mechanics today.
• Skipping the measurement. Age alone is a poor predictor of the correct length.
• Ignoring the lie angle. Repeated pulled or pushed shots are often a lie problem, not a swing problem.
• Judging flex by the label alone. Two shafts with the same flex name can perform differently across brands.
• Bending or modifying graphite shafts at home. This can damage the shaft and void any warranty.

Tips for Getting the Most From a Junior Driver

• Recheck length and grip size at least once a year, and sooner during growth spurts.
• Use a tee height that lets the ball sit at the lead heel. This is discussed further in the guide on 8 Best Golf Tees for Driver Compared for Junior Golfers (2026).
• Practice on a mat or in a controlled space before hitting on grass, so the child can focus on setup rather than the surface.
• Keep a short log of ball flight tendencies. Patterns over several sessions are more useful than a single round.

Recommended gear

A few accessories make it easier to check fit and practice at home.

• Golf tees sized for drivers. Longer tees help set the ball at the correct height for a driver. A tee comparison is available in 7 Best 2.75 Inch Golf Tees for Junior Golfers (2026). View on Amazon
• A practice mat for impact checks. A mat lets your child hit consistently and makes it easier to observe contact. View on Amazon
• A golf practice net. A net keeps range sessions safe in a backyard and lets parents watch swings from a fixed position. For sizing, see Golf Practice Net Size: How to Choose the Right Dimensions for Your Junior. View on Amazon

FAQ

How do I know if the King Radspeed XB junior driver is the right length for my child?

Measure from the wrist crease to the floor with the child in a relaxed address posture, then compare the result to the manufacturer’s length chart. Confirm with a short swing test to make sure the child can stand comfortably and extend the arms.

What flex should a junior driver have?

Flex should match swing speed and ball flight tendencies. A child who hits low, weak shots may need a more flexible shaft, while one who balloons the ball may need a stiffer shaft. A golf professional or fitter can confirm the best option.

Can I adjust the lie angle of a graphite junior driver myself?

It is not recommended. Bending graphite shafts can weaken them or damage the hosel, and it may affect any warranty. Have a qualified club fitter or golf professional make lie adjustments.

How often should I check my child’s driver fit?

Check at least once a year and any time your child has a noticeable growth spurt. Children often outgrow equipment faster than parents expect.

Why does my child keep slicing with the driver?

Slices can come from a grip that is too large, a lie angle that is too flat, or a shaft that is too flexible. Check grip size and lie first, then consider a shaft review if the problem persists.

Is a larger driver head always better for juniors?

Larger heads are generally more forgiving, which helps young golfers make solid contact. However, the head size is only one factor. Length, lie, flex, and grip size all affect performance just as much.

Should I buy a junior driver a size up so it lasts longer?

Buying oversized is usually a mistake. A club that is too long can cause posture problems and inconsistent contact. Fit to current measurements and plan an upgrade when height or swing speed changes.

When should a child move from a junior driver to an adult driver?

There is no single age. The transition usually happens when the child reaches an adult-length measurement, can swing the adult club with control, and has outgrown the junior shaft’s flex. A fitting session is the most reliable way to decide.

Conclusion

Fitting a King Radspeed XB junior driver comes down to a few measurements and some honest observation of ball flight. Check length, lie, flex, and grip size against your child’s current build and swing, and reassess every year or after growth spurts. When the numbers and the ball flight both point to a mismatch, an adjustment or upgrade will do more for your child’s progress than any change in technique.

Related reading

• Tour X Junior Driver Compared: 4 Best Picks for Kids (2026)

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