Diono Radian RXT Car Seat Instructions (2026): Installation, Adjustment, and Cleaning Guide

The Diono Radian RXT is a steel-framed convertible that folds flat for travel and fits three-across in most vehicles — two features that make it uniquely versatile. I’ve installed this seat in everything from compact sedans to minivans, and the SuperLATCH system makes rear-facing installation surprisingly straightforward for a seat this robust. The main learning curve is understanding the different belt paths for rear-facing vs. forward-facing and knowing when to use the angle adjuster. This guide covers every installation configuration plus cleaning, adjustments, and booster conversion.

Forward-Facing Installation with LATCH (22–65 lbs)

1. Read both the Radian RXT manual and your vehicle manual for car seat installation specifications.
2. Adjust the harness height and headrest for your child’s size.
3. Place the seat on the vehicle seat in the upright position.
4. Attach the top tether to your vehicle’s top tether anchor, but leave it loose for now.
5. Route the SuperLATCH strap through the forward-facing belt path and connect the hooks to the vehicle’s lower anchors.
6. Press down firmly on the seat while tightening the LATCH strap to remove all slack. Verify the seat is level.
7. Tighten the top tether strap.
8. Test the installation — the seat should not move more than one inch in any direction at the belt path.

Rear-Facing Installation with SuperLATCH (5–45 lbs)

1. Turn the seat on its side and route the SuperLATCH strap through the rear-facing belt path channel.
2. Press the feet of the seat into the seat bight (the crease where the vehicle seat cushion meets the seat back).
3. Attach the SuperLATCH hooks to the vehicle’s lower anchors.
4. Press down on the base of the seat with your body weight while tightening the SuperLATCH strap to remove all slack.
5. The seat should not move more than one inch in any direction when properly installed.

Seat Belt Installation

This method works for both rear-facing and forward-facing configurations when LATCH isn’t available or when your child exceeds the LATCH weight limit.

1. Place the seat flush against the vehicle seat back.
2. Route the seat belt through the appropriate belt path channels on the back of the seat (clearly marked for each direction).
3. Buckle the seat belt.
4. Pull the seat belt webbing all the way out until you hear a click — this engages the locking mode on most vehicles.
5. Press down firmly on the seat while feeding slack back into the retractor.
6. For forward-facing, always attach and tighten the top tether as well.
7. Test that the seat moves no more than one inch at the belt path.

Using the Angle Adjuster (Rear-Facing)

The angle adjuster is a separate accessory that increases the recline angle for rear-facing installation. This also gives more legroom to the front-seat passenger.

1. Install the seat in the rear-facing position first.
2. Slide the angle adjuster underneath the seat base.
3. Re-check that the seat is still securely fastened and passes the one-inch movement test.

Center Seat Installation

The center rear seat is statistically the safest position. Since most vehicles don’t have LATCH anchors in the center, use the seat belt method.

1. Attach the detachable base and lock it in place.
2. Press the feet of the seat into the seat bight.
3. Make sure the Radian sits completely on the vehicle seat.
4. Route the seat belt through the rear-facing or forward-facing belt path as appropriate.
5. Pull the belt webbing all the way out to engage locking mode.
6. Press down on the seat while removing all slack from the belt.
7. Feed excess webbing back into the retractor.
8. Verify less than one inch of movement at the belt path.

Airplane Installation

The Radian RXT folds flat for travel, which makes it one of the best car seats for flying. The FAA-approved seat can be used with the internal harness on aircraft.

1. Call your airline ahead of time to ask about car seat requirements and whether a seat belt extender will be available.
2. Unfold the seat before boarding.
3. Request a seat belt extender from the flight attendant — it makes installation much easier on narrow airplane seats.
4. Install in a window seat so other passengers can move freely in the aisle.
5. Route the airplane lap belt through the appropriate belt path channels.
6. Buckle and tighten the belt until the seat passes the one-inch movement test.

Cup Holder Installation

1. Lift the fabric on the side of the seat where you want the cup holder.
2. Feed the cup holder attachment through the fabric opening.
3. Push down on the cup holder with a twisting motion and pull the fabric back into place over the seat.
4. Repeat on the other side if desired.

Adjustments

Headrest Height

1. Peel back the Velcro fabric that covers the base of the headrest.
2. Slide the headrest up or down to the correct position for your child.
3. Close the Velcro fabric cover to secure it.

Harness Strap Height

The Radian RXT requires manual rethreading to change harness strap height — this is the one downside of the seat’s slim, steel-framed design.

1. Remove the seat from the vehicle.
2. On the back of the seat, locate the hook that connects the harness straps.
3. Unhook the straps.
4. Thread the straps through the higher or lower harness slot as needed for your child’s shoulder height.
5. Reconnect the straps to the hook on the back.
6. Reinstall the seat in the vehicle.

Converting to Booster Mode (40–120 lbs)

1. Unhook the harness from the buckle assembly on the back of the seat.
2. Remove the chest clip from the front.
3. Pull the harness straps out through the top of the seat.
4. Use a Phillips screwdriver to remove the harness anchor plate on one side of the seat.
5. Fully remove the harness from that side.
6. Repeat on the other side.
7. Store the harness components in case you need them again for a younger child.

Removing the Base

1. Lift the metal tab at the rear of the base.
2. Slide the base forward.
3. Pull the base away from the seat.

Cleaning Instructions

Seat Shell

Wipe down with a towel and warm soapy water. Avoid harsh chemicals or solvents.

Memory Foam

Wipe with a damp cloth only. Do not submerge or machine wash.

Seat Cover

Remove the cover and memory foam from the shell. Machine wash the cover in a front-loading washer with gentle detergent. Line dry only — do not machine dry. Reassemble once completely dry. See the owner’s manual for specific cover removal steps.

Harness Straps

Wipe with a damp cloth and mild soap. Air dry. Never submerge, bleach, or machine wash the harness webbing.

Diono Radian RXT Manual

• Diono Radian RXT Owner’s Manual (PDF)

For our full review, see our Diono Radian RXT review. For other Diono models, check out our best Diono convertible car seats comparison.