Diono Radian 3RX Car Seat

Diono Radian 3RX convertible car seat installed forward facing in third row of Mazda5

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Navigating a Tight Car Seat Spot

Diono Radian 3RX convertible car seat installed forward facing in third row of Mazda5
  • What: Diono Radian 3RX Car Seat
  • When: Birth to booster
  • Why: High weight and height capacity, buy only one car seat
  • Where: Amazon, Diono 

Heavens, I adore this seat. I wish I’d gotten one earlier in our car seat journey. Touted as the original 3 across solution, this Diono Radian 3RX All-in-One Convertible Car Seat still feels solid, yet fits three in a row. 

Diono 2019 Radian 3RX All-in-One Convertible Car Seat on Amazon

I didn’t have to uninstall the car seats (a Graco Nautilus 80 Elite booster) or the Britax Marathon (forward facing) to get the Radian installed properly. It replaced a Britax Boulevard and definitely takes up less room. Yet it will continue to grow with my child, up to 120 pounds. My not quite ten year old only weighs 79 pounds, and as usual for kids, outgrows seats by height. My 45 pound eight year old outgrew the Boulevard when her shoulders reached higher than the straps. While my nine year old wouldn’t fit in this seat, my lighter eight year old fits near the top of harness height limits.

Diono Radian 3RX convertible car seat next to Britax Boulevard convertible car seat
The Diono Radian 3RX replaced a Britax Boulevard sandwiched in the middle position of the back seat of our 2016 Subaru Outback.

I got it installed properly on the first try, which seems like a minor miracle. I spent less than 15 minutes taking out the old seat and installing the Radian, which definitely sets a new record for me. I’ve installed a LOT of car seats. We’ve been through four cars and three kids, and we’ve moved them around countless times. Even with the Britax Grow With You with ClickTight, it took me several tries to get the seat super secure, and I had broken several nails and worked up a sweat (not the mention a backache) by the time I finished. I have no idea how the Diono company makes such a fine seat, but I’m sold.

Diono Radian 3RX between Graco Nautilus 80 elite and Britax Boulevard in back seat of Subaru Outback
I installed the Diono Radian 3RX on the first try, without having to uninstall the Graco Nautilus 80 Elite 3-in-1 booster seat or the Britax Boulevard convertible car seat on either side of it.

I understand the easy installation might have something to do with the car model compatibility. We put ours in the middle position of a 2016 Subaru Outback. It went so well, I bought a second one immediately for my son, who has also outgrown his Britax Marathon at five years old. I still want my kids in a five point harness as long as possible, and these seats give me that option. Plus, when they outgrow the harness, the seat converts to a belt-positioning booster. I have several booster seats that go from harness to booster but no convertible seats that can be used from birth to booster. 

The 3RX differs from the 3RXT because it doesn’t have extra side headrests. That means it has less side impact protection (not as big a concern in the middle position of the back seat this time), but also that it doesn’t adjust. So once your child outgrows it by height, whether in harness or booster mode, they are done. (You can get the 3RXT with an adjustable headrest to make the seat last for another couple of growth spurts.)

Diono Radian 3RX sidewings extended next to Britax Boulevard
We have room to extend the adjustable side wings of the Diono Radian 3RX even squished between two other (non narrow) seats, including this Britax Boulevard installed forward facing.

The manual on this 2019 Radian 3RX stores on back of seat. I find that irksome as you can’t put it away or take it out once you install the seat forward facing. But I see the advantage when you install rear facing. The seat back also goes up pretty high, which helps it last longer, but I’ve read that’s a downside in a rear-facing position, as it takes up more room at an angle and isn’t compatible with the seat in the front row in lots of vehicles.

More bad news: In front facing harness mode, you have to add a Safe Stop strap for kids under 40 pounds. You can’t use this strap in rear facing mode, or in front facing harness mode with kids over 40 lbs. That means you have to uninstall and then reinstall the seat once your child hits 40 pounds if they ride forward facing before that weight. 

Diono Radian 3RX car seat new in box
This car seat installs rear facing, forward facing with a five point harness, or as a highback booster.

My kids all stayed rear facing a minimum of three and a half years, and even the littlest one weighed more than 40 pounds by her fourth birthday. You can avoid this nitpicky bit entirely by not using the seat forward facing until your child weighs over 40 pounds, but it does give you the option to use it for kids weighing less than that if you don’t have an alternative (say other than buying a new car to fit three car seats). You can leave kids rear-facing in this seat up to 45 lbs, so that helps avoid situations requiring the Safe Stop strap.

Harness release button on Diono Radian 3RX convertible car seat
My daughter has no trouble operating the harness release strap herself, a problem we’ve had with other harness to booster seats.

The seat only comes with one removable cup holder. Some little divas prefer more storage, though I’ve learned they just get grubby fast. Having it removable makes it easier to clean, as you can take it out and dump it, or even run it through the dishwasher. But it also means you can lose the cup holder before your kids get old enough to use it. I’ve also heard it can be tricky to position the seat belt through the included guides in booster mode, but I can’t attest to that, since we’ve only used harness mode so far.

Finally, this combination car seat doesn’t expire for ten years. That beats the pants off any other convertible car seat I’ve seen on the market, much less ones I’ve used. My child also prefers it, not only to her old Britax Boulevard, but also to the more limited two mode (harness or highback booster) Brtiax Grow With You seat.

Diono Radian 3RX folded flat
The Diono Radian 3RX folds flat.

Did I mention this car seat folds flat? That makes it easy to store between kids, or throw into vehicles to transfer it without installing. Theoretically it also makes it great for flying, though the seat still weighs a ton at a hefty 23.8 pounds. Even folded flat with the handle keeping it closed, I wouldn’t want to lug it around.

While I don’t think I’d want to use this seat from birth, it makes a great option for older siblings when you need to squeeze three car seats in a single row without buying a new car. It may not last us more than a year or two, but by then, one of my kids won’t require a car seat at all. Not having to buy a new car or having to uninstall and install all three car seats to get a safe fit in the middle position means a lot to me.

Bottom line: if you read every car seat manual from cover to cover, you’ll be fine. If you like to wing it, don’t try this seat. It has lots of finer points that allow it to work for such a wide range of car seat situations, but you have to follow the instructions precisely. If you have a tight backseat and need to install the seat rear-facing, look for a shorter seat that takes up less room, even if you have to give up the booster mode.

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