Britax Marathon Vs. Sunshine Kids Radian

Are you trying to figure out which convertible car seat is better: The Britax Marathon vs. the Sunshine Kids Radian?

“What is the difference between the Britax Marathon vs. the Sunshine Kids Radian car seats?”

Good question! Both of these convertible car seats are favored by car seat technicians and parents alike. Below the images of these car seats are some facts to help you out with your decision:

  • The Britax Marathon 70 is known to be easier to install than the Sunshine Kids Radian. If you are going to have your car seat professionally installed and then keep it there, this may not be a huge concern; however, if you might be switching your car seat between different cars regularly, then this will be an important factor in your decision.
  • The Britax Marathon sits up on a base, which makes it higher than the Sunshine Kids Radian. This is great for younger children, but may be an issue with older — or taller — kids bumping their heads on the ceiling of a compact car when you are getting them in and out of the car seat. On the other hand, younger children appreciate being higher up, as it gives them better access to the view outside of the window!
  • The Sunshine Kids Radian has an eight year expiration, vs. the Britax Marathon, which has a six year expiration.
  • Both the Britax Marathon 70 has a rear facing weight limit of 40 lbs and forward facing weight limit of 70 lbs. The Sunshine Kids Radian 65 has a rear facing weight limits of 45 lbs, and forward facing weight limits of 65 lbs.
  • The top harness height of the Britax Marathon is 17″, while the top harness height of the Sunshine Kids Radian is 18″. Since children generally outgrow car seats by height (rather than by weight), the extra inch of harness height means that the Radian will last you longer as your child grows taller.
  • The Britax Marathon has more cushioning under the seat, and therefore feels more comfortable than the Sunshine Kids Radian.
  • In compact cars, the Britax Marathon is far easier to install in the rear facing position. The Sunshine Kids Radian leans back more and therefore takes up more front-to-back space in the rear facing position, making it very difficult to install correctly in compact cars. (In the forward facing position, the Radian does not have this issue.)
  • Parents reported receiving a better level of customer service via phone from Britax than Sunshine Kids.
  • There is more leg-room for older children riding rear facing in the Sunshine Radian than the Britax Marathon, due to the design of the car seat.
  • The Britax Marathon 70 (not the older, Marathon 65 version) does not require re-threading of the harness straps to raise or lower the height of the harness straps, unlike the Sunshine Kids Radian. If you will regularly be using your car seat for play dates and carpools, this can be a significant consideration. If you will only use the car seat for your own child, then you’ll probably only need to adjust the harness straps height every couple of weeks or months.
  • The Sunshine Kids Radian can fold up when not in use to save space, which is a tremendous convenience if you will be doing a lot of traveling out of your the car. (i.e. on airplanes, trains, etc.) The Britax Marathon cannot be folded.

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12 Responses to “Britax Marathon Vs. Sunshine Kids Radian”
  1. carseatcurious says:

    The Britax reclines to 3 positions. the Sunshine Kids has upright and 1 recline. The FF recline of Sunshine Kids is not comfortable enough for my toddler to sleep in, and her head is not supported. The Britax is used in recline position 3 RF, and position 1 or 2 FF. Even in position 1 FF, it is more comfortable for my toddler with more head support for sleeping from the side impact protection wings.

    Sunshine Kids Radian harness only tightens 1/2 inch at a time – you have to tug it 15-20 times to tighten it. And I have to kneel up on the seat to get enough leverage to tighten it. Britax pulls easily and smoothly to tighten the harness.

    Sunshine Kids Radian requires use of an additional “SafeStop” that attaches to the harness straps in back when using it FF under 40 lbs. So it’s a more complicated installation/conversion, and an extra item to remember (or lose) when traveling and using multiple installations (taxi/airplane/car rental etc.).

    Sunshine Kids Radian is heavier, making traveling with it burdensome. It also did not fit the airline seats I tried to use it with (Alaskan) when flying and I had to gate check it anyway.

    Sunshine Kids Radian’s base detaches, making it possible to lose when changing installations, from car to car, or forward to rear facing. Britax base is not removable.

    Britax has better side impact protection and a snugger fit (width) with smaller toddlers/babies.

    Britax is narrower in the back shell (but wider in front where baby needs it) so in RF, it fits between the front seats better. It also does not protrude through the front seats like Sunshine Kids Radian does.

  2. carseatcurious says:

    also, the Sunshine Kids head pillow does not attach to the seat very well. With a taller child, you just tuck the straps behind the seat cover. My toddler pulls it out and tosses it aside and therefore removes any head support or side impact protection.
    When kids are shorter, you have to feed the straps through the harness slots and tie them together in back. It’s inconvenient.
    The Britax head support is not removable.

  3. T.J. says:

    FYI: the head pillow on the Radian is just for comfort, not side-impact protection. We love that it can be removed so easily because my child typically does NOT want it on, but it offers nice support for car sleeping.

    I have no idea what the previous commenter was talking about the harness. You grab it and pull straight down and it tightens beautifully. Our Britax seat, on the other hand, is very difficult to pull the strap.

    • tammy says:

      I agree, I have never had an issue tightening it. It’s tightens much easier than other seats I’ve used.
      Also my toddler sleeps very comfortable in this seat.. however we still rear face at 2 , so I’m not sure how sleeping is forward facing.

      • Melissa says:

        Tightening the strap can be a bit of a challenge in the RF position, where “pulling straight down” isn’t really possible. It’s certainly is/was not a deal breaker for me, but thought I’d point that out. 🙂

      • Melissa says:

        Oops… I should add that I was referring to the Radian, not the Marathon. I’ve never had any issues with tightening on the Marathon (and we’ve had 4 of them! lol)

  4. Marisa says:

    I agree with T.J. about the tightening of the Britax. We like our Marathon a lot but one of the biggest things is that it is very difficult to tighten the strap! I can’t even do it actually. My husband has to wedge himself into the back seat and pull like crazy for it to move the tiniest bit! When it was rear facing it was almost impossible because of the angle.

  5. Aimee Stoian says:

    I love the Sunshine Kids carseat for both my kids (16 months and 3 years) and they both fall asleep in it all the time. I love that it’s narrow and also quite easy to get into because of its low profile. I take it on planes all the time using the backpack straps (I bought an extra pair so that we can tote both seats through the airports). I did just run into one problem which is that if using the seat rear-facing on the airplane (we had spacious bulkhead seats), the airplane seat belt is impossible to unbuckle once it’s in the small pathway for the belt. Mechanics had to take apart the airplane seat in order to free our carseats. Kind of embarrassing, though the kids got a ton of sleep in their rear-facing seats! The belt pathway on the Sunshine Kids is completely closed, so there’s no way to get in there and release the buckle. I can fit my hand through, but the buckle flap did not have enough room to lift up and release.

  6. Sarah says:

    I have both seats and just returned the Diono (SKR). It was an awful seat! I had issues pulling to tighten the strap and could not get it to tighten the chest strap. I called multiple times and sent emails to Diono. Their customer service was great but I continued to have issues. I felt completely unsafe putting my child in the seat because of the inability to tighten the chest strap. My husband couldn’t even tighten it. The Marathon was also easier to install into both vehicles (an 02 Civic and 10 Tundra). FOr a FF only seat, we LOVE our Britax Frontier 85s!

  7. Sara says:

    I have a Boulevard 70, and just purchased a Radian 80sl as a second car seat/one for baby #2 is due in November. We have a 02 Volvo Cross Country (the big wagon mom mobile). After well over an hour of struggling, wriggling and wiggling, reading and re-reading the manual, you tube videos, I realized there is just NO way to get the Radian in and have any space in the front seat (rear facing, center seat). I’m only 5’1, and I had to put the drivers seat completely forward, and the back of the car seat was still touching the drivers seat. My husband wouldn’t be able to drive at all (6’1). I wouldn’t consider my Volvo a compact car, but there was just no way for it to work.

    On top of that it was INCREDIBLY difficult to install (belt, can’t use latch center seat in Volvo) compared to our Britax. It went back to the store, will be purchasing another boulevard.

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