Britax Marathon 70 Convertible Car Seat Reviews

The Britax Marathon 70 convertible car seat:

A Comprehensive Review from experienced consumers.

The Pros and the Cons and where to get the best price for this convertible car seat. (Everything you want to know about the Marathon 70 is on this page!)

britax marathon 70 convertible car seat review

Table of Contents for the Britax Marathon 70: (Jump ahead!)
- Safety
- Best Price

- Comfort

- Ease of Strap Adjustments

- Ease of Installation

- Dimensions

- Video Overview

- Customer Reviews

- Washing the Seat Cover

- Pros and Cons

- Plus detailed Photos!

Click here to check out daily 20%-60% discounts on Amazon for these car seats for today:

Sales are subject to change daily!

The Britax Marathon 70 is one of the new Next Generation convertible car seats of Britax, and it has vast improvements over it’s predecessor, the Marathon 65 car seat. You’ll be glad to know that it is proudly made in the USA!

The Marathon 70 will fit children rear-facing who weigh 5-40 lbs, and forward-facing for kids weighing up to 70 lbs. The height limit is 49″, however, as with most car seats, the seat is outgrown when your child’s shoulders are above the highest harness slot position, or when her head is one inch from the top of the seat’s shell (that refers to the main shell, not the adjustable head-rest), so it really depends on your child’s torso height and proportions, rather than overall height, as far as how long he will last in any given car seat. The Marathon will fit average children through around the age of 6, as do most convertible car seats, although each child is different. (Most 7-year-old kids are ready for a belt-positioning booster seat, such as the Frontier booster.) The exception with regard to these convertible car seats is always the child with the unusually long torso whose shoulders will reach the top harness position before he reaches the maximum height or weight for the seat.

Is the Britax Marathon 70 Comfortable?

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britax marathon 70 car seat

When you touch this car seat, you will find the Marathon 70 to be soft and plush, like a little luxury recliner for your child! The Marathon 70 has a deeper seat than the 65 model, so your child will have more room for her legs and support for her thighs, translating into an even more comfortable sitting experience.

The crotch strap on the Marathon 70 is long – eight inches long, which eliminates a complaint from the older, Marathon 65 model, that the crotch strap was sometimes too tight while the rest of the car seat fit kids perfectly. It also has two different slot positions to accommodate your child’s growth.

There are 3 reclining positions, and like most convertible car seats, the Marathon 70 has it’s rules: The most reclined position must be used in the rear-facing position, and when it is forward-facing, the middle and most upright positions may be used.

The body pillow for infants gives your baby more cushioning and makes the seat a better fit for little ones, and it’s easily removable when your baby grows too big to need the extra pillow support.

Ease of Installing the Britax Marathon 70 convertible:

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Using the Latch connectors, which come standard in vehicles manufactured after 2002, installing the Marathon 70 was really fast – about half a minute and done! This was tested both in the rear-facing and forward-facing positions.

Here is an informative video covering everything you need to know about installing the Marathon 70 using your car’s seat belt:

The Britax Marathon 70′s Dimensions:

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  • The top harness slot height measured 17″.
  • Bottom harness slot height was 8.75″
  • The depth of the side shell was 7″
  • Inside shoulder width: 14″
  • Crotch strap positions: 5″, 8″
  • Crotch buckle length: 5.5″
  • Internal Seating Depth (leg room and thigh support): 12″
  • Overall height of shell (measured without raising headrest above shell): 23.5″
  • Overall height with headrest raised: 27.5″
  • Internal bottom width: 11″
  • Internal shoulder width: 13″
  • External seat width: 19″
  • Seat weight: 19.2 lbs.

Stated Limits:

  • RF Weight Range: 5-40 lbs.
  • RF Height Range: <= 49 in. standing height OR 9-16.75 in. torso height
  • FF Weight Range: 20-70 lbs.
  • FF Height Range: <= 49 in. standing height OR 12-16.75 in. torso height
  • FF Age Range: 1 year and older

Additional Information:

  • Lock-offs Provided: Has Lock-offs
  • Rebound Control: Rear facing Tether
  • Expiration Limit: 7 years from date of manufacture

Note that nothing was a straight line in taking these measurements, so they are somewhat subjective!

Because of the re-design of this new seat’s overall shape, it actually takes up less room in your car than the older Marathon 65. When you compare both the 65 and the 70, you’ll find that you have about two extra inches between the car seat and the driver’s seat in front of it with the new Marathon 70! This is great because tall drivers with compact cars sometimes could not fit their old Marathon 65 in the position behind the driver unless the driver’s seat was moved too far forward for this tall parent to sit comfortably. (If you do have a tall driver and small car, be sure to keep the box and receipt to ascertain that the Marathon 70 is going to be a good fit!)

Video overview of the Britax Marathon 70 car seat:

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This helpful video shows exactly how you will secure your child in the Marathon:

Safety of the Britax Marathon 70 convertible car seat:

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EPP foam is a higher grade than the older EPS foam used in older car seats, and it is less likely to crack. You’ll notice that it is black, while the old foam was white.

britax marathon 70 car seat review

The Safe-Cell technology can be viewed in this photo taken from the back of the car seat, and I circled it in red. These round, hollow cells are designed to compress in case of an accident, which lowers the center-of-gravity of the seat and absorbs impact, keeping your child from absorbing much of the impact of a crash.

You can see how the SafeCell compresses in the event of a car crash in this short video:

britax marathon 70 review

Britax has patented their energy-absorbing Versa-Tether, which has staged-release tether webbing, anchoring the top of the seat at two points to minimize forward movement. The rubber overlays on the harness are called HUGS, which stands for Harness Ultra Guard System, and it serves to reduce forward torso movement in the unfortunate event of a crash.

Additionally, the Marathon 70 also has a feature called Side Impact Protection, which will minimize impact in case of a collision into the side of the car – which is one of the most common types of crashes.

Britax has built steel bars into all their convertibles for maximum adherence to the vehicle during a crash, which reduces a child’s forward flexing and chance of injury. You can see the steel bars clearly in this video:

Ease of strap adjustments for the Marathon 70:

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britax marathon 70 convertible car seat

One of the greatest improvements of the Marathon 70 is the way that you adjust the harness height. You’ll simply squeeze the handle at the top of the headrest and move it up or down a track. I did it with one hand, and it was a breeze. (On the other hand, I nearly broke my nail doing the same type of adjustment on the Safety 1st Alpha Omega elite car seat – that one required muscle!)

Not only do you never need to re-thread this harness for height adjustments; you also never need to access the back of the seat to make a height adjustment – which means that you don’t need to bother uninstalling and reinstalling it to change the harness height! This is an outstanding feature if you’re going to be doing carpools or using the same seat for siblings of different heights, it will save you much time and eliminate a common frustration when adjusting harness heights in other car seats!

Two crotch strap positions allow you to get more years of use out of this seat than its prior model. You will move the crotch strap to the more forward position as your baby grows.

britax marathon 70 safety ratings

Where can I get the Best Price for the Britax Marathon?

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After lots of surfing, visiting local stores, and calling stores miles away, I found that beat local stores and other websites by $20 – $80 on a regular basis. However, because they are generally the cheapest, it often sells out, so if you see it in stock on Amazon grab it while it’s still available!

britax marathon on amazonNote: Sometimes, when you check out this car seat on Amazon, you will not see a price, rather, Amazon will say, “Check price in cart”. So you add the item to your cart, and then you are shown the price. While this may be inconvenient, it saves you a lot of money: The manufacturer does not allow the product to be sold for less than a certain amount of money publicly. Since Amazon sells this car seat for less than the manufacturer’s allowed price, they cannot display the price until you have added the item to your shopping cart. So, that extra click of your mouse will save you a nice amount of dollars over buying the car seat in a local store or at any other website.

Customer Reviews for the Britax Marathon 70 convertible:

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The legendary Britax quality continues with a solid, intuitive build. Some of the newer head protecting technology from other, more expensive Britax seats has been integrated. The new harness adjuster is amazing, making it so simple and easy to change the height of the straps. We often carpool and I’m glad I can quickly and easily customize the seat to every child. ~ from Kristen on Amazon.

Overall, this is a great quality seat that will keep your little one safe, comfortable and secure for many years. In the nearly nine years that I’ve been using Britax seats, I have found each of them to be worth the price. ~ from Karen on Amazon

Love this car seat, pretty easy to install and fits in my car well. I feel safe with my child in this seat. After HOURS of analyzing different seats and brands. This was the safest seat I could use the longest both rear and forward facing. Worth every penny! ~ from Mandy on Amazon

britax marathon sale best price

Washing the Britax Marathon seat cover:

One of the great advantages of the Marathon over other car seats is that you don’t need to remove the car seat from your car and then reinstall it each time you want to was the cover. Additionally, there is a simple hook and loop system that makes it simple to remove and then replace the cover on your car seat.

As cute as our babies are, we know that they will inevitably have a leaky diaper or get car sick once in a while, and the last thing a busy parent needs is a complicated system for washing the car seat upholstery! And, we certainly don’t want to have to uninstall and reinstall the entire car seat each time a sippy cup of milk spills!

This short video (just over one minute) shows you how easy it is to wash the cover of the Britax Marathon 70:

Pros and Cons of the Britax Marathon 70 car seat:

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The Marathon 70 has exceeded safety standards and is highly rated by car seat technicians, firemen, and independent consumer rating agencies.

This seat has one of the most user-friendly systems of adjusting the harness heights of all the car seats I have seen. (It can be done with just one hand!)

You will get many years out of this seat from the time your child is a baby until around first grade, since it has a high upper weight limit of 70 lbs.


The seat is large, bulky, and heavy, like all convertible car seats. If you’ll be carrying it through the airport and into rental cars on a big trip, be sure to practice weight lifting in advance!

It is pricier than some other convertible seats with similar features like the Evenflo Triumph Advance convertible car seat.

I really could not find any other cons for this terrific car seat!

britax marathon 70 review

Click here to check out daily 20%-60% discounts on Amazon for these car seats for today:

Sales are subject to change daily!


23 Responses to “Britax Marathon 70 Convertible Car Seat Reviews”
  1. Shannah says:

    I have a question based on the size of the car seat. I would really like to get the Marathon based on reviews, etc., but I’m wondering if the roundabout would be a better fit in my Mustang. Does anyone have a comparison between the two in regards to how much room they will take up?

    Thank you! This site is a wonderful resource!

    • Hi Shannah,

      The actual shell of the Britax Marathon and Britax Roundabout are the same. Therefore, there would be no difference regarding the room they take up in the car. There are technical differences in the way the seats are manufactured which make the weight limits different on each car seat.

      Let us know if you have any further questions!

  2. A. perry says:

    I have been spending many late nights researching convertible car seats for my fourth child, who is 1 year and 21 lbs. I had made up my mind that the Britax Marathon 70 was the best choice as he spends many hours in his car seat accompanying his older siblings to school, sports practices, etc. The last convertible car seat (not a Britax) my middle two kids used from 2004 always had their heads flopping when they slept. I wanted something super comfortable as well as safe this time.

    Then I noticed some comments about the toxicity issue with the Britax car seats, due to the reports that came out in early August. I worry about the small amount of lead in the clips. I think the bromine in the seats is an another issue but I tend to wash the car seat covers often (that was another reason I found the Marathon a good choice- the easy to remove cover) as my kids are always snacking and they tend to get dirty.

    Do you have any thoughts on the issue?

    • I read something about toxicity in car seat materials, but it did not seem to be an authoritative source. I will do further research and post back here!

      • A. perry says:

        The main report about the car seat toxicity is on

        There seemed to be a wide variety of results for the Britax seat covers, however most of the clips seemed to consistently test for bromine and a small amount of lead.

        Thanks for your interest and help! I have found the reviews on this website very helpful!

      • Jess L. says:

        I am in the same exact situation as A. Perry. Had made up my mind about the Marathon 70 and then started reading all this stuff about the toxic levels. Ellen, have you found out any more information in your research?

        • Ellen says:

          It seems that some patterns are worse than others. The lead in the clips is the most common issue, but I would really not worry about this if your child wasn’t the type to be sticking it in his mouth. There are some patterns that seem to be worst offenders in the rest of the seat as well for other toxins, specifically Jet Set in the current models.
          If this is a major concern to you, check out our review of the Graco MyRide 65 or Safety 1st Complete Air to see if either suits your need as they led the list of the best picks this year from

  3. Katie says:

    My son is 13 months, 24 pounds and 30.5 inches long. I’ve read that children should be in rear facing seats until age 2, and my son just outgrew his infant seat, would this be a good seat to seat him rear-facing, and will it be confortable for him? Any feedback would be appreciated!!

    • The law is that children MUST ride rear-facing until age 1.

      It is HIGHLY RECOMMENDED that children ride rear facing until age 2.

      It is MUCH SAFER for children to ride rear facing than forward facing, until they have outgrown the weight limit to ride rear facing in their particular car seat. Many people keep their children rear facing due to the safety benefits, until age 3 or 4.

      The Britax Marathon is one of the most popular convertible car seats for rear and forward use, so it will last you a long time! Note that most children outgrow their car seats by height (which is seated shoulder height, not actual height – because their shoulders go over the top strap slot) rather than weight, unless they are very hefty.

  4. Elva says:

    Just bought the marathon 70 and the lower thigh straps are way too tight on my daughter legs. What am I doing wrong?
    thank you

    • Ellen says:

      Hi, Elva!

      That must be very frustrating, especially since the Marathon 70 is supposed to clear up these complaints from the 65.

      Here is how I would try to adjust the harness system and see if it helps:
      Loosen the harness and slacken the thigh straps a bit more.
      Buckle her in.
      Pull the slack up from the thighs to her comfort level.
      Then tighten the harness strap until you notice the double click.

      If it’s still too tight, another method of adjusting it would be to completely loosen the harness by extending it completely and then slowly tightening it back up while one hand holds the harness straps firmly.

      If you’re rearfacing, it is easy enough to see that the harness is smooth in the back and that it’s not being caught on anything which prevents it from getting loose enough for your daughter, but if you’re FF, and you’re still having issues, uninstalling it to look at the back might prove helpful.

      If none of this works, contact Britax. It’s possible the seat is defective or that they have other tips. Their email address in the US is

      Hope this helps!

  5. Susan says:

    So, the new car seat’s straps don’t come off. My daughter barfed ALL OVER this seat. (Fish & Milk – fabulous) How do we get the smell out? Or is there a nifty way the straps can come off of this Marathon 70? My husband became quite a pro at taking apart our old Marathon car seats. (We have 2, one per kid) but when we were in a car accident we needed to change car seats, so the 70 is the one we have now. We have no problems washing the cover, it is the straps that we are having serious issues with. We have only had these new Marathon’s for 2 months. Any help will be appreciated.

    • Ellen says:

      Unfortunately, this is one of the drawbacks of the newer Marathon models: the straps cannot be removed. And even if there was a way you figured out how, it would most likely not be safe to try to reattach them.
      What has worked for me in the past when we’ve had car sickness issues is using Arm and Hammer deodorizing spray liberally. Wipe down whatever you can, and let the deodorizer and fresh air help with the smell. Incidentally, I have a neighbor who had the same exact issue last week and I lent her my Arm and Hammer spray and she said it made the world of a difference. I hope that tip helps, and I’m sorry Britax didn’t have the foresight to envision just how many children will require their entire seat to get cleaned, not just the cover!

  6. Sheryl says:

    Hi- 2 questions I hope you can answer. First, are you able to reach around the carseat from your drivers seat (with some stretching of course haha) and hand your child something in this newer model? Also, can you see your child when using a mirror on their seat? I have the Marathon 65 and had no problems with either of these things. I bought the My Ride 65 for my son and I can not reach him AT ALL to hand him his paci or anything! I can also NOT see him at all in the mirror due to the large “wings” as I call them, that protect the head. THey are SO tall and wide on the My Ride 65. I am taking it back tomorrow but don’t want the same issue with the Marathon 70, which is what I would like to buy.
    Thanks for any input!!

    • Ellen says:


      You ask good questions, but there is no one answer. It will depend on the model of car you have and how far back you sit from the wheel/your height, as well as the angle the car seat is installed. The best bet would be to go try it out in person as many stores allow you to test the seat in your car to see if it works.
      I assume you’re putting your child FF in the middle seat? Or is he on the side? I am lucky in that my vehicle has 2 mirrors — one for rear-view for driving, and one which is more of a “bubble” to see what’s going on in the car; I honestly don’t remember the last time I tried watching my kids in the regular mirror!
      Since the MyRide 65 has a very deep recline, it’s very possible you’ll have more luck with a more upright install in a Marathon.

      Good luck!

  7. Sheryl says:

    Ok thank you! I have captain’s chairs in my vehicle and he is rear-facing behind the driver’s seat. I have a mirror on the back of his seat that I can see in my rear-view mirror. But can’t see him over the tall/wide head safety wings on the My Ride. It’s going back because of this.
    Thanks again!

  8. Korissa says:

    I work at a baby boutique and a lady came in having a problem with her Britax Boulevard car seat. Her little girl is 5 years old and 36 pounds and very very tall. Being up north in Canada it’s very cold and the kids need to bundle up. She has the problem of, the car seat, pulled up to the tallest it can go, so it’ll fit her little girls height, isn’t big enough to fit the extra padding of the winter jacket and snow pants. Other than taking off the winter clothing, what should I tell her?

    • Ellen says:

      That’s exactly what you should tell her!

      You want to make sure that there is no bulky coat that is between the child and the seat. The reasoning behind this is that during a collision the coat gets compressed, and this results in extra slack in the harness. The buckled straps need to remain tight at all times in order to restrain the child properly.
      So how can you keep a child warm without compromising on safety?

      You can get a lightweight coat, such as one made out of fleece or suede, that will keep her warm without the bulk. Use mittens or gloves and a hat as well, and she will feel quite toasty.

      In order to figure out if a coat is too bulky, test the harness adjustment with and without the coat. Buckle the child in the seat with the coat and adjust the straps as you normally would. Without loosening them, have her come out and take off the coat. Buckle the child in again without tightening the straps. If there is more slack than 2 fingers’ worth under the harness by the shoulder bone, the coat is too bulky to be used with the harness.

      If she has a bulky coat and you feel it’s the best way to keep her warm, you can remove it when you get to the car and put it on backwards on top of the straps after buckling.

      • leila says:

        No one feels toasty in -30C weather (for 6 out of 12 months). The car really can’t be heated ahead of time because in these temperatures it takes a good 5 – 15 minutes of DRIVING around before the car starts to heat up. Idling, trying to wait for it to heat up, only wastes gas as it simply cannot warm up in those extreme – yet normal – weather temperature and conditions. It is simply not safe to take a child out in any of the winter months without being bundled up in many layers. Frost bite and/or hypothermia can set in in as little as 5 minutes.
        There must be another answer.

  9. Emily says:

    THANK YOU! for having the most comprehensive reviews on the web. This is just what I was looking for. If I’m looking at the Britax Marathon 70 or Boulevard, what are the main deciding factors between the two? My son is 14 mos. and 18.5 lbs–very small :)

  10. Emily says:

    Nevermind–found your side-by-side comparison. Thanks.

  11. Beth says:

    I am starting my search for convertible car seats and am fairly set on the Britax Marathon. The part I am soooo confused on is: what is the difference between the Marathon 70, the 70 cs, and the 70-G3? I keep seeing ‘next generation’ and such, but can’t figure out what differences that actually entails. And I found a good price on the Britax Boulevard 70… but I can’t tell if this is a next generation? And if it isn’t, what improvements would I be missing by going with the newer Marathon? Thanks so much!

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