Convertible Car Seats

Which is the Best Britax Convertible Car Seat?

In this page, we will see the comparison between popular convertible car seats from Britax, namely, Britax Marathon, Boulevard, Allegiance, and Advocate.

Except for the Britax Allegiance, they all are convertible car seats that are equipped with the ClickTight installation system. They are all great car seats with very good safety ratings and user feedback but there are several key differences that set them apart.

Britax Marathon ClickTight
Britax Boulevard ClickTight
Britax Advocate ClickTight
Britax Allegiance Convertible Car Seat

Dimensions

We always recommend, to first make sure that the car seat will fit inside your car. Here is the size comparison of the Britax car seats.

 LengthWidthHeightCar Seat Weight
Britax Marathon ClickTight23 inches18.5 inches23.5 inches28.5 lbs
Britax Boulevard ClickTight23 inches18.5 inches23.5 inches29.4 lbs
Britax Advocate ClickTight23 inches20.5 inches23.5 inches30.6 lbs
Britax Allegiance21 inches18.5 inches26 inches19.5 lbs

The Britax Marathon and the Britax Boulevard have exactly the same width, depth, and height (23″ L x 18.5″ W x 23.5″ H) while the Advocate is a little wider(23″ L x 20.5″ W x 23.5″ H). On the other hand, Britax Allegiance measures 21″ L x 18.5″ W x 26″ H.

Height and Weight Limits

The dimensions of the car seat are important but there is a more important thing to consider when choosing a car seat. It’s the height and weight limits of the car seat. This will decide how long your child can use the car seat before it is uncomfortable for her or not safe anymore. So you need to know how long the car seat will be able to accommodate your child.

 Rear-facingForward-facingChild Seated Shoulder Height – Rear FacingChild Seated Shoulder Height – Forward FacingChild Standing Height Limit
Britax Marathon ClickTight5-40 pounds20-65 pounds7.6 – 18.65 inches 12 – 18.65 inches 49 inches or less
Britax Boulevard ClickTight5-40 pounds20-65 pounds7.6 – 18.65 inches 12 – 18.65 inches 49 inches or less
Britax Advocate ClickTight5-40 pounds20-65 pounds7.6 – 18.65 inches 12 – 18.65 inches 49 inches or less
Britax Allegiance5-40 pounds20-65 pounds9 – 16.75 inches 12 – 16.75 inches 49 inches or less

Installation and Seat Features

Britax Marathon, Britax Boulevard, and Britax Advocate come with ClickTight installation system, which is truly easy to use.

The Britax Allegiance is also very easy to install using lower anchors that lock into place with a click and are released with the push of a button.

Below we also list other convenient features of each seat for easy comparison.

 ClickTight Installation SystemClick & Safe Snug Harness IndicatorEZ-Buckle System
Britax Marathon ClickTight
Britax Boulevard ClickTight
Britax Advocate ClickTight
Britax AllegianceQuick-adjust 10-position harness

Safety Features

One of the primary differences between the Britax Marathon and the other Clicktight series car seats is the harness system. Britax Marathon does not have the Click & Safe Snug Indicator. The Britax Allegiance also have a different harness system. 

 Layers of Side Impact ProtectionSafeCell Impact Absorbing BaseSafeCell Impact Stabilizing Steel FrameSafeCell Impact Absorbing Harness Pads
Britax Marathon ClickTight1
Britax Boulevard ClickTight2
Britax Advocate ClickTight3
Britax Allegiance1

Here one of the important things to look for is the layers of side impact protection. Every additional layer ensures additional protection, the Marathon and the Allegiance have one layer of side protection while the Boulevard comes with two layers and the Advocate comes with three layers of side impact protection.

Remember that, having more layers of protection is good but that doesn’t mean one layer is not enough, remember all the seats passed certain safety tests.

Our rating:
4.5/5
Britax Marathon ClickTight

Britax Marathon ClickTight

Our rating:
4.8/5
Britax Boulevard ClickTight

Britax Boulevard ClickTight

Our rating:
4.7/5
Britax Advocate ClickTight

Britax Advocate ClickTight

Our rating:
4.3/5
Britax Allegiance Convertible Car Seat

Britax Allegiance

Color Options

Britax Marathon ClickTight Color Options

Britax Boulevard ClickTight Color Options

Britax Advocate ClickTight Color Options

Britax Allegiance Color Options