Hi Tim, Thank you for your enquiry. External dimensions for both the Britax Frontier Clicktight and the Britax Pioneer Clicktight are the same, but the internal head piece on the Britax Frontier sticks out slightly further. Also, the Frontier has higher weight and height range limits. To compare these two seats further or any of our restraints available online, we would recommend using our online Product comparison tool. Once you have found the product on line you are wanting to compare, select the ADD TO COMPARE option (located by the product image) and continue to do so for all products you wish to compare. Then select to “view the product comparison” by clicking on the green highlighted box on the product page, here all product specifications will be displayed in a chart format for you. Alternatively, if you follow the link https://www.babyonthemove.co.nz/store-locations/ this will take you to our online store finder. Here you can find contact details for your nearest Baby On The Move Store where one of our expert Car Restraint Technicians can assist in helping you find the right restraint for you, your child and your vehicle. We hope this has helped with your query.