I'm looking at buying the Liv Thrive 2 (2017 model) which has a D shaped seat tube, I've got conflicting advice so far about whether a child seat can be mounted to the frame (person in Giant shop says yes, person on online store says no). Any idea?

Child seats don't mount on the seat tube. For the most part they mount using the attachment points where you would attach a carrier rack. If the bike has those, the shape of the seat tube is immaterial.

Most child seat for bikes use some kind of clamp which clamp onto the seat post, or it uses metal arms that attach to the quick release of the seat post, or even the rack mount.In any case you should be able to make it work, though if you're seat post is carbon I would be careful not to over tighten.

I will say, however, that if you are planning to use a tag-a-long type trailer in the future when the child is older, the D-shaped seat post is not going to work as this type of trailer requires that the connect collar to pivot on the seat post.

[MENTION=479533]kirstenyork[/MENTION] I'd go with what the tech in the shop says. He can actually see your bike, and also knows which seats he's got in stock and how they mount. I'd also get the seat from the same shop as the bike, and having them do the install, that way, if there's a fit issue, there should be no hassle with an exchange / return.

If your storage space and local infrastructure permits, i'd recommend a trailer over a rear-carrier seat, especially if your riding entails going to and from a destination, rather than 'just riding around'
Kids are squirmy, and they keep growing so they're always heavier than last time. A wiggly two-year-old can do lots of unpleasant things to the handling of your bike, if he's sitting on the rear tire.
If your rides involve destinations like the park, library, zoo, etc., the trailer gives you room to bring along the diaper bag, snacks, and all the things little kids require.
Admittedly not cheap, but there's much more utility to be had, and will fit kids much bigger than you'd want to stuff in to a rear carrier seat.

The majority of child seats I see are the Hamax brand and most of them DO fit to the seat tube. I have no experience of the bracket they use, but I wouldn't be surprised if a non-round design caused problems.

If child seat is a key consideration, I'd buy something you are confident will meet that requirement (i.e. choose the child seat and then choose the bike!)

with Topeak's , you put Their rear rack on your bike, then the kiddy set attaches to that, and so is removable when you are not carrying Jr ..

My LBS Sells those and they will even put it on your bike, included in the price... Internet wont.


What you see , depends on where you look..

Rack mount seats are uncomfortable for the child, especially so with road wheels/tyres.

The ones that clamp to the seat tube are effectively on a pair of big springs, and are far better for the child.