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I had a rear child's bike seat on my old bike (which was stolen, boo hoo). It was a Yepp Maxi and was the kind that sits on a rack, rather than being mounted to the seat post.

The maximum weight of child rating for both versions (rack mounted and seat-post mounted) is 22kg. And, this seems to be the maximum child weight for all rear seats. I don't understand how something mounted on a rack can have the same maximum weight rating as something attached on a diagonal bar to the seat post (which I'd be more worried about breaking) - surely it depends on how strong the rack is? If the rack has a maximum weight of, say, 50kg, then I'd feel very confident about putting a bike seat on it with a 22kg child in it.

The fact that it seems to be 22kg across the board, which is slightly under fifty pounds, makes me wonder if this limit is set not due to any properties of the seat itself but rather due to some regulation. I'm much less worried about breaking a regulation than I am about cycling along with my son and the seat falling off, or something.

I understand why we have regulations but often they are very "dumb" in the sense that they don't take other factors into account: for example, maybe some tests were done with an average bike and rider and found that any greater weight at the back made the bike too prone to tipping backwards. This wouldn't take into account the size of the bike (XL in my case) or the weight of the rider (100kg in my case), which might mean that the bike can hold a heavier child at the back without tipping. This is pure speculation on my part, anyway.

Does anyone know why this limit seems to be so consistent across different makes and designs of child's rear bike seat? thanks

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    It could well be 50lbs rounded down for one country and shared across countries. Some of the rack-mounted ones can take a little more (I'm sure I've seen 25kg). The frame size shouldn't matter -- in fact you want the centre of gravity low, so if an XL frame has bigger wheels that could make it worse. My daughter is getting close to the limit and with the seat quite high a standing start needs plenty of room for maneouvre and time to get up to speed. The bars to the seatpost on mine are 10mm steel - that's not going to break
    – Chris H
    Oct 18, 2017 at 14:15
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    Very closely related: bicycles.stackexchange.com/questions/24533/…
    – Chris H
    Oct 18, 2017 at 14:15
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    Examples with heavier weight limits: bobike.com/en/product/cat/backseats also the Yepp Junior
    – Chris H
    Oct 18, 2017 at 14:27
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    Both the rear racks I've seen have been rated to 25kg. 50kg is a lot of weight to put on the rack, particularly if the rider is quite heavy. Also, regulations do tend to be worst-case. It'd be a nightmare to have regulations that essentially said, "This child seat is safe as long as daddy doesn't lose any weight."
    – David Richerby
    Oct 18, 2017 at 14:37
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    @DavidRicherby I've mostly had 25kg racks too but the one on my tourer is rated to 40kg. There's no seat available for it, but other racks with specific seats to match tend to have 40kg ratings - but only 22--25kg for the seat. Maybe the effect on the centre of gravity, or maybe the greater leverage of side loads compared to mass between the upper and lower fixing points
    – Chris H
    Oct 18, 2017 at 16:46

3 Answers 3

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While Criggie's answer explains the reasoning behind the limit, the reason why the official limit is almost always exactly 22kg is simple: that's the standard.

The 22kg limit comes from the European standard EN 14344:2004:

This document specifies requirements for child seats for cycles, which are intended to be mounted on pedal cycles and electrically power assisted bicycles, in order to transport children with a weight from 9 kg up to 22 kg (approximately 9 months up to 5 years) and who are capable of sitting unaided. NOTE Some European countries have special legislation for child seats for cycles. Compliance with this document may not meet this legislation.

So that's why it's always 22kg, and not 23kg or "approximately 22kg".

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    And there's the "due to some regulation". thanks!
    – Max Williams
    Feb 12, 2019 at 11:05
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To summarise the comments

  • 22 kilos is about 50 pounds, which is slightly above the "recommended maximum one-person lift" weight of 15-20 kilos.
  • The "average" child who weighs 22 kilos is big enough to ride their own bike
  • 22 kilos is about as much weight as you'd want to have up high on the bike. Its easily more than most bikes weigh, and mounting/dismounting and getting going can be a bit tricky with excess top-hamper.
  • 22 kilos directly over the rear axle is putting 100% of the weight on the rear wheel. This upsets the front/back split from 40/60% to as much as 30/70%, causing all sorts of steering variations. Ie, what was a firm and stable corner with 40% weight on the front wheel could easily become a front-wheel slide with only 30% of weight on the front.
  • Finally parcel racks are a bit variable in their load ratings. A rack rated for 25 kilos might be fine with 22 kilos of kid and a 3 kilo seat, but what about a rack rated for 20/15/10 kilos?

My personal preference is for a top-tube kid-seat where they are between your elbows. A bakfiets-style cargo bike would be awesome, but they're significantly priced.

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    I couldn't find a top tube seat for a 4 year old except some dodgy looking imports on eBay. What very few manufacturers seem to realise is that while many 22ish kg children can ride their own bikes around the park, that's very different to transporting themselves. The bobike I bought seems to put the weight just a little further forward than the back axle, a noticeable improvement on the previous seat. But that's a nice summary.
    – Chris H
    Dec 25, 2017 at 8:29
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    To help searching, 'baekefleiets' is mostly spelled as 'bakfiets' (plural bakfietsen) and they are very good for transporting bigger kids and for more kids at one time.
    – Willeke
    Dec 25, 2017 at 10:42
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    @Criggie that's max 35lbs (16kg) so lower than the baby seat I used to have. Also impossible with my knees on all but short gentle rides. What I looked for recently was something just a little more than a saddle on the top tube (as used by Dutch /German colleagues)
    – Chris H
    Dec 25, 2017 at 12:22
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    @DiegoVieira that's a new question, and is likely to get some good responses if you ask it using the "ask question" button in the top right. It also might suit the "parenting.SE" site, for a parent-centric viewpoint.
    – Criggie ♦
    Jul 10, 2020 at 23:23
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    @DiegoVieira Did you ever find a solution to your question? I'd love to hear about child seats supporting more than 40lb. Thanks!
    – Clément
    Aug 13 at 0:49
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The premise of the question is somewhat flawed. There are seat that supports more than 22kg, but they are generally called "junior seats".

The Polisport Move Guppy Junior Rear Child Bike Seat, for instance, supports 22 to 35 kg / 48,5 to 77,16 lb, for 6 to 10 years kids:

enter image description here

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