Seems like most entry level bikes are 27.5, but some are 29, and some are 29 but 27.5 in smaller sizes.

My 10 year old is about 5’0 currently. She’s nervous as hell and will want stability, and hates bumps so larger wheels might help but how feasible is that on a S frame? I don’t think she needs XS.

https://www.ebay.co.uk/itm/LIV-EMBOLDEN-2-Womens-MTB-Full-Suspension-Small/202849686806?hash=item2f3ac89516:g:IxYAAOSwp5ld7me9

XC hardtail? Then a 29er should be fine. Full suss with more travel? Then probably 27.5 to keep it manageable.

Wouldn’t a 29er be a bit on the big wheeled side? Possibly feeling ungainly to a nervous kid?
My 11 year old is on a 27.5 hardtail. I’d be making it as simple and smooth as possible for her. I remember all too well watching my daughter transition from the kids back to a proper mountain bike, she was a decent rider and not nervous, but even she was immediately comfortable with the bigger wheels. (By decent rider I don’t mean doing jumps etc, just confident enough on blue and some red trails)

I’ve always worked on a rule of wheel size should be less than or equal to inside leg.

No, modern 29ers aren’t difficult to ride at any size. But bigger wheels may feel more sluggish/less nimble compared to the same spec smaller wheel. At that height there’s plenty of kids on 29ers racing xc, but that’s only because they want the fastest possible bike.

If unsure get 27.5 with some nice big n’ grippy tyres and that should inspire some confidence.

Short people here are on 26”, then every thing in proportion, lighter bikes, easier to ride twisty bits etc.. But I could be so old skool now.

My 10 and 12 year olds, who are a similar size to your daughter are on a 27.5er hardtail (Ragley Bluepig) and a 26er full suspension (Orange Five) bike respectively.

Both pass the eyeball test and they both seem to enjoy riding them.

I think you’d be better off with a 27.5 wheel than a 29er to be honest.  Check toe overlap on small frames with big wheels.

Our family are all between 4’10” and 6′, and strangely still manage on 26″ wheeled bikes

You can overthink/overspend this!

29er didn’t work for 5’/150cm mrs_oab.
She even felt a 27.5 was big coming off a 26.
XS fits now. But for how long…
https://singletrackworld.com/forum/topic/29er-hardtail-for-a-petite-girl/

But bigger wheels may feel more sluggish/less nimble compared to the same spec smaller wheel.

She wants stability, not nimbleness, that’s why I was thinking about 29.

If it’s not an unreasonable proposition we’ll test some out if I can find one around the £4-500 mark.

29er didn’t work for 5’/150cm mrs_oab.

A big kid is differently proportioned to a typical small adult though. When my daughter stands next to me her hip bone is about an inch below mine, and I’m 5’11!

Used XS 26″ Hardtail. We used to have a ladies Giant Talon 1W. Superb bike. Black with a pink lining made it a hit with my son at 10yo. Sold it to a small work colleague who absolutely loves it now.

XS frames are hard to find. You will have to pay for the privilege.

I’m 5’8″ and would still be happily riding a 26″ bike if it hadn’t got nicked. There’s nothing wrong with 26″ and it’ll fit someone of 5′ much better than a 27.5/29er. If you NEED to spend loads on one I’d err on the side of as small as possible. I doubt there’s any tangible benefit to going bigger but it’s your money.

There’s nothing wrong with 26″

Well there is with her current bike cos it’s a kid’s one and is to small. And for me, yes there is a lot wrong with 26 bikes but let’s not get into that here. I’m keen to hear about actual short people or preferably kids on 29ers.

I think she’s too big for XS. She can fit on my wife’s 26 women’s specific bike and that’s a medium.

A big kid is differently proportioned to a typical small adult though

Very true.
Next month she will be eye to eye with you.
The next month you will be referred to as ‘shorty’.

If it’s not an unreasonable proposition we’ll test some out if I can find one around the £4-500 mark

We sold an 18mth old Trek Superfly for £550.
The Giant Liv FS was £700.
It is more than doable.
Fill your boots.

Not a 29er…they don’t have legs long enough to make it worthwhile. At 5′ even a 27.5 may not be as useful as a 26, but a 27.5 would be far better than a 29er for that height.

Not a 29er…they don’t have legs long enough to make it worthwhile.

But her legs are nearly as long as mine.