So my elder daughter (9 1/2) is looking rather tall on her Isla Beinn 24 and I’m wondering what the next step up is. She’s about 140cm / 4’7” tall, 71cm / 28” leg and various companies seem to put that on the cusp of 26” and 27.5” wheels.

I’ve got quite a lot of parts from my old 27.5” 150mm hardtail (the frame is clearly too big for her). Can shorten the fork and could rebuild a (rear?) wheel as 26” for a mini mullet. I realise that her legs are already as long as some adults’ but I’m so puzzled about the reach/ETT for someone her height – if I had to guess I expect she’ll end up 5’7”+ so whatever size she’s going onto next is unlikely to fit her in her teens.

At that age my younger son was riding my wife’s old Orange Five Diva (one of the original numbered limited edition) and one of his friends is on it now.  My elder son didn’t grow into that bike until he was significantly older.

Just to add more confusion, younger son (now 11) is on the next size up of Orange Alpine (last of the 26ers) but the friend who has the Five Diva, though the same height, needs the smaller bike.

So if that made sense, what I’m saying is children are not only different heights at the same age, they’re different proportions.

You probably need to offer a bike up to the child and see if it fits or can be made to fit.  Heights and ages are definitely only a starting point.

Bike being too long seems was an issue for our youngest when moving onto the 24 inch wheel bike (a frog which tend to long top tube). I had to get an inline seat post to shorten the reach.
The kids do seem to grow legs first like beanpoles (or my two have). Eldest is now on a 26 inch wheel Squish which I think is a bit shorter than most adult bike. Fits him well at the minute (but probably won’t in 6 months at current rapid rate of increase!).
The wheel size depends totally on the design. We all rode 26 inch wheels a few years back. Some makes move up a wheel size in smaller frames. Squish do 2 sizes in 26 inch, others move up a wheel size on a smaller bike. It’s a total minefield.
Edit: I think the 24 inch Isla is smaller than some brands so that may change the moving up point.

My 9 year old has just moved up to a 26″ Hoy Bonally and his riding has definitely gone up a degree or two. Great bikes. Maybe fit a bigger front tyre for proper trails. My boy is just a bit taller that 1.4m

My 11 yr old is now on a S size Vitus 27.5 womens model and it’s definitely working out for her after coming off a 24inch wheel bike. I’d say get the largest wheels you can as the rollover really helps.  She’s about 145cm ish I think.

Thanks that’s really useful! Vitus looks great for the money, good geometry and decent parts.

I’ve done some measuring of the kids’ bikes as Islabike don’t share geometry figures. We have a 14”, 20” and 24” and the “downtubes” (actually BB to top centre of head tube – hypotenuse of reach and stack) are 400, 520 and 610mm respectively.

That Vitus in XS comes out as 698mm, in a small (sadly out of stock) is 714mm. My old Zero AM is 761mm. So that would make the sizing steps 120, 90, 88 and 63mm (14”-20”, -24”, -Vitus XS, -Zero AM) which feels pretty logical.

Vitus looks great for the money, good geometry and decent parts.

Very pleased with it.  Got it with 30% off so under £450, which when compared to other brands there was no competition.  Air forks so can set up for a lighter rider, hydro discs, 8 speed box gears seem fine, it’s not boat anchor heavy, even had a Nukeproof bar for style points.

It’s routed for a dropper too, so will add a Brand x when she’s tall enough (had to cut the seatpost down).

It’s 25% off at the moment so almost as good a deal. It’s looking to me that on the XS my eldest would be able to fit a 150mm dropper which I think would be a revelation for her.

Just get her sat on something about the right size … either in a shop or mates etc. and measure from there.

A quick and easy “what if I swapped 27.5 to 26?” is easily achieved by deflating the tyre.

My lanky kid was on a Bird Aeris (old model MK1.5) at 9 with 26″ wheels and within a year he went through mullet to full 27.5. 142mm cranks now he needs some 150mm or so … when I get round to finding some suitable donor cranks

He’s also gone from a 120mm-150mm-now “needing” 170mm dropper.

Just been through this with my lad this weekend
he’s 11, 65cm inseam, 145 tall.
took his 24″ Orbea MX out (rigid) and the beginner trail he tested was horrible for him the ruts made hte smaller wheel a bigger deal than they were

i spent some time was lookign at
Vitus Nucleaus 26 @430 with wiggle plus, but i didnt like the drivetrain, 40t top cog…
Vitus Nucleaus womans 27 (smaller standover) but hes a little too short on inside leg
Nukeproof cub scout 26, too aggressive for his all round riding, tyres would need to be swapped etc.. and the price
Ended up finding an Orbea Mx 27 XC 2021 model at Everdean Cycles with a good discount, which had a decent 10 speed deore drivetrain giving hi ma good bailout gear, and beign the Orbea it will be light and a good all round geometry. grabbed some ebay bargain Manitou’s and a set of DT Swiss XC wheels should shed almost another KG. Happier to get a 27.5 than a 26…

Seems to be quite difficult fitting up this age. Our 10 1/2 yr old is still on her 24″ orbea mx (139cm tall) but it looks small and she is also over the top of the min insertion on the kids dropper (only just bought that which is double annoying). Her club coach thinks the reach is too short however it is not that different to the 26″ MTBs (couple of cm). I do wonder how much of that is it being more a road/cx club and MTBs are short comparatively to the cx bikes. I don’t want to get her a cx bike yet as she has only just started the club and I think she would find the difficult on the rides she enjoys outside the club. The nukeproof cub scout frameset ticks lots of boxes but appears to be a boat anchor (we have nice 26″ hope/717 wheels and reba black box forks to use so looking frame only).

Just been through this and had to go extreme to make it worthwhile.
SturdyLad Jr just turned 11 and had outgrown his 24″ frog flat bar.
The perfect size replacement was a small men’s Trek Marlin 27.5 BUT…. Perfect for about 3 months at best. The frame was really quite small. By the time he come to ride it in anger next spring it would be too small. (Birthday was this month!!)

We ended up getting him a size M that come with 29″ wheels!
He’s not ridden it more than a test ride so far but the biggest concern is handlebar width.
I’m going to order a cheap set and cut them down until he’s a bit bigger.

He’s also a beanpole!!

I found my eldest outside our local shop on the way home and she had a go at riding my (large) Levo back up the hill – had to have the 185mm dropper down all the way to pedal but that was actually a good pedalling height for her. Did some measuring and that’s 560mm to the top of the saddle, 515mm to the rails.

Looks like she’d fit an XS Nucleus VRW with a 125mm dropper if my sums are correct! Will have to see if she can operate either of my droppers as they are.

My 9 year old, 1m36 tall, daughter has just moved onto a 13″ frame, 26″ wheel trek 4300. Bought the full bike with 3*8 gears and crappy forks from eBay for very cheap and then stripped it down to rebuild with nice but old 26″ bits (mx pro forks, Mavic/Shimano wheels) and 1*10 deore gears with 152mm cranks. No idea on the final cost, but she loves it and it’s significantly quicker rolling than her previous Kona hula.

Given that, I’d try to do something similar and then swap all the bits onto a 27.5 frame once she grows a bit more.

I looked hard at the xs nucleus vrw then discounted it. It looks to be smaller than the nucleus 26 (reach etc) so I think it’s a false economy. The small would be the choice if it was available. Have ordered the 26 now with a view to fit the lighter wheels and forks we already have. Will probably also swap the 1×10 from her existing bike as then the new one will also go on the turbo since she keeps asking to use it.

Geo numbers are all on geometry geeks btw.

Thanks, useful points!

Looking at the VRW XS vs the Youth 26, the latter has longer reach but shorter stack, so on the diagonal it’s a bit smaller.

had my nipper out riding around the car park a bit on his new orbea 27
hes at the minimal height for it really. but hes riding it more confidently than his 24 which he still sort of fits.. yet on the 27 he’s riding quicker and hes actually out of the seat more etc, and enthusiastic
it was £80 more than the the nucleaus, the spec is a little bit better in some ways worse in others..
full deore 10 speed 11/46 but on 170mm cranks
suntour coil fork with lockout (going straight on ebay, found a set of Manitou marvel/machete for £60) not that its the worse fork for his application, but he doesnt need the complexity of remote lockout (too many options) and the near extra KG over the manitou, plus its default on medium weight spring…
No dropper routing, might be able to go internal route and around bb, but at the moment his sea is probably way under a 100m of extension.
Surprisingly, it weights a lot more than i thought/hoped but i was weighing it on shonky scales subtracting my bodyweight (which can be half a kg different every time) at 14.5kg from factory
Wheels are weighty….
rear brake was routed through the LHS of the frame…
I was eager to get a 27.5 bike as ive got a shed load of tyres/wheels etc and is more future proof which put me off the nucleus 26

my 10yr old daughter is on an on-one jack flash framed 26er. (£50 for teh frame!!) seems to get on with it really well. been on it for a year or so now and if she keeps growing she`ll be on a bigger frame soon. she can get through the small pit jump line at WP. been to BPW and allsorts.

your nipper can have a go if you want to see and check sizing?

Looking at the VRW XS vs the Youth 26, the latter has longer reach but shorter stack, so on the diagonal it’s a bit smaller.

I make it bigger, i.e. longer with a slightly lower front so more stretched out position.(https://bikeinsights.com/compare?geometries=63525e01de2e56001d0f2c4b,62262a58d3ec5c001c9a184e,)

I did look at the jack flash having had one of those in the distant past. I remember it being heavy though and poor tyre clearance (as well a quite stiff).

That’s a useful overlay! I was just looking at things from a more DH perspective – BB to head tube top centre is the dimension that dominates sizing when you’re standing. Taller front ends make a bike feel bigger when your standing but smaller when you’re sitting.

Ah got you now.

Yes its a rather cool and useful.

“your nipper can have a go if you want to see and check sizing?”

Thanks Mark, I’ll catch up with you when she’s a bit less rusty – having three children, one much smaller than the others, rather scuppered this summer’s riding plans but I’m on a mission to correct that!

@razorrazoo – how’s your daughter getting on with her bike? And if you don’t mind checking, exactly how tall and inside leg length is she?

Just measured my eldest at 144cm tall (which would put her on the XS) with 67cm inside leg (which would put her on the Small). Don’t want her to grow out of the new bike too fast – but she does have younger siblings to pass it onto.

Bit late to this but voddoo nzumbi is a great 26 kids bike, come set up 1×9 already, discs, OK forks & wheels, decent weight too.