MTB frame sizing & geometry for a 12 year old

My 12 year old son has out grown his 24” cannondale.

We’ve discovered we both like Bike Park Wales blues 🙂

He’s currently 148cm (i’m 173cm & the Mrs is 152cm so he ain’t gonna be huge).

I’m looking at a Whyte 403 (26”/100mm) or a Commencal Meta HT Junior (27.5”120mm).

He’s already at the upper limit of Whytes recommended 125cm-152cm height range.

The Commencal height range is 140cm-160cm, so he’s bang in the middle.

But, looking at the geometry:

WHYTE: Reach = 383mm, ETT = 540mm, Stack = 539mm, Stand Over = 706mm
COMMENCAL: Reach = 366mm, ETT = 545mm, Stack = 584mm, Stand Over = 615mm(?)

So, the smaller Whyte is longer and lower & the Commencal is shorter & higher.

Does this make a mockery of the height guides? And will the Whyte actually “fit” him for more years than the Commencal.

I know the answer is “go and test ride” – but this is a paperwork exercise at present.

Any input appreciated (i’ve no idea how tall the post man was).

Is he at the age where you’d be better served buying ‘the one he likes best’, than worrying about geometry (assuming neither choice is particularly terrible?

Hi, IHN. I don’t want to buy one that will only last 1 year before he out grows it. They’re not cheap. Although the kit on the Commencal could all swap over to an “adult” frame better than the Whyte.

BuMp

Any other input?

I’m currently thinking the small bike is bigger.

Ask him which he prefers.

FWIW I’m 10cm taller than you and only happy on mountain bikes with 26″ and a short reach by todays standards (400mm to 425mm). I like all my bikes to ride like little dirtjumepers though. haven’t owned longer than a 55mm stem in over 20 years and back then it was only because I didn’t know any better.

sorry. my point is. depending on how his riding comes along. He may never outgrow the 26″ Whyte

The commencal seems very very (like far too) short for a 27.5″ wheeled bicycle. got a link to the full bike geometry?

got a link to the full bike geometry?

its the “junior” size

https://www.commencal-store.co.uk/meta-ht-junior-shiny-red-2018-c2x22592130

&

https://www.whyte.bike/403

Its only 17mm difference in the reach.

Yeah. They shouldn’t make 27.5″ wheeled “junior” bikes

actually… Commencal should probably just give up making bikes completely.

Its a bit of a void in the market place, most of the kids bikes go up to 24″ and then you get to adult sizes. He’s an inbetweener at present. On paper the Whyte is bigger, but both companies gumpf points him to the Commencal by height. A local shop have the Whyte in so we’ll go & have a look.

his height points him to 26″ wheel though.
surprised the “industry” haven’t marketed this new junior wheelsize… yet. 😉

What about a good, second hand, small 26″? There must be some bargains out there.

I think my 11 year old son has had a new bike every year as he keeps outgrowing them.
I recently bought a bargain Canyon Spectral in a Medium off my mate thinking I will keep that until he grows into it, turns out its a perfect size for him.

I am about to put his old bike up for sale, its a small Sunn Charger, Fox Float, Lyrik etc. which was perfect for uplift days.

Should have said he is currently 165cm, but was probably about the height of your son when he first started riding it.

I know theres lots of options, secondhand, etc.

Another is to build one, maybe put 26″ wheels in a 650b frame…

Involve the lad.

Then if it’s all wrong…

*shrugs*

😉

Another is to build one, maybe put 26″ wheels in a 650b frame…

Seems a good idea to me!

If you go with a small 27.5 hardtail frame and fork, shortest stem possible, fairly narrow bars, 26″ wheels and the shortest cranks you can find, then you can gradually upsize it with bigger rims, longer stem and cranks, wider bars. You’ve still only got 1-2 sizes of leeway before a bigger bike is required though.

I don’t generally trust sizing recommendations or standover numbers (the lowest ones tend to be measured just in front of the seat post – where you can’t stand because the saddle is in the way!)

My son is 11 and also 148cm. he is now riding a small framed Orbea mx27.5 with short stem and seat dropped down. He gets on great with it and his riding has came on leaps and bounds since going onto the bigger bike. We didn’t look at any charts or frame geo we just went to LBS and tried out a few bikes and took the advice of shop.

Small second hand 26″ would be my choice – because then grow so damn quick….

Our 12 year old is now on Specialized FSR 16″ frame / 26″ wheels – moving up from Specialized Hardrock HT 13.5″ / 26″ wheels.

(Edit: he is 155cm at moment, moved up at 150cm.)