We bought two complete, and added a couple of new bits. They are ace. Geometry is king, next to weight.
If you build, I think it is hard to find short cranks or light wheels etc. It will be costly.
We buy second hand.
Kona was £120, is heavier, but great geometry for the kids when they first get on – low bb and high bars.

What light evenings are for… by matt_outandabout, on Flickr

The Scott was £80, and is much lighter. The brakes were crap, so I put new ones on. Better geometry now they are taller – and the kids prefer this bike as it is noticeably faster.

Comrie Croft pump jump track by matt_outandabout, on Flickr

My lads just on the cusp of outgrowing his 20″ Islabike.
I’ve been putting him a 12″ framed, 26″ wheel Hotrock together. Awful Suntour fork is going in the bin, in lieu of an Exotic rigid I picked up. Gears down to a 1×9 set-up. Have picked up some Deore disc hubs so I can rebuild the wheels, & put some old Jucy’s on. To be honest it’s more a future project. I did look at building some 24″ rims on it as a stop gap, but it’s a frame that’s still too big for him for at least a year.

So I’ve just picked him up a 24″ Hotrock last week. Again the awful Suntour fork will go in the bin. Few other upgrades, 1×9 gears etc. That will shed a couple of pounds. The 26″ wheeled one can wait a while for him. He’s got a younger brother who’s just grown into his Islabike. 🙂

Probably a 420mm Exotic again.
They do a 24″ wheel version, but I think a 420mm rigid should be ok, given the 25mm drop from the wheel radius.

9spd depends on what’s on it…
I think 6 & 7spd are same width, but 8,9 & 10 are wider.
I’ll just lace a new hub on if needed, need to check the dropout width first.

Our eldest boy went from beinn 20 large to beinn 26 small. He now also has a 13 inch trek 4300 (he is 10). His wee bro is still on the beinn 20 and age 6, but only about 3cm seatpost available, so big fights coming soon !

Dezb…changing the forks was more to get some weight off it, rather than some that worked better.

My daughter has grown out of her 24″ Hotrock Full suspension so it’s up for grabs. Have got the original seat as I swapped it for a ladies one for her. Great condition apart from the seals on the forks are cracked, but can be replaced, forks and rear shock all work very well, condition is very good, but has some signs of use. Available to see/collect in Leeds or can drop in Sheffield, Darlington, central Machester. Mail me if of any interest, looking for £250

Yet another one for sale.

Hope brakes, XT shifters, mech and cassette, disc specific wheels, shortened 150mm Raceface cranks, shotened Sid air forks.

Another bike for sale here –

2011 Giant XTC JR 1 24″ – decent condition, odd scuff but generally very clean, newish tyres £120

Same as this one http://www.giant-bicycles.com/en-gb/bikes/model/xtc.jr.1.24/7903/45583/

Out of interst how tall are your kids that are going from 20″ upto the 13″ Treks etc

It’s used but is in good nick. Email me and I’ll send pics. It’s no where near the bling tastic one above but then it is only eighty quid. If it doesn’t sell I’ll save it for the grand kids….

sorry for the cross thread, cheers for the opinion ianv

@citizen kane I’m interested in that Trek if it’s still for sale? My son’s 24″ Hotrock FSR has given up the ghost. Can you email me at matt at studiolift dot com with an idea of price and location?

Should get around to putting the Exotics on my lads 24″ Hotrock this weekend, so will post up some pics. Decent lightweight 24″ Rims are an issue because the only thing availabe are heavy dirt jumping types.