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Decent rear shock for kid's DH bike????

freshwire

freshwire

Monkey
May 24, 2007
105
0
Roanoke Virginia
Tried this in "The Shop" but no joy...so here goes

My 10 yo son's bike is an '04 Spec. Bighit Grom...nice bike...but stock set up is for an adult rider???
Rear shock has 400lb spring???? WTF??? on a 24" kids bike???
anyway...it's got an i to i of 7.75 which is standard...but can't find a light enough spring for it to give him the correct (any) sag...he is small...maybe 75-80lbs with gear...an air shock was suggested..but which one???...don't know much about them and don't want to spend a ton...any suggestions would be greatly appreciated.

Thanks in advance for your help!
 
bullcrew

bullcrew

3 Dude Approved
Dec 8, 2004
9,334
3,068
I'm dude playing dude pretending to b another dude
I did a air shock on my kids grom a few years ago... Worked great I could set it and as he grew it got aired up a bit...

Call Jerry at hippietech.com he has some SMOKIN deals on rockshox air shocks (NEW / bought a pallet of stuff last year closeout)) and hes a hell of a tuner to boot...
 
freshwire

freshwire

Monkey
May 24, 2007
105
0
Roanoke Virginia
Thanks for the info. I'll check them out...what fork is on your kid's grom??? This one is an MZ Comp. Just like the rear shock...it was stiff he could barely compress it. I took one of the springs out of one of the stanchions and it's way softer...but the rear shock it out of balance with it.

I don't have a lot of $$$ to burn right now....are the rockshox very expensive???

THanks!
 
doc gravity

doc gravity

Monkey
Oct 25, 2004
152
0
highlands ranch, CO
May not fit with the budget, but....
We used an RP23 for a little one. He rode it all the way from 58 through 80 lbs before we went to a coil rear (found a used fox spring, listed as 250#, measured out at 225#).
Front was a cut down float (125 worked out well to match what the rear of the bike was doing). We were able to reduce the air on both ends of the bike to compensate for a lack of body weight. Not that familiar with other manufacturer's air products, but I assume this could be done with many combinations of products. Have fun!
 
weedkilla

weedkilla

Monkey
Jul 6, 2008
362
10
My son is on the same bike and he weighs about 80lbs, he has an old Fox Vannila RC with a 300lb spring (5th element) and about 25% sag. The low levels of compression damping on these shocks suits smaller riders. However he has a 7.5" shock - I thought that was standard. With a 36 talas, set for 20% sag (overkill but it was what I had when he broke the Manitou black I had fitted on there originally) on the front set at 130mm it has a 12.5" BB and a 66degree HA - seems to work out well. The only problem I have with the bike is the incredibly long head tube for the size, just cant get the bars low enough.
Our club has a strong under 13's class and his bike is clearly more balanced through the rough than any of the other kids bikes - all I did was use the same rules as setting up an adults bike. Set the sag, as close to 30% on the rear as you can get and a little less on the front.
One of his friends has a Kona howler that I used an air shock on to get a low enough spring rate. I used a swinger 3 way but the damping was way over the top so I am swapping the oil to 2.5wt to get the rebound fast enough and the compression light enough. I would suggest a swinger or monarch if you go air as the rebuilds are easy and there are well documented rebuild instructions available. I always use 2nd hand stuff on kids bikes as you are probably going to rebuild it anyway to get the damping right so I cant see the sense in paying for new.
The other key I have found is using 165mm cranks as any thing else is just too long. You can clearly see kids hips going up and down as they pedal when you use anything longer.
 
S

slowitdown

Monkey
Mar 30, 2009
553
0
weedkilla said:
The other key I have found is using 165mm cranks as any thing else is just too long. You can clearly see kids hips going up and down as they pedal when you use anything longer.
Click to expand...
Huh?

Hip rocker is a function of saddle height. Not crankarm length.
 
E

ebarker9

Monkey
Oct 2, 2007
879
258
slowitdown said:
Huh?

Hip rocker is a function of saddle height. Not crankarm length.
Click to expand...
For an 80lb 10 year old the crankarm length is a much greater proportion of their leg length/height...I can definitely see this causing their hips to rock. Imagine pedaling with 250mm cranks. Pretty awkward.
 
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