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Discussion Starter · #1 ·
Hi

I am building a DH bike for my 7 year old and helping my brother-in-law set up his sons hard tail. I was wondering if anyone could suggest a shim stack and oil weight to start with for each bike.

( I have emailed shockcraft.nz.co and manitou and ask the same questions but being Easter I have not heard anything back from them yet) just wondering if any one on here has experience to share about setting up ether fork for very different duty's then they were ever intended.






The first bike is a big hit grom I found a manitou R7 xc fork for it and a dnm shock both air springs. While looking for the fork I stumbled apon shockcraft.nz.co and their mini shim kits (and the manitou shim tuning guild). Previous to that I had never seen shims for sale anywhere and had not realized how easily tune able a manitou fork could be. I was also unaware that manitou made a kid specific fork but I had already bought the R7 by the time I found the JUnit, however the price tag would have scared me away eather way. I had put a fast yari-up on my sight and spent a few days setting it up and it completely changed my bike. So realizing I may be able to do something similar for the kids bikes has pecked my interest.


My son has a 24 hotrock as his trail bike so this bike will not be being pedaled any great distance. He weighs 21.4 Kg fully kitted.


I was planing on putting 2.5 wt oil in and using the lightest linear shim stack in the pdf (CV-11411-08).But if anyone on here has done something similar tare able to suggest a better starting point I am open to suggestions (might save me a lot of false starts). Also I have read that the R7 will lose some travel at the sort of low pressures he will be running. As long as it its not too much I am not to concerned. But I did see shock craft had negative springs for the R7 if the travel does prove to be a problem would changing to a lighter a spring help.


My Nephew is 10 but weights around 65 kg fully kitted his bike is a norco Sasquatch with a manitou expert circus 130mm. After finding shockcraft.nz.co I had a good look around and ordered a soft springs to fit his fork.


I was planing on changing the spring but leaving the oil as standard wt and using one of the trail shim stacks but I am honestly lost as to which one. I was thinking CV-11811-07 as it will give a large variation in fork feel based on the ABS + setting. Which may be helpful to give him a distinct difference in feel on each settings to allow help him find a setting he prefers.


Thanks Kyle




 

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Just replied to your email, but I'll post the key points here.

The issues I expect you'll have with the R7 with such a light rider is getting full extension with the coil negative and getting too much unwanted damping from the rebound piston in bypass.

The CV-114844-08 linear tune is your starting point. I'd go straight to corex 5 oil to minimise the unwanted compression damping from the rebound piston and to put the rebound range closer to where you need it. We have slightly lighter R7 negative coil springs here: https://www.shockcraft.co.nz/r7-negative-spring-steel-80-mm-manitou.html

The circus we are out of stock soft springs, may have something else we can dredge up from new-old-stock. If the inside of the stanchion isn't scratched then they can be converted to an air fork. Which helps a lot with lighter riders. The soft coil isn't that soft.

I'd also start that rider with the same CV-114844-08 tune and see how it goes. If he wants more damping with LSC fully closed then to go to the next firmest linear tune and repeat until he's good.
 

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There is no change in oil spec in the j-unit forks. Maxima 5wt (85/150) is stock

Stacks are lighter, I would suggest going with a linear stack or light trail stack from the abs+ guide.

The biggest issue with light riders is the spring. J-UNIT forks use a negative air spring. The R7 use a negative coil spring and a top out coil spring that will be too stiff for a kid. It still works but is not optimal

Circus forks are coil spring or coil with air assist (expert with act air). So in the case of the circus, you will need a lighter coil spring to get the spring rate correct. You may have a hard time finding one if it's a circus expert, circus forks are the only fork in recent years running the act air system and they run a stiffer spring on purpose because of the intended purpose (dirt jumping)
 

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Discussion Starter · #8 ·
Hi
I have a soft spring on the way for the circus. And a soft spring and some lighter oil for the r7 both from shockcraft. I am going to try the lightest linear stack in both. Thank you all for the advice hopefully will be able to take them out for a spin in the next 2 weeks. Then I will report back
 

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Hi
I have a soft spring on the way for the circus. And a soft spring and some lighter oil for the r7 both from shockcraft. I am going to try the lightest linear stack in both. Thank you all for the advice hopefully will be able to take them out for a spin in the next 2 weeks. Then I will report back
Sounds good. The rebound piston is slightly different on the J-UNIT forks, but you should be able to tune it and get it working better with a few shim changes. Mainly running a 14x.2 gap shim to allow for more oil flow.

For what it's worth (not much at the moment), there will likely be tuning kit in the future to convert older 30 and 32mm forks to the J-UNIT spec, including new pistons, in the future. Not for a while though.
 

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Discussion Starter · #11 ·
Hi all

I went with the lightest stack (CV-11411-08), the Corex 5 oil and the lightest negative spring.

First ride down. We shuttled 2 of the tracks at Atherton MTB Park (just out of cairns Australia). The first one we did was a trail bike track (13), rocky with some technical off camber sections which undulate and were a bit hard for him to keep enough speed to get up the other side. The down sections he seemed to find easy I had to keep telling him to stop doing wall rides as they were on the rock walls beside the track and we had no idea what the end of them was like. He was confidingly hucking off little drops (1 foot or 2) with in 5 minutes of being on the bike. The second half of the track involved some pedaling so we decided to head over the other side and stick to the Dh only track.

The next track we did is a blue down hill track a lot rougher and more tenical but no off camber and no ups. his 9 year old sister hopped on his bike to give him a break I put a bit more air in the fork (it looked like he was using it all) and she loved it too. I am now on the look out for a another 24 inch dh/full suspension bike. Between them they did 8 runs. I had to remind them both to slow down repeatedly which is good they felt so confidant so quickly. Was kind of funny seeing Violet getting loose and sliding in turns while yelling at her 12 year old sister ahead of her on a demo to ''hurry up''.

Leto says the bike is better in every-way then he expected.

My nephew still has not pick up his bike but I think he will love it too. I put the same stack in but did not change the oil and a 120 mm soft drake spring. I had to get a bit inventive as I did not have enough spaces to fit but I think my solution will not cause any problems.

I will leave the set up like that for now and maybe get out a camera and get some slow-mo footage from the side to see what its doing they cant tell me anything but that its good.

Thanks for the advice Tire Wheel Vehicle Land vehicle Soil
 

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Given the price and the ease of tuning, the R7 seems like a decent option for kids.
I have a 22kg 7yo on one and it seems to work pretty well. It has something close to the CV-11711-01 compression stack (lightest trail stack) and a reduced stiffness rebound stack. The standard rebound stack has 5 equal sized shims, I reduced this to 3 and it is just fast enough, could probably go down to 2 rebound shims but haven't bothered to do it as yet.
The coil negative spring is too stiff to allow full extension (at ~35-40psi, 80mm travel setting) but given the geometry of the 24" bike, the HA actually ends up looking pretty good when it tops out at about 70mm.
Given how fast it is to disassemble for tuning it will be easy to make changes as they grow also.
 

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Just replied to your email, but I'll post the key points here.

The issues I expect you'll have with the R7 with such a light rider is getting full extension with the coil negative and getting too much unwanted damping from the rebound piston in bypass.

The CV-114844-08 linear tune is your starting point. I'd go straight to corex 5 oil to minimise the unwanted compression damping from the rebound piston and to put the rebound range closer to where you need it. We have slightly lighter R7 negative coil springs here: https://www.shockcraft.co.nz/r7-negative-spring-steel-80-mm-manitou.html

The circus we are out of stock soft springs, may have something else we can dredge up from new-old-stock. If the inside of the stanchion isn't scratched then they can be converted to an air fork. Which helps a lot with lighter riders. The soft coil isn't that soft.

I'd also start that rider with the same CV-114844-08 tune and see how it goes. If he wants more damping with LSC fully closed then to go to the next firmest linear tune and repeat until he's good.
How do you convert an expert to air?
 

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How do you convert an expert to air?
Take the spring and spring compression rod out, install TS or ISO compression rod and appropriate piston.

It all depends on the condition of the inside of the stanchion. If it's scratched from the coil spring then it's a no-go. But that's not that common as the air piston sits a lot higher inside than the moving end of the spring.
 
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