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Discussion Starter · #1 · (Edited)
I found a relatively simple way of increasing the 40mm travel on the SR Suntour fork. The SR fork is a very simple spring only fork. Of the two legs, the left leg is an empty tube and the right leg has the spring and preload adjuster. Remove the pre load adjuster on the right leg (do nothing with the left as it is not bolted in any way). You may need to use pliers/channel locks to unscrew the adjuster. Once you unscrew the preload adjuster push your fork legs up to present the spring. Remove the spring.



Next remove the 10mm nut on the bottom of the fork leg. The fork legs can now be removed. You will notice that there is a ~1.5" rubber piece on the bottom of the fork. The distance from the top of the rubber bumper to the bottom of the stanchion is what determines the amount of travel.



Use your fingers to unscrew the nut below the rubber piece and remove the rubber bumper.



You can cut the rubber bumper down but I wanted to make sure I wasn't over looking something so I simply made an make shift bumper out of a old rubber hoses and plugs that I had laying around. I made the new bumper about 20mm smaller so the fork should now have around 60mm of travel. Here is a pic of the rubber bumper I made. It's specifically stepped to function progressively (me overthinking).



Notice the new distance from the top of the new rubber bumper to the bottom of the stanchion. This is the new amount of travel



Reverse assemble the fork and have your kid enjoy the new travel.

A couple of observations;
1. The air pressure starts to play more into the ability to compress the fork with the added travel. I'll probably drill air holes in the bottom of the fork to allow it to compress easier.
2. Depending on the outcome of observation 1, I may look for a lighter spring. The current spring is around 60 lbs/in. I may look for a lighter 40 lbs/in. spring.

Hope this helps anyone who likes to tinker. The conversion is very simple and takes about 20 minutes.
 

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Wēk Sôs
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Looking into this as well. There's no nut at the bottom of the fork leg, just some exposed thread. I tried hitting on it with a hammer, while pulling down on the fork legs, it's not budging. I'm stuck there for now.

I noticed the white spacer/reducer on the spring is up in your picture. Mine was down at the bottom. I'm not sure if it's supposed to sit on anything.
 

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Very interesting! The Hot Rock 20 of my son also has a Suntour fork that matches the description. I will have a look into this. Looking at the weight of my son, he will certainly benefit from a less stiff spring, so I am curious if anybody has already tried that.

Kind regards,

Clemens
 

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Wēk Sôs
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Just following up on this, my daughter's fork was a 6mm bolt through. That is there is no nut at the bottom, but you need a 6mm socket with a long extension or a long 6mm hex handle. Unscrew it from inside the stanchion where the spring sits. The bolt, goes through the bottom of the fork sleeve, there is no nut. The sleeve is threaded.

The white part also goes down at the bottom and not the top. It sits on the bolt head, and gives it some relieve instead of metal to metal contact.

I haven't found a lighter spring, but haven't looked. The daughter hasn't ridden it yet, but she can get down to the bump stops before the mod. I'll see where it goes now.

I cut off about 30mm. I can always restack the rubber spacer after the cut to get back to original height or cut off another section if I need see contact.
 

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Clipless pedals? Wow. The fork on my sons trek mt60 is a suntour but has stanchion boots and when I lift them up I just see spring no sliders or stanchions. It's a couple years old.
 

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Wēk Sôs
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lol, i never noticed the clipless. Where do you get shoes that small?

You don't lift the stanchion boots, you remove the rightmost top cap (imagine sitting on the bike, the stanchion on the right). Removing the cap allows removal of the spring. From there, you either remove the bolt inside the fork, or the nut at the bottom of the fork.
 

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Hello All,
SR Suntour does have lighter springs available depending on the fork model. Feel free to contact us and we can verify if we do or not.

Just to let the DIY'er and others know that the rebound rubber that has been tampered with here helps control the top out and rebounding effects of the fork. Also I would not recommend drilling any additional holes into the lower casting.

Best,
Nick
 

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Wēk Sôs
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Do you sell rebound rubbers to allow for more travel? The website lists 63 (50) (30), is that for 26" fork, 24" fork, and 20 inch fork? Or are those numbers indicating travel options regardless of fork size? I think I'm around 30mm.
 

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Hello,
You are correct.The travel is limited to the size of the fork for this series of bicycle so the 26" has 63mm, 24"-50mm and 20" 30mm.

If you would like to replace the rebound rubber that you cut feel free to give us a call.

Cheers,
Nick
 

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lol, i never noticed the clipless. Where do you get shoes that small?

You don't lift the stanchion boots, you remove the rightmost top cap (imagine sitting on the bike, the stanchion on the right). Removing the cap allows removal of the spring. From there, you either remove the bolt inside the fork, or the nut at the bottom of the fork.
I think the fork on my son's bike is different. It's a black Trek MT60. To the guy from Suntour, can I get softer springs for this fork, too? It does not have stanchions like a regular fork. When I lift the boots, the springs are right there with some damper inside. Like a coilover shock on a car.

This is the bike, I just found this image on the web, but it's the same model

 

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Hello All,
SR Suntour does have lighter springs available depending on the fork model. Feel free to contact us and we can verify if we do or not.

Just to let the DIY'er and others know that the rebound rubber that has been tampered with here helps control the top out and rebounding effects of the fork. Also I would not recommend drilling any additional holes into the lower casting.

Best,
Nick
Can you give us a rundown on the differences between the XCT and XCR 24" model forks? It seems most 24" bikes come with the XCT which is extremely stiff and heavy (I have a hard time compressing the one on my sons Specialized Hotrock A1 FS).

Is the new 2012 XCR LO Air a lighter higher performance shock? And where can it be purchased?

I know alot of these bikes may be used on road and the suspension seams to be more of a novelty item, but some of us actually take our kids off road and would like the benefit of a higher quality, lighter suspension fork. Thanks for your help.
 

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The XCT model fork will use a steel steerer. crown and stanchions in a 28mm platform. In most cases it has a single coil and aluminum lower castings. We do offer it aftermarket with a mechanical lock out.

The XCR model fork will use a steel steerer, crown and high polish stanchions in a 28mm platform. The crown does have a larger stance to it by 10mm giving the rider more stability. It has a single coil spring and Magnesium lower castings giving it a lighter weight.

Cost between these forks is only $20 retail but the XCR is a much higher level performing fork do to the quality of parts used in manufacturing and overall tolerances.

As for the XCR with Air, that fork is going to be available at the first of the year. It will have a aluminum upper assembly ( steerer, crown, stanchions). It will utilize an air cartridge similar to the Raidon series and have a hydraulic lock out. This is no doubt the best fork we make in the 24" catergory and I believe has a target weight of 4lbs.

Hope some of this is helpful.
Nick
 

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Discussion Starter · #16 ·
lol, i never noticed the clipless. Where do you get shoes that small?
Not to derail my own thread but you can buy clipless shoes from Fly or THE (Toby Henderson Enterprises). The smallest size they make is a 13. My son started using clipless just before turning 5. I told him he could use them once he turned intermediate in BMX racing. It was movtivational because he continued to win his next 3 races to bump him up.

Nick @ SR - Thank you for making yourself available on these forums. A support that is rare to find and always welcome. I've sent you a PM offline. Thanks.
 

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Discussion Starter · #17 · (Edited)
Thought I would update everyone on my quick fix from the first post. I'm still looking for a legit air/oil solution. The only 2 air/oil solutions somewhat available right now are a $720 White Brothers or a $200ish Spinner Air (if Demo9 can make it happen). In the mean time, I'm stuck trying to make this Suntour XCT for work.

In my original post, I thought removing the bottom bumper provided an extra 20mm of travel. It doesn't. Removing the bottom bumper only gives you an additional 10mm of travel. So it increases travel from 40mm to 50mm.

There's an additional 3/4" piece of rubber on the top of the guide rod which I didn't originally take out and review. The purpose of the rubber is to prevent the fork from topping out and making a metal on metal "clack". I removed 5/8" of the rubber and it gave me the full amount in additional travel. The fork crown to axle is now 15mm taller but with the upside of more travel. I also verified that the plastic stanchion guides still operated well and they did.

Now the issue is the stiffer than stiff spring. With my full body weight of 160lbs, I was able to compress the stock spring 1.25". Basic calculating, it would take 256lbs static weight to compress the fork 2" or 336lbs to compress to 2.6" of travel! Far too much for a 6 or 7 year old kid to be able to use the full travel. Maybe there are some superhuman kids out there.

I than realized my wife's old '01 Stumpjumper had a Rockshox Judy SL coil fork. I unscrewed the non-damped leg and what do you know, a coil that looks like it will work as a perfect replacement. The new coil was slightly longer but a whole softer. With the new coil, my full weight compresses the shock all the way down the 2.6" of travel. I would estimate that 140ish pounds could go through the complete travel. A much more realistic load if you ask me. My son rode the bike and noticed the additional compliance instantly.

If other's would like to look into this modification, ebay has spring kits available for the Rockshox Judy SL. There are multiple versions out there so be cognizant of which one you buy. I can provide more specifics if necessary. The one that I put in was the standard red spring. I also used the spring spacer on the bottom from the Judy fork. Surprisingly, the static sag with my son is the same with the old and new spring. I still have the preload adjuster fully open so if needed I can add more preload to the spring. We'll go for a ride this weekend and see how it performs. I'm sure he will be much happier. The next thing to overcome is the stiction on the fork tubes. Don't think I will be able to fix that one but I'll try.

The bottom spring is the stock spring and the top spring is the Judy SL. The rubber piece at the right is the piece that I cut down to extend the travel.


Here's my wife's bike (read donor of the spring)


Close up of the Judy SL


After picture showing with increased travel and higher crown to axle height.


Picture of the coil in the fork.
 

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Discussion Starter · #18 ·
UPDATE: Went for a 7 mile ride this past weekend and the new spring worked awesome for his weight. I could actually see the fork working over the rough stuff. It was nice to see. Unfortunately the fork still has a lot of stichion and small bump sensitivity is non-existent. I used Manitou fork seal grease on the plastic guides but the viscosity is too thin and wipes away too quickly. I'm looking for recommendations on thicker grease that can work with plastic to metal interfaces. Any recommendations would be appreciated.
 

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Wēk Sôs
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I'm not sure what Manitou fork seal grease is made of or it's viscosity, but you can try dielectric grease from the auto parts stores. It's 100% silicon. You can also try "Superlube". I've only used that on cars and re-packing bearings though. Superlube is thicker than dielectric grease.

Congrats on getting the fork to work well.
 

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Discussion Starter · #20 ·
Here's a quick video showing the action of the fork. I replaced the Manitou Prep M grease with a Silkolene Pro RG2 grease. It's a lithium based, NLGI 2 rated grease. The action is smoother than previous but I'll have to see how it performs after a ride. Since the fork is so simple to take apart (held together with 1 bolt), I don't mind cleaning and re-lubing after the ride.

Testing Front Suspension - YouTube

And I know, I forgot to put his helmet on for the video...

I'll have to take another video of him doing a rough downhill section for a better look. The spring rate seems to be ideal for his weight. I still can add preload to the spring if needed.
 
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