Scott Scale RC Jr w/ mods and weights
I bought my son a Scott Scale RC Jr for his 9th birthday. He still fits his 20" well but will soon be too big for it (52" @ 61lbs).
The Scott is nice out of the box, but there were a few things I wanted to do to make it more kid and height friendly, such as, convert to 1X setup and change cranks lengths.
Some initial thoughts on the RC Jr;
Frame - The weight with headset (~100g), and seat clamp (~15g) came in at 1504g or 3.31 pounds which is heavy. They could have easily made it less than 3 pounds. There's a super thick and large kick stand plate right behind the bottom bracket. Why?
Fork - Finally an air fork! Unfortunately, it's heavy at 1839g or 4 pounds. It does come with an aluminum steer tube and magnesium lowers but the thing is still a tank. The travel is limited to about 50mm because of the strong negative springs. I've varied the air pressure from 50-100psi but there's not much difference. The air chamber in the damping/air spring unit is just too small for any significant change.
I've already dissected the whole fork. Removing the negative springs will allow the fork to have 80mm of travel but removes all small bump compliance. There's a whole lot of stiction without the negative springs.
I'll let him try it for a few rides and see what's more important; a cush ride or more travel. I think more travel will prevail. In the end, I'll probably reduce the negative spring which is comprised of 2 stacked coil springs (heavy and light) and increase the travel to 75mm with an added top out bumper.
Syncros Components - Scott bought Syncros which is why you now see them on the bike. The parts are ok but not the lightest options. Probably part of the 2 pound increase over the previous year RC Jr. The other weight increase was probably because of the fork. The Syncros handlebars weighed in at 290g! That's insane for a kids bar. I swapped it out for a Truvative T30 @ 162g cut to 560mm.
Drive Train - I liked the Shimano hardware. Looks like they put some thought into which components should go where. The 3X cranks are too long. I understand why they did it. No one makes a 3X crankset less than 165mm though I would think at the volume they are buying at, someone would redrill/tap new holes. It would have been cool if they would have removed the 44T and spec'd a bash ring. Also, the two inner chainrings are steel.
Wheelset - The pair came in at 1632g w/ rim liners. Not bad though about the same as a standard 26" wheelset. Also, the tires are not Kevlar as spec'd on their page. They came in at 548g a piece. Not bad though will probably change to Kenda SB8's @ 425g.
Brakes - Fairly standard brakes. Not as smooth as an Avid 7 or XT but that may be the brake liners which are Jagwire. I thought the Jagwire brand was supposed to be decent but I may change them to get smoother action. I also removed the lever return springs but that didn't help with the action.
Drivetrain - Converted to a 1x10. I could have used the stock stuff but I wanted a 36T cog. I could have achieved this 3 different ways;
1. Bought the HG61 12-36 but it's a boat anchor @ 424g.
2. Bought the HG61, remove the 36T cog and mate it with the stock XT cassette and remove the 11T inner cog.
3. Buy a 10spd drive train.
I ended up going with the 10spd because the cost differential was only the rear derailleur @ $60 and chain @ $31. It alleviates me from the boat anchor HG61 or home brewing an 9spd XT 36T hybrid.
Crankset - Too long and too heavy. Swapped out for a simple Sinz single 34T. I had a spare Ti bottom bracket so I threw that in the mix too.
Weighty stuff - I swapped out the handlebars because of weight but that's about it.
Enough with the banter already, here are pics and weights.
Stock RC Jr. bike
After changes with 1X setup.
New gear ratio's. Highlighted is the 34T. I toyed around with getting a 104bcd crank and getting a 30T front but didn't want to drop any more dough.
Last edited by stom_m3; 10-21-2013 at 08:36 AM.
Great thread! Thanks for all your work on this one. Your kid will love it.
Great start. Lighter tubeless tires and a lighter fork and you should be able to hit 20 pounds.
I am curious to figure out if there are any available kids 24" frames that weigh less than 3 pounds. Should be entirely possible for a lightweight custom high end 24" frame to weigh closer to 2 pounds, just curious to know what lightest production frame currently is.....
Thanks for detailing the weights out. My son has the Scale Jr (non RC) and bar/stem/post/tire swap dropped 2 pounds. What are these RC JR models going for new now? Curious what $ total do you have into it with the mods? Check out Rocket Rons. 465 grams and way better grip than Small Block 8's. Well worth the extra weight in my experience.
Great job with the excel sheet, I like seeing the differences, Now I want to make one.
It would be interesting to know the weight of the non-RC frame if you ever have the bike stripped down.
Originally Posted by GSJ1973
As for the costing, a new RC Jr retails for $1050. I was able to negotiate 15% off as I've bought other bikes from this store. The extra parts added to $410. I know some people would balk at the price but I have the means and if it allows me to be able to enjoy spending time with my family, it's worth it.
In the end, this is what it's all about. Picture of me and my boy (6 at the time) riding his Marin Hidden Canyon 20".
Also, I'll check out the Rocket Ron's. The SB8's work well for the SoCal dusty hardpack. What terrain do you use your RR's?
Last edited by stom_m3; 10-21-2013 at 11:14 AM.
We are in the Denver metro area so the trails are not too different than SoCal. Lots of loose rock here and small rock over hard pack. SB8's were the scariest tires I've ever ridden so I knew my son would lose skin knowing how he rides.
I've never gotten it to the point of stripping it all the way down, but I can tell you the standard Jr. of my year doesn't have the rear dropout design nor a replaceable hanger like your bike does.
I've found the RST forks have a great deal of stiction when new. My son couldn't get any movement out of the forks on his first few rides even with hardly any air in it. Now that he's a little heavier and the seals are broken in a bit, he bottoms out the fork. So I've had air him up.
try driving your car less
Cool write up. Well done.
Let us know if the fork breaks in and rides well. My son has a specialized with a RST Capa T4 24 fork and it basically does not move. I have been looking around for an air fork and found some through this site, but I am first going to try a 26 fork...
Only boring people get bored.
Very nice. Scott did a good job with the new style paint job/logo's.
Shame they are adding so much weight to the bike. That Syncros stuff should be hanging off the side of the Queen Mary - not a bicycle. The old spring fork was 1688 grams. I think they've added weight with the hubs as well as the previous RC Pro hubs are likely lighter.
I would switch brake cables like you mentioned as those brakes work effortlessly on my son's Spark RC 24" and are as strong as discs.
For the fork stiction I would remove the seals and pack Slickhoney suspension grease under them. The stuff is amazing. I used it on my sons Hot Rock fork and my Wife's very sticky Fox fork and it made a huge difference.I also use it when servicing all of our rear shock air cans. I found out about it from an X-Fushion Tech as they use it on their suspension components.
Good stuff. Thanks. I'll have to look for that Slickhoney stuff.
Originally Posted by xc71
Finally got time to get pics of the Suntour Air fork dissected. Here are some thoughts on the fork.
- Not an open bath system. Instead uses an air cartridge with fixed dampening. This simplifies the fork design but limits overall ability. The air chamber/piston area is too small for much adjustment. On a side note, I believe the RST First uses an open bath design if it's similar to the rest of their 26" line. This would also explain why RST is able to run lower pressures. From what I can tell, the design is very similar to the older Manitous which would be impressive if true.
UPDATE: I looked at the exploded view of the RST 24 First fork and it is an open bath design.
- There's no clearance for the shock pump nozzle to thread on to the valve. If you have the lowers removed, do youself a favor and file away enough to clear the nozzle.
- The opaque plastic piece in the left leg is the bottom out bumper though not really a bumper since it's hard. The Stanchion to crown distance w/ bumper is 0.6". I plan on reducing the height of the bumper by 0.5" which should increase travel by the respective amount but need to verify tire clearance.
- The negative spring is comprised of 2 springs (soft, hard). The hard spring is very stiff and doesn't move sigificantly compared to the lighter spring. By changing the height of the negative spring, it's possible to get more travel from the shock but it also increases axle to crown measurements. With the current negative spring, there's only about 1" left of down travel. I was planning on reducing the height of the negative spring by 0.7". I also verified that the stanchions stay within the working range of the magnesium lower bushings.
- The cylinder (limiting travel factor) has a max throw of 3.875". With the mods above, I'm hoping to be able to get 3". Unfortunately, the limiting factor will be the progressiveness of the cylinder. The small air chamber will not lend itself well for long travel.
- I wish Scott Bikes did a little more homework and picked the best air fork of the current 3 24" models available, Spinner, Suntour, and RST. In the end, the RST is the fork to get.
The tools needed are as follows;
- Shock Pump
- 5mm Allen wrench
- 1 1/16" socket or adjustable wrench
- 10mm deep socket or 10mm box wrench
- Needle Nose Pliers
General procedures for fork disassembly;
1. Let the air out of the right fork leg
2. Remove bottom nut from right leg
3. Remove blue lock out lever (lift up) and unscrew top cap. No need to remove clicker (parts under blue LO lever) from top cap.
4. Unscrew bottom bolt from left leg 4-5 turns. Use mallet and tap on the screw to release negative spring rod from lowers.
5. Use the needle nose pliers to unscrew the left leg top cap. To prevent damage to the plastic cap, use the tips of the pliers to lock into the teeth of the plastic cap (as opposed to clamping on the cap).
6. Push the lowers all the way up, use the 5mm allen and insert into the bottom screw hole of the left leg and push out the negative spring.
Here are all the pieces to the fork.
Here is the crown and stanchions
A co-worker gave me his old 2004/2005 Manitou Skareb Super to experiment with. It weighs in around 1450g which would drop about a pound off the Suntour fork. I may have to lighten up the negative spring and try to get the A to C lower by modifying either the travel or dropouts. I also have to verify the reverse arch clears the frame. Should be a fun project. I have yet to take it apart but the internal design and weight looks promising.
Last edited by stom_m3; 11-18-2013 at 03:53 PM.
If you want to stay with V rim brakes instead of switching to disks, might be worth a try to grind the skareb's dropout axle slot upwards as much as the casting allows. I would expect that you can get the axle located about 10mm upwards from current position, combined with moving the brake pads fully down in the brake arm adjustment slots, this could get you the 26mm of adjustment needed to compensate for using a 507mm rim in a fork designed for 559mm rim.
If that doesnt work, might also be possible to just grind away the entire existing dropout and fabricate a new dropout than can be clamped around the lower tubes exactly where needed to compensate for the smaller rims and also to keep the A-C as low as possible.
try driving your car less
Thanks for dissecting the fork for us all. I did something similar to the RST Capa T4 on my son's hard rock. I just unscrewed the plastic top cap with pliers and a rag to keep from ruining the plastic. THen I just pulled out the spring. There was nothing else in there! I put it back without the spring in one side to make it softer. I wonder if there is a way to just buy the guts of the RST F1RST and pop them into the fork I have.
I thought about an air fork, but my son seems to enjoy riding regardless so I am saving my resources for the 26" wheel bike in the future. He turned 9 today and I thought about the fork as a bday present, but in the end went with a giant box of LEGO tecnic with the motor and everything. I think he liked it better.
Only boring people get bored.
Thnx much for the awesome right up. Im modding my sons mt60 20" atm but expect in another couple seasons at most, Im going to be building a 24" and since that will be junior MTB class racing time, Im going to go as weight weenie as I can possibly afford on it. Glad to see more and more parents getting serious on their kids bikes, especially parents that know way more than me
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Hi all - since there is interest in this model, I wanted to let you know that I have just posted my Scale RC 24 Jr on ebay. The auction started today and ends next Sunday.
storm_m3, please let me know where i can find one of these RST F1RST air forks for sale in the US.
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