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  1. #1
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    New Scott Spark JR 20" Modifications?

    I just bought my 8 year old daughter a 20" Scott Spark for a good price at a LBS.

    It is a really great bike as it is, however, I am interested in lightening it a bit and making it more user friendly without breaking the bank.

    I have read the other thread about the 20" Scott build and liked the 2 inch riser handle bars, since the stock ones are real low.

    The bike weighs the same as her Huffy 20" or less.

    The gearing seems to be low enough for her to go up hills, but I am not sure if she will need that big outer chain ring?

    What are some options for riser handle bars, stem, wheels, tires, and possibly shifters?

    This bike will be passed on to my 4 year old son, so I do not mind spending money on it, especially replacing parts that wear out.

    Thanks
    Bill
    Attached Thumbnails Attached Thumbnails New Scott Spark JR 20" Modifications?-2012-06-22_07-57-08_967.jpg  


  2. #2
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    Check you PM.

    Congrats! I'm sure your kid is happy. If you want to drop weight, check the tires. I was able to drop 1 lb just by swapping out the stock tires. You will also find the cranks and BB to be on the heavy side. Good luck. We're heading up to MT. Laguna on Sunday if you want to give it a run.

  3. #3
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    Couple of suggestions:

    1) replace the bottom bracket, that will save some weight.
    2) handlebars - any riser bar will work you'll just have to cut it down. Two things to consider: 1) be sure to buy a bar that works with the existing stem (that is if you're going to keep the stem); and 2) if the seat height is already lower than the bars you may want to go with a flat bar instead of a riser, adding a riser bar that increases the bar height will make the bike feel too "chopper" like. I used a FSA XC190 riser bar for my son's bike, it's alloy (so it was cheaper than carbon) and was easy to cut down, and its relatively light.

    3) Replacing the wheels is the best way to knock off some weight, but it will cost you. I purchased a set of 28-hole hubs and SunRingle rims on eBay and had them built by a local shop. This saved considerable weight, but I also had to buy a 9 speed cassette, new rear derr. and a set of new shifters. Works way better, but cost lots.
    Better at pedaling than typing

  4. #4
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    Quote Originally Posted by stom_m3 View Post
    If you want to drop weight, check the tires. I was able to drop 1 lb just by swapping out the stock tires. You will also find the cranks and BB to be on the heavy side. Good luck. We're heading up to MT. Laguna on Sunday if you want to give it a run.
    Thanks! We are planning to go to Mt. Laguna in two weeks to camp and will ride the trails, thanks.
    Quote Originally Posted by ThornPatch View Post
    2) if the seat height is already lower than the bars you may want to go with a flat bar instead of a riser.
    Her seat is a little lower than her handle bars, however she is used to them being a little higher.
    Quote Originally Posted by ThornPatch View Post
    3) Replacing the wheels is the best way to knock off some weight, but it will cost you. I purchased a set of 28-hole hubs and SunRingle rims on eBay and had them built by a local shop. This saved considerable weight, but I also had to buy a 9 speed cassette, new rear derr. and a set of new shifters. Works way better, but cost lots.
    That is good to know, both what is possible and that it is expensive.

    This bike is perfect for where my daughter is as far as riding skill, height, strength, etc. I was planning on waiting for a 24" diameter wheeled bike, but she would not be ready for that for at least a year. Even with this bike she is slowly getting used to shifting gears and the handle brakes. I will pass it on to my son, so I feel justified buying the bike.

    Thanks
    Bill

  5. #5
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    Bill, I spent about $550 on a new custom built wheelset for my son's bike, which is crazy expensive for a 20" wheelset, but that price also included a new Sram 990 cassette, x-9 sort cage rear derr, and x-7 shifters. I built the bike for my 9 yr old, he's average hgt, and some might say I should have put him on a 24" bike, but since he likes to jump a lot he's better off on the smaller 20" wheels. The small wheels gives him more control over the bike, and boosts his confidence. Hopefully I can at least 2 -3 years out of it before he's ready for a bigger bike. Either way the parts can transfer over to a new bike pretty easily.
    Better at pedaling than typing

  6. #6
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    Quote Originally Posted by ThornPatch View Post
    Bill, I spent about $550 on a new custom built wheelset for my son's bike, which is crazy expensive for a 20" wheelset, but that price also included a new Sram 990 cassette, x-9 sort cage rear derr, and x-7 shifters. I built the bike for my 9 yr old, he's average hgt, and some might say I should have put him on a 24" bike, but since he likes to jump a lot he's better off on the smaller 20" wheels. The small wheels gives him more control over the bike, and boosts his confidence. Hopefully I can at least 2 -3 years out of it before he's ready for a bigger bike. Either way the parts can transfer over to a new bike pretty easily.
    Thanks, I got your PM too. That really helps me out. Did you build the wheelset for better performance and/or weight reduction? I would spend that kinda money to make my daughter's bike better, if I know she is going to use it. My goal is to spend more time with my daughter doing stuff we both enjoy.
    Thanks
    Bill

  7. #7
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    Quote Originally Posted by ThornPatch View Post
    Bill, I spent about $550 on a new custom built wheelset for my son's bike, which is crazy expensive for a 20" wheelset, but that price also included a new Sram 990 cassette, x-9 sort cage rear derr, and x-7 shifters. I built the bike for my 9 yr old, he's average hgt, and some might say I should have put him on a 24" bike, but since he likes to jump a lot he's better off on the smaller 20" wheels. The small wheels gives him more control over the bike, and boosts his confidence. Hopefully I can at least 2 -3 years out of it before he's ready for a bigger bike. Either way the parts can transfer over to a new bike pretty easily.
    I did something similar to ThornPatch. Sun Envy Lite, XT hubs, Sapim dbl btd spokes. Cost was $280. Dropped a ton-o-weight. I reused my cassette and shifters from an older bike so I didn't have that cost. You can purchase 2010/11 Sram shifter/cassettes cheaper than 2012.

    Finished Wheel weights
    Front Wheel 739g
    Rear Wheel 906g
    Last edited by stom_m3; 06-22-2012 at 03:06 PM. Reason: added wheel weights

  8. #8
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    Is the cassette flip-flop hub compatible?

  9. #9
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    Is it possible to buy a Middleburn 140mm cranks, with a 32 chainring and bashguard? And a Irod 7 speed cassette, 15, 17, 21, 24, 28, and 32? That is considering the bike has a 34 and 42 chainrings and a different cassette? Thanks Bill

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    I used cranks from bikesmithdesign.com, he recommends much shorter than that, I believe he said 10% of height plus 5mm, max length on the cranks. Anyways, if you look at a serious kid specific bike manufacturer like islabikes.co.uk then you'll see their 20" models have cranks from 114-127mm max.
    I downsized the stock 152mm cranks on my son's 24" bike to 137mm and have been really pleased with the outcome.
    I got the race face bash guard on race face rings. The crankset looks awesome and he delivered it fast too! Well worth it, imo.

    Correction: he said 10% +5 mm at most.

  11. #11
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    Quote Originally Posted by ridemtn View Post
    I used cranks from bikesmithdesign.com. Correction: he said 10% +5 mm at most.
    I calc'd 136.5 for my 51" tall girl. Thanks. I have read good things about bikesmith. Bill

  12. #12
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    Quote Originally Posted by Billinsd View Post
    I calc'd 136.5 for my 51" tall girl. Thanks. I have read good things about bikesmith. Bill
    If she is 51" she needs to ride 145-150mm length crank arms. I would go 145 conservative and 150mm for growth. For reference, my son is 48" tall and uses 140mm. The 10% thing is way off for kids. If you are planning on running a 1x setup, buy Sinz, redline or AC mini cranks ($50-70). If you need to run 2x/3x setup, bike smith will shorten cranks for a price. I like the 1x setup and personally run it on my mtn bike.

    The right way to decide gear ratios is to review the numbers. Look at the gear ratios and decide where your kid will be able to operate best. Below are quick charts I did to show you some gear inch numbers. If you would like to know the roll out, multiply by pi (3.14).

    The first chart shows a single speed gear inch setup for your 20" (15-32t setup). The next chart shows my son's 1x8 setup. And for comparison, the last chart shows 26" mtn bike gearing for 1x, 2x and 3x setups. For example, my 1x10 setup uses a 36 front and 11-36 rear cassette. My gear inches run from 25" to 83". My son uses a 35 front 12-32 rear cassette or 21" to 57". My son rarely uses his top 3 gears except on the occassional down hill but that usually involves more coasting, feet flat and looking way ahead (+20mph).

    Based on the cassette that you want to run, 15-32, I would be a little worried about running out of steam on the upper (tougher) gears. Either increase the cog count or include a 13t in there. If you build custom wheels think about doing a 9 or 10 spd. This will solve most of your issues. Hope this helps.

    Gear inch chart for 20" mtn bike 7spds


    Gear inch chart for 20" mtn bike 8spds


    Gear inch chart for 26" mtn bike (provided so you willl know what the level of effort is needed to push on a pedal per respective gear on your own bike).
    Last edited by stom_m3; 06-23-2012 at 08:48 PM.

  13. #13
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    Great info, thanks!! I was meaning to also ask, if I get the Schwalbe Mow Joes, I would get the 20 by 2 inches wide for the stock wheels and if I upgrade my wheels those tires should fit on say a sun envy lite, right?

    Seems like the Mow Joes are not carried by many places? What are some good lightweight inner tubes?
    Thanks
    Bill

  14. #14
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    Quote Originally Posted by stom_m3 View Post
    If she is 51" she needs to ride 145-150mm length crank arms. I would go 145 conservative and 150mm for growth. For reference, my son is 48" tall and uses 140mm. The 10% thing is way off for kids. If you are planning on running a 1x setup, buy Sinz, redline or AC mini cranks ($50-70). If you need to run 2x/3x setup, bike smith will shorten cranks for a price. I like the 1x setup and personally run it on my mtn bike.
    I agree with this.
    My 48" son has no problem spinning 140mm arms at high cadence. Anything shorter than 135 for him would be super awkward. The cranks on his 16" bike were ridiculously short and were the main reason I built him a 20".
    +1 for Sinz and AC cranks. Good stuff.
    *** --- *** --- ***

  15. #15
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    Actually, after further thinking, I wouldn't go larger than 145mm on a 20" bike. At 51" she could ride either 145 or 150mm cranks but on a 20" bike you may get a lot of pedal/ground strikes. If she was on a 24" you could go larger.

  16. #16
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    I cut about 2.5 pounds by exchaning the spark with a scale. I did this a few days after I bought the spark. The LBS has great customer service!!

    I let my daughter ride the bike around for the last month or so and decided what else I wanted to do.

    I recently bought an IRD 13-32 freewheel in place of the Shimano 14-28. I cut off the big outer chainring that my daughter will never use. I bought a Paul Compents chain keeper, purple handle grips and a Shimano Trigger Shifter.

    My daughter likes the improvements and it seems to help her confidence.

    Thanks again all for the help!!!
    Bill
    Attached Thumbnails Attached Thumbnails New Scott Spark JR 20" Modifications?-2012-08-13_19-01-54_680.jpg  

    New Scott Spark JR 20" Modifications?-2012-08-13_19-02-11_94.jpg  

    New Scott Spark JR 20" Modifications?-2012-08-13_19-02-00_102.jpg  


  17. #17
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    So is your local bike shop unloading a used Spark? Wonder if they'd ship it? It isn't easy to find used Spark 20's

  18. #18
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    My daughter rode the spark around the block and it showed no signs of use. The LBS is selling it as new. He sold it to me for $400 and could come down. I don' t know about shipping. Bill

  19. #19
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    ideas

    I got a fusion x air shock from the manufacturer. Big differences in adjustability. Had cranks cut down to 130. I also am getting a new wheelset built up. Stock they weigh 28 pounds with pedals. My goal is to get it sub 25.

  20. #20
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    Quote Originally Posted by bugger View Post
    I got a fusion x air shock from the manufacturer. Big differences in adjustability. Had cranks cut down to 130. I also am getting a new wheelset built up. Stock they weigh 28 pounds with pedals. My goal is to get it sub 25.
    Great score getting the X-Fushion air shock. So nice having adjustable rebound damping so the rear end isn't a pogo stick. With this shock on the Spark its the best rear suspension you will find on a kids bike - works awesome.

  21. #21
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    I've got a used Spark 20" (White) Full Suspension, that is like brand new. She's only ridden it a few times and may have hit a mud puddle once or twice. She outgrew it and needs to move up.

  22. #22
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    x-fusion

    Quote Originally Posted by xc71 View Post
    Great score getting the X-Fushion air shock. So nice having adjustable rebound damping so the rear end isn't a pogo stick. With this shock on the Spark its the best rear suspension you will find on a kids bike - works awesome.
    Hi, where and how to buy X-fushion schock to scott spark jr? What is the cost?
    I live in Poland, but I have friends in the U.S..
    Thank you for your reply.

  23. #23
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    I picked up a Scott Scale Jr 20 for my son as well, I'm hoping to make a few improvements over time... are those Velocity Aeroheats really the best bet for at 20" rim? I'm thinking about picking up some Novatec or Circus Monkey hubs to build wheels.

  24. #24
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    Hi, look at the weight of new models islabikes. 1 kg down each model.
    Beinn 20 small 7.8 kg!!!!!!
    I need to talk with son to sell his scott spark jr.

  25. #25
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    Quote Originally Posted by heckler11 View Post
    Hi, where and how to buy X-fushion schock to scott spark jr? What is the cost?
    I live in Poland, but I have friends in the U.S..
    Thank you for your reply.
    Not sure on cost as this shock came stock on my son's Spark RC JR. I would contact X-Fushion USA.

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