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  1. #1
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    The 20-pound Geared 20" Hardtail Project (Customized Marin Hidden Canyon)

    Been quite a few threads on kids' geared mountain bikes lately, and ideas on how to get their weights down, so I thought I'd present my own project.

    A little background: I have a 6 y/o son who started racing BMX shortly after his 5th birthday in 2008, and quickly accumulated local and state wins, eventually taking an ABA Northern California State Champion title/plate for his age class that year on an 11-lb. bike built and spec'd by myself. He used the very same bike (re-geared, and with slightly modified ergos) to earn a championship title for his age group in a local kids' triathlon series (50m swim, 4 mile bike, 1 mile run) in 2009. For these little guys (and gals!), bike setup can be every bit as important as how quickly they can spin those pedals -- especially when you have a little guy like mine, who at 46" and 45 lbs, is in the 15th percentile for his age.

    So when he mentioned that he wanted to start MTB racing in 2010 (same club that runs the triathlons), I adopted the same (admittedly obsessive) approach that I had with his BMX and Tri racing. (He's grown tired of BMX, but will continue with Tri's for 2010.) After a fair amount of research, it became quickly apparent that even the respected manufacturers are not willing to put too much effort in spec'ing geared 20" mountain bikes (and perhaps, justifiably so). Some of my priorities were:

    Geometry - This always comes first, whether it's my bike or my kids' bikes. If the bike doesn't feel right, they won't want to ride them. Fortunately, with experience from his BMX bikes, I had a ballpark idea of what types of numbers I was looking for -- around 17" top tube, and 12" or less of seat tube. The first MTB he tried was a Gary Fisher Precaliber, and while he was able to ride it, it was quite apparent that the top tube was too long -- his upper body was too stretched on it. (And the Fisher website confirms it -- 504mm top tube, almost 20"!) Most other bikes were in the more reasonable 16.5-18" top tube range. You also want to consider crank size -- you will see everything from 120mm to 160mm on these kids' bikes -- a 40mm range of variation! That's a huge range for an adult, let alone a young child. My son was spinning 135mm cranks for BMX and Tri's, but I wanted to focus on 140mm cranks for this project -- he's growing, and he can use the additional leverage when climbing bigger hills.

    Weight - A high priority, but it seemed that everything was at least 25 lbs. Hmm, being somewhat of a weight weenie, I knew I was going to need to do some tweaking regardless of which bike I chose. Based purely on subjective feel, the Scott Scale JR 20 seemed the lightest (albeit not by much). The Kona Shred 2-0 (last year's model, with double chainring) was an absolute TANK -- in a bad way. I really wanted to like that bike, especially with its disc brakes and shorter frame, but its heft was undeniable.

    Gearing - The types of riding we do locally require some climbing, so that ruled out single speed. Most of the bikes I was looking at were 2x6 or 2x7, but I was initially convinced I needed a triple up front (and for a while was looking only at the Ibex Alpine 320k, which fits that description). But for a 6 y/o with no previous multi-gear experience, I realized that managing gears front and back would be sensory overload at this age. So I was determined to come up with an optimal range of gears with a single chainring up front, even if it meant some customization.

    Suspension - Unfortunately, at this price point ($300-400ish for a complete bike), they can't afford to spec a quality suspension fork for 20" wheels -- nor is there a market for one among the OEMs. In fact, you're pretty much going to find your choices limited to Spinner Grind, RST Capa, and SR Suntour -- all simple spring/elastomer designs. Make no mistake, these all pretty much work the same (which is to say, badly), and any differences you may see can be attributed to varying quality control (or lack thereof). I have seen a Spinner Grind on a one bike require my full weight to compress, but another Spinner Grind feel properly sprung on another bike. Similar results with RST Capas. So my advice is, don't let the fork model be a deciding factor in your choice of bike -- they're all crap, but it's what we are given, so once you've found the model of bike that suits your child's needs, make sure the fork can compress without Herculean effort.

    With the above in mind, I was leaning toward the Ibex Alpine 320k, the Scott Scale JR 20, or the Marin Hidden Canyon. The Ibex was hands-down the best-spec'd out of the bunch -- and also unavailable, with Ibex now out of business. The Scott was nice, but nearly the same cost as the Ibex. Marin was not particularly a standout in any area, but it fit my son reasonably well, but my sister-in-law works at a local sporting goods chain that carries them, and I could get 25% off its $330 retail price. Knowing that I was probably going to spend some money customizing the bike, I decided that buying the Marin at discount was my most cost-effective choice.

    Then fortune struck. The local sporting goods store had an unridden 2008 model onhand that they could not sell at retail because it had unusable cranks (long story). They were willing to sell me the bike for $100 (while signing disclaimers acknowledging it was not warranteed or returnable). I jumped at the opportunity to take the bike down to bare frame and fork, and start from scratch on a custom build.

    Within hours of taking the bike home I was removing old parts, placing orders for new parts, and scrounging around for other parts from around the garage. Here are some of the key components that were replaced:

    • Cranks - Stock: with 42/32 chainrings, 773 grams. Replacement: Crupi BMX race cranks, 140mm arms, and a FORM BMX 36t chainring, 455 grams.
    • Seat - Stock: 297g (and way to big for a little kid's butt). Replacement: Odyssey Junior BMX seat, 186 grams.
    • Seatpost - Stock: 290 grams. Replacement: spare Ritchey Comp I had lying around, cut down to minimum, 180 grams.
    • Stem - Stock: 240 grams. Replacement: Race Face Evolve XC 70mm, 130 grams.
    • Brakeset - No real weight savings here, but the stock set was pretty bad -- almost "Walmart bike" bad. I replaced them with some Avid FR5 equivalents that my LBS had lying around.
    • Bottom Bracket - Stock: 311 grams. Replacement: Sinz Titanium Euro Square Taper, 166 grams. I was REALLY surprised here. The replacement came off his BMX race bike, and I was surprised by not only how much lighter they were, but much more easily the cranks spun compared to the stock BB.
    • Wheelset/Tires - Stock: front and rear, including hubs and 7-speed 13-28t freewheel, Kenda 20x2.1" tires, 3676 grams. Replacement: Custom build with Crupi/Rhythm BMX rims, IRC Siren 20x1.5" tires, SRAM PG-970 11-32t cassette, Shimano Tiagra hubs, 2911 grams. About a 1.7 lb. reduction in rotational mass, not the monumental reduction I was hoping for, but still quite significant, and with more oprtions for gearing than the stock drivetrain.
    • Rear Derailleur/Shifters - Stock: Shimano Tourney RD, SRAM MRX twist shifters. Replacement: SRAM X5 medium-cage RD, SRAM X7 twist shifters. No huge weight savings, but higher quality and more options for gearing / components.
    • Front Derailleru/Shifters - Stock: Shimano Tourney TY-22, SRAM MRX twist shifters, est. 250 grams w/ cables. Replacement: Completely removed.
    • Fork - Stock, but about 2" of unused steel cut from the steer tube.
    • Handlebars - Stock (and surprisingly light), but about 1.5" cut from each end for better ergos.


    End result: a sweet 1x9 setup that weighs 20.2 lbs. sans pedals (20.8 lbs with), compared to its stock weight of 25 lbs., and has already provided the little guy with tons of grins on his first trail ride during winter vacation. Only changes I plan on making are going with a 34t chainring to give him some extra advantage for climbing, and a chain guide like the one from Paul Components.

    I could have easily saved a bit more weight by going with SUN CR-18 rims (350g each, vs. my 410g Crupi/Rhythms) but I'm a sucker for blingin' white rims. Other areas for weight savings would come at significantly higher cost: SRAM X-0 short cage rear derailleur (100 grams ligher, $160); KCNC Scandium seatpost (40 grams lighter uncut,$90); Xpedo flat pedals (60 grams lighter, $80). But a combination of these could easily take the bike weight below the magic 20-lb. mark.

    A few pictures below.











    Last edited by quasi888; 12-29-2009 at 11:53 PM.

  2. #2
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    That's awesome. Enjoy your time with your son.

  3. #3
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    That is awesome. Nice work.
    I like turtles

  4. #4
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    Sweet !!!

    I have a 4yr old and the bike you built is just what I would want for her. Sell it to me in two years, Please!!!!

  5. #5
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    Quote Originally Posted by yetipop
    I have a 4yr old and the bike you built is just what I would want for her. Sell it to me in two years, Please!!!!
    I may consider that! But it all depends on whether or not his (now) 3-year-old little sister has inherited the same 2-wheel passion!

  6. #6
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    Awesome build. I really like the 1 x 9 gearing. Looks great too!

  7. #7
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    Hey all,
    Been thinking about doing some mods to my Daughters bike.
    Very awsome build

    I saw some Aeroheat 406 24mm width, 300 grams $ 65.50. These rims would save a further .5lb frm the curernt wheels I am looking for even a lighter rim if anyone knows of one.

    Hope you are having fun

    Cheers,
    Paul

  8. #8
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    Put a chain device to avoid chain drops, other than that it's a great ride for a youngster.

  9. #9
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    Quote Originally Posted by DiRt DeViL
    Put a chain device to avoid chain drops, other than that it's a great ride for a youngster.
    Definitely was part of my original plan (I was looking at the chain keeper from Paul Component Engineering), but he has yet to throw a chain so far, knock on wood. I had shortened the chain to the point where there is a fair amount of tension (while still barely maintaining an "S" shape through the rear mech's pulleys in the largest cog), so that has helped.

  10. #10
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    Here is our version:
    Rav-x carbon bars (22" wide)
    Straightline 35mm stem
    custom bent/tuned levers and XT V brakes (long levers and the right setup has him one finger braking)
    Sram attack 9 speed shifter
    Ame mini grips
    King headset with +5 base
    XT hubs laced to stock rims
    Intense tubes
    Kenda Small block 8 DTC kevlar ( lost 2 lbs with just tires and tubes)
    Sinz 135 cranks, 34 tooth ring and pro ISIS BB
    BBG bash ring ( destroyed the stock big ring on the first ride)
    Mod. to front der as guide until I build a new style using old MRP parts or someone makes a ST mount style.
    Sram 990 12/34 cassette
    Sram hollow pin chain
    Ultragra rea 9 spd. short cage der.
    Thomson post ( off an old Dh bike and was chopped short)
    Oddyssy saddle ( may go back to stock for comfort)
    Drilled out cable stops to run full cables
    stock pedals
    Sinz QR seat clamp
    Hope QR's on the wheels
    Custom fork mods by Push ( well stickers anyway and a bit of grease )
    21lbs I wasnt shooting for loosing weight as much as making the bike more functional.

    Rode it stock for a few rides and found too many falts to not dive into it.
    So far the gearing change has made a huge difference! He can climb all but the steepest climbs and bombs down everything. Hes only six and has been riding his 16" pitboss on the trails but just gets rattled. His riding pace had jumped by leaps and he does 10 mile rides with a smile. Worth every penny. Speaking of $. I have a total of $600 ( half being the original purchase) out of pocket. I started by robbing my old parts bin.Thanks to e-bay deals, friends in the industry that hooked the little guy up ( thanks LikinBikin.com) and my local shop, its really a small investment. with a 3 year old brother that is now riding his 16" bmx ( been on 2 wheels since 2 1/2) it should get well used. Mini MTB might not be for every kid but this one is loving every second of it. It takes "family rides" to a whole new level.
    Attached Images Attached Images  
    Last edited by m-dub; 03-01-2010 at 11:19 AM.
    Enjoy every ride!

  11. #11
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    Nice build m-dub! Would love to see more pictures of it.

    I'm curious how you got an XT hub to fit in the rear. Did you modify it? Rear dropout spacing on this bike (like most other kid's 20" MTBs) is 130mm -- the same as most road bikes, which is why I went with a Tiagra (road) hub. Most MTB rear hubs are designed for the standard MTB rear dropout spacing of 135mm.

  12. #12
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    You sure? I thought I mesured it as 135? Well it works with no mods! I got a set of non-disc XT hubs new for $30 on flee-bay and built them up. Chain line works ( bike has long stays) and dish was fine. I wanted to go with a 34 in the rear for the sake of climbing and it has worked out much better. Still a bit tall at times but he does great. I also had the shifter, rear der. off my old 4X bike so that helped with the cost. The Sram Attack shifter has a indacator in the clamp to help in the gear selection confusion with the little guys and the pod style is easier to set up proper brake lever location with his little hands. I put a red sticker on the one shifter so he knows were the " fast button" is I will try to get some more photos up.
    Last edited by m-dub; 02-28-2010 at 11:33 AM.
    Enjoy every ride!

  13. #13
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    Here are a few. I will try to get a shot of the rear for you also.
    Attached Thumbnails Attached Thumbnails The 20-pound Geared 20" Hardtail Project (Customized Marin Hidden Canyon)-b2.jpg  

    The 20-pound Geared 20" Hardtail Project (Customized Marin Hidden Canyon)-b.jpg  

    Enjoy every ride!

  14. #14
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    Sinz 135 cranks with their pro BB ( Ti was out of stock and I got impatient) The stock front der. is fixed in place to work as a chain guide. I have rubber just above the chain and it keeps its quiet and in place ( old school fix) also a piece in the lower part to eliminate chain slap. I plan on making one out of a use MRP guide but hope they come out with a X1 that is seat tubes mounted. He dropped his chain 10 times on the first two rides ( its rough and he likes little drops) but now with the new cranks and home brewed guide it hasent dropped yet.The bash ring is nice and keeps the chain in place and his pants out of the chain plus he crushed the stock 44 tooth on the first ride into a rock.
    Attached Thumbnails Attached Thumbnails The 20-pound Geared 20" Hardtail Project (Customized Marin Hidden Canyon)-cranks.jpg  

    Last edited by m-dub; 02-28-2010 at 11:34 AM.
    Enjoy every ride!

  15. #15
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    The XT brakes were new on fle-bay for $30 bucks, how can you pase that up? The levers were cheepies from someone upgrading and I bent the levers to fit his hand. Also filed the thickness out of the lever to help the fit and drilled "speed holes" for no other reason than looks Then painted black. All the cable stops were also drilled out to run full cable housing. I took all the tention out of the springs and the kid can do stoppies( endows) in the yard with one finger I had to tell him to cool it before he slammed the der. into the grass one to many times. The Small block 2.1's fit with a ton of clearence and are aired at 18lbs. The float great in the soft and cushion on the rough but roll awesome on the pavement.
    Attached Thumbnails Attached Thumbnails The 20-pound Geared 20" Hardtail Project (Customized Marin Hidden Canyon)-brake-lever.jpg  

    The 20-pound Geared 20" Hardtail Project (Customized Marin Hidden Canyon)-brakes.jpg  

    Last edited by m-dub; 02-28-2010 at 11:36 AM.
    Enjoy every ride!

  16. #16
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    Here is a shot of the rear. its a 09 model and the 135 works awesome. A lot of people talk about running singlspeed is all kids need. Well I think it depends on the kid and the terrain your riding. Where we live that would mean a lot of walking.The extra gearing has made a huge difference on his riding.
    Attached Thumbnails Attached Thumbnails The 20-pound Geared 20" Hardtail Project (Customized Marin Hidden Canyon)-rear-hub.jpg  

    Enjoy every ride!

  17. #17
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    Hey, nothing like a "pushed fork" The mod included custom stickers on both legs and a bit of greese The fork and tire give almost 1.5 inches of cush and that alone has ended any sore hand complants and has me yelling at him so slow it down for that sake of my own nerves
    Enjoy every ride!

  18. #18
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    oops. This is a shot before the re-lace of the xt hubs.
    Attached Thumbnails Attached Thumbnails The 20-pound Geared 20" Hardtail Project (Customized Marin Hidden Canyon)-fork.jpg  

    Enjoy every ride!

  19. #19
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    Great pics m-dub!

    You sure? I thought I mesured it as 135?
    Well I measured the rear dropout spacing today, and got.......132mm!! LOL. Don't know if it's simply a loose tolerance during manufacturing, or an intentional effort to allow either size hubs to work (doubtful), but I can see how either 130 or 135 would fit.

    A lot of people talk about running singlspeed is all kids need. Well I think it depends on the kid and the terrain your riding. Where we live that would mean a lot of walking.The extra gearing has made a huge difference on his riding.
    100% with you there. Recently we've been going up some real extended (for a kid at least -- about a mile at 6% incline on rutty dirt) hill climbs, and he's definitely in the big cog most of the time. In fact, there are some times I wish I had gone with a 12-34 cassette as you have...perhaps I'll swap it out later. If we're talking fairly flat trails with short elevation changes, sure, go for SS. But the types of trails we choose to ride out here mandate the gears.

    Your son looks taller than mine. (Mine is now 7 y/o, but at 46" is short for his age.) If yours is taller than that, you might consider longer cranks than the 135s -- at least 140s or 145s. It'll give him the extra leverage for hill climbs. The nice thing about going 1x gearing as you and I have, is that we've got tons of choices in lightweight, square-taper mini BMX cranks. I've been through most of the brands during his (successful-but-short-lived) race career, and the lightest by far are Crupi and LDC (Little Dude Components).

  20. #20
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    My son is 48" and just turned 6. The reason I went with 135 was the BB is super low and his pedals were really close the ground. I love a low BB and as a DH racer / skills instructor, I swear by them. But his pedals were only 2 inches off the ground and he would clip them in the slightest turn. I even went with a +5 head set spacer/base to lift it up a bit. He has now gotten very aware of them and has no issues.
    Oh I know about the cranks! Tons of sweet stuff out there and almost pulled the trigger on some ( sucker for US made stuff) but my friends at LikinBikin sent him a set and that saved me some cash.
    I had to keep myself in check as not to go overboard and drop a ton of money. The Sinz are farley light and I could of lost weight in other places as well ( XT hubs are anyontg but light) but $ is tight these days Also the shorter cranks alow him to sit and spin without his knee hitting him in the chin. If you do the math, compared to my 35" inseam, they are still on the long side.
    Fun, isnt it?
    Last edited by m-dub; 03-01-2010 at 11:21 AM.
    Enjoy every ride!

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    Awesome thread. I just picked up a Norco Ninja for my 6 year old. He already had a 13 pound mini bmx and rides the track but wants to come with us on some trails too and needed gears.
    Stock was 28 pounds. removed the kickstand, QR's (lots of theiving at school) rear der guard and presto 26 pound bike. I'll be changing the cheap heavy seat post with a short KCNC I have lying around and some cut down carbon handlebars. The big change will be going to a single front chainring and crank. The wheels have fairly nice rims but a 5 speed freewheel. I'll swap out the tires and tubes to some IRC Sirens which I think are the lightest 20" knobbies. I would like to ditch the Suntour suspension fork as it is useless and throw on a lighter rigid fork. All the carbon BMX forks don't have brake bosses. Any fork sugestions?

  22. #22
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    rroadie,

    Some of the 20" forks work reasonably well. It seems to be hit and miss, but you could get a new one for under $100.

    Another option is a mod trials fork. They come with various brake bosses including disc tabs. I'm not sure of their weight though - probably nowhere near as light as the BMX models you mentioned.

    Finally, on a more ridiculous scale, White Brothers sells a 20" air sprung fork for recumbents. I think it is in the $700 range.

  23. #23
    turtles make me hot
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    Quote Originally Posted by DWDW
    rroadie,

    Some of the 20" forks work reasonably well. It seems to be hit and miss, but you could get a new one for under $100.

    Another option is a mod trials fork. They come with various brake bosses including disc tabs. I'm not sure of their weight though - probably nowhere near as light as the BMX models you mentioned.

    Finally, on a more ridiculous scale, White Brothers sells a 20" air sprung fork for recumbents. I think it is in the $700 range.
    I mentioned swapping 20" suspension forks in another thread. The Suntour fork that came on my son's bike may as well have been rigid. It was useless. The LBS got me an RST that was way softer. Works much better.
    I like turtles

  24. #24
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    I would like to ditch the Suntour suspension fork as it is useless and throw on a lighter rigid fork. All the carbon BMX forks don't have brake bosses. Any fork sugestions?
    For a rigid 20" fork, look at flatland forks, primarily designed for stunts/tricks. Most don't have front brake bosses, but some do. Two that come to mind are the KHE Tanaka and Odyssey Pro Flatland (new model might be known as Freestyle Classic). (See, I had the same idea too, so I already did the research. ) Both of these come in at around 2 lbs; about twice the weight of a good carbon race fork, but roughly half the weight of the 20" suspended forks.

    EDIT: Hmm, just found out that both of the above forks have "990" mounts, e.d. designed for U-brakes. V-brakes wouldn't mount on them unless you found some sort of adapter plate.
    Last edited by quasi888; 03-08-2010 at 08:45 PM.

  25. #25
    turtles make me hot
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    I just went through my parts bin and found an old Moby Post and it fits my son's GF Precaliber. I also Ebay'd a set of Sinz cranks and an Easton Monkeybar which I can cut down for him. This is fun.
    I like turtles

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