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  1. #1
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    Project Specialized Hotrock 20 and lessons learned

    I have read almost every thread I could find on upgrading a hotrock 20 and though I would share a few lessons learned in the process.

    I started with a stock 2012 Boys Hotrock 20. Only real difference from 2012 to 2013/14 is it looks like they added disc tabs in 2013. (I had the option to go 2012 or 2013 and liked the green color and missed that tabs at the time)

    My original goal was to replace some of the stock drive train and brakes with better parts from my parts bin and improve his gearing ratio.

    I looked online for deals as best as possible. Lots of close out on 9 speed parts and lower top tier bike parts (x-7, deore, ect....)

    Brakes - My first thought was to go disc. I tried an A2Z disc tab adapter with no luck. (There was a pinkbike story early this year which went this route on a Scott). There is a bit of round tubing on the rear drop out that prevents the A2Z adapter from fitting the Hotrock. My son had bent his brake levers in a couple of crashes so I went ahead and replace the brakes with Avid SD7 levers and V-brakes. They fit his hands well and have a excellent reach adjustment.

    Drivetrain - Goal was to use 9 speed saint I had sitting around and go 11-34 with 32 T ring vs the stock 14-28 and 36T ring to improve climbing and off road ability. He really likes the numbering on the stock gear indicator and it quickly became apparent that he wanted an optical display. I found a deore 9 speed shifter on sale and printed a label to give him the numbers. I did have to run the brake levers outboard of the shifters which was not my preference. I also swapped out the cranks and bottom bracket for a sinz 135mm crank and shimano Un-52 bottom bracket. This was probably not needed but I was on a roll. (Specialized listed the bb as a 68x128...this is wrong... stock was a 68x113)

    I planned to use an existing chain ring but did not notice the 5 bolt 110bcd pattern. I ended up with a non ramped 32T suigino ring.

    There are not many options for a wide / narrow 5 bolt ring if you are hoping to go that route. Raceface makes one but it starts in a 38t for cyclecross which was bigger than I wanted to go.

    Chainguide - The specialized guide is a nice idea with marginal execution. It still dropped chains on occasion. I am trying a bionicon guide. Added a bbg bash guard...cheap and well made.

    Cassette and Wheels - Since I was not going disc I had planned on using the stock wheels and swapping the cassette. It looked like a standard rear bolt on hub till I pulled the cassette and the hub started raining bearings. Specialized used a hub that the cassette doubled as the freehub body and held the loose ball bearings. This meant I could not simply swap cassettes and needed a new rear wheel. I am still finding bearings in my garage.

    There are not many off the shelf options for a 20" wheel with a 9 speed (or 10, 11...) compatible hubs so I built my own. For the rear I went with an Sram X-7 disc hub and Sun envy 20" 32 hole rim. I like cartridge hub bearings but not many 32 hole options to be had for under $50. I decided to ditch the front wheel too while I was in a building mood and get away from the bolt on wheels. This should make changing flats trail side easier since the stock requires a 15mm wrench (not found on our average multi tool). I went with a Shimano deore disc front hub and Sun envy 20" 36 hole rim. (I could only find one Sun Envy 32 hole rim or I would have gone with an x-7 hub up front). I opted for disc hubs just in case the opportunity to go disc presents its self. I can always move them to the next build.

    I picked the Sun Envy 20 rims based on weight (sub 400 grams), width 22mm internal, and machining for v-brakes. Make sure to get the rear rim for both front and rear if you plan on using V-brakes. All in all the wheels turned out pretty nice. I probably spent $175 on all the wheel parts not counting my labor. (its hard to find spokes cheap) I did look at the Sun Cr-18 but the Envy was wider with a modest weight gain.

    I swapped out the stock tires for some Schwalbe Moe Joes...true 2.0 width and sub 400 gram weight. The stock tires were closer to 700 grams each. I also went with some lighter weight schwalbe tubes.

    The stock fork was swapped for a Spinner Air. Its an improvement but I am still working on that one.

    The bike dropped a couple pounds and is sitting around 23lbs. I think he will enjoy it more on the trail and it definitely will handle single track better.

    Most importantly...I can be honest and say the project was 25% for him and 75% for me...I had fun!
    Attached Thumbnails Attached Thumbnails Project Specialized Hotrock 20 and lessons learned-img_3766.jpg  

    Project Specialized Hotrock 20 and lessons learned-img_3767.jpg  

    Project Specialized Hotrock 20 and lessons learned-img_3768.jpg  


  2. #2
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    Nice setup. I do like the green. The shop where we bought ours only had teh red on stock. Anyways, I too modded my son's 2012 Hotrock 20. I didn't build wheels though so that saved a lot of cash. The stock suntour fork is decent btw because it can be modified to suit the child's weight. My son got a year out of the bike before he outgrew it and into a 24er. Though, we did get a couple good rides in Big Bear with it. Hehe, I could not imagine how much harder it would have been with the stock bike, lol. The bike went to my daughter and I hope she doesn't sprout too fast hehe.

  3. #3
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    wh0a, please post an update on that Bionicon Guide. I'd love to hear how it works out. I might need to get one of those.

  4. #4
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    We finally got some trail time on the bike and the bionicon guide. I had some trouble with chain line, bottom bracket length, the 34T cassette and the bionicon guide but think I finally got it sorted out. Initially I had trouble getting into the 32 & 34 T on the cassette with out the chain rubbing on the derailleur cage. The guide seemed to make it worse pulling the chain outboard.

    Moving to a 107mm bottom bracket and adding some chain ring spacers solved the problem. I also need to run the bionicon guide as close to the cranks as possible and angled slightly inboard toward the tire. I think there is more wiggle room on larger bikes with full length chain stay but makes for tricky angles on a kids bike.

    First trail ride it worked like a champ. Did not drop a chain and everything ran quite and appeared to shifted smooth. Its a light a simple guide that I think is an improvement over the stock chain guide system.
    Attached Thumbnails Attached Thumbnails Project Specialized Hotrock 20 and lessons learned-img_3825.jpg  

    Project Specialized Hotrock 20 and lessons learned-img_3824.jpg  

    Project Specialized Hotrock 20 and lessons learned-img_3822.jpg  


  5. #5
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    I found it very hard to stop the chain dropping even with the c-guide and clutch RD. I ended up having to make some custom guides which combined with the c-guide have eliminated the problem. Short chainstays and wide rear cassettes are probably the cause.

    On one bike I could make a BB mount version:



    On the other I needed to make a more complicated seat-tube mount version:


  6. #6
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    That's really nice work. I am hoping the chain will hold but have been worried it will not. I was planning for a seat tube mount guide if needed.

  7. #7
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    String. Sweet project.
    I'm headlong into my own Hotrock 20" project for my 5 yo daughter. I've got everything except the disc wheels. I'm probably going to build it from scratch like you but struggling to find the right length spokes that are not too spendy.

    I have question about your BB upgrade. I'm getting a Turn3 square spindle crankset but I would like to replace the stock. I read that you switched to 107mm BB spindle. Did this solve your chain line or whatever issue and have you stuck with the 68x107 bb? How's the Spinner Grind fork now? I'm getting that too.

  8. #8
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    Quote Originally Posted by TigWorld View Post
    I found it very hard to stop the chain dropping even with the c-guide and clutch RD. I ended up having to make some custom guides which combined with the c-guide have eliminated the problem. Short chainstays and wide rear cassettes are probably the cause.

    On one bike I could make a BB mount version:



    On the other I needed to make a more complicated seat-tube mount version:

    Are you selling this guide?? Sweet.

  9. #9
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    The 107mm BB worked but just barely. A couple more mm shorter would have been ideal. The chainline with the 107 and the 34T cog rubs a bit but does the job. I had to teach my son to use it as a climbing gear and not a normal cruising. I angle the bionicon guide toward the wheel a bit more than needed and that seems to give the range we need.

    I never did get the spinner working and ended up switching to the MRP. Expensive but very much an improvement. We did some resort riding this summer in deer valley and it handled great.

    I bought the spokes from Dans Comp (bmx store) https://www.danscomp.com/. I am glad I used disc hubs since with MRP fork I had to go disc with an Avid BB7. Plus I can always rebuild and use the hubs in future.

  10. #10
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    I've added up all the parts I needed for the wheels and without labor (I'm not knowledgeable about wheelbuilding on my own yet), the price i's getting up there. So I'm thinking of going for this with a bit of customization. Working on the shipping cost with them at the moment.
    EMS NOVATEC 406mm 20" Inches Folding Bikes Wheelsets Rim DS041 042 hubs 32Holes for Disc V Brake Chain wheel Free shipping-inBicycle Wheel from Sports & Entertainment on Aliexpress.com | Alibaba Group

    So with a 34t in the back you think you could run a bit more narrower than 107mm bb spindle? There are 105 and 103 I saw I could pick up.

    Everyone I've talked to and read here have had the same issue with chain drop. So I decided to go narrow-wide chain ring upfront and a clutch XO rear der I have sitting around. I was thinking of running an 11-36t but may just stick with a 34t and then a 30t NW chainring. As an added insurance, I'll probably jimmy-rig an E13 XCX high clamp top guide to fit. I also just purchased a Spinner Grind Air from lil shredder.

    I'll post a photo of the ride when I finish both Phase one (without disc wheels and 10 spd drivetrain).

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