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  1. #1
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    And Another Hotrock 24" Build

    I just finished building up my sons Hotrock 24. It was a 2009 I picked up on Craigslist. I was thrilled to find one but pretty underwhelmed once I got it home and really went through it. I decided to fix it up with a big compromise being cost. I'm a total weight weenie for the kids BMX race bikes but I'm doing my best not to get hung up on their road/off-road bikes. The big goal was to make them work well.






    Like everyone else, I quickly realized that the front fork was crap. Since there are no decent low cost (OK, real low cost) 24” forks, I decided to go with a 26” fork. What is old now is great for a kids 24” bike. I decided to hunt down a 99-01 SID Air fork. They are pretty light, air adjustable which works great for a 80lb kid and totally rebuildable. I ended up finding a bike on Craigslist locally with a 2000 SID XC fork and a new set of Avid FR5 brake levers for $75. I kept a few other parts and donated the rest of the bike. The Rock Shox fork is only 1-1/4" longer than the stock fork.




    The fork mounted up great but then left me with the brake dilemma. Originally I was going to use the adapters they use for BMX to move the brake pivots. I decided that would work but I might as well take advantage of the disk mounts on the fork and frame. A quick eBay scan came up with a guy in Hong Kong selling complete sets of Avid BB7 brakes with rotors and all hardware for less than $70 shipped. I decided to use the cable brakes since I didn't want to deal with bleeding etc. When combined with some Jagwire cable, they work great. So good in fact, that I’m getting a set for my old hardtail.




    To fit the disks, I needed to change the hubs. XT or XTR would be awesome but I decided to just get some Deore hubs. The front cost me $18 new and the back was only $10 out of the local bike Co-ops part bin. I actually found a guy with a partial box of DT spokes on eBay that were the right length. I combined these with some alloy nipples and the stock rims. Yep, the stock rims. To be honest they aren’t that heavy and by reusing them, I saved $80-100. This was my first attempt at lacing wheels. It was actually real easy. I was surprised how round and true they were at the beginning. It probably took me a coupe hours to do each wheel but it was kinda fun. To round the wheels off, I threw on some CST (Cheng Shin) Tracer tires. Relatively light and cheap. I wanted something under 2” wide and these fit the bill.


    For gearing, I first needed a cassette. I again hit the bin of the local bike Co-op and came home with a super nice light Ultegra 9-speed cassette for $10. It’s only a 27 tooth but combined with the 22 low on the crank has worked out just fine. The front derailleur is a LX I picked up for $7 and the rear is an XT. Originally I got a long cage Shadow XT rear off eBay for $32. It was a rapid rise model. Huge mistake. I could never get the bike to shift to the low gears. Essentially I had a 9 speed cassette but could only use 7 speeds. I subsequently tossed it and found a short cage regular XT. Eureka! I had 27 speeds and a cage that wasn’t dragging the ground. The front derailleur is actually the one with issues now. The spacing of the chainrings on the original crank are a bit wider than the derailleur likes. It doesn’t have the range to prevent rubbing in high or low when cross chained. Oh well. My kid doesn’t notice so I’m not telling him. For shifters, I got a pair of LX’s on eBay for $15. Whatta deal. Again, new Jagwire Hyper cables.





    I kept the stock seat and post. The quick release is a bit cheesy and will probably get replaced. The bars are a set off an old Giant. I narrowed them down to around 23 inches. The bike ended up around 25 pounds with the Shimano clipless pedals. Not light but better than when we started. Actually a pound lighter than my others sons 20” Hotrock 7-speed.





    Chuck

  2. #2
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    Nicely done. Doing it cost effectively with maximum re-use is all the better.

  3. #3
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    What air pressure did you end up with on the fork? i am thinking 20 pos and maybe 25-30 neg to make it plush.
    Just Ride!

  4. #4
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    My fork is a single air version so all I have is air for preload and a rebound adjuster. I think I have been running between 20-30psi in the fork depending which kid is riding the bike. The shock pump I have is real high pressure so it's accuracy at low PSI is questionable. I wish I had one of the old low pressure Rock Shock fork pumps. The rebound is a bit high so I think I'm going to put new seals in and drop the weight of the oil in the fork. Either way, cool that I can adjust it and even cooler that I can easily get parts to rebuild it. The dual air you are using should be real nice.

    Chuck

  5. #5
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    One thing I forgot to mention. When I first put on the LX front derailleur, it didn't have enough throw to shift to the large chain ring. To fix this, I swapped in a narrower bottom bracket. I pulled the stock bottom bracket that measured around 117-118mm and put in a Shimano UN-51. The UN-51 is 113mm. This reduced the chainline by ~2mm. I think this put the final chainline right around 45mm which is where Shimano wants it. Before it was around 47.5mm.

    Chuck

  6. #6
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    I just got a sinz expert 113mm bb. Weighs 210grams and is pretty smooth. On the fork pump, marzoochi still makes a low pressure fork pump. I got one from chainreaction last year. You can get down to 2lb increments. I use it on my marzoochi marathon sl, the sid, and my newer xfusion velvet. A must have for fork fine tuning.
    Just Ride!

  7. #7
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    Awesome build! I'm not made of $, so I appreciate the steps you took to keep the cost somewhat reasonable! Thanks!

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