Latest Kids' Project... Mountain Bike. (Updated pic on pg5)

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xnavalav8r
Posts: 2594
Joined: Mon Jan 21, 2008 12:09 pm

by xnavalav8r

I just bought a used Scott Spark Jr 24" on Craig's list. I paid a low enough price to make it worth stripping off all parts and starting over with just the frame and fork. Though, depending on height, I may run a 50mm travel 26" fork instead of the stock RST Capa.

Here is the link to the manufacturer's page.

http://www.scott-sports.com/us_en/produ ... 901/215634" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

At more than 13 kg this thing is a tank. My goal is to get it below 10 kg. Upgrades will include drivetrain, wheels, disc brakes, and cockpit.
Last edited by xnavalav8r on Sat Dec 10, 2011 11:31 pm, edited 3 times in total.

xnavalav8r
Posts: 2594
Joined: Mon Jan 21, 2008 12:09 pm

by xnavalav8r

Here are photos of the bike in "as-is" condition. It's on its way via FedEx. I expect to have it by the end of the week. I'll let my son bounce around the neighborhood on it will I start gathering parts for the upgrade and rebuild.

by Weenie


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trikobe
Posts: 187
Joined: Tue Dec 16, 2008 9:16 pm
Location: California

by trikobe

Love to see where this goes. Keep us updated.
I too was looking for a scott but a scale 24 for my kids. Curious how light you will be able to get it down to.

xnavalav8r
Posts: 2594
Joined: Mon Jan 21, 2008 12:09 pm

by xnavalav8r

As I consider my options, it is becoming clear to me that the only thing that will remain after I am finished is the frame... and maybe the fork (if I can't find a better alternative).

xnavalav8r
Posts: 2594
Joined: Mon Jan 21, 2008 12:09 pm

by xnavalav8r

Step One: Wheels

Disc specific, 24" wheels, converted to tubeless.

Rims: Alienation Deviant 24x1.75, 28 hole, 415g Front and Rear = 830g
Hubs: Circus Monkey HDW CNC 6 Bolt Disc MTB Hub F&R set 28 hole = 392g
Spokes: Union Titanium, 2.8g x 28 = 78.4g x 2
Alloy Nipples: 16g (56)

Total: 1394.8g (not counting rim strips or skewers)

Tires: Schwalbe MowJoe 24x1.85, 330g each = 660g
Skewers: Circus Monkey Ti = 49g (set)
Cassette: Recon 11-36 = 155g
Stan's No Tube Rim Strips = 55g

Grand Total: 2313.8g

Approximate price is US$350.00 depending on ebay vs. retail availability.
Last edited by xnavalav8r on Sat Oct 29, 2011 3:51 pm, edited 2 times in total.

xnavalav8r
Posts: 2594
Joined: Mon Jan 21, 2008 12:09 pm

by xnavalav8r

A question for the mtb suspension gurus...

What's better for a lightweight rider, air or coil sprung suspension? Air suspension is lighter but, as I understand it, is less tunable for small bump compliance. Coil suspension tends to be heavier, but I believe it offers a more supple ride.

In the case of my son, he is only 60 pounds, so I am trying to reduce the weight of his bike as much as possible while improving performance. But I don't want to sacrifice usable suspension for lower weight.

Suggestions?

109er
Posts: 746
Joined: Sat Jan 05, 2008 5:08 pm
Location: Oklahoma City

by 109er

are there 24inch air sprung forks out there? if so, i dont know if the quality would be that great. you can tune air forks for tiny riders. I've sent forks off to PUSH to get them tuned for 80lb riders.
green jacket, gold jacket...who gives a sh*t

xnavalav8r
Posts: 2594
Joined: Mon Jan 21, 2008 12:09 pm

by xnavalav8r

I'm not aware of a 24" air sprung fork. But the 24" coild spring forks are crap anyway. I'm considering using an older model, Rock Shox Sid (dual air) with 50mm of travel. It raises the front end very slightly, which slackens the head angle a bit. But that actually doesn't seem like a bad thing for a young rider.

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schmiken
Posts: 329
Joined: Sat Jun 30, 2007 9:53 am

by schmiken

Air definitely. It's possible to tune air suspension for tiny riders, but very difficult to do the same on coil/oil. It's possible, just not worth doing.

xnavalav8r
Posts: 2594
Joined: Mon Jan 21, 2008 12:09 pm

by xnavalav8r

The bike arrived today. It came disassembled and, to be honest, I'm too lazy to reassemble it just to weigh it. Suffice to say, it is a tank. I think the 28 pounds advertised by the manufacturer is a bit ambitious... this bike is nearly as heavy as my adult-sized, 6" travel, dually trail rig. That bike weighs over 30 pounds.

Anyway, right now it looks like only the frame will survive for the final build. I may stick with the fork if I don't find a better alternative. But used Rock Shox Sid dual-air forks can be had on eBay for under $100.00. I have found a couple of tuners who can rebuild the fork with 50mm travel, reduce the airspring to something appropriate for my son, and get the axle to crown length close to the 395mm of the current fork. Still working on a price though. It may not be worth it.

Drivetrain will be 2x9 (or possibly 2x10). I have most of the parts for that already. Just trying to determine if my sons thumbs are strong enough for trigger shifters or if we will use a grip-shift system.

The stock cockpit parts are steel (bars, stem, seatpost) and will all be changed for lighter versions. I have a carbon flatbar and several stems already. I might have to buy a seatpost.

I intend to switch to disc brakes. Avid Juicy brakesets are going as low as $75.00 on ebay. I just have to get something with adjustable reach for small hands. Wheels are discussed above.

I am confident I can get this bike down under 25 pounds. The only retail purchase I envision is the wheels. So I should be able to do this relatively inexpensively using parts I already have and a few good ebay deals.

Any thoughts or recommendations?

janbo
Posts: 31
Joined: Sat Aug 11, 2007 6:00 pm

by janbo

Old SID, when fully compressed has more than 1" of stanchion exposed. They could be rebuild in the way that stanchions fully get into lowers so you can have 80mm fork with ~410mm A2C.
If kid likes riding, it won't have complains on a bike. Let him ride it the way it is and upgrade when you get good deal on parts.
Buy him SPD :) I missed that in my cildhood riding.

xnavalav8r
Posts: 2594
Joined: Mon Jan 21, 2008 12:09 pm

by xnavalav8r

Thanks. That's what I was thinking about the fork as well. I've found one fork manufacturer that can tune a stock fork to get 65mm of travel with a 449 axle to crown length. But I'm afraid that will excessively slacken the head tube angle. 410mm sounds much better.

My son has been riding on SPD pedals for BMX and road the last 2 years. So that's a no-brainer for this build.

mika
Posts: 101
Joined: Sun Mar 01, 2009 5:39 pm

by mika

hello, i would like to know if it is possible to install quick release on 20" mtb wheels for kids? sorry for the hijacking xnavalav8r :oops:

xnavalav8r
Posts: 2594
Joined: Mon Jan 21, 2008 12:09 pm

by xnavalav8r

I think it depends on the hubs that came with the bike. If the hubs use nutted axles, I don't think you can change them over to quick release.

xnavalav8r
Posts: 2594
Joined: Mon Jan 21, 2008 12:09 pm

by xnavalav8r

OK, I have found several suspension tuners who say they can reduce the travel and axle-to-crown length of a Rock Shox Sid air fork to something closer to the stock fork. Stock axle to crown length is 395mm. The tuners say they can get close to that by removing shims. Price quotes vary between $80.00 and $150.00. So now I have to get my hands on a fork in decent condition at a reasonable price.

by Weenie


Visit starbike.com Online Retailer for HighEnd cycling components
Great Prices ✓    Broad Selection ✓    Worldwide Delivery ✓

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