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  1. #1
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    About to Start a New Build - GT Aggressor 20"

    My son's 7th birthday is coming up. After 3 years of riding BMX on his Intense race bike (and the occasional trail ride on the race bike), he has his mind set on a mountain bike and starting to ride the trails with Dad!

    I did a ton of research, looked at all the specs, thought I had my mind made up. Then we went out and actually tried out a few of the bikes. Specialized Hotrock was very nice, but I feel overpriced for what it is and the fork barely moved. Giant XTC Jr20 just looked and felt cheap. Cheap brakes and I seriously could barely make the fork move at my weight. Looked at a bunch of others, but was surprised when both I and my son preferred the GT Aggressor. Getting it for $299

    It has good geometry and decent spec. The fork actually works, and it has decent wheels. It was the lightest of the three at 11.4 kg (25.1 lb) with all of the reflectors and kickstand.

    I will pick it up in a few weeks and already have the upgrades on order. I got the following from CRC for just a hair over $100:

    Schwable Moe Joes front and rear
    Maxxiss lightweight BMX tubes
    SRAM PG730 12-32 cassette (to replace the 14-28 stock)
    Kore lightweight stem (130 gram)
    FSA lightweight bars (190 gram)

    Plus laying around I have:
    lightweight seatpost
    Ti front and rear QRs (bike has QRs)
    Alloy Seatpost collar
    Upgrade brakes - Sinz from his BMX and Avid Speed Dial

    I will post pics when its all done. I should get it down to about 21-22lbs and he will have a sick bike. $400 all up.

  2. #2
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    nice mods, can't wait to see pics..

  3. #3
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    Definitely want to see pics, this should be good. By chance do you know the weight of the frame alone? I'm planning way ahead for my build.

  4. #4
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    OK, time for an update. Bought the bike yesterday for $299 all up. Still very happy with the purchase, but there were a few surprises/observations. Here are my thoughts on the bike:

    Good frame, good weight and geometry. Low standover, long top tube (relative to other kids bikes)
    Cranks are actually pretty nice and light weight. Happily surprised to confirm they are 140mm, not 152mm as some specs show
    Fork works better than any others we tried. Actually moves under a kid, althought there is no rebound control
    Brakes - calipers are decent, levers are junk (plastic tektro, too big, etc)
    Stem, bars, seatpost - all alloy, but still quite heavy
    Bottom Bracket and headset - appear to be basic low end steel
    Tires and tubes - cheap, heavy
    Pedals - junk plastic, but my son likes how they look. Will replace once he destroys them
    Rear wheel - this was my biggest surprise. Uses a thread on shimano freewheel hub rather than a cassette. The freewheel unit on its own must be almost 2 lbs. This is the single heaviest part on the bike, and not sufficient gearing (14-28). Unfortunately my plan to replace this with a light cassette with wide gearing was foiled by the fact its a freewheel, not a cassette.

    OK, on to the fun - upgrades:

    Stem - kore alloy 90mm, 6 degree
    Bars - FSA Vdrive alloy - may need to cut these down as they are a bit wide
    Seatpost - FSA alloy - had laying around
    Seat - Revell - had laying around - much lighter than stock and honestly not that much bigger
    Tires - Schwalbe Moe Joe 2.0 front and 1.8 rear
    Tubes - Maxxis BMX Ultralight
    Skewers - A2Z Titanium - had laying around
    Brakes - replaced rear calipers with Avid SD7 (front caliper stayed stock), levers are Sinz, full length blue housing - all of which I had laying around
    Cranks - decided to swap the stock cranks to his BMX and move the Sinz cranks to the MTB. Honestly, the weight was extremely close. I did it purely for cosmetic reasons. The stock cranks were silver and looked out of place. His BMX is silver, so it worked perfectly
    Bling - anodized barend caps, top cap bolt, chainring bolts, dice and skull inner tube caps - had all laying around

    So far, all upgrades cost me under $100.

    The one upgrade that I could not do which annoys me is the rear cassette. The stock one is a boat anchor and it needs better gearing. So, what to do? More upgrades!!!!!!

    On the way:

    Rear hub - LX 36 hole, 8/9 speed - found online for $12!
    Cassette - SRAM PG730 12-32 7-speed - already bought in the original $100
    Cassette spacer - to put 7 speed cassette on 8 speed hub - $4
    Bottom braket - not really necessary, but found a lighter upgrade for $10
    Shifter/derailleur - considering a swap to SRAM x.3 trigger and med cage der. - have seen the feedback that the grip shift can be hard to use and it does seem pretty tight, even for me. - Seems like a good upgrade for $35.

    So, $400 so far and will be under $500 in total. All the important parts have nice upgrades. I have not been able to weigh it yet, I will do it after I replace the rear hub. I'm guessing 20-21 lb when its all done.

    Most importantly, he gets it at his birthday party in 2 weeks. I can't wait to see his reaction. And I already have a ride planned for the day after his party. Then the work will all be worth it!

    About to Start a New Build - GT Aggressor 20"-2013-03-014.jpgAbout to Start a New Build - GT Aggressor 20"-2013-03-012.jpgAbout to Start a New Build - GT Aggressor 20"-2013-03-015.jpgAbout to Start a New Build - GT Aggressor 20"-2013-03-016.jpgAbout to Start a New Build - GT Aggressor 20"-2013-03-017.jpgAbout to Start a New Build - GT Aggressor 20"-2013-03-018.jpgAbout to Start a New Build - GT Aggressor 20"-2013-03-013.jpg
    Last edited by jamescbrennan; 03-10-2013 at 08:15 PM.

  5. #5
    eBiker
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    Nice build! Your kid will love it.

    If it's not too late and you can stand the weight penalty, there is a Shimano 7 speed Megarange 14-34 cassette (freewheel) that can be had for cheap.

    More important than the rest is dumping the grip shift for trigger. That grip shift can be hard even for me, but the trigger is so light and intuitive, my 5 year old rocks it without issue.

    P

  6. #6
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    Thanks, I did look at the megarange 14-34, but didn't like the fact that there is a huge jump from the 24t to the 34t cog in that cluster (it basically replces the 28t with a 34t). Also, with a 34t chainring up front, I want to have the 12 in the rear for the top end as well. Plus, its a huge, heavy hunk of steel that I want to remove.

    I got such a good deal on the hub ($12) that the only real cost will be in the labor to relace the wheel.
    Last edited by jamescbrennan; 03-13-2013 at 03:58 AM.

  7. #7
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    Great job on the upgrades so far! Where did you get the hub? Do you think you can reuse the spokes? I'm working on the same exact bike but in the green color. I was really disappointed to find that its a freewheel in the back too, as I already bought a sram pg950 cassette. I'm also having trouble getting the bottom bracket off. It's different from all the ones I worked on before. It seems to have seized on the the frame. I will take it to my local lbs and see if they can give it a go. I will post pics of the bike when I'm done, if I'm able to since I might noe have enough posts.
    Last edited by kaochaos1; 03-15-2013 at 12:27 AM.

  8. #8
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    Found the hub on chain reaction cycles. Not sure the spokes will fit, but both hub flanges seem very similar. I'll find out next week when i take the wheel and new hub to the shop.

    I have not gotten the botton bracket yet, now im a bit concerned about the work to remove it. Hopefully mine is a bit easier.

  9. #9
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    Hi nice looking bike, what I am wondering about is why you didn't go for a 24", he's 7 and will grow out of the 20" pretty quickly, the 24" would have given him at least 3-4 years before you have to take the next jump to a 26"

  10. #10
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    He is on the shorter side, so there are no 24 in bikes with low enough seat or standover to work for him now. The bike fits him perfectly now and will for at least another 1-2 years. He is already a very proficient rider from his BMX racing, so we will be progressing pretty quickly to technical stuff. He really wants to start doing some downhill with me as well. So, the smaller bike will suit the type of riding we plan to do. I want him to be confident in riding, not struggling due to the bike being too big. Secondly, I have 2 more after him, and plan to hold onto it for his sisters. So I should get my money out of it.

    He could certainly do it, he rides my BMX cruiser and even my 26" DJ bike on the street, but I wouldn't put him on technical trails with a bike that big.

  11. #11
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    Further update - I changed out the Shimano grip/twist shift and Tourney rear derailleur for a SRAM x.3 Trigger shifter and derailleur. HUGE DIFFERENCE!!!!!!! My son can now shift his bike so much easier. He used to have to take his hand off the bars and really twist the prior shifter. Now he is shifting with his hands in a totally natural position and shifting much easier. Best $35, 60 minute upgrade I could have done. FYI, I also went with a midcage derailleur which helps with clearance.

    The only thing I have left is to rebuild the rear wheel with new hub and cassette.

  12. #12
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    Finally finished everything, rebuilt the rear wheel by myself (first time ver building a wheel!) with the new LX hub and real cassette. The bike weighs in now at just under 21lbs. And with the improvements in shifting and gearing, my son is now out on the trails with me and getting better every time. Last weekend, we rode the Olympic XC Course in Melbourne. He loves flowy, winding tracks, is getting faster and more confident on downhills, and riding technical sections without even thinking about it. I'm really excited, because this is just the start and I know I'll have a long term riding buddy! Well worth the effort building up a great kids mountain bike.

  13. #13
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    Thank you so much for this thread! I am considering buying my 6.5 year old son a GT Aggressor 20" bike.

    What model year do you have? 2013? It looks like they've changed the specs for 2014.

    I wonder about the new specs and how they compare to what you found on yours (some of the parts which you said surprised you). For example, it looks like they're now using a cassette in the rear? And the fork is rigid?

    2014 Aggressor 20" Boys - Boys Bikes - Kids Bikes - GT Bicycles - 2014 Bikes

    Also, I don't like the idea of plastic levers for the brakes. It's hard to tell what the 2014 speced.

    Could you take a quick look at the 2014 specs and give me your take? I personally don't mind the rigid fork as long as it may have made the bike lighter and they may have upgraded some of the other components. I'm not as educated on parts as you are so any advice or insight on how the 2014 stacks up would be greatly appreciated! Thank you!

  14. #14
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    2014 specs read as:
    14-28T F/W

    I am pretty certain that is still a freewheel, not a cassette hub. The stock components are nothing great.

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