# Giant XTC Jr Build



## lem2 (Mar 2, 2008)

My son Reuben who is 7, likes the color Blue Red and Orange and is tall for his age.
He enjoys going on the trail with me on his 18" Haro BMX. He is thin and the BMX is heavy, so I looked around at 20-24" mountain bikes. The ones from Lil' Shredder and Trail Craft are nice but could not afford them. And I have a ton of parts laying around.









My plan was to modify my daughters 26" XS GT frame which she outgrew with 150mm cranks and 24" rims.










It was a pain looking for 150mm cranks, and modifying a standard crack cost a lot. Thorn makes cranks from 140-175 in 104bcd. (UK sjscycles.co.uk) About US$ 70 to my door, And looking for a decent 24" rims is also a pain. Good thing Stans have them.

















As I took apart the GT Frame, even after grinding away the seat tube to make it smaller, its still tall for him and would hit his balls if he stands over them. So need to sell a GT XS frame!!









I was looking at the 2016 Pivot Point frame which only have 11.25' of seat tube. With a 24" rims and 150mm cranks he can grow old with it, but again cost was the issue at $500++ for the frame alone. Point - Pivot Cycles | Pivot Cycles | Performance Redefined

There are nice 20" MTB out there but he will outgrow them fast, So 24' is the way to go. After searching and researching. I decided on getting a Giant XTC Jr 24" Disc








(all I need is the frame with disc brake tabs and this is the cheapest, Sad that they could not sell just the frame set, there are a lot of used 24" wheeled frame for sale online but shipping + adding a disc brake tab and removing the caliper tabs + Repainting will cost more)

The Giant XTC Jr 24 Disc is nicely equipped in nice Orange but heavy at 28.5 lbs and handle bar is narrow, seat tube was still tall so I grinded 1.5inch off of it! 




I will just convert it to a 1x9 with a 150mm Thorn Crank + 32T Raceface + bashguard with a 12-36 at the back, which is enough for the trails we go to.

Here are the pictures of what I did!! Big thanks to my LBS Buena Park Bicycles for getting the parts that I need and giving a me a great deal on the Bike. And to this Website MTBr for all the tips and tricks I got from building this Bike!









Disassembled the bike!








Could not find the size of the headset so posting it here for reference.








He's helping!








BEFORE








After. wider handlebar, with redmonkey grips! He wanted to know how fast he was going.









Before








After! 203mm in front and 180mm in the rear! Shimano 1x9


















Future plan, change the travel from 140 to 100, need to save up for it. 
It is noticeable lighter at 25lbs from 28.5lbs.

Giant should do away with the kickstand to make the chainstay shorter like the ones in lil shredder and trailcraft.

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## Steve-XtC (Feb 7, 2016)

Did you by any chance weigh the frame by itself? 
I'm curious as Giant actually make their own frames ....


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## lem2 (Mar 2, 2008)

Steve-XtC said:


> Did you by any chance weigh the frame by itself?
> I'm curious as Giant actually make their own frames ....


3.8 lbs with the bottom bracket


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## Steve-XtC (Feb 7, 2016)

lem2 said:


> 3.8 lbs with the bottom bracket


Cheers, that seems to confirm my suspicion that choosing a frame from any decent manufacturer has little to do with the overall weight of the bike.

I get that to be 1.712 kg... and taking away 312g for a BB (a bit of an average) leaves 1.4kg

Even a complete "money no object" metal 24" frame in alux alloy or Titanium seems to be at best 200g lighter (a heavy tube and less than a tire) or difference of stock pedals. (carbon might be different)

So you might as well choose based on colour


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## POAH (Apr 29, 2009)

why do you have 140mm forks on a bike that comes with 50mm ones?


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## Steve-XtC (Feb 7, 2016)

POAH said:


> why do you have 140mm forks on a bike that comes with 50mm ones?


 The ones from Lil' Shredder and Trail Craft are nice but could not afford them. *And I have a ton of parts laying around*.

Future plan, change the travel from 140 to 100, need to save up for it.


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## lem2 (Mar 2, 2008)

POAH said:


> why do you have 140mm forks on a bike that comes with 50mm ones?


I know, looks stupendous.  but going through the forum, a lot used a fork for 26" wheels and did fine. The old fork that I had was 14o adjustable travel but still a lot for a 60lbs kid. It was also lighter than the stock fork.

Will have it down to 120mm or the smallest possible travel that they can modify in the next paycheck. And also adjust it to his weight.

Will post pictures when it's done.


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## POAH (Apr 29, 2009)

you'll need to lower it down to 50-60mm


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## POAH (Apr 29, 2009)

Steve-XtC said:


> The ones from Lil' Shredder and Trail Craft are nice but could not afford them. *And I have a ton of parts laying around*.
> 
> Future plan, change the travel from 140 to 100, need to save up for it.


I had a ton of parts too but I didn't put my old 120mm manitou minutes on a bike designed for 60mm. it will make the front too high and stress the frame out


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## slapheadmofo (Jun 9, 2006)

I imagine that frame is going to be fine handling the 'stresses' put on it by a 50lb kid. 
Doesn't look too slacked out to me either. My kid would've loved that thing!


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## Steve-XtC (Feb 7, 2016)

POAH said:


> I had a ton of parts too but I didn't put my old 120mm manitou minutes on a bike designed for 60mm. it will make the front too high and stress the frame out


I'd not worry about the frame stress given the kids weight and the over-specced tubes....

It will be interesting to see what it does to the handling though.

Depending how faithfully it follows the adult XtC geometry I'd think that *some* extra front height will actually produce a better all round balanced bike!

My XtC adult 27.5 climbs like a demon (makes me look a lot fitter than I am) but could do with some extra slackness for trail riding and the stuff we ended up riding.

TBH the main reason I haven't looked into changing it is the fact I'm more scared of breaking my (carbon) frame on a wipeout/rock..... I managed a full forwards somersault the other day (with only a little help from my head and the floor)... Ollie thought it was very cool and I explained it was only cool when you do it deliberately!

First thoughts were ... Oh heck .... hope the frame didn't hit a rock.... after checking out the frame and straightening the bars I discovered blood pouring from my leg!


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## lem2 (Mar 2, 2008)

Looking at the frame as it stands, and comparing it to the old fork, the front was raised by 3" which is slacker.










I did not think of that when I built the bike! Now I really need to lower the front by at least an 1nch to make it less "slacker"

The trails we ride are normally flat with minimal climbing. The angle is still wrong, will correct it and post pictures soon.

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## dc40 (Oct 4, 2013)

Steve-XtC said:


> Future plan, change the travel from 140 to 100, need to save up for it.


You should be able to lower your 140 to 100... you should be able to get two 20mm spacers from fox.

Also, remember 10mm = .5 HA change


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## lem2 (Mar 2, 2008)

dc40 said:


> You should be able to lower your 140 to 100... you should be able to get two 20mm spacers from fox.
> 
> Also, remember 10mm = .5 HA change


Thank you for the tip! I don't know how much would that cost or if I have the skills to do that. On My own. Hope it's a cheap fix

Having a front 20" wheel built up will be cheaper I think! But the bike will look like a circus bike with a smaller wheel up front.


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## dc40 (Oct 4, 2013)

I heard it is not to difficult and spacer shouldn't cost that much. You should be able to lower it all the way down to 80mm.

http://service.foxracingshox.com/consumers/Content/Travel_change_32mm.pdf


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## lem2 (Mar 2, 2008)

dc40 said:


> I heard it is not to difficult and spacer shouldn't cost that much. You should be able to lower it all the way down to 80mm.
> 
> http://service.foxracingshox.com/consumers/Content/Travel_change_32mm.pdf


Thank you for the link! Looking at him, I need to lower it just a tad bit. Will see if my powers can do the job myself.


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## hallin222 (Oct 13, 2005)

Very nice build. Fun read. Thanks for the details. But....Whoa, that saddle looks way low. I'm sure it's to gain confidence on the new bike, or to allow his to stand flat footed while straddling, but he's nowhere near proper leg extension when pedals are at 6:00 and he's near kicking his own backside when at the 12:00 position. I recommend raising it as soon as possible.

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## lem2 (Mar 2, 2008)

hallin222 said:


> Very nice build. Fun read. Thanks for the details. But....Whoa, that saddle looks way low. I'm sure it's to gain confidence on the new bike, or to allow his to stand flat footed while straddling, but he's nowhere near proper leg extension when pedals are at 6:00 and he's near kicking his own backside when at the 12:00 position. I recommend raising it as soon as possible.
> 
> Sent from my SAMSUNG-SGH-I337 using Tapatalk


Yea you are right, just building his confidence, I will change/increase it little by little. It's a big jump for him from 18" to 24". I told him we will add a suspension seatpost later, that's his goal. Thanks for noticing forgot to mention that.


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## Steve-XtC (Feb 7, 2016)

lem2 said:


> Looking at the frame as it stands, and comparing it to the old fork, the front was raised by 3" which is slacker.
> 
> I did not think of that when I built the bike! Now I really need to lower the front by at least an 1nch to make it less "slacker"


Just comparing the photo's it is surprising they don't look a lot further off.

One completely subjective but possibly easier to use gauge is the rear triangle.
Stock it drops to the BB but modded its rising.

You could print / stick in photoshop etc. and try and visually get an idea of how much that might need to change?

This is something I did when looking at various 24" frames prior to buying one and then you see what it is that is different in geometries more visually. It works much better on screen (as you can change transparency etc.) but its noticable that the XtC Jr. (Yellow) starts off a *lot *higher than the parent or Whyte at the front. (Aligned on seat tube and headset) but if you centre the wheel hubs its different again!



> The trails we ride are normally flat with minimal climbing. The angle is still wrong, will correct it and post pictures soon.


Like I said the "parent bike" is a hell of a climber.... much less an all-round trail bike.

On a few occasions I had to hire a "all rounder" bike (local trail centre entry level Whyte 603) I noticed the differences both positive and negative. The Whyte is much easier to manual, you notice this before even getting to the trials.

Anyway..... the point is is you are messing with the geometry then you don't necessarily want to go back to the stock bike...


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## POAH (Apr 29, 2009)

dc40 said:


> Also, remember 10mm = .5 HA change


no it doesn't


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## dc40 (Oct 4, 2013)

POAH said:


> no it doesn't


From doing google searches online, it is good reference/estimate to baseline off of... 10mm equals .5 degrees. or 20mm equals 1.0 degree. Depending if you reduce or increase your travel will change it by -+ HA. The .5 degrees is not taking into consideration sag.

Now if reducing and swapping out forks you need to take into account travel and the axle to crown height.

You can even check against the below geo calculators... I have validated against others too w/ similar results.

geometryCalc


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## GSJ1973 (May 8, 2011)

dc40 said:


> From doing google searches online, it is good reference/estimate to baseline off of... 10mm equals .5 degrees. or 20mm equals 1.0 degree. Depending if you reduce or increase your travel will change it by -+ HA. The .5 degrees is not taking into consideration sag.
> 
> Now if reducing and swapping out forks you need to take into account travel and the axle to crown height.
> 
> ...


Correct, rule of thumb has always been 20mm increase in travel slackens the HTA by 1 degree if all things are equal with fork mfg crowns, etc.. Also verified by swapping out a 140mm Pike fork for a 160mm Pike on my Santa Cruz.

So to the OP, a 140mm FOX suspension 26" fork if memory serves has a 510mm A-C, and the bike probably has a 410mm A-C fork on a bike designed fork. You are probably 4" too high on the front end over stock regardless of the super slack head tube angle that Fox fork created. Taking it down to 100mm will only reduce about 1.6 inches, which still probably isn't enough but should work until you can get a 24" fork with an A-C of 410-430mm's which would be ideal.


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## POAH (Apr 29, 2009)

dc40 said:


> From doing google searches online, it is good reference/estimate to baseline off of... 10mm equals .5 degrees. or 20mm equals 1.0 degree. Depending if you reduce or increase your travel will change it by -+ HA. The .5 degrees is not taking into consideration sag.
> 
> Now if reducing and swapping out forks you need to take into account travel and the axle to crown height.
> 
> ...


in reality it doesn't actually work like that


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## dc40 (Oct 4, 2013)

POAH said:


> in reality it doesn't actually work like that


Please explain then... because I have got similar results when lowering my Talas and GSJ1973 states similar results in his post and have confirmed same conclusion with my local bike shop owner/mechanic.


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## hallin222 (Oct 13, 2005)

This is all very basic trigonometry. Remember your SohCahToa?

Head angle changes due to fork length increase are completely dependent on the original frame geometry. For example a shorter wheel based bike with a steep head angle will be more greatly impacted by a longer fork than would a longer wheel based bike with a slacker stock head angle. 

This is why your son's bike's geometry changed so much. If you'd have added a similar length fork increase to an XL downhill bike, for example, the angular change would be less.

Make sense?

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## lem2 (Mar 2, 2008)

Our second ride!! He like it a lot!! Waiting in a new wheelset so I can raise the seat higher.















Hope the 20" wheel will be finished soon. I tried to slowly increase the seat but he is too scared to ride if he can't plant his feet when he stop. It will only be temporary. Then back on the 24" when he is more skillful!!!

He is much faster on this one compared to a BMX bike! And I agree on someone that if you could build a quality bike, or afford to buy one. DO IT! If you build it they will ride!

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## Trekkie8 (Jan 21, 2016)

He is big enough for 24" , but adjust the reach of the lever and position them right. He can't brake if you look at the last picture. If he learns how to brake he will get the saddle up,in no time


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## lem2 (Mar 2, 2008)

Trekkie8 said:


> He is big enough for 24" , but adjust the reach of the lever and position them right. He can't brake if you look at the last picture. If he learns how to brake he will get the saddle up,in no time


Noted! Thanks.


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## Chillout (Sep 19, 2010)

Nice, job. Much braver then me though. I don't know if I'm ready to go chopping away at the frame yet lol. Def need to bring mine down too. 28.8 is heavy imo. I didn't realize the kickstand was a 1lb. Might look for a lighter version because my son likes the stand.

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## lem2 (Mar 2, 2008)

TEMPORARILY, changed the 24" wheelset to 20" so he could have better leg extension. See the seat height difference. 
I know the bike looks super awkward but he is more comfortable riding it being able to plant his foot right away when he stops.

Also changed the drivetrain from XT 1x9 to Zee 1x10. I like the short profile of the Zee. Changed the pedals to composites and the grips to match!










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## bme107 (Jul 23, 2008)

Reminds of a monster truck when they put on regular wheels for trailer-ing.


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## GSJ1973 (May 8, 2011)

lem2 said:


>


Needs a serious stem flip and spacer removal. Otherwise looks good for a short term solution!


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## lem2 (Mar 2, 2008)

So far so good!

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## steh-fan (May 27, 2006)

*headset*

Hi,

pretty impressive work!
Could you maybe post more specifics about the headset?
It is impossible to find any information on it.
What was the original Giant one and which one did you use?

Thanks a lot!


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## DirtyDayv (Mar 22, 2020)

*100mm forks is a geometry improvement To XTC SL Jr 24, IMO*







Upgraded a 2019 XTC SL Jr 24" for my 9yr old including 100mm travel forks (Rockshox Reba) & thought it worked out well. Actually think the geometry is just right now. Head angle was steep with the old 63mm Suntours. Didn't swap out the straight stearer but looks like the head tube will take a tapered style headset. Not sure if this is the case but if so, this would give you more options on late model forks.


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## DirtyDayv (Mar 22, 2020)

I stayed with the original ‘straight steerer 1’1/8” headset’ & installed the appropriate Rockshox Reba 100mm accordingly. However, I noticed the head tube was tapered & it looks like a tapered headset could be swapped out. Apologies, I don’t have further details, I expect it’s just a case of measuring the upper & lower sections of the head tube & ordering the appropriate headset. Would have done it myself but every project has it’s limits : )


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## WarioTX (Jul 28, 2020)

first of all congrats on your kid's bike, it looks amazing, this is the setup I just finished for my 9yo, Giant XTC jr disc, pretty basic upgrades, new pedals, new shifter, new grips, removed kickstand and left shifter, he is a small guy but he is already doing some pretty decent drops and now I am looking to get a dropper that could work with his weight, hard to tell on the droppers I've seen what the minimum weight is in order to move the post down. has any one tried getting one for your kids?

another thing I'd like to do is change crank to single gear and tubeless tires, but I am not sure if the existing wheels will support tubeless tires, getting new wheels is where the next big spend is...and I am not really sure if I should go for it


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## DirtyDayv (Mar 22, 2020)

Hi WarioTX, Most droppers need about 20kg+ on them, any lighter & they can’t get it down. You may find a brand that works with a bit less weight but I used the ‘PRO droppers’ on both my kids bikes, mainly because these were the neatest of the external cable type, & they require around 20kg of butt : )
Cranks are alloy so I’d keep them & change the chainring & chain for ‘1x’. I just changed everything to Shimano XT (brakes, discs & gears 1x11) from a sale. One good thing about going 1x on this bike is you can use the spare cable routing for your dropper so it all looks nice & tidy.
The wheels are also alloy so I kept, don’t think tubeless is compatible, maybe run inserts if worried about punctures. I’d definitely change tyres if you’re hitting the dirt, 2.2-2.3” is as about as much as you’ll get into that rear triangle, obviously you could go wider up front. From memory, rear was Maxxis DHR 2.3” & front was Maxxis DHF 2.4”. Hope this helps : )


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