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Head tube angle for kid

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TheSandwichProtector

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Discussion starter · #1 ·
I'm looking at building a bike for my 11yr old starting with a HT Chinese carbon frame. Something like this:

262.02US $ 41% OFF|THRUST Carbon Frame 29er 15 17 19 Carbon mtb Frame 29 er BSA BB30 Bike Bicycle Frame Max Load 250kg 2 Year Warranty 18 Colors|frame 29 er|carbon frame 29ermtb frame 29 - AliExpress

However, I'd like to get something a little more slack. All the HT frames I can find seem to have a head tube angle of 69.5 or 70 deg. I guess my question is how much can I change that through fork, and other parts? I've seen a few companies like wolftooth put out an adjustable headset. If so is that the right move? Or should I just take the 70deg angle, build the bike and not worry about it? I was hoping to get to 67-68 deg if possible.
My daughter is 5ft, 65lbs and fairly timid on trail. I was thinking Carbon XS frame, 27.5 wheels and 120mm fork. I'm really nervous about buying all the parts and building the bike since I've never done anything like that before, but I'm willing to try.
Any help or advice would be greatly appreciated!
 
#2 ·
Not really answering your questions, but my daughter started riding about your daughter's age although I think my daughter was a little shorter than 5 feet tall at the time. The frame you linked appears to be too big for your daughter at her current height. The dimension specs on that bike are all over the place and do not appear to be accurate. The small 15 shows the seat tube to be 400 mm which is 15.78 inches and the reach to be 580 mm which is way out there for a small xc style bike, lol. My daughter who is now 5 foot 5 inches tall rides a 27.5 medium chameleon frame that I built up and she loves it. My daughters biggest issue back then was wanting her dropper to go low enough that she could stand flat footed while still being seated which I had to find a bike with a very short seat tube length in order to accomplish. I guess it gave her some sort of peace of mind by thinking if she could touch the ground if things went south then she'd be ok, lol. Some brand name frames aren't too much more than the price of the frame you linked. Good luck with your venture.
 
Discussion starter · #3 ·
Thanks for the response Tommy. I was using the previous link more as an idea. Here's one with better numbers...

1943172

228.8US $ 45% OFF|Carbon bike frame new geometry carbon bicycle frame T1000 148mm and 142mm thru axle carbon racing bike frame 29er MTB|Bicycle| - AliExpress

I've been looking at all the brand name stuff, but they're either too heavy or too $. I'd like to stay around $1500 and as far under 30lbs as I can get. We rented her an xs full sus when we were in Bentonville for a trip and she hated pedaling it up hill. I think it was around 33lbs. My thought was I can build her a super light weight HT while adding a dropper and some nicer brakes and fork then what I'd get with a heavier budget HT like a Rockhopper or something.
 
#4 ·
My daughter has been riding a medium Salsa Timberjack (last gen, not current) frame since she has been 5' tall.

I could not find a new bike to buy her, so I built up the frame I had on hand to test how it would be, she fit it great.

Put on a 40mm stem, cut some bars to about 680mm, put 165mm cranks on it with 27.5+ wheels and a Whiskey No.9 boost carbon fork.

I have several spacers above the stem so that as she grows, I can raise the stem up, put wider bars on, longer stem...

She loves it.

1943183
 
Discussion starter · #5 ·
Thanks Frank! That's helpful to know you were able to get her on a medium, size down the parts and make it work well. How much does the bike weigh? I was originally looking at the Timberjack, Specialized Fuse, and Fezzari Wasatch Peak. All of the sub 2k models come in around 33lbs. I was hoping to do better if I could, which lead me to the Chinese carbon frame option.
 
#6 ·
Bad geometry is bad geometry. I'd take the weight penalty any day, unless you are thinking straight XC or bike path rides. The same holds true for my kids' bikes. Within reason.

Bikes can be tough to get right now, but I would probably just keep an eye out for a decent quality complete hardtail within your budget. Don't just limit yourself to new, either. If you're patient, you can still find decent deals on site like pinkbike and local classified groups.
 
#7 ·
Putting a longer fork on the bike to slacken the head tube angle will increase the bottom bracket height and slacken the seat tube angle. Roughly, you need a 20mm longer fork to decrease HT angle by 1 degree. Seat tube angle will slacken by the same amount. Bottom bracket height will increase by about 8mm (40% of 20mm, ratio of chainstay length to wheelbase).

To compensate for the slacker seat tube angle, you can use a 9point8 fall-line-R dropper with 'forehead' option. You will need to check the max drop you can use because the seat tube length is on the long side. The nice thing about the 9point8 post is that you can shim down the stroke.

To compensate for the higher bb, your could buy a 29 frame, run 27.5 wheels, and use a short crank, which would probably be better for your daughter anyway. (My son, at 4'8" runs 140mm cranks. I'm almost 5'10" and running 165mm). The wheel switch alone would drop the bb by about 25mm. Most frame are designed around 175mm cranks so you could probably run 150mm cranks with no issues.

Depending on headtube standard the frame uses, you could get a -1.5degree headset from Works Components or Cane Creek. Actual angle will be a bit less because the raked out fork will drop the head tube which will steepen the head tube angle. The advantage here is that the seat tube angle will actually sharpen up a bit and the bottom bracket height will drop a bit. (To determine what a 'bit' equals, you would have to do some trig with the actual frame numbers, or find one of those bike geometry websites that are supposed to be out there.) I would still strongly suggest you consider a 29er frame with 27.5 wheels to drop the bottom bracket, and run height-appropriate crank length. Lower BB height will lower stand over and provide confidence boost.

Anyway, a fun rabbit hole to go down:)!
 
#8 ·
TheSandwichProtector said:
Thanks Frank! That's helpful to know you were able to get her on a medium, size down the parts and make it work well. How much does the bike weigh? I was originally looking at the Timberjack, Specialized Fuse, and Fezzari Wasatch Peak. All of the sub 2k models come in around 33lbs. I was hoping to do better if I could, which lead me to the Chinese carbon frame option.
Click to expand...
Keep in mind that much of the weight of those sub-$2k bikes is from the components as much as the frame. You'll run into the same challenge trying to build up a bike from parts within your $1500 budget. Unless you have a lot of lightweight parts laying around? I'd bet to stay in budget your bike build will still be 31+ lbs with one of the Alibaba carbon frames.
 
#9 ·
rton20s said:
Keep in mind that much of the weight of those sub-$2k bikes is from the components as much as the frame. You'll run into the same challenge trying to build up a bike from parts within your $1500 budget. Unless you have a lot of lightweight parts laying around? I'd bet to stay in budget your bike build will still be 31+ lbs with one of the Alibaba carbon frames.
Click to expand...
So true! It's amusing to hear folks complain about how heavy kids bikes are, and, in the same breath, how expensive they are! Kids bikes use adult bike components. Getting them lighter costs the same as getting an adult bike lighter. The weight difference from shorter bars, smaller wheels, etc. is negligible.
 
#10 ·
Don't over think it Dad... just let her ride, learn and have FUN!. I started my kids on tanky hardtails (spesh hotrocks, dirt jumpers etc.) at the ages of 5 & 7. They're now 14 & 17 and pretty good riders and doing high school mtb racing. Honestly the best bike upgrade I can't recommend enough is to put a dropper post on the bike. Makes a world of difference, especially for a timid rider.
 
Discussion starter · #11 ·
Thanks so much for all the responses and advice everyone! I guess I'll go back to searching for one of the budget friendly HTs we've been discussing above. Anyone have any experience with the Fuse or Fezzari Wasatch Peak?
abeckstead said:
Don't over think it Dad... just let her ride, learn and have FUN!. I started my kids on tanky hardtails (spesh hotrocks, dirt jumpers etc.) at the ages of 5 & 7. They're now 14 & 17 and pretty good riders and doing high school mtb racing. Honestly the best bike upgrade I can't recommend enough is to put a dropper post on the bike. Makes a world of difference, especially for a timid rider.
Click to expand...
Haha, but I'm a Dad, it's what I do!
 
#12 ·
TheSandwichProtector said:
Thanks Frank! That's helpful to know you were able to get her on a medium, size down the parts and make it work well. How much does the bike weigh? I was originally looking at the Timberjack, Specialized Fuse, and Fezzari Wasatch Peak. All of the sub 2k models come in around 33lbs. I was hoping to do better if I could, which lead me to the Chinese carbon frame option.
Click to expand...
Honestly, I haven't put it on a scale. If I had to guess, it's in the mid 20's.

The carbon fork trims a ton of weight. All the bikes you mentioned come with pretty hefty forks and fairly heavy entry level parts spec.

I built hers with a mix of XT/SLX 11 speed parts, carbon seat post (cut so that I could slam it at first), Stans Major wheelset…

1943197
 
#14 ·
I doubt your daughter will be ripping around hard enough to be affected by the angles of the bike. Really the slacker the bike the better it is at speed and the steeper the bike the better it is going slow. Of course that has it limits but a slack head angle flops around at slow speeds especially when climbing and an inexperienced rider will have a hard time with that. Having better control of the bike will give her more confidence. Having the right size is also part of the equation, maybe a 26” wheel is better.
 
Discussion starter · #16 ·
Thanks guys. For sure I'm overthinking things a bit, lol. Started down this rabbit hole in an attempt to save weight and $. Even though back in the day we rode anything we had...the more my girl enjoys her ride and wants to ride the more fun I'll have as well. She just wasn't having fun pushing the 34lb FS uphills. Complicating everything is the fact that I can't get her on any bikes to try out. I just have to choose one wait a few months for it to get here and hope it works out. If I don't do the Chinese carbon I think I've narrowed it down to the Fuse, Chameleon, Fezzari Wasatch Peak, and possibly Trek Roscoe 7. I found a Chameleon that's available in a size that will work for her even though it's a little more then we had budgeted:
Santa Cruz Chameleon A D 29 Mountain Bike '21
The other part of me wants to try building a frame up cause I've never done and think I'd learn a lot.
 
#19 ·
Lots of room in the budget for upgrades. But old geo. Mostly depends on what your kid rides.

phoenix.craigslist.org

Diamondback APEX mountain bike - bicycles - by owner - bike sale

Size XS or 12inch frame with 27.5 inch tires. Good for up to 5'2 height. excellent beginner bike for kids. Shimano APEX components. Good condition.
phoenix.craigslist.org
 
#20 ·
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TheSandwichProtector
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