haaseg

I sent this message to Trek customer service a few months ago and never heard a response. I sent it to a local dealer and was told my son likely needed something custom built. I thought I'd post it here and see if anyone else had similar experiences and had figured out what to do about it:

I have concern for the gear ratios on the Trek kids bikes. Since we've gotten the training wheels off of my son's Jet 12", I've noticed that he seems to be going nowhere fast, despite the fact that he seems to be spinning like crazy. I looked at several high-end 16" and 20" kids bikes on the market and I applied Sheldon Browns "Gain Ratio" calculation (https://sheldonbrown.com/gain.html). I was disappointed to find that the Trek Jet 16" had an even LOWER gain ratio than the 12" (The Jet 12" has the equivalent ratio of 34x21 on a typical 700c bike, the Jet 16" the equivalent of a 34x22). For this reason I was thinking of skipping the 16" altogether and going directly to 20". I noticed some other brands had "slightly" higher gain ratios (equivalent to an adult 34x17).

Another issue that my son suffers from is that the when he's making a tight turn, his inside pedal will slap the ground and cause back wheel to jump up in the air. This hasn't caused him to wreck yet - although that may just be because the gearing keeps him from going fast enough for it to be a real problem. I realize that I should be teaching him to keep his inside pedal in the 12 o'clock position when he's rolling through the corners, but he's only 4 and these things are hard to explain.

The other day my son was out with the neighbor on his $40 Huffy and it was immediately obvious that the kid was pedaling 1/2 as slow and going 2x as fast as my son. That cheap bike is also significantly lighter than the Trek. I noticed among other things that the bottom bracket on the Huffy is a full inch higher and the cranks are significantly longer.

So, are there any "good" small kids bikes that aren't over-built and under-geared? As adults, we like to think we are buying our kid really nice stuff. But if a disposable chain store bike is going to outperform we have to question our judgement.

himespau 

is he tall enough for the 20"?

haaseg

It would depend on the geometry. He rides a 20" trail-a-bike all the time, but even with the seat slammed he can't touch the ground with his tip-toes. The big question is can he stand to wait a while longer vs. how long will a 16" be good enough. I don't mind upgrading the bike every year... as long as the gearing is okay and it doesn't weigh more than my bikes.

ebartom

The Specialized Hotrocks are light. You can see reviews of the 16" here: https://www.mtbr.com/cat/bikes/kids/s...9_6179crx.aspx

It's definitely a lot of pedaling for relatively little forward movement, but better than the 12". We thought about building a 16" wheel with an internal gear hub, and putting that on the 16", but it's a lot of work, and my son can handle the 20" now. Probably I should look more seriously into doing that, because my daughter will be ready for it soon. And if anything she's a better biker at the same age than my son was, and she'll want to keep up with her big brother.

cabledawg

We've got a Schwinn 20" that has good gearing for cruising but not so much for hill climbing. It's a trade off we decided was acceptable. This bike has a very short seat tube and not a super long top tube, so by moving the handle bars back a little, it should accomodate smaller riders. Couldnt tell ya the model but its black and green, BMX style and only a year old. Was $100 at a sporting goods store.

Mongoose used to make decent bikes, both 16" and 20", that had good gearing and medium weight. All of ours were older dumpster finds that I brought back to life so I'm not sure if any of the newer stuff is any good. If you're good with fixing bikes, I suggest this route for growing kids. Replace old/broken stuff with quality parts and you'll have a bike that'll last for years.

Wildewinds

How tall is your kid?

My daughter is just shy of 48" and I just got her a 20" Specialized Hotrock 6 speed. She LOVES the gearing. I couldn't imagine a much smaller kid riding a bike that size, though.

haaseg

I went to like 6 different bike shops in the last couple of days and did a bunch more research online as well.

I think the 16" Hotrock is the best option right now. I measured the 20" Hotrock and it would be about an inch and a half too tall for him. Interestingly enough, the Trek Jet 20S will fit (the seat goes lower). However the Jet 20 has a 32x19 compared to the 36x16 on the Hotrock 20. When you take into account the crank length, the 16" Hotrock with it's 28x16 actually has a better gear ration than the Jet 20. The Jet 16 only has a 26x19 - it's way under geared.

So I'm really leaning towards the 16" Hotrock. I'm thinking have him run it stock until he gets used to. Later I can put front and rear handbrakes on it and buy a 16" freewheel (Niagara has them for under $25). Then I can run a smaller rear cog. If it's possible, I'd like to eventually ditch the chain guard and swap out the cranks with 3pc BMX cranks - that way I can increase the chainring size. Or see if I can at least get the cranks from the Hotrock 20 moved over.

kuan

I feel your pain. You are going to have to deal with this all the way until you get to a 26" wheel. Think this is bad? Wait until the kids outgrow the 20" wheelsize but are too small for a 24".

What you get is a pit bike like an SE LIL Ripper. I said like, because what you do then is change out the crankset for one with shorter arms and a larger chainring. Here's a picture of my kid's old Ripper reborn. Make sure though you get one where there is a crimp in the chainstay so you can replace the chainring.

NormDeplume

We're in this stage right now with my son. Hoping at this point he waits on a growth spurt until the fall, so we can get through another season on current bike.

kuan

The growth spurt will happen... as soon as you get him a new bike!

fietsbob

Often component pick is price point focused, then,
thru your Retail Shop you change things.
to be more ideal.. to your needs..

Such as changing the sprocket/cog on the rear hub, altering chain length.

Most people don't take the effort, and leave it as is.

haaseg

Thanks all. We ended up with the 16" Hotrock and the kid really likes it. It's fast enough where I can actually ride my bike with him and not be in danger of tipping over going so slow. Hand brakes are on order. The shop said the wheel would take a standard BMX freewheel if I wanted to drop a few teeth there. Also, the bottom bracket shell appears to be standard 68mm if I want to upgrade to a 3-piece bmx crank later. The chainstay is NOT crimped, but it looks like I have enough space to add an extra inch to the radius of the chainring before it becomes an issue. I should be able to add plenty of teeth if I need too.

Sixty Fiver

Something to consider for down the road...

My daughter is a small 12 year old and finally grew enough to retire her old bicycle and ride the new one... which is a 1977 Raleigh 20 folder with a 3 speed hub.

She loves the new bike and unless she ends up being 6 feet tall it will be a bike for life and despite is weighing 35 pounds she has no trouble keeping up a good pace... she also has a 24 inch wheeled mountain bike and a very small road bicycle.

The old bike was also a vintage 3 speed that we restored and she rode it for nearly 3 years without a single issue...



The new bike rolls on a 20 by 1 3/8 or 451 wheel... she loves it and her bike is on the right while mine is on the left.

1987cp

I've had that sort of idea myself ... saw an old 3-speed wheel from a folder for sale, tempted to get it even though it costs $$ and the 16" bike we're using now is a department store brand we got for free (dumpster find). My reason is more that I'm developing an axe to grind against coaster brakes since they do my son little good and don't allow convenient positioning of the pedals.

At least my old Predator is chromo and freewheeled ....

thenomad

I skipped the 12" and just got a 16" hotrock. BB is lower, cranks are shorter and gearing is smaller than some other 16" bikes. He learned fine, got rid of the training wheels and is riding it around but spinning fast like you said. All that is really needed is a chainring or crank change and itll go faster.

Right now though i'm looking for 20" bikes for his next step up. He is now almost 6 and the seatpost is pretty high on the 16" bike now.

If you want to get a lightweight bike for a smaller rider with a good build quality you'll need to look at real BMX racing bikes like the Redline Micro-mini (smallest) the Mini (lil bigger) and the Junior or Proline. Skinny 20" knobbies, Low slung top tube, cro-mo or alloy frame with total weight of 14lb. There are rider weight limits of 75lb I think.

I'm looking around for something like it as it should fit for a good while. Remember, once they are around 7 they'll be riding regular BMX style standing up a lot.
I also have a 20" drop bar road bike from the 70s I'm refurbishing but the top tube standover is the limiting factor right now, as is brake lever reach.

ratdog

I did the same as Sixty Fiver and found a 15 year old Brompton folding bike. My 10 year old loves it because he finally has some gearing and the bike grow with him just by raising the seat.

ebartom

We got our 5 year old a 20 inch specialized street, and it has been an awesome bike for him. He put in a 22 mile day on that bike, this Saturday, mostly on compressed gravel. It has 6 speeds and hand brakes and street tires, and the relatively low standover height means he can ride it, even though he's not particularly tall.

Wolfvegas

I wondered into the wrong part of the forum.... I thought you guys were all taking about your children driving 16-24" frame size haha I didn't realise you were talking about wheel size... God do I feel stunned today..

PatrickGSR94

Wow that sure is a lot of thought process going into a kid's bike. When I was younger we were just happy to have bikes and we rode them everywhere. No one thought about gearing, crank length, or any of that stuff.

ebartom

When I was a kid, I also had a basic bike and rode it everywhere. But I rode by myself or with my brother, and speed was not an issue. We had free reign of the town, and bikes were our main way to get around. I don't think that scenario is as common now as it used to be. Unfortunately.

Now I have kids, and we do a lot of family riding. If the smallest member of the family has the clunkiest bike, it slows everyone down.