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Absolutely, if you can make a bike fit a growing child for a longer time, that's great.

The point that people seem to be missing here is that changing wheels does not change geometry(at least not crucial fit related geometry). It has nothing to do with sacrificing optimum fit or handling. It simply doesn't help.

Obviously stack and reach don't change if you swap wheels.
If you are unfamiliar with the stack and reach system give google a shout.

If you want to feel it to believe it try this:
Put your kid's bike in a trainer. Try riding it. It's too small right?
Now, put some boards or blocks under the trainer and front wheel and try riding it now. Does it fit any better? Of course it doesn't, everything you touch is still the same.
Yet, raising the bike of the floor is the exact same geometry change you would get by switching to a larger wheel.

Perhaps the reason this misconception is so persistent is an error of causality:
We see bikes with small wheels which fit small kids and we see bikes with big wheels which fit big people, so we think: "big wheels must make a bike fit bigger people"
The mistake of course is that it's not the big wheels that make the bike fit bigger people.

If you want maximum 'growth range' out of a bike, start with a bike with a very low bottom bracket and very short cranks. Then select the bike with the biggest stack and reach that still has sufficient standover.
Then, throw on a narrow handle bar, super short and slammed stem.
After the child grows, you raise the saddle, using a longer seatpost if necessary, use a longer stem with all the spacers underneath, and perhaps a wider bar.

These changes will actually make the bike FITbetter, unlike a wheel change. As a side benefit they are about 15% of the cost of a set of wheels and tires.
I didn't mean to suggest that changing wheel/tire size would alter the geometry. Perhaps I should have clarified that the rider would have to sacrifice optimal geometry either initially, or after the rider has outgrown the frame....depending on whether the bike purchased was a good fit to start, or purchased with a good fit in mind down the road.

I understand the concepts here, but it doesn't change the underlying issue for me, and that's money. Being able to throw a set of 26's to help with rolling speed and clearance would, at least theoretically, buy some time...albeit without a great fit.

That bolded part is very beneficial information, and I'll use this as I try and hone in on the right bike for my kids...but I'd still like to find something with just a little more versatility. Specialized is marketing a Grom bike that changes wheel sizes, but it's about $500 bucks out of my price range.

It looks like I'll have to pay closer attention to BB and crank sizes as well...

Cheers!
 

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I understand the concepts here, but it doesn't change the underlying issue for me, and that's money. Being able to throw a set of 26's to help with rolling speed and clearance would, at least theoretically, buy some time...albeit without a great fit.
Cheers!
Aha, I had not considered that.
From the way I read your' and others' posts, it seemed to imply that people were thinking that swapping in bigger wheels would make the bike usable for a longer time for a growing child, which I took to mean fit a bigger kid.

I shouldn't have made assumptions like that, we all know what assume stands for....

I guess my view is that if money is the issue, spending a lot of money on a new wheelset and tires seems seems like a lot of money spent, simply for some better roll-over capability and perhaps some rolling resistance gains. Especially since those gains are offset by higher weight, worse center of gravity and less standover.
All that, and it would be something only used for a short time.

I like, and ride, 29ers, but in all honesty the difference from 26" was not night and day.
So for me personally, if my kid was at the larger end of fitting on their 24", I wouldn't spend the money just to cram wheels 2" larger into it for one year or so.

On a different note, Trek is offering a kids bike, the FuelEX Jr with 26 wheels, basically the 29er under the 24" wheeled bikes :)

So, if you value 26 much higher than 24", that might be just the ticket.


Fuel EX Jr - Trek Bicycle
 

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kids bike geometry

Here are a couple of kids (and one xs women's) bikes.

Transition Juliana Trek Specialized Islabikes
Ripcord Origin Fuel ex Jr Camber Grom Beinn 24"

stack 503 547 519 547 500
reach 366 364 381 388 340

standover 576 689 653 621 600
chainstay 381 424 429 420 390

BB height 309 312 316 291 245
effectibe BB 284 287 294 264 245

cranklength 165 ? ? 170 140

travel 100 100 90 110 rigid
wheelsize 24 27.5 26 24 24

Notes:
Standover is the most critical, too tall is too tall. Unfortunately it is a very unreliable number from bike websites, as it depends where you measure it. So, take that number with a big grain of salt.

Stack and reach are the real numbers that determine fit. Of those reach is probable the most critical one, since bars a bit high is not the end of the world.

The Syntace Dropforce stem can really help with that. It's quite short and super low:
Syntace

Pedal stance width is very important but no site lists it.
Crank length is also a big issue, but not every site mentions it.
Think about a child 2/3 of and adult's height, to get a similar feel, they should have a crank that's 2/3 as long, ie 117 mm long.
Shorter cranks prevent rock strikes, allow for more normal pedaling motion, better technical riding out of the saddle and most importantly, allow for a low bottom bracket.

Bottom bracket height:
Lower bottom brackets make a bike more stable, easier to flick from left to right hand cornering and most importantly, allow kids to get their feet on the ground without setting their saddle to low.
Effective bottom bracket height is bb height after sag, in other words while riding.

Chainstay length:
Shorter stays make pumping and manualing easier, crucial to young riders developing feel for the bike and skills.
They also keep the riders center of gravity back, important on these tiny frames with very short front centers.
 

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geo per bike

Transition Ripcord:
Great:
-chainstay length. Very nice and short. If you are going to have tiny wheels, you might as well have tiny stays.
Good:
-standover, if these numbers are accurate, this is the best one.
-stack, nice and low in case your rider needs that, you can always raise it.
-shortest reach. Not better per se, but it's smallest bike on here that gets you full suspension and at least 24" wheels.
-most trail (slackest head angle). Given their weight, none of these are xc race bikes, and due to their small wheels and short wheel base they don't have a ton of high speed stability anyway.
Neutral:
-cranks, too long, but no worse than the others.
-bottom bracket height, again, if you have a short rider, and a short travel bike you can give them short cranks and drop that bracket down.

Notice how the other 2 full suspension bikes are really similar in geo to an adult 27.5 bike? Save for standover and seattube length.
So, another option to consider is to put get a 24" wheelset for an adult bike for a while if standover is to high for the kid.
 

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Got the ripcord built up last week. Turned out pretty nice. There was not too much wrong with the stock spec build (cranks too long and saddle to long...covered more of the top tube than I would have liked) but since I had the parts I figured might as well upgrade. I also cut the handlebars from 27" to 25" and am still playing with the hope levers (the older tech levers don't play well with the optical gear display). droped the weight from around 30lbs to 26lbs.

The stock Kenda kinetics turned out to be a folding version and weighed in around 690 grams (nicer tires than I anticipated). I have some schwalbe Fat Albert 24's on the way for a tubeless meatier option (although the Kenda's are better than I thought so might send back). The Maxxis snypers are a little narrow and could use a little bit bigger knobs in my opinion.

Couple pics...pretty sure one could not fit a 26" in the rear.
 

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Nice bikebling! The blue spokes rock! And that weight is great for a full suspension bike with high end but not crazy parts.
Thanks, I was building the wheels for a black frame and then the blue on the transition came along as a bonus. The spokes added some weight but sometimes you just have to go for looks. :thumbsup:
 

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Adapting to the bigger frame is a bit intimidating at first.
that's always been my experience with my son - every time he steps up to a bigger frame there's a short term step back in confidence. the jump in frame size from his 20" wheeled bike to the ripcord was substantial, and he didn't blink an eye. especially on the dh, he was riding faster and hitting things with more confidence right away. i think whatever issues the increase in size may have introduced, the geometry more can compensated for
 

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Final build swapping out the Maxxis Snypers for Schwalbe Fat Albert R. Added about a pound a ton of tread.

I tried mounting tubeless but could not get the schwalbe's to mount with the Deviant Rims using stans tape. A 24' tubeless rim strip might work but have not found one and didn't want to guinea pig my son by making one. It was a very loose bead which makes me think the deviant might be a little undersized.

We will get the first real ride this weekend.
 

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Final build swapping out the Maxxis Snypers for Schwalbe Fat Albert R. Added about a pound a ton of tread.

I tried mounting tubeless but could not get the schwalbe's to mount with the Deviant Rims using stans tape. A 24' tubeless rim strip might work but have not found one and didn't want to guinea pig my son by making one. It was a very loose bead which makes me think the deviant might be a little undersized.

We will get the first real ride this weekend.
Any chance you got a weight on the frame/shock only?
I emailed Transition and got a "we don't know."
My 6yr old son is on a 18.5lb bike I built him but would like to get him some rear suspension if it actually works and doesn't weigh a ton.
 

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Think about a child 2/3 of and adult's height, to get a similar feel, they should have a crank that's 2/3 as long, ie 117 mm long.
Everything else you said is fairly reasonable, but 117 is a super short crank. Kids aren't generally 100% scaled down adults, I think in general, their legs are longer proportionally to their torsos. Except my son, he's built just like a lego man. Hope he grows out of that...
 

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The stock Kenda kinetics turned out to be a folding version and weighed in around 690 grams (nicer tires than I anticipated).
I'd like to get some of those Kendas for my son but I don't see them on the Kenda site and they don't appear in the 2015 bicycle tire catalog either... maybe they are an OEM only model?

Currently he's got the Snypers but they could use a bit larger tread in my opinion...
 
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