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  1. #1
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    Kids Fat/Chubby Bike

    So last winter in Anchorage when the conditions were ideal, I took my two sons, ages 9 and 11, out snow biking with their regular mountain bikes.

    There had not been a new snow in weeks and the trails were firm and the temp in the teens - and they had a great time! So much so, that they said they enjoyed it much more than the x-country skiing that I've been only marginally successful in getting them hooked on with years of effort. (Maybe it is not such a surpise because I also enjoy fat-biking better as well.)

    Since they had so much fun that first time, we tried it a number of times since then, and I quickly realized that for anything but ideal conditions even these 60 and 75 pound kids needed more floatation (or else it was work and not fun).

    I tried to outft them with fatter tires/wheels on their regular mt bikes. My oldest is on a 26" wheel size and so there were many more options. I tried swapping out the wheels on his extra small frame with my old snowcats and some WTB 2.7 tires with the knobs trimmed and it barely fit with but a couple millimeter on each side, he also noticed the extra wheel weight (and probably the increased resistance from slightly softer but still fairly firm snow). So I took the snowcat rims off and he just used the regular rims and the 2.7 WTB Timberwolf tires. This setup expanded the conditions he was happy riding in from not just "ideal" but to any time conditions were "good" - a few days after a fresh snow when the trails were fairly well packed. Of course next winter he'll be ten to fifteen pounds more than last winter and the winter after ...

    My younger son fits best on a 24" bike and we had a much more difficult time. His bike frame has less clearance and by going to a 24" downhill tire with the knobs trimmed we gained minimal floatation, LOTS of tire weight, and the tire was SO stiff that it negated most any benefit of running low pressure.

    My youngest might make do with the setup my oldest had last winter and it will probably work ok.

    So, I am looking for advice on building up an extra small "chubby" bike for my oldest son that will do the job for a couple of years when he is probably 85-120 pounds. I have been very resourceful in building up some nice summer bikes for them by scouring craigslist, plundering my own parts bin and searching the net for deals on needed kid sized parts that I can't find used or for sale locally. I am hoping that I can piece together a "chubby" bike for less than $500. (Probably optimistic to think I can do it for that cheap, but that is what i am shooting for.) The bike will likely only be used only when conditions are "fun" and I expect it might see a total of around 60 rides (1-2 hours each) since we are looking at maybe 15 times a winter for 4 winters (2 winters for each kid). Of course I would love to ride with them more than that, but one thing I have learned is that forcing them to do MY activities is the surest way to turn them off to those activities, so i want to be conservative in my expectations. (I may enjoy frost on my beard but for some reason they have an aversion to sub zero weather, pushing through soft snow, and darkness).

    Anyhow, I have been thinking of all kinds of crazy things like trying to mod an existing extra small mtb frame and make it a fat rear, but honestly, I've had limited success trying to mod an old Evinson frame to fit an Endo (for me) and instead of making a full-blown pint sized fat bike that will take all the conditions, I may be better off going "chubby" and lighter and limiting outings to when the conditions are good and keeping the fun factor high till they are fully "hooked" on fat-biking. After all, half the floatation for someone that weighs half as much should work!


    Anyways, for those that have tried to make "chubby" bikes:

    What relatively light mtb frames can handle a wider tire and rim combo?

    Should I consider a dirt jumping bike or some other specific type of frame? (I'd switch out the suspension fork with a fat fork I already have, and I see lots of dirt jumping bikes on craigslist. They are built with low standover heights and the geometry seems about right if you drop the front a couple inches since the fat fork is not suspension corrected.)

    What are the widest tires (other than heavy downhill tires) with the most floatation that fit an apropriate/recommended frame?

    Has anyone discovered any cheap relatively wide, relatively light trials rim out there? I am willing to try drilling out a rim but want to make sure the tire and rim I order will fit the frame and also will make best use of available clearance.

    The rule has always been you can have strong, light, or cheap - pick any two. With a light rider I am more inclined to trust light and cheap but only to a certain degree.

    Thanks in advance for your suggestions!

  2. #2
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    Quote Originally Posted by Scoobytao View Post
    ...What relatively light mtb frames can handle a wider tire and rim combo?...
    It's very hard to look past the Surly 1x1.

    You could keep it light by using appropriate parts, eg V-brakes instead of disks, singlespeed, rigid fork, etc,
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  3. #3
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    Quote Originally Posted by Scoobytao View Post
    I may be better off going "chubby" and lighter and limiting outings to when the conditions are good and keeping the fun factor high till they are fully "hooked" on fat-biking. After all, half the floatation for someone that weighs half as much should work!
    I've tried making a chubby 24" bike for my daughters but on the beach it was worthless on the soft stuff.
    They're riding an XS Sandman now, it fits my 9 & 11 year old kids very well with enough standover (haven't tried it in the snow). The 5-year old is jealous as hell

  4. #4
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    Scooby-
    I am local (eagle river) and dabble with frame modification and frame building (brazing). If you find a somewhat suitable steel frame and tires, I would be game to assist with widening it. I have little kids that will no doubt want to be riding in a few years too so stand to eventually benefit from the knowledge.

  5. #5
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    Scooby-
    It looks as if DH and trials tires come in 24x3.0 size. I would think it would work well for a kid snowbike if you were to buildup a wheelset with 50mm+ wide 24" trials rims and 3.0" tires, probably somewhat close to rolling diameter of a 26x2" tires. You could likely fit the 24x3" wheels into a small sized 26" MTB frame. Since kids are 1/2 the weight, they probably dont really need full endomorph width to achieve float on snowy trails.

  6. #6
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    Although they're more than you were looking to spend, The Mukluk comes in a 13" XS size... But the re-sale value would help, when they out grow them.
    eSpeCially CrAzy IrRegular TrailBuildin' Crew
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  7. #7
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    Choppers US has 24 x 4.25 tires and 24 x 4" rims. You would probably be looking at a custom frame, though.

    http://www.choppersus.com/store/prod...-4.25-Chopper/

  8. #8
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    supposedly chain reaction is working on an something in the 12 to 13 inch. built up with snow cats or uma 50's and an old pace rc31 it could fit the bill. i have a 10 year old that loves riding in the winter when the conditions allow.
    Attached Thumbnails Attached Thumbnails Kids Fat/Chubby Bike-ethan-ride-1.jpg  

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  9. #9
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    Quote Originally Posted by ak greeff View Post
    supposedly chain reaction is working on an something in the 12 to 13 inch. built up with snow cats or uma 50's and an old pace rc31 it could fit the bill. i have a 10 year old that loves riding in the winter when the conditions allow.
    Sweet ride! You’re the awesomest dad in your neighbourhood!
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  10. #10
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    I am waiting for my 10 yr old to grow up to a 14" 1x1 size. Could be a while. He is happy on a step through 24" bike meantime, no real pudgy options for that frame though. Are there smaller rigid frames for 26" I should be checking out instead?

  11. #11
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    I am making some progress merely by rummaging through my collection of past failed efforts at snowbiking on the cheap that sort of represent the evolution of fatbikes.

    I purchased a mid-nineties vintage MTB that has a teensy 12" frame but takes 26 wheels and was pretty light (had some nice parts from that era like ringle hubs and a titanium bars). It also had quite a bit of clearance betwen the stays. Enough tthat it fit my old snowcats mounted up with the WTB 2.7 timberwolfs. I previously trimmed the tread on these tires to try and fit them to a different bike, and now even on the snowcats it seems like there is a good amount of clearance with this frame. I did swap out the crappy old suspension fork for a slightly lighter rigid one with adequate clearance, but that dropped the front end about an inch and a half. Not many options for this frame since it will only accept a 1" steerer tube. The total weight of the bike prior to some other weight saving mods is currently about 27 lbs. Since this bike settup will be used by my youngest som at 65 lb weight, he will have substantially more floatation than I.

    My question for this group: How significant will the change in geometry, coupled with the much fatter tires and rims and the super short stem affect the handling?

    Seems like fatter heavier wheels slows things down, but dropping the front end makes the handling faster, and I read somewhere that shortneing the stem supposedly makes the handling slower but that seems counter-intuitive to me.

  12. #12
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    I had been looking for a potential snowbike frame suitable for my older son. I was told by a sales guy at Chain Reaction that the Trek 3 and 4 series had about the widest stays on any commonly available aluminum bike. One of the kids in Mighty Bikes (kids mtb club) had a medium size Trek 4300 and it had lots of tire clearance. But once I found an extra small size on Craigslist, I realized that it did not have significantly more clearance than my son's current Gary Fisher (kind of makes sense since Trek makes Fisher). I finally just settled on Nic using his Fisher, but I felt like it was a serious compromise since he probably could not use Snowcat rims and the WTB 2.7 tires on the Fisher (there would only be a couple millimeters clearance). Last winter when he was using his regular rims and the WTB's, I could tell he would benefit from some extra rim width.

    Then I started looking around for rims for a semi-fat wheelset. I ordered a pair of 39mm wide trials rims from Tartybikes.com that supposedly weigh 593 grams and I may try and drill them out some more.

    Still I only had a pair of WTB 2.7 tires for one kid. Someone here mentioned the Vredestein Bull Lock was very large for it's stated 2.35" size, so I figured I'd check it out. They were on sale for $16.99, and, So, I ordered 3 (one pair plus a spare).

    They showed up this past weekend and it turns out the casing is actually BIGGER than the 2.7" WTB and my scale shows they weigh just 670 grams. Okay, the casing is virtually the same, maybe about 1 millimeter bigger, but they are incredibly supple. When inflated to the 8 psi, the sides of the casing feel as soft as a baby's butt.

    The Bull Lock tire's profile is different than the Timberwolve's and it gives up a couple millimeters in width while it gains several in height. But the WTB tire weighs almost 400 grams more each (prior to any knob trimming). So now I am thinking, "I am going to need a pair of these BL tires for both kids". Dang! Why didn't I have the foresight to throw in for another $16.99 and get a fourth tire - now I'll have to pay for another shipment to Anchorage. (It must have been entrenched in my mind that three of a kind beats two pair.) I really did not think they would be good for snow tires- but I think they are going to be great (at least for my purposes).

    GrayJay and AK Greef, you guys are local, wanna share shipping costs and outfit all our kids? Heck, I wonder how many Mighty Bikers might want a pair?

    Now since the Bull Lock's are a couple millimeters narrower than the WTB's, Old Nic may be able to run the 44 mm Snowcats on his bike after all, and Lil Ben can use the smaller and lighter 39 mm rims.

    So, I am not spending $1500 or more each so my 65 and 90 pound kids can ride a 35 pound fatbike (with 18 pounds of wheels, tubes and tires to get rolling). Instead, they will be on 25 pound bikes with about half the rolling mass of a fatbike (and coincidentally about half the floatation).

    Everything is a trade off. There will be days when the extra float of a fatbike would be helpful. But I am not sure they would be excited about going out in sluggish softer snow conditions on a bike that is about half their weight. I think our setup will work out well for most of the conditions that we are likely to be out in. When there is fresh soft snow we might be skiing while you all pack the trails down!

  13. #13
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    Sounds promising! I would be up for getting a pair of the BullLock tires to try when you order next time.

    Back to your lowered front end bike, biggest effect will be that the shorter fork will steepen the head tube angle and that in turn effects the amount of geometric fork trail. The amount of fork rake needs to be matched to the head tube angle in order to get suitable amount of trail or else handeling will be squirrly (too little trail in your case). If you have a steel fork, it wouldnt be too hard to de-rake the fork a bit in order to restore the trail for more neutral handling. http://yojimg.net/bike/web_tools/trailcalc.php
    How wide do the BullLocks+Snowcats measure for width? Let me know and I will keep an eye out for a useable 1" fork.
    Have any pictures of the kids bikes you can put up?

  14. #14
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    im planning on getting one of the chain reaction 13 inch frames. i want to run snow cats with endos. still looking for a used set built offset. cost is going to be a bit more but i think he will get a few years out of it. thanx for the offer on the tires though. post up some pics when you get your set up rolling, sounds great.
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  15. #15
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    Quote Originally Posted by ak greeff View Post
    im planning on getting one of the chain reaction 13 inch frames. i want to run snow cats with endos. still looking for a used set built offset. cost is going to be a bit more but i think he will get a few years out of it. thanx for the offer on the tires though. post up some pics when you get your set up rolling, sounds great.
    I recently built myself a wheelset with new snowcats (44mm). Chain reaction in Anchorage had them in stock for $60 each and with no shipping involved it seemed to be cheapest option for getting my hands on some somewhat large rims. Coupled with 27 tpi Larry&Endo and some light bontrager tubes it was about $250 total and then I built them up with an old set of 100/135mm MTB hubs that I already had laying around.

  16. #16
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    A slight bit off topic, but I'm trying to find a BMX frame for my oldest son that I can put some 3" (chopper bike) tires on. He wants the wide tires and the neighbor has some he'll sell, but fitting them into a BMX frame may be impossible sans modding it. Would be a cool "almost equivalent" though. I don't know why they make all those horrible chopper bikes but nobody utilizes the wheelsets for an upright frame? It would end up having a very similar geometry to the 907 in the upper right of my screen!

  17. #17
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    Bull Lock 2.35 tire mounted on a snowcat rim measures 2.55 inches at the widest spot.
    Timberwolf (folding not downhill) 2.7 tire on a snowcat rim measures 2.65 inches at the widest spot.

    For comparison I measured an Endomorph tire (127tpi) mounted on a Large Marge rim and came up with a measurement of 3.65 inches at the widest spot.

  18. #18
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    I didn't know there was a 13" 907 frame. I thought the smallest was 15". Looking at the CR website shows that the stand over is about the same as a 16" Pugs although the top tube appears to be a bit shorter. I was thinking about a very small fatbike for my sons to ride but had sort of given up.

  19. #19
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    Quote Originally Posted by nm13 View Post
    I didn't know there was a 13" 907 frame. I thought the smallest was 15". Looking at the CR website shows that the stand over is about the same as a 16" Pugs although the top tube appears to be a bit shorter. I was thinking about a very small fatbike for my sons to ride but had sort of given up.
    How tall are your kids? My wife is 5' and the smallest Fatback is just small enough.

  20. #20
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    The youngest is 5"2". My small Pugsley is too big for him. My oldest is 2" taller and can get by on the Pugs but would prefer a smaller frame. The specs on the CR website say the 15" 907 has basically the same stand over as the small Pugs so unless they measure differently the 907 wouldn't work for us yet. That's why I was intrigued by the idea of a 13" frame.

  21. #21
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    Oops, I wrote before reading carefully. Yes the Fatback looks like it probably would work. But I'm hesitant to go that route and have a whole new set of wheel specs to deal with. I like the idea of interchangeability with my Pugs although I admire the elegance of the 170mm hub/wheel.

  22. #22
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    Quote Originally Posted by nm13 View Post
    I didn't know there was a 13" 907 frame. I thought the smallest was 15". Looking at the CR website shows that the stand over is about the same as a 16" Pugs although the top tube appears to be a bit shorter. I was thinking about a very small fatbike for my sons to ride but had sort of given up.
    coming soon to a venue near or far from you, depending on where you live. My wife is 5-2 and rides a 14inch fatback. Nice bike.
    litespeed's break

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