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  1. #1
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    New question here. Using a 26" Air Fork on a Custom Made 20"/24" Wheel Frame?

    After doing a lot of research and asking a lot of experts on here, I think I am leaning towards trying to use a 26" air fork on a to be custom made frame that can accept a 20" or 24" wheel, and using the same sized wheel up front. Not being much of a frame designer / expert, can I design the headtube height and angle so that the A2C difference of the 26" and 20" fork can be taken up? I would reduce the travel of the fork down to 60mmish. I assume this is in the 3" area of difference.

    Is this a decent idea or totally ridiculous? The main reason for doing this is that I started off trying to find a frame only that has rear disc tabs (another thread), with limited success. I have a Spinner Air on there now, and it is pretty crappy. Lighter than the original coil beast by 3/4 lb, but has a lot of stiction, and doesn't do much for my 45 lb daughter. So I was hoping I could get a better fork (she runs a disc brake on front so no problem with V-brake tabs), and a frame that she could use for the next 3 or 4 years. I know it won't be cheap, but her brother is 2.5 years younger, so I will get double use out of it.

    I don't want to get the head tube angle too small, as this bike is to be ridden up hill just as much as it is to be ridden down. I'd reverse the stem to give it a drop too. I have never seen anyone do this, and probably for a good idea, so please tell me why I am a fool.

    Thanks for any info - BS

  2. #2
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    There are several 24" bikes with disc tabs. You could buy the whole bike on craigslist cheaper than building a custom frame. I also think there is no way to have a bike that can run 20" or 24" wheels. the BB would be all over the place in addition to the HA. A 26 inch fork, even with 63mm of travel, on a 24" bike changes the A2C a good bit, but is manageable. On a 20" I just don't think it will work. Search the forum for Older SID forks on 24" bikes. that is what most people do. I have 2 Specialized A1 Hotrocks with SIDs for my kids. One is full disc, the other is disc front and v-brake in the back. Both stop very well. The v-brake is about 150g lighter than any disc setup. and for kids, weight reduction is one of the most critical aspects.
    Just Ride!

  3. #3
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    It should be possible to build a new frame to work with the tall 26" fork and have the HTA wherever you want. Challenge will be that the bars/stem will be high up, particularly for a kid at 20" wheel size. Changing both the wheels together (20" to 24") will not alter the HTA, just the bottom bracket height will change by 2". THis could be partially compensated for with different length cranks, but probably only around 1" change of crank length so pedals will probably be either a bit too high for a 20" or too low for a 24".
    Changing wheels would help to adjust the standover height as the kid grows but it does nothing to change the top-tube length which also needs to change as they grow. The chainstay length and clearance, and the front/center measurement (and thus front wheel toe overlap) would need to be built to accommodate the larger 24" wheels. While you could then stick smaller wheels on a 24" frame, the geometry will not really be optimized for the smaller wheels. If you were to just try to build-up an existing 24" frame with 20" wheels, the HTA with a 26" fork might still be close enough to work OK but the top tube length of a 24" bike will likely be way too long for a rider needing the extra standover clearance.

    Particularly since you have 2 kids 2.5 years apart, I think it makes more sense (and probably much cheaper compared to custom frames) to just build up both a decent 20" and 24" bike, you are going to need them both at the same time eventually once the younger kid is ready for the 20". A bolt-on rear disk adapter would be a workable solution for adding disks to the 20" if you are set on having a rear disk. You might first try a different (better) rear v-brake, better pads. Using a brake lever designed for cantilever brake together with a V-brake would make for even more mechanical advantage (less hand strength needed) to match the feel of the front disk, just watch that the lever does not run out of travel before it contacts the bars.

  4. #4
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    There is a member here (kosayno) that built 20 or 24 bikes for his kids using a 26" fork. He made them himself out of bamboo. See post #2 and 4 in Kid's Mountain or Road Bike Ride Picture Thread
    You can get the feel for the frame geometry.

  5. #5
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    Quote Originally Posted by bme107 View Post
    There is a member here (kosayno) that built 20 or 24 bikes for his kids using a 26" fork. He made them himself out of bamboo. See post #2 and 4 in Kid's Mountain or Road Bike Ride Picture Thread
    You can get the feel for the frame geometry.
    Crazy! Seems like having the handlebars level with the kids eyes would hinder their ability to see where they are going!

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