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Old 01-01-13, 05:11 AM   #1
Blues Frog
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Fat tire frame for 25" standover???

Is that workable or just a pipe dream? I have a Trek 520 with a good standover and 700C wheels. But my road bike has 650 wheels to get the standover right. I find that top tube realllllly short. I need to make some adjustments to that. So that is the history. What do frame builders see here for a fat tire frame?
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Old 01-01-13, 09:35 AM   #2
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25 inches is difficult in an adult bike. How tall are you?

A mixte frame with 26inch wheels will provide 25inch standover. This Soma has room for 1.5 inch (38mm) wide tires: http://www.somafab.com/archives/product/buena-vista

These bikes can provide 27 to 28 inch standover.

Rivendell A. Homer Hilsen. Room for 40mm wide tires. It comes in sizes 47cm thru 71cm; and the 47-50-52-54-56-58 frame sizes are for 650B wheels. http://www.rivbike.com/product-p/f-hilsen.htm

Soma San Marcos. Room for 38mm wide tires. The 47 and 51cm are designed for 650b http://www.somafab.com/archives/prod...rcos-frame-set

Surly Long Haul Trucker for 26inch wheels. Room for 2.1 inch wide tires. 42-46-50-52-54 and larger frame sizes. http://surlybikes.com/bikes/long_haul_trucker
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Old 01-01-13, 11:47 AM   #3
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I'd explore the 559 diameter as a start. But I don't know what you mean by fat tires exactly, now we have 4"+ stuff and maybe the 2"+ widths that are very common with 559 is not enough? Making a frame with a low TT is not too hard but the angles (of the TT) and the possible extra tubing (for best triangulation) are not the usual. Often the need for heavier walled tubes comes into play and the lightness one would want is lost a bit.

The other, and unspoken, aspect of this fit need is your seat/bar relationship. You make passing reference to the 650c TT being too short but no mention to the seat/bar height differences. Making a TT longer is quite easy (it's getting one less then 45/58cm that's a challenge without going to straight gauge tubes). But if you need a bar height that's up there the HT top will be up there too (even with a custom stem) and this will complicate the TT stand over.

In the ideal world you'd first plot out your three contact points (seat/bars and pedals) then move to components like crank arms and bars before looking at what frame designs (and I include the wheels at this point) will fit all together. BITD we use to draw out a scale blueprint for the fitting step then a full scale frame design to further confirm/tweak the dimensions.

The last point I'll make is that the rolling feel of a small wheel is, for some riders, not prefered. This is where mixing wheel sizes might be another option. Andy.
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Old 01-01-13, 01:09 PM   #4
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I have a Bike Friday, Its standover , (on top of the Abus Lock Pouch mounted on the top tube), measures 24".


Is the plan building a step through, or a Mixte frame?

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Old 01-01-13, 03:28 PM   #5
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I'm looking at a fatbike, AKA/ Pugsley, Mukluk, Necromancer..... Faaaat tires. I'm 5'2" tall. As I meant to say the Trek 2300 has 650Bs and is the right standover. It is a bit short in cockpit length(top tube?). The Trek 520 is the right height and has 700Cs, standover is acceptable. The fatbike with the huge tires and 26" wheels would give at least 29" tall tires. This is not coming out in words. I use the 2300 for road and club rides. The 520 for commutes and tours.

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Old 01-01-13, 04:51 PM   #6
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Quote:
Originally Posted by Blues Frog View Post
I'm looking at a fatbike, AKA/ Pugsley, Mukluk, Necromancer..... Faaaat tires. I'm 5'2" tall. As I meant to say the Trek 2300 has 650Bs and is the right standover. It is a bit short in cockpit length(top tube?). The Trek 520 is the right height and has 700Cs, standover is acceptable. The fatbike with the huge tires and 26" wheels would give at least 29" tall tires. This is not coming out in words. I use the 2300 for road and club rides. The 520 for commutes and tours.
What is the standover height of your current bikes?

A Surly Pugsley has a 29.8 inch standover in the smallest size. A fat bike will not improve your cycling and is really not needed for a lighter cyclist. A regular 26 inch mountain bike with 2.25 inch tires will cover the same terrain as a fat bike if you weigh less than 130 lbs.
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Old 01-02-13, 02:15 PM   #7
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I suspect you could do something. Do you know your pedal to saddle height?

do an image search online for 36er, and you'll see what people have done in a similar situation. Squishing the seat in there is the one concern I have. The fact that you have short legs and a longer torso probably helps in this case

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Old 01-02-13, 05:05 PM   #8
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Active forum thread over at fatbike forum on small rider fit;
http://forums.mtbr.com/fat-bikes/any...er-831163.html

Concensus is that extra-small 907 frame is the smallest available standover, I saw an 8-year old girl riding a XS 907 this year, you should be able to get a good fit no problem.
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Old 01-02-13, 08:33 PM   #9
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those are some really small bikes. Pretty neat
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Old 01-04-13, 11:46 AM   #10
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That 9zero7 looks good. Almost out of my range though. I'm not accustomed to building frame up. I guess I could start with a frame. It would give me the incentive to continue. Have you seen the one Black Sheep calls "Two Face"?
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Old 01-04-13, 12:00 PM   #11
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fat bikes are very expensive, even if someone gives you a frame. Is that what you mean by "out of my range"?
If you are going to go to someone like Black Sheep, they will make you a frame that fits, but there is going to be a premium over a stock bike.
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Old 01-04-13, 04:31 PM   #12
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Fatbikes definitly can be fairly expensive, it wouldnt be too hard to blow $800-$1000 on a fat wheelset with surlys latest extra-wide tires, supple casing and folding bead, 100mm wide rims and 170mm hubs. THe 100mm bottombracket shell cranksets can also be expensive.

I managed to rebuild an on old hardtale 26" MTB with a fat clearance rear triangle and got rolling over the snow for a total of around $500. Build Album at;
https://picasaweb.google.com/1102452...eat=directlink

A few fatbike cheapskate build tips;

For my frames 68mm BB shell, I used an old extra wide (137mm) square taper MTB spindle to shift the crank out enough for fat chainline using the middle and inner chainrings. If you have "real" fatbike frame with a 100mm BB shell, there are 100mm ISIS bottom brackets that allow use of cheap ISIS MTB crankset and are probably the cheapest solution for a fatbike crank. I am using an old 7-speed casette & hub in the rear which also helps with the chainline. Using an offset frame setup for regular 135mm hubs is a big cost saver over symetrical fat frames that need very expensive 170mm hubs.

Cheap Neon trials bike rims are 47mm wide and work fairly well for semi-fat bike. Not all the floatation capabilities of wider rims but 3.8" tires fit them and provide 90% the benefit for about 1/3 the cost of wider rims
http://www.nwtrials.com/apps/webstor...s/show/3003280

Surlys stiffer 27tpi tires are a bit of a cost saver but the fat v-rubber devistator tires can be had for as cheap as $45ea.

I managed to get an old manitou suspension fork working with fat tires, saved over buying a fat-specific fork.


For my next framebuilding project, I am planning a singlespeed fatbike with symetrical 135mm rear end. If you dont use gearing, a singlespeed chainline provides clearance for fat tires without needing asymetrical offset.
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