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 190mm Drop Outs
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daytriker
Starting Member

Canada
2 Posts

Posted - 09/14/2020 :  21:20:33  Show Profile  Reply with Quote
Our Fat Trikes all have 190 mm rear Drop Outs. I would like to add the Sturmey Archer SX-RK3 3 speed Internal Gear Hub to the Fat Wheels but the OLN Measurement is only 170 mm. Is there an adapter that will allow the use of narrower hubs in wider Drop Outs? Narrowing the frame is not an option on these as they are built with reinforced chain stays. Thank you.

Spend each day smiling, Tomorrow could be worse.

warren
human power expert

USA
6560 Posts

Posted - 09/16/2020 :  10:47:50  Show Profile  Visit warren's Homepage  Reply with Quote
Wow, 190mm is huge. Why so wide? What kind of hub is normally used? Isn't standard fat bike 170mm? Are the axles long enough so that you can just add a nut to each side of the hub to make it wider?

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Balor
recumbent guru

Russia
991 Posts

Posted - 09/16/2020 :  12:17:57  Show Profile  Reply with Quote
Actually, the standard for 4+ inch fat bikes (up to 5") is 197 now :)
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warren
human power expert

USA
6560 Posts

Posted - 09/16/2020 :  14:51:38  Show Profile  Visit warren's Homepage  Reply with Quote
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Balor
recumbent guru

Russia
991 Posts

Posted - 09/17/2020 :  03:23:10  Show Profile  Reply with Quote
That's pretty cool actually. Leads to a latterally stiffer wheels, which is especially good on trikes. I think using fat bike (or at least 'boost') hubs with 'plus' sized rims is a good idea for heavy, faired HPV that needs lots of rigidity for good control, and allows for 'aero' disk wheels with very fat road (think 40mm) tires. Lateral forces on a fully faired HPV, even singletrack, are NON-negiglble due to side winds, and having flex in the system is not good for control.
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Balor
recumbent guru

Russia
991 Posts

Posted - 09/17/2020 :  03:25:51  Show Profile  Reply with Quote
https://forums.mtbr.com/29er-bikes/ugly-truth-about-hub-width-wheel-stiffness-190125.html

An interesting quote from the thread:

"Wider flanges = more lateral stiffness but _less_ radial stiffness. If you built a wheel with infinite flange spacing you'd have infinity times your standard of lateral stifness but the rim itself would be the only thing that would keep the wheel from turning into an oval. I've ruined more wheels due to flat spots then due to tacoing, so personally I woudn't discount radial stiffness as a design consideration in addition to what has already been mentioned."

Point is, wheels are already *more* radially *stiff* than we need and massively stronger, too - barring catastrofic crashes.

So, less radial stiffness and more lateral stiffness is, actually, a 'win-win' - a wheel that rides softer due to more spring of the spokes, but more ridid laterally for good control!

Edited by - Balor on 09/17/2020 03:56:25
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Jeroen s
Starting Member

Netherlands
34 Posts

Posted - 09/17/2020 :  03:46:18  Show Profile  Reply with Quote
I doubt any thing would work, the axle is hollow, because the shifting cable runs through it. It is also a part of the gearing set up, wich gets a lot of torque to that axle.


Greetings, Jeroen
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