Working rear triangle to accommodate different hub widths. How much is too much

Manbeer

1 kW
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Aug 7, 2020
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I seem to struggle to find a definitive answer, i know i have done as much as 5mm with no issue...yet i see old school cyclocross and road guys posting looking for 126mm hubs cause they can't use 130, etc

I also know that different materials and construction will change the variables a bit. seems like a lot of stretch and you would also be limiting the amount of rear axle that sits flush in the dropouts

Bikeisland has some blem fatbike frames for dirt cheap that use 170mm rear spacing. Problem is, that standard is becoming obsolete so i am trying to figure out if i could rig something up. There are like a handful of companies making that size but i am looking to run a narrower 3 inch tire and i got me thinking

For my buddies trek xcaliber, we swapped endcaps on a set of hope hubs to convert a 148mm to the 141 QR needed for his bike. I am wondering if i did the same with 157 super boost, if 20mm in would be too much. similarly, 20mm out would put me at 190mm which again has more options...you see where i am going

I am not dead set on doing this, just finding other options vs getting hubs i dont want or spending $$$ on hope since the frames and forks are 125 shipped
 
Create a "bolt on" solution, not a "bend to yield" solution.
You can easily lessen dropout width by extending the swinger a few inches and layering the anchors. Or increase the dropout width for a wider dimension.

.....like a cheap extended swingarm on a rocketbike... They make nice expensive one piece extended swingers for those Hayabusa bikes... or... the cheap "bolt on " extension of the swinger. Layered on a 150mm dropout, the extended dimension changes. I plan to do this with a 135mm bike to make it a 150mm bike.

Metallurgy is an art. Bending, memory, yield tension vs compression, torsion, ect. Forces move in metal and are going to affect the final product. Do not wonder: Know.

"how much you can definitively" is really a hard question without being the person who designed the bike. usually not to much. "Strong" and "light" ( bikes) mean two very balanced things.. the ability to be strong enough tat it don't break, and light enough to peddle. "Flex" is built in for compliance and so things dont break or are to heavy. Once stressed, in a certain direction, it may be hard to " un-stretch it" .

I wouldnt be to scared of bending like 10-20cm on a steel frame. Hardest thing is to keep it square IMO.

Aluminum would be a different story of course.
 
yup...aluminum. i was thrown off since the tubes did not look that thick and im so used to hydroformed tubing nowadays. that being said, i guess as dog dipstick said, spacers on the inside would make a better fit. i was originally intending to do a mid drive on this one, but it seems there are still a lot of 170mm hub motors out there. Perhaps i will reconsider and run something like that on 35a/52v or so. I want to use it on the beach so im worried about bogging it too hard in the sand, but i suppose it'll make do for mild use . either way 125 shipped for a frame and fork is almost too good a deal to pass on
 
I would think that the tires would spin out from lack of traction before they bogged down in the sand. The hub motor sounds like it might be more reliable than a mid motor in that situation. You won't have to worry about sand and salt air causing the chain to fail. I suppose if you use hot wax or a dry lube on the chain and clean it often, it will be fine.
 
good call, i have been meaning to try the chain wax. beach bike seems like the perfect application

the tide had just come down the other day on the bay side here and i took my tsdz2 stumpjumper on the beach. i was surprised it actually did reasonably well, now im hooked on this idea
 
I’ve bent steel bmx frames that are 110mm to 140mm no problem using a fat threaded rod and a lot of nuts. Be careful and lock the rod to the dropout so it doesn’t get shot off the back while you’re doing and also stretch each side consistently doing maybe 4mm each side back and forth. Depending on how good the steel frame is it could require you separate them to much further and they will spring back to around 135mm
 
A dirtjumper with a 130mm drop out is just the ticket for a build i got lined up, remove crank and its seating tube cut the frame to fit a 100mm id pipe and weld it back up spread the drop out to 130mm so ill need an old steel frame with the slot dropouts and i can run chain tensioners on the axle for a robust back end that be up for riding hard down the local trails.

100mm watercooled motor and 219 chain direct on its 12mm motor shaft gearing everything works out for a 20 inch wheel to do close on 50 mph at 14krpm on the motor using a 9t drive and 105t rear that fills the wheel like a dinner plate still enough clearance to ground but its not far off the size of the rim.
 
damn thats a lot of spread but yeah on steel id imagine no issue. unfortunately for me, the frame looked steel, almost like a copy of a surly or something, but it isnt.

i did the threaded rod trick on a customers e-BSO a few months back, which arrived to him damaged and couldnt fit the wheel. worked like a charm
 
Steel you can bend and take it as far as you dare. Aluminum you can't bend, so just 5-10mm at the most, because aluminum doesn't do well under stress. You can't do the threaded rod stretching with aluminum. Steel ebikes are the way to go, then you can't easily mod and make any changes you want. If going with an AL ebike, then get a fatbike, which will already have nice wide dropouts. Plus even being wider at the cranks works in your favor as it gives you more width to fit batteries.

With steel you can pick up a cheap inverter welding machine and easily learn to weld.

The only AL ebike I have is a Cannondale Super V, and for it I modded by fabricating a longer swingarm out of steel. That was my first extreme performance ebike, and though it was only good for smooth riding on the street or beach after the mods, it did have a top speed of 107mph.
 
About five years ago when I could only locate rear hub motors with 135 mm axles and wanted to convert a Mongoose Dolomite, the rear was squeezed from 190 or so to 135 without incident. Of course, it was necessary to make spacers for the disc brake and freewheel.
 
Leaf sells a 110mm hub. I wish I’d gotten it and I don’t know what current others are doing but at 90 amps from a vesc I barely get this giant 135mm spaced 1500 watt leaf motor warm no matter what mountain I climb( and the eBay clone)
 
I still haven't pulled the trigger on this frame as incant decide which route i want to take. I probably will choose between a cyclone or one of the generic "1500w" rear hub motors and push it closer to 3kw. Given the lack of options as far as 170mm non motorized wheels atm i am leaning towards the hub motor option as it kills 2 birds with one stone, but hoping it has enough punch down low for sand. my previous experience with a 9c clone on 30a and i was a bit disappointed with the lack of torque.

Apparently there is a 1000w rated geared Bafang out there that is handling 2500-3kw nicely for people so perhaps it is worth consideration, but i am concerned with constant breaking and regaining traction over roots, etc damaging the internals
 
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