Non-Traditional 3 Speed Fat Bike

[Voaraghamanthar]

Has anyone ventured into the realm of a single fixed gear rear wheel but using a 3 sprocket crank to get a reverse effect 3 speed? Tell me about your findings or share your knowledge if it would work without using a rear derailler or Archer setup.

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[kchurch86]

I've thought about this as well...subscribing for future posts.

 

[macncheese]

Two issues i see are:

1. You need the derailleur to take the slack out of the chain as your chain length requirements change between gears.
2. "Fixed gear" doesnt work with derailleurs because the chain needs to be tight in both directions.

 

[deorman]

Two issues i see are:

1. You need the derailleur to take the slack out of the chain as your chain length requirements change between gears.
2. "Fixed gear" doesnt work with derailleurs because the chain needs to be tight in both directions.

Perfect summary.

 

[Voaraghamanthar]

So what if we add the rear derailler back into the equation only for slack? It wouldn't require indexing of course.

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[macncheese]

You still couldnt run "fixed" because you can't lower your cadence or skid with the derailleur. You could run a freewheel but at that point, you may as well run the rear derailleur as a derailleur. Front derailleurs suck.

What are you trying to achieve by this?

 

[Voaraghamanthar]

It's all related to pedal assist on an ebike build I'm doing. I want both worlds. Ebike to get to my trail. And regular bike to ride my trail.

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[Duchess]

Why does it have to be fixed gear?

 

[Voaraghamanthar]

Not enough room to fit a cassette... And... This is a fat bike with 190mm dropout.

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[Voaraghamanthar]

Also? I really only need a 3 speed on the trails I use. 18T freewheel is on the hub.

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[Duchess]

If you have a freewheel, you can use a rear derailler to keep chain tension. It's definitely the easiest solution.

 

[rickpaulos]

Yep, Single speed is not the same as Fixie.

There have been some internally geared cranks with 2 or more gears. The 1960s Dana 3 speed probably would not stand up to trail use and was made for normal spaced 1-piece crank bikes like old Schwinns. Most newer models require frames made specifically to accommodate them and the prices would be in the 4 digit$ range or more.

Another option, run a dual rear hub. The kind that is threaded on both sides. Many gas motor kits run the motor drive line on the left side and that leaves the right side gear train intact.

Yet another option: run a hub motor. (electric motor built inside the hub: front or rear). Then add your normal driveline for pedaling.

 

[Duchess]

There are at least a couple of new bottom bracket internal gear set ups, but IMO, the prices are ridiculous. Maybe it's because they're really robust, but I have no idea.

 

[Voaraghamanthar]

Yep, Single speed is not the same as Fixie.

There have been some internally geared cranks with 2 or more gears. The 1960s Dana 3 speed probably would not stand up to trail use and was made for normal spaced 1-piece crank bikes like old Schwinns. Most newer models require frames made specifically to accommodate them and the prices would be in the 4 digit$ range or more.

Another option, run a dual rear hub. The kind that is threaded on both sides. Many gas motor kits run the motor drive line on the left side and that leaves the right side gear train intact.

Yet another option: run a hub motor. (electric motor built inside the hub: front or rear). Then add your normal driveline for pedaling.

Above is a couple snap shots I took of my chain tensioner. If it only had a spring... It would make the idea work.

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[pholTmonx]

Can we see picks of the build

 

[us56456712]

My friend has built a 1 x 9 mid drive fat e bike. He uses it on the trails, His major problem is with cross chaining in low gear. He keeps wearing out chain wheels. He has to use too large of a front chain wheel for an off set chain wheel to clear the motor diameter and fix the cross chain problem. This makes it too hard to peddle for our trails in some places. It seems ridiculously powerful. The whole central triangle is filled with batteries, the most powerful he could get to fit in there. On snow he can stand beside the bike and burn rubber while downshifting to get to a lower gear to start out. I'm not sure how he does this as the bike drive is only susposed to engage when you are peddling. I seem to recall he spins the crank with his hand and then downshifts while the wheel is spinning like mad in high power mode and he is waling beside it shifting. Probably centrical force keeps the rear wheel spinning after he has stopped cranking. He built it last winter so perhaps there is a better design out there now that avoids cross chaining 36 tooth chain wheels? Mid drive is the way to go if the cross chain problem can be sorted. It works really well, only providing power when you are peddling so you don't go flying off the trail when you want to slow down. On hills it takes some getting used to because if you stop peddling to clear a technical obstacle it then takes a few turns of the crank before the assist kicks in again. You can be left with a very heavy bike to push up the hill. On low power it basically takes the weight of the bike away so it feels like you are peddling next to nothing or going slightly downhill. He said the system cost about $1000. If you don't have steep technical hills then the larger front off set chain wheel that solves cross chaining would work for you. I am convinced that the mid drive is the best for a heavier fat bike.