Highway gear mid-drive cassette

[Alaskavan]

This is something I'm working on for my trike, but I thought it might be applicable for any bike with a chain run long enough to use idlers.
The problem I'm addressing is that , even with a 52t chainring, I "pedal out" at 25-30mph (20" rear wheel). Since I usually cruise at 35mph, I don't bother pedaling. This has 2 impacts: 1. I'm not getting as much exercise as I feel I should, and: 2. I'm not utilizing the most efficient source of power available, me.
What I propose to do about this is to replace the second idler (there are 2 on the chain run on my trike) with a cassette with probly 3 cogs. My intention is to run a chain from the chainrings to a 14t cog on the cassette, and run the chain back to the rear wheel cassette from either a 28t cog on the mid-cassette (for highway riding), or from a 12t cog on the mid-cassette (for city riding, or in case of breakdown of the motor). Changing gears on the mid-cassette doesn't have to be "shift on the fly". I hope to be able to make it so the change will involve a simple manual adjustment (a minute or less).
This should result in having the equivalent of a 104t chainring for the highway, and somewhat less than a 52t chainring for city or non-motorized riding. I know I will get some resistance from the addition of a chain tensioner for the front chain run, but I hope the result will be worth it.

If anyone has experience, opinion, or ideas about this, I'd like to hear it.

 

[Alaskavan]

Well, I have the initial setup. I do have some chain run issues, but I have ideas about how to overcome those.

Here's the rear chain run. I need to move the Teflon chain tube forward on the top run so it will guide the chain onto the mid gear better. I'll make it adjustable so that if the bike breaks, I can change it so it guides the chain onto a smaller cog.


A view of the front chain run and the derailleur I put on there to act as a chain tensioner.


Here you can see how close to the ground the bottom rear run is.


The large link chain holds the derailleur at the correct angle. Not pretty, but functional.


The rear chain occasionally runs off the mid cassette, but I'll cure that. I can easily pedal at 40mph, so I can shut the motor down on long downhill runs.
Initial results: I made 2 runs from town to the cabin and back. 132 miles + a little going from pub to pub. It used .6 gal. of gas. You can do the math.

 

[vegaspaddy]

"I can easily pedal at 40mph"

alaska what more needs to be said , try that after 10 pubs !!!!!!! hehehe

xcellent work as usual, that trike is amazing !!!!

 

[PatrickW]

Alaska...quick question. My tired old eyes can't tell from y9ur pics, but how many gears do you have, total, and how do you shift them (levers or grip-shift?)

 

[Alaskavan]

I have 21 gears I can shift with levers. The mid- drive I intend to have set with 2 options - VERY low, and VERY high, changed manually, so I guess that makes 42 gears total.

 

[PatrickW]

21-Gears...

Hi there again, Van...Unfortunately shifting a 21 gear setup is not quite the same as a 7, 10, or 12 gear setup. You have, in effect, only about 14'usable' gears. Here is why...it has to do mostly with geometry and alignment.

Normally, you should be using the second (gear 2, middle) on the front chain ring, with all 7 of your rear cassete gears...this equals 7 (seven) gears.

Think of the smallest, (gear 1, inside) on the front chain ring as a 'a very low stump-puller, or very steep hill gear.' Use along with only #1, 2, 3, and maybe 4 gears on the rear cassette...this equals 4 (four) more gears.

Think of the largest, (gear 3, outside) on the front chain ring as a sort of "over-drive" for limited occasions when you are going very fast and only need a few pedal revolutions to keep it moving along. Use with only #5, 6, 7 gears on the rear cassette.,,this equals 3 more gears.

Now, you have 14 'usable' gears, which should be plenty.

ALWAYS downshift, and start from a low gear, or the torque will do serious damage to the chain, rear casette and axle/jack shaft from slippage.

Shifting this way, will give you max chain alignment, and help prevent slapping, jumping, 'throwing the chain', or bending gears and other delicate parts. Never try to use to use the smallest ring gear with the largest cassette gear, or the largest ring gear with the smallest cassette gear. I can guarantee, that it wouldn't be long before you would hear, "PING, Thwap, Thwap, Thwap, Sprong!"...before you went airborne into the weeds, or worse.

I hope this helps.

 

[PatrickW]

Van...P.S. Btw, have no idea about the 'mid-drive' that you talk about, but I would suspect that all of the same principals would apply. What I do, is put the whole thing up on blocks (I have several concrete, and a mess of short 4X4's...all the better if you happen to afford a stand or jack stands.) Get it up in the air, shift thru gears as you lay on a mat or creaper on the floor, and just see what is happening in the way of alignment as you go slowly thru the gears while pedaling with your hand. You want to keep the chain as parallel to the frame as you can...use a ruler to measure from from the front of the chain to the frame, and the back of the chain to the fraime.

When I joined MBc I was quite confused about the new motors and/or combining them together. I try to express that I didn't know much about either motors, or bicycles/trikes in general...just wanted to clear that up a little for anyone interested. I'm still learning and try to learn something new everyday. <g>
I hope I didn't come off as being pedantic or condescending here...K? And, Gee...I really hope I didn't get way too long winded. But, I have a penchant for trying to make things as clear and complete as possible...otherwise advice is worthless. Now, Good Luck.