Singlespeed/direct deive chain load (strain) estimate, anyone?

[FurryOnTheInside]

not sure how those are different from freewheel or cassette with only two sprockets on them

They are, but Surly's explanation might be more understandable! They are to be used with two front sprockets, to make two different side-by-side single speed pairings that have different ratios: one for flat open riding, the other for hills/ in town.
By having the same total tooth count, like 10:44 (54 total) and 14:40 (54 total) gives you a 1:4.4 and 1:2.86 ratio, and you can use the same chain but not have to split the chain to switch from one ratio to the other.
It is not gears, but it gives a single speed more versatility.
You have to get off the bike, release the chain tensioner or pull it out the way if it's a spring tensioner, and manually pull the single speed chain over to the ratio you want while turning the wheel by hand.
It is certainly useful for pedal power bikes, but after a bit of thought I decided IMO not a big advantage on motored bikes.. unless there is a lot of room around the drive sprocket to get a second sprocket of a significantly larger tooth count (ie 10 and 14), and enough lateral space to use a 1/8" chain to spread wear and last longer than a 3/32". Still, it's an option that is out there but doesn't get mentioned so I had to have a think about it and see what potential it has.

 

[CrazyDan]

I'd guess a 2000lb chain is OK for these - the 415 chain that comes with most kits works well when installed correctly - saving a 1/4lb there doesn't seem worth the effort (skipping breakfast would probably do more).

Decreasing the weight of any rotating mass that is sapping energy from your motor to the ground will have far greater benefits than losing even twice that weight anywhere else on the bike (including the breakfast that can reside in his stomach because he decreased his rotating mass). I find swapping my kit chain for an HD bmx chain increases my acceleration more than fasting for longer than I feel comfortable .

 

[FurryOnTheInside]

Not that there is a difference in ultimate tensile strength between a 1/8" and a 3/16" chain, all things being equal. The strength is in the side plates. Some "track" 1/8" chains are actually slightly stronger than a 3/16" (DID for example).
There is a difference in wear rate. If 1/8" lasts 100miles then 3/16" theoretically lasts 150miles and 3/32" lasts 75miles.

 

[crassius]

if I had room for two chains, I'd put them on free spinning sprockets and run a detent ball up from the inside of the shaft to lock the one I want to drive the rear

 

[FurryOnTheInside]

if I had room for two chains, I'd put them on free spinning sprockets and run a detent ball up from the inside of the shaft to lock the one I want to drive the rear

I have no idea what you mean.. How a ball detent would do that.. Mm.
Anyway you don't need room for two chains or the clearance space between them to do a dingle, with only one chain only one or other of the side plates needs to sit between the sprockets, so actually it's more like 1.75 chains wide. You do need the room for the chain to be pulled over the larger sprocket.

 

[crassius]

but them one doesn't seem able to shift it as one would other transmissions

free spinning sprockets have small notches in the bottom where the ball fits to lock it to the shaft - to shift to other one, the ball gets moved inside shaft to catch opening under next one

 

[FurryOnTheInside]

but them one doesn't seem able to shift it as one would other transmissions

free spinning sprockets have small notches in the bottom where the ball fits to lock it to the shaft - to shift to other one, the ball gets moved inside shaft to catch opening under next one

No, that's right, it's not gears, you do have to pull over and get off, but it can be done out on the side of the road. It's just a lot easier than the disassembly involved in changing a single speed rear sprocket and chain.

I am really not able to picture how free spinning sprockets would work, what they spin on, how the position of the ball detent is controlled.. I'm lost. Sorry

 

[crassius]

old method from 20s thru WWII - haven't looked, but may be back now in paddle-shift cars

 

[Steve Best]

A good place to start your reading about chains is:
http://tsubaki.ca/pdf/library/the_Complete_guide_to_chain.pdf

More on the engineering and calculation data (pg34):
http://www.iwis.de/uploads/tx_sbdownloader/KettenHandbuch_E.pdf

I figure about 2hp running 800rpm at the sprocket with moderate shock loads
= 800N (180 lbs) to 1500N (340 lbs) shock load on the chain.

You are not going to break 410 (1/8") BMX chain.

Steve

 

[FurryOnTheInside]

If those figures are correct then you're not going to break any chain.
Some half link chains have been said to stretch, due to the kink in the side plates.. But
Most chains are around 9500 -10000N+ breaking strain. Even the cheapest nine and ten speed chains are at least 9100N according to what I have read with just a little online research. So size really doesn't matter.
It really is only a question of wear rate. Better material lasts longer, and wider chain divides wear to last longer.
Which is why I thought this thread had been put to bed, lol.
Thanks to all those who contributed information.