#25 chain for pedal input

[John in CR]

I want to be able to pedal at high speeds, but I'd like to avoid a giant and costly chainring, because it takes up a lot of room and ground clearance. I plan to run the pedal input to a jackshaft anyway, and I won't need to change gears at the chainring. Plus I already have a variety of #25 sprockets, and can easily get a 7 or 8 to 1 gear up in that initial stage. I want to have a leisurely 40-60 cadence at about 1000rpm at the wheel, so I really do need a big initial step up and getting most of the way there with just a 6-8" diameter chainring at the cranks is quite appealing.

Anyone see any problems with the idea other than fitting the small cog on the jackshaft?

John

 

[boostjuice]

It depends how hard you want to pedal. Repeated standing on a crank under chain tension would apply far greater strain force than casually pedalling along.

Standard #25, Tensile strength 781 lb (354 kg), Working load 140 lb (64 kg) [Working load = de-rating to allow adequate service life]

Bicycle chain [9spd~BMX], Tensile strength 2204~3306 lb (1000Kg~1500kg) , Working load 397~597 lb (180kg~271kg)

That being said, higher grades of #25 chain are available at least up to 150% higher tensile strength and 170% greater shock loading compared to the ANSI standard.
http://tsubaki.eu/chain/ansi-heavy-duty-roller-chain/

 

[John in CR]

Thanks Bootsjuice. I won't be doing any jumping on the pedals with my full weight cranking on the chain, so it looks like it should work fine. I'm just tired of not being able to pedal assist for more than the first few strokes at takeoff. I'd like to get a bit of exercise while riding. Plus I want to see the look on motorists faces as a pass them on the highway while I'm just leisurely pedaling along. Fake pedaling just feels wrong, so I want to have some resistance and add some input power, however slight, even if the added wind resistance makes it a negative.

 

[FMB42]

This is an interesting project.

I too thought about running a jack shaft on a future "high speed" project for some of the same reasons (i.e. lack of ground clearance due to a huge chain ring). However, I decided that it might be best (i.e. easier) for me to go with a more "traditional" low speed "off the line pedaling" setup coupled with a "low torque-high speed" hub motor wind.

BTW, I had a mini bike that ran a jack shaft back in the day. The cool thing about it was that you could "swap" the jack shaft gears around for a high or low gear range (this, of course, required minor chain and engine mount position changes).

 

[John in CR]

FMB,

I haven't decided yet on whether to go hub motor or not, but I would like to combine the jackshaft and rear suspension pivot, or at least have them share a common center. That will save a bit of weight through dual use and a single support structure for both, but my biggie is that it will avoid any issues of changing chain length during compression of the suspension. Then I can have a nice tidy chain with small sprockets at both ends like I've seen on those mountain bikes with the bottom bracket gearboxes.

John

 

[FMB42]

OK, you're way ahead of me in ebike design and fab.

IIRC, Aermacchi (Italian) based Harley Davidson 250cc road racers of the mid "70s" incorporated a swing arm pivot that was located on the same axis as the front drive sprocket. This was some pretty cool engineering at the time (BTW, I think the AeroHD won at least one 250cc world championship during the '70s).

 

[spinningmagnets]

Found $12 (11T) nylon sprockets for #25 chain, 9T up to 45T available. Bore is 1/4", but theres plenty of room to bore it out bigger, easy to thin if you wanted to use bicycle chain...cheap experiment?

I recall a friends motorcycle that had nylon (plastic) sprockets and a metal o-ring chain on a Honda 750 (novel to us at the time in 1974). Ran quieter and cleaner, as each link has some grease sealed inside, no spray-lube needed. Just a thought...

http://www.mcmaster.com/#nylon-sprockets/=9ke2g2

 

[torqueon]

I am using 25 pitch primary to a jackshaft, than it goes to standard bike chain and sprocket It works quite well so far, time will tell. The 25 pitch handles high R.P.M. well