Crank/sprocket combo questions.....

[TexasXXX]

Hey guys, forgive me, but I'm having a brain fart this morning. What I want to do is run a crank like this:

Problem is, this crank is made for multi speed Schwinn Krate type bikes....and it's a 52 tooth. Now, I'd like to run it on my 20" Sears Spyder single speed bike.......but I'm afraid that peddling a 52 tooth sprocket might be heck if using the stock crank length.

Now, IF I were to run this 52 tooth sprocket.....what size crank would be best to run in order to change the ease of peddling it??? A 3 1/2" crank, 4" crank, or a 7" crank???

I'm sorry if this seems like a really basic question....for some reason I sometimes can't grasp simple concepts...lol

Thanks in advance for any and all help,

Brian

 

[Multipass]

A longer crank arm will provide more leverage, making the effort to pedal easier. You'll probably want to run a fairly large rear cog too. A small cog like a 14T or 16T, while giving you a whole pile of top end speed, would be brutal for climbing. 18T - 22T on the rear would probably be OK.

Frame clearance could be a problem with a big sprocket/long crank combo on a 20" bike. For example, some of the Stingrays cannot fit anything larger than a 36T on the front. I don't know what the Spyder is like in this regard.

I think Schwinn also made the mag style sprocket in a 46T version.

As usual, the good Mr. Brown has a comprehensive article on the matter of crank length:

http://sheldonbrown.com/cranks.html

Hope this helps

-Mp

 

[TexasXXX]

MP, THANKS for that link...and insight.

I'm having a hard time trying to find out much info on these exact sprockets. The Schwinn forum just isn't yielding me much info

 

[ricksterr1221]

Not this kind, I WANT one for me. Use short peddal ar,s

 

[Markm]

throw it in and try it out...sometimes things just work out

 

[TexasXXX]

throw it in and try it out...sometimes things just work out

I've gotta score one first :wink:

 

[ParkRNDL]

hey, Brian, it's funny... i started building up a Sears Spyder project similar to yours-- see this thread:

http://www.ratrodbikes.com/forum/viewtopic.php?t=2073

It had a pretty big sprocket and fairly short cranks, which made it tough to pedal on my cruises around the block with the kids. Turns out the girls' Columbia donor bike where I got most of the other parts had a crank with arms an inch longer (I think it was 6" to 5"). I swapped sprockets and used the longer cranks with no problems... easier to cruise around and you don't lose top speed. You DO, however, lose clearance on turns... that inside pedal is that much more likely to scrape if you're still pedaling...

--rick

 

[TexasXXX]

Rick, that makes sense.......

I know darn near every trick in the book has been done with a bicycle.....but I somehow want this bike to be unique....so I figured that flashy Mag sprocket might do the trick.

I'm also fond of "Firebikes" "Salt Flat" sprocket....but I don't know if that thing would come close to fitting...AND it's also $69 It definately looks awesome though....and would give a definate "muscle car" look to this project :mrgreen:

 

[new_dharma]

schwinn solved the "large-sprocket-hitting-the-chainstay" problem by using a slightly curved chainstay on the drive-side of the 5-speed sting-rays (it's also an easy way to tell an original from a fake)...