What crankset for a 7 speed cassette?

[PRW]

I am about to build up a Kaffenback (700c road bike) with a Mac 10T and mini battery as a street commuter - I live very close to work. What crankset could I use / is recommended, if I have a 11-34T 7 speed cassette, and want to pedal? I can find 50/34 double cranksets, but they all seem 10/11 speed...

 

[motomech]

You shouldn't have to change out the entire crankset, just the big chainring.
You want the largest one you can fit, 50T would be good.
In the past, I have used an 8-speed cassettes and free wheels with a 9-speed system and it shifted ok. There is some overlap in mixing parts(Sheldon Brown talks about this). You should just try what you have and see how it works. My guess it won't adjust to where all 7 speeds shift smoothly, but if you can give the bottom(tallest)3 gears to work, that's ok, because w/ a Mac, that is all you will ever use anyhow.
If it doesn't work out, just buy a inexpensive 8 or 9 speed cassette. I like the cheap ones because I wear out the 11T sprocket so fast and the ones that are held together w/ pins(and fall apart in your hands), have replacement sm. gears.

I'm assuming you truely mean "cassette"(the new Mac's have a CST version) and not a freewheel.

 

[999zip999]

I went from a 115mm to 122mn bottom bracket and installed a 52t double ring and 11t on my mtb and peddle at 36mph maybe windmill at 38mph. But my bike does 47mph. A little to fast as I turn down to 40amps. Why 10t and not a 8t ?
I also took a hammer to frame the the crank arm wouldn't hit. Just a dipple. If you are getting a small battery you need the best cells. No feabay crap. 10ah is small. Plus your battery needs to match your controller 30amp ? How many volts ?

 

[PRW]

You shouldn't have to change out the entire crankset, just the big chainring.
You want the largest one you can fit, 50T would be good.
In the past, I have used an 8-speed cassettes and free wheels with a 9-speed system and it shifted ok. There is some overlap in mixing parts(Sheldon Brown talks about this). You should just try what you have and see how it works. My guess it won't adjust to where all 7 speeds shift smoothly, but if you can give the bottom(tallest)3 gears to work, that's ok, because w/ a Mac, that is all you will ever use anyhow.
If it doesn't work out, just buy a inexpensive 8 or 9 speed cassette. I like the cheap ones because I wear out the 11T sprocket so fast and the ones that are held together w/ pins(and fall apart in your hands), have replacement sm. gears.

I'm assuming you truely mean "cassette"(the new Mac's have a CST version) and not a freewheel.

thanks motomech -yes, it's the motor for cassette. I have just the frame at the moment (and the 11-34 cassette), so can get any crankset. Getting a new cassette is an option as well.

 

[PRW]

I went from a 115mm to 122mn bottom bracket and installed a 52t double ring and 11t on my mtb and peddle at 36mph maybe windmill at 38mph. But my bike does 47mph. A little to fast as I turn down to 40amps. Why 10t and not a 8t ?

it's on a 700c wheel, I am not the lightest creature out there, and I don't really need the speed - I wanted it as a semi- stealthy street bike. Will have spoke protectors, and big rear brake disc, purely to obscure the motor.

 

[motomech]

...I have just the frame at the moment (and the 11-34 cassette), so can get any crankset.

If you are looking at cranksets, you might want to take into consideration how your PAS is going to mount. For example, a space for the disc between the bottom bracket and crankset shoulder.
Or perhaps, a single ring?

 

[PRW]

I wasn't going to use PAS - just the throttle - decided too much detail for me to try install!

 

[Chalo]

11-34 is plenty of gear range for the street. Use a single ring crank, and set the front derailleur as a chain retainer. Anything from 48 teeth on up will give you a super high top gear, so choose according to how low a bottom gear you want.

 

[999zip999]

What size battery and voltage ? How fast do you want to peddle at ?

 

[PRW]

thanks Chalo. I see 48T gives me around 25mph at 70 cadence, which is perfect.
999zip999, a 52v 14s2p 30q (Mighty Mini) - I don't need more than 10 miles range for now, and I want to pedal along. I will use the CA to set max amps - say 25A?

 

[motomech]

I wasn't going to use PAS - just the throttle - decided too much detail for me to try install!

That would be a mistake, PAS is the only way to go, especially on a build like that.
This site is full of members who didn't install PAS, were eventually talked into it and all have said they now prefer it.

 

[Warren]

I'm at 38K miles, between two bikes, throttle only. What is this PAS you speak of?

 

[MadRhino]

With a single chainring, I would prefer a 5 spd cassette. 7 is hard on the chain line, and motor assist is making it easy to use fewer cogs.