Northernbike

hi, I have a Rize ebike, it's a mini with 20" fat tires. due to the design the crank is higher off the ground than a regular bike.
I know they are 170mm but I dont know how to determine what will fit as a replacement. I need something like a 145 to 150mm crankarm. Is there a guide somewhere. The stamping on it says prowheel forged chariot 170mm. I think a shorter arm will help me find a more comfortable seating position.
tia
G.

Geepig

It looks doable, they look like they are mounted on a standard square type of bottom bracket axle.

With that fixed saddle it kind of reminds me of the mopeds I used to ride that had pedals to comply with UK law - and where you had to stand up to pedal them 'effectively'. Other than that if you fit shorter cranks then it will be harder to pedal unless you compensate by changing the sprocket sizes as well, which will mean replacing the chain for a longer one.

shelbyfv

I doubt much pedaling is involved so whatever length makes the riding position comfortable should be OK. Swapping the crank probably isn't something you will be able to do yourself. Best to take it to a shop, tell them what your issue is and let them source and install the parts. Cool machine, those wheels/tires look like they'll go anywhere.

Northernbike

i actually pedal quite a bit but use pedal assist even though there is a throttle option. It surely goes anywhere. I have had it through slush, snow, on ice, in mud, on pavement, beach sand etc. I think it will be a lot of fun and might end up replacing my Honda Forza at some point.

alcjphil

What is the problem with your saddle position? If you think it is too high shorter crank arms are the opposite of what you need

Northernbike

the issue is that the pedals is too high when at the top of thr cycle, causing too sharp of a bend in my knee. I had to put my seat way up to counteract this. If the crank was lower, there might not be as much of an issue or maybe I coukd find a way to back my seat up a bit. it is as far back as I can put it now.
tks

imakecircles

It sounds like your seat is too low. A good rule of thumb is that with your heel on the pedal at the bottom of the pedal stroke, and while sitting on the seat, your knee should only very slightly bent. This position often seems really high to new riders.

Northernbike

I put my seat up but I find I have to put it too high for comfort in order to get proper leg extension. It all due tonthe fact that the crank is high off the ground compared to a regular bike. I can still use it but I will plugging away at this little nuisance.

Bill Kapaun

Get a longer seat post?
Different bar?

shelbyfv

Seatposts do come with different offsets. More offset will move your saddle further back. Would be much less expensive than changing the crank. You will need to know the diameter of your post and the proper length. Those numbers are usually engraved or etched somewhere toward the bottom of the post.