Crank set/chain rings

[lbz5mc12]

I have an ezip skyline. I replaced the original electrical components with a 36v 800w rear wheel kit. The problem I was having was that I could not pedal with the motor at full throttle. The chain ring it comes with looks like something you would find on a bmx bike. I believe it was 22 tooth. I found a 52/39 tooth set on amazon for $26.97. I only use the big one because I don't have a front derailleur. Its supposed to be a 7 speed bike but my hub motor only has room for a 6 speed. It's great; I no longer have to feel like I'm sprinting when I pedal with the motor at high speed. My average pedaling speed went from 15mph up to 21mph. I can now get to where I'm going quite a bit faster now. When I'm going down hill I can out pedal the motor. The thing looks huge on my bike. The crank set is by Shimano. I posted this in case anyone else was having a similar problem and needed a good crank set at a low price. It ships from bikeworldusa.com. It shipped from New York to Cali standard and it only took about 4 business days USPS. Oh yeah it's a square bottom bracket crank set. I got the one with the chain guard. "Sometimes faster is better", that's definitely not what she said.

 

[dogman dan]

cool you were able to make it fit. Many mountain bikes have frames that don't allow any bigger than 48 tooth. The first idea then doesn't work, putting an old 19 speed 52 tooth crank on the bike.

 

[dfar]

I am also running a 53/39 front sprocket on my mountain bike. To allow the sprocket to miss the frame I had to convert the standard 113mm bottom bracket to a 128mm bottom bracket, works nicely. Only problem to work out now is fitting a front derailleur and shifter to shit between sprockets. I bought a standard 2 speed shifter and front derailleur but the amount of cable that needs to be taken up to shift between gears is two much for the shifter to work properly, I think I'm going to fabricate a lever shifter.

 

[lbz5mc12]

You probably need to get the shifters for a ten speed road bike. I don't believe the shifters that click one shift at a time will work with the larger size ten speed cranks. I'm trying to think of a way to describe it better. You know the kind of shifters that give you more play between the gears. One good thing about the design of the skyline frame is the slot for the battery behind the seat. This pushes the rear dropouts further back which makes room for the larger chain ring with room to spare. I'm going to have to take some pictures of the crank area of the bike to better illustrate my point.

 

[FastDemise]

That happens to be the exact same crank I got for my bike. It fits only after adding some 2mm spacers on the BB to space out the crank so it would not grind on the frame. I've been successful at using a simple twist shifter. Seems the 2 gears are much closer together than normal MTB gears so either a simple lever or twist will allow you to shift without too much trouble. With a 52/14 I can pedal just fine around ~28MPH up as high as 32MPH.

 

[lbz5mc12]

I took a closer look at my bike today and realized I would not be able to use a front derailleur even if I wanted to. The way it's designed puts the chain rings too far away from the frame. Also there is a big gap between the seat tube and the location of the cranks due to the slot for the battery and the controller box underneath the frame. However I also realized that if I ever go with a mid drive on the bike, that gap would be a good place to mount the motor. I was actually thinking of mounting the original Currie motor there and using it in tandem with the hub motor. Basically I wouldn't have to pedal any more. I'd still need to install a freewheel crank set just to keep up appearances. I'd run the motor behind the chain ring. I'm pretty sure you guys have seen the freewheel crank sets that run from like $60.00 to $100.00 plus shipping, right?

 

[Kingfish]

Here’s the low-down on chainrings…

There are two groups: Road Bikes, and Mt. Bikes. They are related in that they both use a chain and even a similar chain pitch. Width of the chain varies directly with the number of gear rings on the freehub/freewheel; a greater number of gears results in a more narrow chain (natch).

As a rule, Road Bikes accept 30-53 range on the forward-mounted (triple) chain ring. MtBs however are limited to 22-44 range, though some extreme go up to 48. (Larger chain rings are available though they are very difficult to find.) The Crank has to match the chain ring class; Road to Road (5-spoke), MtB to MtB (4-spoke). Also the Bolt-Circles of the two classes are different, so you can't mate a 5-holed Road chain ring to a 4-holed MtB crank. We're talking earth-shattering major conspiracy here! :? :wink: :lol:

The next bit that is important is that the seat tube is different for a Road Bike (smaller) than for a MtB (larger). Lastly, Full-Suspension MtBs have one other condition which causes problems in that the swing of the rear suspension causes the MtB chain ring to migrate away from the frame so that the chain clears the framework.

I haven’t worked with BMX before (except to adapt a frame into a trailer last summer) however it’s in a slightly middle realm – not quite Road Bike or MtB. The seat tube can go either way; at least there is no rear suspension issues to worry about.

Now we focus on the derailleur: Road and Mt. Bikes are different here as well. The derailleur must match the class of chain ring employed. If you are using the 39-53 (double I presume) then you’ll need the Road derailleur. The angle of attack on a Road Bike is slightly different than a MtB; I think that for a double-ring you will be fine, but I had a triple and it caused some frustration.

In addition, Index-Shifting for Road Bike is slightly different than with MtB, and that is directly related to the distinct evolution between the two bike classifications; the throw or pull length (or offset) is mechanically different ever so slightly between the two so that adapting one to work with the other is difficult, though achievable with patience and coin.

This likely will not an issue with BMX frames... however the larger roady chain ring rubbed slighty against my FS-MtB frame. To resolve I ordered a custom Bottom Bracket from Phil Wood that allowed for the Campy chain ring to extend far enough to clear the frame.

The last tricky part was mounting the Campy derailleur (matching the chain ring size) to the MtB, and this took some custom machining to accomplish (read: $$$).

In the end, I was able to adapt an 11-34 9-speed MtB Freewheel to a Campagnolo 30-39-53 Triple (Road) Chain Ring using a MtB rear derailleur and a Road front braze-on derailleur with custom mounting bracket. The caveats were:

• The chain was not long enough to link the 34-53 ratio (largest to largest)… but then why would I need to do that? :wink:
• I could not completely ratchet between 30-39-53; I was stuck between 39-53, or 30-39. If I dropped from 53 to 30, there was no return. So I gave up the lowest gear and instead leveraged the freewheel gearing. The reality is that On the Road, I used 39-53 in the front between the 3 smallest-sized (highest) freewheel gears to create the highest ratios for pedaling at the fastest speeds (33-36 mph). Thankfully never had to resort to lower ratios because I always had battery power.

I spent a lot of money in this exercise to discover that these two gearing philosophies are overtly and strategically designed this way for a reason… And I guarantee no one anticipated the needs of eBikes

All the best with your experimentation, KF

 

[lbz5mc12]

I was somewhat mistaken as to the location of the seat post in relation to the cranks. I'm going to post a picture I saved from "Currietech.com" so that you can see the frame size. It's kind of a cross between a unisex mountain bike and a bmx cruiser frame. You'll see what I mean about the rear of the bike being further back which allowed for easy installation of the larger chain ring. It would be great to get a hold of more of just the bike frames because from experience I've learned that they are really good for hard tail ebike projects.