Crankset Upgrade

[adamsavage79]

I'm trying to figure out if I can put on a much larger crankset. I have a Trek Marlin 5 that has a Ebike Kit on it. The current Crankset has 36-22T with this Bottom bracket, which is also combined with the freewheel being 14-34T range. It makes pedal assist rather useless, as you have a higher rotation. I feel like I'm going to spin my legs off trying to assist the motor.

I believe I have covered everything, and given as much information as I can. Suggestions would be helpful. I'm also considering going with a 11T 7 speed freewheel.

 

[Papa]

Your OEM crankset appears to have riveted-on chain rings. Means you need to replace both arms and the chain rings to employ larger (removeable) chainrings (check ebay). Depending on your chain length, you can increase the larger chainring to 46-48t, but you may need to replace the chain if is appears too short. However, if you replace or eliminate the 34t cassette sprocket, you shouldn't need to replace the chain. Also, I would encourage shorter 170mm crankarms.

You'll also need one of these crankset removal tool

 

[E-HP]

I'm trying to figure out if I can put on a much larger crankset. I have a Trek Marlin 5 that has a Ebike Kit on it. The current Crankset has 36-22T with this Bottom bracket, which is also combined with the freewheel being 14-34T range. It makes pedal assist rather useless, as you have a higher rotation. I feel like I'm going to spin my legs off trying to assist the motor.

I believe I have covered everything, and given as much information as I can. Suggestions would be helpful. I'm also considering going with a 11T 7 speed freewheel.

I believe you mean larger chainring not crankset. One of the main limiting factors is the chainstay clearance. Looking at this pic, I'm not sure how much larger you can go without the chainring interfering with the chainstay, but hard to be sure from this angle.

 

[adamsavage79]

To me, the Crankset is everything. The chain rings, and arms. Looks like according to the site, it should support up to 3x: 42T. I don't necessarily need 3x, but I could just use for the larger main chain ring. I would never use the other 2 chain rings.

 

[adamsavage79]

What would give me a bigger pedal power increase ? Going from 36T to 42T on the Chainring, or the 11T Freewheel. I could just do both.

 

[Papa]

Combo Ratio

42/11 = 3.81:1 Slowest pedal cadence Vs. Ground speed
36/11 = 3.27
42/22 = 1.90
36/22 = 1.63 Fastest pedal cadence Vs. Ground speed

 

[Chalo]

I'm trying to figure out if I can put on a much larger crankset. I have a Trek Marlin 5 that has a Ebike Kit on it. The current Crankset has 36-22T with this Bottom bracket, which is also combined with the freewheel being 14-34T range. It makes pedal assist rather useless, as you have a higher rotation. I feel like I'm going to spin my legs off trying to assist the motor.

I believe I have covered everything, and given as much information as I can. Suggestions would be helpful. I'm also considering going with a 11T 7 speed freewheel.

I would recommend against the DNP Epoch 11-34 7-speed freewheel. It's crummy. There are some freewheels with 13t high gear, and one of those would likely be fine.

Consider switching to a 50-34 "compact road double" or 53-39 "road double" crank (or a 52-42-30 "road triple" crank if your front shifter supports three speeds). You might need to use a longer bottom bracket to make a bigger chainring clear the frame.

 

[E-HP]

To me, the Crankset is everything. The chain rings, and arms.

I missed Papa's response. It would never occur to me that Shimano would use rivets.

What would give me a bigger pedal power increase ? Going from 36T to 42T on the Chainring, or the 11T Freewheel. I could just do both.

For me, 46:13 is comfortable up to the low 20s (mph) with 26" wheels. I rarely, almost never, shifted to the 11 tooth cog of the DNP freewheel I was using at the time or anything else. I'm still using the same ratio with 24 inch wheels now, with plus size tires, the diameter is right at 25 inches, so not a big change. 19 to 20 feels good now. I switched to a 6 speed Shimano freewheel with a 13 tooth small cog and chucked one spacer, so now it's pretty easy to get the wheel on and off. 42:13 would probably be fine with 29 inch wheels.
BTW, the ratcheting mechanism of the DNP wore out after a few thousand miles. I got a replacement, but never installed it because I didn't want to go through the same hassle a only few thousand miles down the road.

 

[docw009]

Everyone says the DNP's are crummy. Me too.

I also had two wear out the pawls around 3000 miles. Just like a timer, they blew at the same miles. Nonetheless, where else can you get 11T without switching to a cassette. Especially needed with my 20" wheels. Since they cost $30. it's like a penny per mile.

 

[adamsavage79]

I guess I should of mentioned the motor is 1,000 watts. I can do about 32 mph, with only throttle. Trying to pedal past 20 mph is fruitless. My legs are going too fast.

 

[lnanek]

I pedal at 30mph without any issues. I use a 75t front cog: Amazon.com and 11-34t back: https://amzn.to/3ELmNt2

 

[adamsavage79]

I pedal at 30mph without any issues. I use a 75t front cog: Amazon.com and 11-34t back: https://amzn.to/3ELmNt2

Well I would hope so. The difference from a 75T front cog and a 11-34t back, vs 36T and 14 to whatever ( too lazy to check), is pretty big. I didn't even know a 75T existed. How did u even fit on your bike ?

 

[Chalo]

I guess I should of mentioned the motor is 1,000 watts. I can do about 32 mph, with only throttle. Trying to pedal past 20 mph is fruitless. My legs are going too fast.

I currently ride a 29" wheeled bike with 52/11 high gearing. I can only reach 32 mph with a downhill or a tailwind, but I can easily pedal along at that speed even with 190mm cranks. I do most of my high speed cruising in the 52/13 gear.

 

[adamsavage79]

My Goal isn't necessary for speed. I have plenty of that. It's to extend my range, by reducing how much the motor needs to work. Thus using less power. I could go slower of course, but I like getting from A to B quickly vs slowly.

 

[Chalo]

My Goal isn't necessary for speed. I have plenty of that. It's to extend my range, by reducing how much the motor needs to work. Thus using less power. I could go slower of course, but I like getting from A to B quickly vs slowly.

Note that at speeds above 30mph or so, the continuous power you produce by pedaling is unlikely to exceed the additional aerodynamic drag it causes. So there may not be a range benefit at all.

 

[adamsavage79]

Looks like my best option is to just go with 11T freewheel and the max possible chain ring for my frame. Where do I get a good quality 7 speed 11T freewheel ?

 

[Chalo]

Looks like my best option is to just go with 11T freewheel and the max possible chain ring for my frame. Where do I get a good quality 7 speed 11T freewheel ?

Shimano made a really great one decades ago. They're expensive if you can find one for sale now.

Shimano Re-invents the Freewheel

Shimano has re-invented the thread-on freewheel for bicycles.

www.sheldonbrown.com

SunRace allegedly makes some, but not in 7 speed as far as I know.

MFEX9 9AU

E-Bike 9-Speed Freewheel

sunrace.com

Best bet for you is to get a better rear wheel with a cassette hub. If you're zipping around at 30 mph, you will bend rear axles often until you get rid of the freewheel hub.

11-34 7 speed cassettes are cheap and widely available.

 

[adamsavage79]

Best bet for you is to get a better rear wheel with a cassette hub. If you're zipping around at 30 mph, you will bend rear axles often until you get rid of the freewheel hub.

I don't understand your comment on replacing the back wheel. It's an Ebike. The motor IS the wheel. I can't just swap out the motor like that, and most Hub Motor's if not all, use a freewheel anyway.

 

[Chalo]

Ah I see. There are other ways to have an e-bike kit, and I assumed you were dealing with the stock rear wheel and had either a front hub motor or a mid drive.

Your rear motor doesn't have the drawback of an easily bent axle. On the other hand, it also can't easily be respaced for an 8/9/10 speed freewheel. You're dealing with the limitations of the bike and the kit you chose. Best approach is probably to use as large a chainring as your bike allows.

This is one of the reasons I favor front hub motors when that's a viable choice. They don't interfere with, or even interact with, the bike pedal drive. But they do interfere and interact with suspension forks. I already generally avoid suspension forks, so that's not really a drawback for me.

 

[adamsavage79]

I upgraded to a 42/34/24 Crankset and a DRIFT MANIAC 7 Speed Freewheel 11-28T. I didn't see any other options availble to me for freewheels. However, the stack height is causing clearance issues. So unless I can find a freewheel with a smaller gear, that is the exact same Stack Height, the old one is going back on. The gear ratio will still be better. So I might not even mind going from a 3.81 gear ratio to a 3.0. I personally find the gears a little too small, so going up might not be a big deal.

 

[adamsavage79]

Here are some pictures to show the clearance. Puting washers in on the brake side won't help things.