changing gear ratios

Hi have a 1500w DD powered Trek Marlin 5 2018.

It's been going really well, done a couple of hundred KMs and will start using to to commute 60k round trip soon.

One issue though is that the bike is quite low geared, and I think the freewheel set on the hub might be quite large which doesn't help, pretty sure its a 14-32 which makes my top gear 42/14 or 3:1. I think closer to 4:1 would be better for an ebike.

What are the best options for increasing the gear ratio?

Should I be looking to change the freewheel to something like an 11-28?

Or is changing the crankset out to a 48T or even a 50T single and removing the front shifter better?

Or both? Anyone else been through this issue?

What speed do you need to pedal at?

That will determine the gear ratio you need to change to.

Knowing the ratio will determine which end you change (maybe both).

11-12t wear chain quickly

13-14t smallest rear cog practical longevity

if you must

best enlarge diameter drive wheel or chainring

amberwolf said:

What speed do you need to pedal at?

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All speeds?

Currently I'm just leaving it in top gear pretty much all the time but my legs cant keep up enough to really do anything above about 35-40kph. Would like to be able to still help the bike at 40kph, as much for exercise as for efficiency. Just spinning your legs with no load on them isn't much exercise.

kcuf said:

11-12t wear chain quickly

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I didn't consider this. How quickly is quickly though?

Could I fit a 50-34T road crank and remove the front shifter so just use a single front gear?

lionman said:

kcuf said:

11-12t wear chain quickly

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I didn't consider this. How quickly is quickly though?

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The only 11T cogged freewheel I've seen available is made by DNP, and based on the reviews, only lasts a couple of years before something major goes wrong (not reliable). The only 12T I've seen is probably decent quality, by SunTour, but they don't make them anymore, so you pay an arm and a leg for one on ebay (like around $130 or more). I'm using 13T with a 46T chainring, which is comfortable at 22-23 mph or so.

I use the 11t-28t DNP

Haven't had a problem, some people say they don't last, if i have to replace it every 5000 km's it doesn't bother me

Without the 11t rear your front chainring will have to be absolutely enormous to pedal at any decent speed

lionman said:

Could I fit a 50-34T road crank and remove the front shifter so just use a single front gear?

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My situation is similar to yours. 50 km round trip, conventional mountain bike frame. Rear DD hub motor. Typical speeds in the 22-28 mph range (35 - 45 kph).

I installed a road crankset with a 53 tooth and 42 tooth chainring AND I installed a DNP freewheel with the 11 tooth small cog (7 speed 11-32). My typical gears when riding are 53x18, 53x15, and 53x13. The 11 tooth is nice for fast downhills, but I can feel the chain vibrating as it goes around that smaller gear. I think these smaller gears are less efficient and it feels that way subjectively. I'd prefer it if that were a 12 tooth gear. I would use that more often. But that's is a bit of a nitpick.

I left my front derailer installed. I just shifted it up a bit to accomodate the larger chainring. Fortunately, the derailer clamps to the seat tube making that possible. I use the 42T chain ring when climbing steeper hills like the nearly 15% grade hill that is my last hill on the way home. I also like the idea of having a smaller chainring in case I ever have to limp home without power. 42x32 is still a decent road "granny" gear.

If you do install a larger chain ring, make sure that you have clearance with the chain stays. For whatever reason, my bike had plenty of clearance. I don't think that's typical. You can gain a little extra clearance by using a different spindle width on your bottom bracket if needed. But you have to be careful about shifting your chainline too much if you go that route.

I have about 5000 miles on my DNP freewheel. It seems to be holding up fine and it is clearly higher quality than the cheap freewheel that came with my motor kit. It shifts cleanly with the indexing. I lube my chain with paraffin wax.

Thanks for the replies.

I think the DNP freewheel is worth a shot.

Changing the crank out sounds harder. Shame my chainrings are riveted or I could just change a ring out.

I have been using the dnp 11 tooth with with a larger chain ring for a few thousand miles on the two bikes i own and can report no problems on either bike,shifting is still as good as ever.

no need to change the crank all you do is buy the peddels with chainring attached and swap over.

andy1956 said:

no need to change the crank all you do is buy the peddels with chainring attached and swap over.

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I've never seen chainrings come with pedals. They do often come with a crankset which is the two crank arms and often includes chainrings but not usually pedals. Pedals are typically sold separately.

You should probably get a crank removal tool since the crank arms are usually pressed onto the bottom bracket spindle and don't come off easily with such a tool. You need to make sure any new crankset matches the spindle type (shape of spindle where the crank presses on) that your bike has or you will also have to change out the bottom bracket. If you change out the bottom bracket (bearings with the spindle that the cranks attach to), you need to make sure you have the right thread type and the right spindle length so that the chainring is spaced appropriately.

This all assumes a typical setup as used on most bikes from probably the late 70's until now. There may be more modern setups that I'm not aware of. This also assumes that you don't have the old style single pieces ashtabula crank that does not use sealed bearings. It probably sounds more complicated than it really is. But you do need to go to some trouble to gather information to make sure you get the right parts.

You can find lots of good info on this on sheldonbrown.com.

I should have said crank arms and not pedels

In general, a road crank will rub on an MTB frame. Because they are designed to go with a skinny frame. Really old frames might have better clearance, but the more recent stuff tends to be built to clear a 48 tooth front ring at best. If your frame is tight, you can see it now. if it looks like a bigger ring will clear, then go for it, but it won't be with a road crank ring. You will need to find a big ring that fits an/ your mtb crank, which has wider offset to clear the wide tire. Big rings for mtb cranks are rare, but out there. Happy hunting ebay.


The road stuff needs little offset to clear that skinny tire, and then on top of that, the bolt pattern is almost always different than a mtb crank.

Think I'll just go for the freewheel swap first. Probably a bit easier. I want to remove the rear wheel to change to a fatter tyre anyway.

Does anybody know what tool is required to remove the shimano freewheel from the chinese hub motors?

lionman said:

Think I'll just go for the freewheel swap first. Probably a bit easier. I want to remove the rear wheel to change to a fatter tyre anyway.

Does anybody know what tool is required to remove the shimano freewheel from the chinese hub motors?

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You probably need this tool or the equivalent. The key feature is the wider diameter center hole. The hub motor's large axle won't fit through the standard tools. The spline pattern for this tool is probably right, but it wouldn't hurt to take a look before ordering just in case.

https://www.ebikes.ca/shop/electric-bicycle-parts/repair-tools/fwtool.html

I see that your are in Australia. So shipping from Grin may not be so cheap. But you can order the freewheel from them and you'll need that tool for the DNP freewheel anyway.

Here's an Amazon link to one that also has the 14mm center hole.
https://www.amazon.com/Park-Tool-Freewheel-Remover-FR-1-3/dp/B01FI8WWZY/ref=sr_1_4?ie=UTF8&qid=1547448569&sr=8-4&keywords=freewheel+removal+tool

11 tooth sprockets are inefficient, quick-wearing, hard on chains, and intended for only occasional use. Yours will only hold up if your pedaling is weak.

It would probably be best for you to use a normal 53-39 tooth road double crank and a compatible front derailleur. It's easy enough to find these things secondhand if you want to economize.

Chalo said:

It would probably be best for you to use a normal 53-39 tooth road double crank and a compatible front derailleur. It's easy enough to find these things secondhand if you want to economize.

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Yep. I find myself using either 53x13 or 53x15 for most of my steady-state nearly level riding. I only drop to 53x11 when riding downhill faster than 28 mph where my motor cuts out. The 13 & 15 work fine for most of the 20-28 mph speeds I ride at when I'm on the 53 T chainring.

If his current chainring is 42 tooth, then he's at a 90 rpm cadence to get to 27 mph. Most people who aren't avid cyclists will find that a cadence of 90 feels a bit fast. Also, the jump from 11 to 13 is proportionally larger than the jump from 13 to 15. Sojust changing the freewheel will help for sure. But I don't think it will work as well or provide the same level of flexibility as changing both.

The OP might want to look up one of the online gear calculators and see how certain gears, cadences and speeds work out. Then he can make a good guess as to how a particular combo will work with his riding style/situation.

http://www.gear-calculator.com/

Assuming I have enough chainstay clearance and wanted to go to a single chainring (would free up some room on my handlebars), would this crank set work?

Can you build your own triple crankset by just stacking chainrings on one of these? I'm guessing a derailleur can only handle a certain range of chainring sizes though between the biggest and the smallest?

I'm assuming i would need a longer chain with a larger chainring as well.

If a chainring says its for 8-9-10 speed, what issues do you have using a 7 speed chain on it? I guess the 7 speed chain is bigger and may not mate well with the thinner chainring causing it to fall off or wear quickly?

lionman said:

Assuming I have enough chainstay clearance and wanted to go to a single chainring (would free up some room on my handlebars), would this crank set work?

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It depends on the kind of bottom bracket spindle that you have. This crank has a square spindle. I'd assume your Trek has something more modern. So my bet is that you'd have to buy both the crank and a new bottom bracket to make this work.

lionman said:

Can you build your own triple crankset by just stacking chainrings on one of these? I'm guessing a derailleur can only handle a certain range of chainring sizes though between the biggest and the smallest?

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No. That's not the way they are built. The rings mount to the crank spider not to each other. Of course, a clever person could probably figure out a way. But that's taking the hard way for sure.

I'm sure there is a limit to chainring size that derailer can accommodate. But you shouldn't need more than two of moderately different sizes (53 - 39, 53 - 42, etc.). So I doubt that would be an issue.

lionman said:

I'm assuming i would need a longer chain with a larger chainring as well.

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Yes. But you generally want a new chain any time you change chainrings and rear gears anyway.

lionman said:

If a chainring says its for 8-9-10 speed, what issues do you have using a 7 speed chain on it? I guess the 7 speed chain is bigger and may not mate well with the thinner chainring causing it to fall off or wear quickly?

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I'm not sure. I don't recall ever seeing chainrings referenced to cluster sizes. Generally you need a narrower chain for the narrower gear spacing on the rear. I'm not sure about the chainring.

lionman said:

Assuming I have enough chainstay clearance and wanted to go to a single chainring (would free up some room on my handlebars), would this crank set work?

Click to expand...

Yes, though as wturber points out, you might need to transplant a different bottom bracket to use it.

Can you build your own triple crankset by just stacking chainrings on one of these?

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Technically, yes, but there are easier cranks to start with if that's your goal. If you must use that one that has an unconventional offset chainring, then the inner position chainring must be spaced inward to give the correct interval between rings. Then if you want a third chainring, you would have to use a triplizer ring for the middle position, so the inner ring can hang from it:

I'm guessing a derailleur can only handle a certain range of chainring sizes though between the biggest and the smallest?

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A front derailleur has a maximum chainring size to fit its curvature, and a maximum difference between the smallest and largest ring.

A rear derailleur has a maximum sprocket size and a maximum "wrap capacity", which is the difference between the smallest and largest chainrings, plus the difference between the smallest and largest rear sprockets.

I'm assuming i would need a longer chain with a larger chainring as well.

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Usually that's true.

If a chainring says its for 8-9-10 speed, what issues do you have using a 7 speed chain on it? I guess the 7 speed chain is bigger and may not mate well with the thinner chainring causing it to fall off or wear quickly?

Click to expand...

7 speed chain runs just fine on rings for 8 to 12 speeds. However, the spacing between the rings may not be adequate to clear the wider chain, and thus it may be necessary to shim the chainrings to a wider spacing. In practice it's usually cheaper and easier to use a 7/8 speed crank (whose rings are a little thicker and more durable if materials are equal).