Upgrading chainset on Cannondale F6 - how large can i go?

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Jan-Erik-86   100 mW

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Upgrading chainset on Cannondale F6 - how large can i go?

Post by Jan-Erik-86 » May 24 2019 4:02am

Hi,

I currently have a Cannondale F6 bike with a 1000W DD hub motor, a 6-speed freewheel, and a 42-32-22 chainset in the front.

My problem is that this gearing works fine until around 30-32 km/h, but once past that i need to pedal at an excessive speed to help the motor, and for the most part i end up just ghost-pedaling past this speed.
What i wish is to be able to still pedal at a normal speed up to at least 40 km/h, but i'm not sure how i would be able to do this.

The bike originally came with an 8-speed, but it looks like i'm stuck with no less then 14t in the rear now with the hub motor, so that leaved me with only the front. With the 42-32-22 that i have now, i always just leave the rear on the 14t, and mainly just use the 42t in front. While i occasionally use the 32t for steep hills, i've never ever even used the 22-gearing, and simply won't miss it.

So then my question is, what options do i have when it comes to replacing the chainset, how large will i need to go to pedal normally at 40 km/h, and how do i know how large of a gear i can actually fit on the bike without hitting the frame?

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Re: Upgrading chainset on Cannondale F6 - how large can i go?

Post by markz » May 24 2019 4:19am

Well you'd need a road crank set of 52T and whatever 2nd to fit the capacity of the derailer/derailleur and an 11T rear. I have recently read in the last day or two that you can buy expensive rears with as low as 9T but the wear would be horrible for the price you pay.

You need to think about whats more important to you, pedaling at 30+kph, or pedaling at slower speeds.

Do you have pedal assist, thats why you ghost pedal?
Can you just go throttle only?

There are calculators called gear ratio or gear inch calculators.
https://sheldonbrown.com/gear-calc.html
You can choose 40kph @ pedal cadence rpm. As you can see the 52T & 9T at a 60rpm cadence, will get you 42kph, but your hill climbing ability may not be that great.

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Re: Upgrading chainset on Cannondale F6 - how large can i go?

Post by markz » May 24 2019 4:31am

Here is a cadenze chart.

https://coachlevi.com/cycling/high-vs-l ... ing-speed/

Very zlow: 50-70 RPM
zlow: 70-80 RPM
Moderate: 80-90 RPM
Fazt: 90-100 RPM
Very Fazt: 100-110 RPM
Extremely Fast: 110+ RPM

I chooze 60 rpm, becauze I dont pedal much :P
90rpm would zeem right for zomeone like yourzelf, cazual rider.

I would zkip any thoughtz of 9T or 10T cazzette/freewheel, and do your clazzic 11-36, with a triple 52/42/32 if you can, to keep your hill climbing ability to 36/32 which iz like a 1.125:1, where az your 36/22 iz 1.63:1. Driven/Driver.

Its give and take, you want to pedal at higher speeds, you lose your slower speed gears. Some have gone to an extreme of using an IGH between crank and rear.
igh mid.jpg
https://www.electricbike.com/mid-drive-kit-igh/
Here, the Italjet #59 uses an IGH to add several gears to a rear hubmotor that only has enough room to fit a single-speed freewheel. If the sprockets that attach the IGH to the rear wheel had a 1:2 ratio, it would cut the stress on the IGH in half, doubling its input torque capability without breakage. It would have the same practical effect as switching to a rear wheel with half the diameter. The gearing shown is 4:3 from the chainring to the IGH, and 1:1 from the IGH to the rear wheel. If the chainring had an 8:3 ratio, with the rear chain having 1:2, the pedal-cadence (and rear wheel RPMs) would be the same, but the IGH would have the pedal-torque cut in half (if it was a mid-drive).

RunForTheHills   100 W

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Re: Upgrading chainset on Cannondale F6 - how large can i go?

Post by RunForTheHills » May 24 2019 9:56am

How big of a chainring you can put on it will depend on the frame and the chainstay clearance.

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Re: Upgrading chainset on Cannondale F6 - how large can i go?

Post by flat tire » May 24 2019 3:10pm

Google "custom chainring" you can get a really huge one to put on.

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Chalo   100 GW

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Re: Upgrading chainset on Cannondale F6 - how large can i go?

Post by Chalo » May 24 2019 3:20pm

flat tire wrote:
May 24 2019 3:10pm
Google "custom chainring" you can get a really huge one to put on.
But if you actually put it on, it will make contact with the frame. So, ignore the above advice.

53-39 and 52-42-30 "road double" and "road triple" cranks are common and can be less expensive than unusual size chainrings for an MTB crank. One of those is likely to work, but you'll probably have to try it to find out for sure.

11t sprockets are a mixed blessing. They enable gear ratios that are difficult to get otherwise, but they accelerate wear and tear on the chain drive parts.

Another thing to do is train yourself to pedal faster. It's wholesome for your body and it smooths your pedal stroke. Visualize it in terms of spinning pedals rather than pushing them.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

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Re: Upgrading chainset on Cannondale F6 - how large can i go?

Post by Electric Earth » May 24 2019 4:00pm

Figure out what model crank you have, or what the BCD(bolt circle diameter) is. That's what you really need to know in order to easily figure out if you can get a larger chain-ring. If you know your BCD is 104, for example, then you can just go search for "104bcd chainring" or something of that nature, and find the biggest one you can get. You may find, as Chalo said, that it's cheaper to get a road crank with a charge ring. If you go that route, look into chain-line. You may want a different bottom bracket spindle length to keep your chain-line reasonable. Also, I Think you should be able to find a 13t cog on a freewheel. I may be wrong, though. I'm not as familiar with older bike stuff.

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Re: Upgrading chainset on Cannondale F6 - how large can i go?

Post by markz » May 24 2019 5:54pm

What about elliptical crank?
https://sheldonbrown.com/biopace.html



Chalo wrote:
May 24 2019 3:20pm


11t sprockets are a mixed blessing. They enable gear ratios that are difficult to get otherwise, but they accelerate wear and tear on the chain drive parts.

Another thing to do is train yourself to pedal faster. It's wholesome for your body and it smooths your pedal stroke. Visualize it in terms of spinning pedals rather than pushing them.

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Chalo   100 GW

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Re: Upgrading chainset on Cannondale F6 - how large can i go?

Post by Chalo » May 24 2019 11:04pm

markz wrote:
May 24 2019 5:54pm
What about elliptical crank?
https://sheldonbrown.com/biopace.html
Biopace isn't quite elliptical-- more of a rounded parallelogram. I like them, but when I use them, I rotate them more like a traditional elliptical ring (the "hard" gear coincident with my power stroke).

It's tougher to spin an elliptical ring quickly than a round ring. They are more about mashing on the pedals. Also, an elliptical requires as much frame clearance as a substantially larger round ring.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

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Re: Upgrading chainset on Cannondale F6 - how large can i go?

Post by amberwolf » May 24 2019 11:26pm

Keep in mind the ellipsoid rings aren't going to make anything faster.

Also, they change the point at which the most pressure occurs on your knees/etc., and this varies depending on where the seat is relative to the cranks.

Some people have trouble with that. For instance, it helped my knees on regular upright bikes like DayGlo Avenger, but the change in position and angle to the cranks meant they didn't work the same on my semi-recumbent CrazyBike2 (and the SB Cruiser trike). So I went with round chainrings on them. I could probably make a crank and spider that would secure the rings in the "original" orientation relative to the seat, and still use them, but...it's more work than I have time / energy for vs other stuff I have to do (like a bajillion other ideas I'd like to try out).

There are other ellipsoid cranks that put the load in different spots than the Biopace if you find BP doesn't work for you.

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Re: Upgrading chainset on Cannondale F6 - how large can i go?

Post by MadRhino » May 25 2019 2:16am

I once said to a rider in your situation:

Feed your motor as much power as it can survive, and pedal a coolant pump instead of a drive train. Just another way to ‘help your motor’, when the little power you could add seem useless. :twisted:
Make it fool-proof, and I will make a better fool.
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Jan-Erik-86   100 mW

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Re: Upgrading chainset on Cannondale F6 - how large can i go?

Post by Jan-Erik-86 » May 25 2019 12:22pm

Thanks for all the helpful feedback guys! :)

As for PAS vs throttle; I have a throttle, but i choose to mainly use PAS to appear "legal". EU law state motor can only help when pedaling. I ride trough the city daily, so i don't want too much attention when i'm there.

I haven't been able to find a 6-speed freewheel smaller then 14t for the rear, but i did find a 12t single speed though. As i only use the 14t anyway i think i'll consider the single speed 12t instead.
Hill climbing ability is not really an issue as the motor alone is strong enough to pull me up any hills in my area, and i guess i can always just shift down in the front if needed.

I'm not sure what BCD i have, but i will try to find out.

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Re: Upgrading chainset on Cannondale F6 - how large can i go?

Post by markz » May 25 2019 2:03pm

Yea it would seem to be smashing the pedal hard, then laying off. Not smooth a cadence.

I keep digging the IGH mid drive (Crank to IGH to wheel) easy for the stretched feet forward cruisers I like.
A front hub motor, with a good IGH rear wheel may suffice for a very wide gearing. I've looked at the high end IGH's and a grand for a Rohloff is beyond my peasant means. The more affordable, Nexus/Alfine 11's may have the gear steps, your still left with a front hub, good for casual users. Beyond that, have to find a frame to allow such a large gear for a traditional road triple setup, then the derailer/derailleur to fit said 52T+ dubs/trips.

Chalo wrote:
May 24 2019 11:04pm
It's tougher to spin an elliptical ring quickly than a round ring. They are more about mashing on the pedals. Also, an elliptical requires as much frame clearance as a substantially larger round ring.

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