swapping cassettes

[Bud G.]

The Cannondale Carbon 2 lowest gear ratio is 1:1 (34t chainring & 34t sprocket). At my advance age I need more help in climbing, but don't want to lose the top end capability. There is a 11-40 12 speed cassette made by Classified Powershift. Can this be installed in the Cannondale Carbon 2 without any other major changes?

 

[BikeGremlin]

The Cannondale Carbon 2 lowest gear ratio is 1:1 (34t chainring & 34t sprocket). At my advance age I need more help in climbing, but don't want to lose the top end capability. There is a 11-40 12 speed cassette made by Classified Powershift. Can this be installed in the Cannondale Carbon 2 without any other major changes?

Hi and welcome,

I will assume we are talking about the 2x12 speed road bike (like this one) and base my answer on that, so please correct me if I got that wrong.

That bicycle seems to have little range for moving the front derailleur (FD) down. That may limit the effectiveness of my first idea, but I will put it out for consideration:

1. 46-30 cranks instead of the factory-installed 34-50​

With a 46 instead of 50 tooth largest chainring, you will need to move the FD a bit down, to get good and fast front shifting (and the shape of the FD may still not ideally match the now sharper curve of the smaller largest front chainring).
Shimano GRX ("gravel") group offers such cranks as far as I know.

Despite the less-than-ideal front shifting (may end up being good enough, depending on your criteria and the room for moving the FD down), a 30-46 crank will give you a more reasonable gearing for most normal people (i.e. not superlight and superstrong & superfit).

The 46 T at the front does not let you accelerate on downhills, but with an 11 teeth cassette sprocket on a bike with 622mm wheels (and say 25+ mm wide slick tyres), that gets you to around 42 km/h with a relatively slow/comfortable pedalling cadence of 80 rpm (with 90 rpm which is still in the reasonable range, it gives over 48 km/h).

The smaller 30 T chainring, even with the existing 11-34T cassette will reduce the lowest gear's ratio from 26.8 gear-inches to 23.6 gear-inches (explained).

2. A larger cassette, like 11-40 T​

This is also a viable solution. It may require adding a rear derailleur (RD) hanger extender, like Wolf-Tooth makes (road groupset with an MTB cassette using RD extender video demo).

IMPORTANT note:
Classified Powershift cassette may not fit, because it uses a proprietary standard as far as I know. Also, be careful about sourcing other replacement cassettes for this bicycle. Why?
Please check your freehub standard - when you remove the cassette, does it have 18 splines, or 13?
A new cassette must fit the wheel's freehub mount (freehub standards explained).
Based on the available manufacturers' specs, your bike's rear hub has the 18-spline Shimano HG spline L2 12-speed road mount that will not take normal 13-spline Hyperglide cassettes, nor the 23-spline Microspline Hyperglide+ MTB cassettes. It will only accept 18-spline HG spline L2 12-speed Hyperglide+ road cassettes.
Yes, they did make it complicated and I am convinced it was deliberate, by design.
To fit a really big MTB cassette, you would need to swap your freehub.
If specs are correct, your bike has a DT Swiss hub and for some of their models, it is possible to swap the freehub section depending on your needs - so you may be in luck there.

Provided that the above-noted cassette mount compatibility issue is fixed (or that you can source 40T HG L2 compatible cassette), this is the outcome:

A 50-34 crank paired with an 11-40 cassette will provide a lowest gear of 22.7 gear-inches.
That's a bit lower than 23.6 gear inches provided by a 46-30 crank combined with the 11-34T cassette.

In this case, rear shifting may be less than perfectly fast, but it may be OK (electronic shifters can be more "picky" with "non-standard" cassettes compared to mechanical shifters).

Another problem with this option may be exceeding the RD's chain wrap capacity by 6 tooth in total (the RD model I presume to be on the bicycle is Ultegra RD-R8150). That should generally not be a big problem apart from chain slack when riding the small-small combinations, but still less than ideal.

Which of the above-noted two is better?​

Each option has its pros and cons. I lean towards the first option because it may have fewer things to consider. Also, for average riding that may also result in a better chainline for most of the time (50T is on the large side for flat-land riding unless you normally use it with the smallest three cassette sprockets on flats). Of course, your preferences may differ. Neither option is technically better in and of itself.

Also, one doesn't exclude the other - though I would recommend changing one thing at the time, for easier tuning and troubleshooting.

I will propose a third, out-of-the box solution. Can't say that it is better, that is a matter of personal preference too.

Durable and simple - the "radical" option​

One can change bikes. Sell and buy used. Steel frames with threadless (a-head) forks (and lugs) are not very easy to find nowadays, but not impossible.

Steel frame with down-tube shifters is a durable option. To go a step further, I would recommend using down-tube shifters that are friction shifters.

That should allow one to use whatever gearing is needed, especially the cheap and robust stuff. My travel/gravel bike now has a triple crank: 44-32-22. That smallest 22 T front chainring gives me super-easy gearing for long steep climbs even with a heavily loaded bike (with a tent and all the other gear). And it gives that using a normal 11-34T 8-speed cassette (while even using any 11 or 12-32 cassette still results in low enough gearing).

This may be more difficult to source and assemble (hardly any pre-built bikes with such a configuration nowadays). Still, if one's goal is to have a bike that serves them (not the other way round), this option can give many, many trouble-free miles and years and become superior in the long run.

I hope this helps.
Feel free to ask if you have any other questions.

Relja RetroGrouch Novovic

P.S.
I wish to thank you for this question because it made me realise I had forgotten to update my compatibility articles with the 12-speed Shimano road standard.
With well over a thousand articles published, I have a habit of re-reading them before posting to answer questions, and that is the most efficient way I could find to keep my info up-to-date - which in turn helps me with my work (those are the notes I too rely on, just published publicly).

 

[Bud G.]

Thank you for the detailed reply. You are correct that the Cannondale Synapse Carbon 2 is the bike in question.
Option two, changing the cassette, is the preferred choice. I live in a very hilly area and still, after 50+ years of road riding, enjoy pushing 80-90km/hr on some of the downhills and can hit almost 60km/hr on the flats. I'd prefer to keep 50+ t on the chainring. Now that I am in my 70's, climbing those same hills with any gear ratio greater than .9 is a problem for me. With age, it is only going to get worse

I have a 21 year old Specialized Roubaix that has well over 40,000mi on it. It has a triple chainring, which has been great. In your answer, you said that sourcing parts can be a problem. That was the case on this bike. I needed a new front derailer and it took the bike shop several months to find one for the 3 x 9. Nobody does triples anymore. Sourcing parts is only going to get more difficult.

Thank you again for the answer. I'll be taking your response to my local bike shop and see if we (ie. "they") can make it work. --Bud

 

[BikeGremlin]

Thank you for the detailed reply. You are correct that the Cannondale Synapse Carbon 2 is the bike in question.
Option two, changing the cassette, is the preferred choice. I live in a very hilly area and still, after 50+ years of road riding, enjoy pushing 80-90km/hr on some of the downhills and can hit almost 60km/hr on the flats. I'd prefer to keep 50+ t on the chainring. Now that I am in my 70's, climbing those same hills with any gear ratio greater than .9 is a problem for me. With age, it is only going to get worse

I like to joke that: "After so many decades of practice, we should be getting better and better!?"
Jokes aside, yes, it is wise to get a lower gear ratio for the climbs, and for those top speeds, a 50 T largest front chainring and an 11 T smallest rear chainring would be preferable.

I have a 21 year old Specialized Roubaix that has well over 40,000mi on it. It has a triple chainring, which has been great. In your answer, you said that sourcing parts can be a problem. That was the case on this bike. I needed a new front derailer and it took the bike shop several months to find one for the 3 x 9. Nobody does triples anymore. Sourcing parts is only going to get more difficult.

As a cycling enthusiast:

I've learned to embrace the used parts market (along with mix-matching covered in my compatibility notes). In the US, Gevenalle used to make brake lever mounted friction shifters (practically cleverly mounted down-tube shifters). Not sure if those are available, but it's arguably a more ergonomic solution, and for road frames with thick or non-round down-tubes, it may be the only option to elegantly mount friction shifters.
Gevenalle bomb-proof “brifters”

That Roubaix sounds like a great backup if not a perspective long-term solution (a good front derailleur can last for dacades unless it gets in an accident). Regardless of how marketing frames it, triple is the more reasonable solution for a wide gearing range (without huge gaps in adjacent gearing ratios on the cassette).

Thank you again for the answer. I'll be taking your response to my local bike shop and see if we (ie. "they") can make it work. --Bud

As a bicycle mechanic:

Cassette swap may require sourcing a new freehub for the wheel (if not relacing it with a completely new hub), and a RD hanger extender - plus some "fiddling" with gear tuning to get it to acceptably good if not perfect.

Generally, a new hub is faster and easier to source than a freehub mechanism for an existing hub (if at all available at the given time or at all), even though that takes building the wheel with the new hub (often with new spokes of matching length).

Depending on the weather and climate in your area, the spring hectic rush in bike shops may not have started yet. Once it starts, non-straightforward repairs and parts that take weeks to source become a lot more of a burden (as bikes start "piling up"). Offering to take the bike home while a part is being sourced is a super-nice thing to do and may be highly appreciated (depending on the situation) - though I understand that is not alway possible or practical.

I'm curious to hear what the shop recommends and does. It is an interesting problem to solve (or a "challenge" as the modern managers like to call problems ).

Relja

 

[VlPo]

and can hit almost 60km/hr on the flats

Now that I am in my 70's...

However... My respect for your physical fitness at such an age
I'm only 60, and I don't really like road discipline. I would like to go to the woods, to the fields. And 36 + 11-42 is enough for everything.