sartorious

Howdy all,

Looking at getting a larger chainring for an old cannondale to improve power on the downhills. Right now there is a 22/32/42T set up in the front, was thinking about changing out the 42 for something larger, maybe a 50 or 52. In terms of shifting, would this still be compatible if I leave the other two rings on there? The nice thing about this cannondale is the front shifter is a grip shift with a good amount of adjustability. If 50 is too big, what would be the upper limit?

Any thoughts would be much appreciated. Thanks,

HillRider

From the chainrings currently there, I assume it's an MTB crank and the bolt circle diameter is either a 94 mm 5-arm or 104 mm 4-arm. The largest chainring QBP stocks for these are 44T for the 94 and 42T for the 104 BCD according to the Harris Cyclery (Sheldon Brown) web site.

The only way to get a 50T or larger big ring is to change the entire crank.

sartorious

Thanks Hillrider. The bcd is indeed 94mm, not sure if it is a mtb crankset, CODA, came stock on the cannondale touring bike. I think I've found a 94mm 46T, but would upgrading from 42 to 44 or 46 make much of a difference? Thanks again for the thoughts!

DMF 

You're gonna find shifting a bit of a problem if you go past the 10-tooth gap between middle and big. I mean, you're talking an 18-20 tooth gap! And that's if the FD will handle the big ring at all.

Try a 46T if you can get one cheap and cross your fingers. Also look at the cassette. What's your smallest cog? 14T?

SJP0tato

Is this why bicycle manufacturers don't "space out" the front ring sizes more than 10 or so teeth increments from small->med->large?

I've always wondered why they would have so much overlap in overall gear ratios. For example: on my bike the middle gear up front will cover 80% of the range, with only 2 of the highest and 2 of the lowest of available 21 speeds go beyond what the middle cog can provide.

I often wondered why not space it out 50% above and 50% below, without really understanding the technical difficulties behind such a choice.

DMF 

If you consider shifting performance, avoid cross-chaining, and are strong enough to use a close-ratio cassette, there's not nearly as much overlap as you think.

In particular, the wider the spacing up front the worse the shifting will be. Since the granny on a triple is essentially a bail-out gear and is rarely used, that shift gap is acceptable. But that wide a gap between the other two would get real old real fast. (That's why I don't understand the proliferation of compacts.)

DaJMasta

Is it a 5 or 4 arm crank? What kind of front derailleur do you have?


That should shed some insight on your options.... Knowing the derailleur should give you the max chainring size and the max difference between the lowest and highest, knowing the BCD and the number of arms can get a chainring to match.

It does sound like you're using mountain components, which means your highest ring can officially be 44t (probably) but could potentially go a little higher. If your cassette doesn't have a 11t high gear, that could be an easy drop-in replacement (unless it's a freewheel...) to get a significant boost, even from a 12t highest gear.

sartorious

5 arm crank, CODA CF2, 22/32/42 teeth

Rear cog is 11-30T

Shimano STX-RC front derailer with Sachs Power Grip Plus Wavey levers.

So, how does the fact that they are mountain bike parts make 44T the largest possible? I seriously have no idea. Have found 94mm 5 bolt chainrings up to 48T online.

laura*

The rating for your FD is 42t max, middle to big difference of at least 10t, and small to big difference no more than 20t or 22t depending on the model of FD.

Note: I am running 22/32/44 just fine with an STX FD-MC32.

Once you raise the FD up high enough to handle a larger big gear, the bottom of the derailleir won't clear the chain when on your small gear.

Those are probably trekking gears that were used in something like a 28/38/48 triple.

HillRider

Where? QBP only lists up to 44T for a 94 mm bcd so I'd be interested in knowing where larger rings are available.

Garthr

A 94mm bolt circle can take up to a 50 tooth chainring! TA makes them.... a bit pricey but they are the excellent. Scroll down to the 94mm sizes here: https://www.peterwhitecycles.com/chainrings.asp

Vuelta makes up to 48 for less $$, but won't last as long as the TA. https://www.vueltausa.com/products/ch...chainrings.htm

But, you're limited by your current FD. Easy to change that. First, step outside of the Shimanautomatic box that they think is best for everyone. They don't ride real bikes. You can run any gears you want as long as you are aware it won't have the shifting you're used to. You can't have it all.... fast, smooth shifting and a 22,32,50 setup. Do you need a 22? Try a 24. Try a 24,34,48 or instance. You'll get no repeating gears, if that matters to you.... and you'll get a massive 124 inch top gear. It will shift pretty good, depending on your skill.

For the front D, get an older one made for 6,7or 8 speeds even.... it won't matter. They'll all work.

Chris_W

Don't worry about this, normally FDs are much longer than they need to be for the original application. You can certainly add 4 or 6 teeth before having to worry about the chain rubbing on the bottom of the FD in the small-small combo (which you shouldn't use anyway), and possibly 8 more teeth. The main thing to worry about is the radius of the arc of the outside plate. When you raise the derailleur up enough to clear the new big ring, you may have quite a gap at the very top between the FD and the ring, which will make overshifting and losing the chain to the outside possible, although still not very likely. To avoid that, you could try one of the FD's designed for 'trekking' cranksets that have a 48 tooth big ring, I believe they still do a version in the Deore LX range, and maybe at other levels of quality, too.

sartorious

Nice guys, I am psyched to try this out. In the current set up, I think I have used the 22 up front once, and it was by accident. I think I'll try bumping the 42 up to a 48 and see what happens!

meb

Unless this is a BB mount front der, it's actually an optimization rather than an absolute limit. The curvature of that ring is designed for the 44T ring. Road FD have a larger radius arc on the cage for optimization on about a 52 or 53T big ring.

If it is a BB mount front der, the cage won't go high enough. If this is a braze on, you might also need to move your braze on point higher on the seat tube to clear a 50T ring.

sartorious

the front der is clamp on as far as I can remember, so I think there is enough room to scoot it up