bikerjp

I use my CaadX mostly for commuting and the occasional zone 2 or recovery ride. It has a cross crank (46/36) but I have a nice Force compact (50/34) laying around and thought it might make a better overall option on the CaadX. Outside of having to move the front derailleur and replacing the chain, what are the potential issues with this? I ride a compact on the other bikes but usually ride those faster too. Does the 46/36 crank work better for commuting?

fietsbob

Depends ... on your route .. single ring could be fine too . what gear ratios do you use Most ?

bikerjp

Has an 11-28 cassette and I probably use the 19, 21 and maybe 23 the most with the 46 in front. Commute is short and flat and I usually don't ride it fast. Pretty sure it won't matter much which crank I use but was thinking the compact might help make the bike more versatile - more road ride friendly. The cross crank though might be better for slower around town riding. Just kind of wanted to find a use for the nice crank.

jaxgtr

I use my cross bike for commuting about 95% and have a compact 50/34 and ride a 12-25 cassette on it and really like it

ThermionicScott 

This topic depends so much on a person's strength and preferences. That 46/11 is already a bigger gear than I have on any of my bikes, so a 50/11 wouldn't get any use from me -- I stop pedalling over 30 or 35 MPH.

fietsbob

you could use a Single ring 42T.. People Race, Cross on single ring set ups. 42:11 ought to be high enough.

if you already primarily use the 46: 19/21/23..

bikerjp

True, but different bikes meet different needs. I use my 50/11 quite a bit on my Evo - granted, on descents but still use it. It would not get any use on a commute. I guess the compact probably isn't much use on this bike but seems a waste to let a nice crank sit. Maybe it's time to build a bike

ThermionicScott 

Now yer starting to make sense!

benda18

So many variables. Sheldon Brown's Bicycle Gear Calculator

jyl

Or Mike Sherman's Bicycle Gear Calculator

It sounds like you do your commute all in one chainring, the 46. With the 50/34, would you be shifting between chainrings? Should check.

gregf83 

The single ring 42 works for my commute. Mostly flat with a couple of hills. On the steeper hill I stop pedaling around 120-130 rpm. 46 would be fine for anything but sprinting in a race.

Ridefreemc

I had the same on my Vaya, but rarely used the 50 up front. On my Velo Orange I went with a 46/30. I don't believe in going very big up front, unless you are very fast. I ride in the 46 the majority of the flat Florida riding, but have the 30 for steeper rides. In fact, I am not sure that I used the 53 on my Trek more than once or twice.

My point is that I think smaller chainrings prove more useful for commuting.

AlTheKiller

If you are fast, and have any hills the compact could be limiting. I'm not very fast but I often max out my 46/11 on mild descents. Even on flat ground I find I'm only one or two gears from maxing out when I have good wind and strong legs.

However, for flat commuting I find I can live in the middle of my cassette and mostly use the fd when starting/stopping, then jumping into my cruising gear.

Make sure your rd can handle the extra gearing if you switch.

modernjess

I'm running a 48/38 on my CX/Gravel bike/Commuter with a 26/11- 10 spd rear. So not too dissimilar to what you are running. For commuting and around town it's plenty of everything so I wouldn't bother to go compact.

But for long gravel races/rides I sometimes wish I had a compact on that bike. The wider range would come in handy on those long gravel climbs 80 miles into the day. Since it's a 130 BCD I can't get any smaller than the 38 inner, and if I had an extra Force compact sitting around I'd put it on. I have a force compact on my road bike and love the range.

bikerjp

Was mainly wanting to use the nice crank and hadn't thought about using different rings. Anyone know what other, if any, sizes of rings a compact Sram Force crank can use? A 48/36 or 48/34 might be a good mix.

ThermionicScott 

In theory, you could run any two 110BCD chainrings you wanted. They're generally sold as sets, so that the shift ramps and pins will line up best between them. I'd agree that a 48/36 or 48/34 would be a nice combo, and all else equal would shift a little easier than the 50/34.

modernjess

+1 ^ what he said. If it were me I'd do a 48/34 set for the cx bike.

Darth Lefty 

Here's my opinion, it may not match others'.

The shift ratio of the rings on a cross crank (46/36=1.2777) are similar to the ratios on a road crank (52/39=1.333) or the top two rings of a MTB crank (42/32=1.313). This ratio of about 1.3 gives nice double shifting with a wide ratio cassette sequence with about 1.15 ratio per shift. 8x11-28 or -30 or -32 are good examples. This still works with a higher number of speeds, because for a wide cassette range like this, most of the cassette is still the same, and they just pack in an extra intermediate cog at the top end you don't use much, or add one more that's 4 teeth bigger on the bottom. The overall ratio gets lower from road to cross to mtb due to probable riding conditions for these bikes.

However the overall range is still not very high. It basically gets you two more ratios compared to a single. In order to maintain the same double-shift-ratio philosophy and get lower gears you need a road triple (52-39-30). In order to get a really huge range, like on a MTB, you keep the ratio for the outer rings and make the inner ring a much bigger jump. The huge downshift is ok because you use it when you really want a big bailout downshift. If you ignore the double-shift philosophy in favor of sticking with a double, you go compact, and the front downshift is huge. It's more like a low and high range. With a compact, you can get a wider gear range by sticking with the original cassette; or if you want to keep the same overall ratio as the double with a compact you use a narrower cassette and it gets you more useful ratios.

bikerjp

^Thanks for the info but I'm not sure what you are trying to say. I have compact rings in 3 bikes and never have any real issues with shifting nor do I notice much difference between the compact and the cross setup. My thought was going with 48/34 rings on the "compact" crank would give a bit better mix of ranges on the cross bike - a lower low and a higher high and still slightly better shifting than 50/34 (though I don't really see that as an issue/benefit).