Compact to standard crank
 

I currently run a 50/34 with a 12-27. I've had the opportunity to demo a Scott Foil and Fuji Altamira both with a standard crank during my usual weekly group ride. Now sure, there could be a placebo effect in place but I felt as though I could keep up much better with the group on the compact. My question is, can I simulate the gear ratios of a standard crank by changing the cassette while using the compact or should I just buy a standard crank and swap them as needed? I do not know what cassette the demo bikes were using.

Try swapping the cassette first, it's significantly cheaper than replacing the crank. I went from a 12-27 to a 12-25 and while it took a ride or two to get used to the change in cadence, it was a welcomed change overall.

One of my bikes is a compact with an 11-23. Actually higher top gear than a standard 12-25 that my other bike has. Cannot tell the difference except I rarely use the small ring on the compact.

this calculator allows you to layout graphically how various gear combinations work.

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

As pointed out above a 50/11 is actually a bigger gear than a 53/12. Thus by swapping out your cassette you can get pretty much the same gearing with the compact, as with a standard crank.

There will be differences here and there, in what point you cross over from the little to the big ring, and there will be diffferences in the gaps between various gears.

Depending on your terrain, how fast you usually cruise, and your desired cadence, you may prefer one setup over another because the spacing of the setup fits you better.

That said, your gearing is not affecting your ability to keep up with the group, with the only exception being if the lowest gear on the standard crank is requiring you to pedal too high of cadence on climbs, and the compact with a lower gear allows you to spin more efficiently.

This gear calculator is GREAT! Thanks!

On paper the Compact gives you more gearing. IMO in practice it's easier to keep up with a standard, also, the small ring is relatively useless on the compact unless thre are BIG hills.

What type of Bottom Bracket do you have? This plays some role in the cost to swap, also, is your chain long enough to accomodate the standard crank? It's not difficult to change the crank, and there are plenty of standard cranks that won't break the bank, especially if you check Craigslist/eBay. You'll need to adjust the front derailleur accordingly.

If you have the 2nd crank, you can always swap back/forth.

im a 36yo 155-160 pound racer in hilly colorado and i am a strong 3/almost 2 and i run a compact with a 52-36 combo and its perfect for my needs.

i have 11-23, 11-25, and 11-28 cassettes that a switch among depending on the course.

I cross chain more often with a compact 50/34 than a standard 53/39. I also spend a lot more time on the 39 than the 34.

That gear calculator is one of the cooler things I've seen in awhile. I love how it greys out the cross chained gears. The two on each end are exactly where I draw the line. I have a 36/46 compact cross crank with a Miche customized (cogs are all individual) 13-29 9 speed cassette (13-15-17-18-19-21-23-27-29). I'm about to order a 16 and a 20 as the cassette is real easy to take off, swap cogs, and put back on. They also make campy and shimano compatible 10 speeds.

To the OP, a cassette change is cheaper and potentially far more customizable.

Having gone from a standard to compact I find the same to be true for me.

What's a compact?

I don't understand, if you keep up better with your current compact than a standard, why do you need to change anything?

50-34 or 50-36

Unless you're spinning out in your highest gears with the compact, it's a placebo effect.

As you can tell using the link Merlin supplied, your top speed with your compact in its tallest gears and a cadence of 100rpm is around 32mph. With a 52-39 12-25, it's 34 mph.

Your speeds when using the big ring are nearly identical, as are the gaps. The real difference in the above scenario is on the low end.

If you are not mechanically inclined, constantly changing the cassette will be a PITA, unless you have two wheels with different cassettes.

I don't really see much reason to change.

OOOOOOOOOOOOOOOOOOOH! You meant sissy rings. Got it.

Or Granny gears

Well, you sure went to a lot of effort to get that in. :rolleyes:

You can match the range but that's not the only issue.

With the same cassette a standard crank provides a high gear about one tooth smaller (50x11 is like 53x12 or 50x12 like 53x13) and low gear about one size smaller (34x23 is like 39x26). You can often compensate for that.

The more significant difference is in where the small to big ring transition happens. The same cog acts like one two teeth smaller (34x13 is like 39x15). With the power to overcome aerodynamic drag proportional to the cube of velocity that's a _HUGE_ difference in when you need to shift up from the small ring which can lead to front shifting like you have ADHD.

At 100 RPM 34x13 is 20.5 MPH and about 170W for a hypothetical cyclist like in Gibertini and Grassi's paper with .4m^2 Sd and .760 Cd riding on the brake hoods, 75kg weight, and .004 Crr on flat ground. 39x13 is 23.5 MPH and 245W. Upping the RPMs a bit as on VO2max intervals 39x13 at 110 rpm nets 25.8 MPH and 315W. For a small ring sprint you could hit 33 MPH at 635W at 140 RPM.

For a small guy with ~240W of threshold power this is the difference between the small ring only being usable at a fast endurance pace and it working for most solo rides on flat ground.

This is why so many anecdotal reports comparing compact crank use indicate riders spending much less time on the small ring, shifting the front much more often, or riding nearly cross-chained (34x14 and 50x21 instead much less time on the small ring, shifting the front much more often, or riding nearly cross-chained (34x14 and 50x21 instead much less time on the small ring, shifting the front much more often, or riding nearly cross-chained (34x14 and 50x21 instead much less time on the small ring, shifting the front much more often, or riding nearly cross-chained (34x14 and 50x21 instead of 39x16).

Personally where my weight/fitness/terrain choice precludes spinning a 39x21, 23, or 26 (depending on whether I prefer an 11, 12, or 13 starting cog assuming 10 speeds; you can adjust that up a size with 11 cogs or down with 9) up nearly all my climbs and being manageable elsewhere I run a triple with a 39 or 42 middle ring, cassette with one tooth jumps to the 19 cog, and whatever small ring it takes to make that work.

or, as previously mentioned, 52/36

Me also.

I went with a compact with 50/34 to ride the U.S. Pro Cycling Challenge course coming up in a few weeks.

Everyday use around here, I'll put on 52/36 chainrings.

It also limits you to riding with groups that are organized enough to decide ahead of time what route they'll take instead of it being an ad-hoc thing once people show up and express their opinions.

i default to the wider cassette like a 25 or 26 when i'm just ridin for fun, its only on races when i try to figure out the optimal solution, which tends to be the tightest cassette i can comfortably run. no reason to ride a crit with a 28, but it sure is nice for a race with steep climbs.