lineinthewater

I found a deal on a Shimano R700 Compact Crankset (50/34), which includes an english-threaded BB. I'm a little nervous I missed something when doing my research.

I've made the following assumptions based on some research (are these accurate?):

1. I'm assuming it is an external BB that is compatible with my Caad7 Cannondale.

2. The R700 will work with my current Shimano 105 FD.

3. My 105 shifters will work with a double.

4. The R700 will work fine with my 9-speed drivetrain (it does say 9-speed compatible).

Did I miss something?

Assuming this crank is compatible with my current setup, I'm still a little nervous the compact crankset may not be a good fit. I currently have a TruVatiV Elita SL Triple, 30/42/52 and a 12/27 cassette. Because of cross-chaining, rubbing on the FD, and overlap, I probably only use 20 (at most) of the 27 gears on my current setup. I spend almost all my time in the 42 chainring right now ... but I do use the 30 on steeper hills. I'm not too worried about the reduction from 52 to 50 on the high side.

My primary reasons for switching were: better chain-line, smoother shifting, more responsive crank, easier maintenance, better fit/use of gears, good price. I don't race - I'm just a recreational cyclist who primarily rides for exercise.

Feedback?

HillRider

You shouldn't have any real compatibility issues. Your current 105 triple fd will probably work and, if it's not perfect, replacements are relatively inexpensive. I'd try it first and see how it performs.

The only downside is the loss of your lowest gear. Your current low gear is 30 gear-inches and the new crank will give a low of 34 gear-inches. That's a 13% higher gear. If you never use the 30x27, fine, but if you need it, you won't have it.

The triple also has the potential for even lower gears by substituting a 26T or 24T chainring for the 30T. The compact already has the smallest chainring that will fit on the 110 mm bcd. (yeah, I know a 33T will fit but no one is going to bother).

lineinthewater

It is my understanding that the R700 was designed to be compatible with "normal" derailleurs, unlike some of the other compact cranksets. Yeah, I've read the FD's are very cheap.

Yeah, that is my biggest worry. I guess I won't know till I try it. I've been trying to think of the worst hills I run into, and how much "13%" would really impact the climb. I've also had ITBS issues in the past, but not in the last 2 years. But I think that was more related to my seat height. Hopefully that doesn't rear its ugly head with the compact.

Unless I move, or go on some travel-touring, I don't see myself as ever needing lower than my current 30T.

A few more questions:

1. How would you gauge the upgrade from my current crank to the Shimano in terms of quality, smoothness of shifting, and responsiveness? Is this a major upgrade or more a sideways movement? I really have nothing to compare it to.

2. As I'm sure you know, the 105 shifters actually have 4 positions ... large Chainring, two trims for the middle, and one for the small. When installing and adjusting the FD limit screws for the double, do you use/allow both trim positions for the 34T??

3. I'm 6'0" (inseam 33-34) ... and I currently have a 175mm crank. I went with the same length on the compact crankset. Does this sound correct?

HillRider

1. I don't think you will see a dramatic improvement. The double will be simpler to shift but "smoothness" and "responsiveness" aren't likely to be a lot different. Having "only" 20 out of 27 gears usable with a triple is very common. There is usually so much overlap and duplicate gears that it isn't a problem.

2. The two trim positions are set to work with the smaller ring for a double. Shimano's tech documents or Park Tool's web site give directions for setting up these shifters for a double as well as a triple.

3. Get the same arm length you are used to. The crank type and chainring choice have no bearing on the arm length.

joejack951

Some marketing nitwit came up with the concept of a "compact" FD. They have never been necessary AFAIK. Normal FDs have been used with many different large chainring sizes without ill effects for many years.

Or if you decide to carry some extra gear, or gain weight, or take a longer ride than ever before. In my opinion, if you already have a triple, there is virtually nothing to be gained by compact and a lot to be lost.

Shimano cranksets are known for their shift quality. It will likely be an improvement. A Shimano triple would offer the same benefit. I'm using a similar Truvativ crankset on my commuter though and haven't found any major gripes with the shifting. My inner to middle shift is occasionally slow but I'm running a 52/42/28 so it's somewhat expected.

You should also have a trim position for the inner ring, though I could be mistaken. My Ultegra 9 speed shifters have one.

When you use your shifters with a double crank, you'll get to choose whether you use the lower two or upper two shift positions. There are pluses and minuses to either approach. Shimano has recently recalled a bunch of triple shifters that were being used with double cranks set up using the first two positions. Apparently, people tried shifting past the stop and broke the shifter. That's a definite minus for that arrangement if you don't think you can remember not to force the shifter. If you set it up using the last two positions, you can end up with a really slack FD cable by shifting to the missing little ring. Also, assuming you have trim positions like my Ultegra shifters, using the first two positions gets you the ability to trim on both rings whereas using the last two only allows trimming on the inner ring.

It's a personal thing. I've biked thousands of miles using 175mm cranks and I'm 5'8". I did discover that my knees prefer 172.5s so I'm moving all my bikes to those cranks as I upgrade or replace them.

lineinthewater

Hmmmm ...

Thx. I'll check it out.


HillRider, thanks for your help/input!

cyccommute 

All of the above isn't a problem. Installation should be easy.

Here, however, you have some misconceptions. There is almost no gear system on a bicycle where it is possible to use all of the gears. 20 useful gears out of 27 is actually pretty good. There are just certain combinations that you shouldn't use, like large chainring/large cassette cog and smallest ring/smallest cassette cog. There are other combinations that make little sense in a recreation situation, like middle ring and smallest cassetter cog, because the next shift up is too large to be useful (92 gear inches to 113 gear inches or a 24% increase). There are other gears that are closer to the 92 and make the increase in effort more progressive.

For example, your 52/15 gear is about 92". The next gear (52/14) is only 7% higher as are the next 3 gears. You get to the same place with the same over all increase in gear size but you do it more progressively. Big jumps between lower gears (the 42/15 to 52/15) are big but your leg strength can take them better than a huge jump at higher gears.

If you look at your gear combinations...you can calculate them here...and compare them to the compact, you may see more combinations using the compact but the transition between the low range and high range is so large and the ratio so poorly laid out that a compact looks like two separate 9 speed drivetrains. There's no place to switch from the high range to low (or vice versa) that wouldn't be a jarring transition. The jump between the gears is 47% which is almost twice that of the 52/42 crank. It means that when you change gears, you'll either be spinning like crazy or massing. Neither seems efficient.

And you lose your high and low end gears. I'd suggest going for a test ride on a compact before you spend money to see if you like then combinations. At the very least, run the numbers on Sheldon Brown's calculator and compare the results.

Edit: Running some numbers of my own, I found a curiousity. Going with an 11-34 or 11-32 (the gear selection is different) and a compact yields a bit better gear pattern...not great but better. You also end up with a low that is similar to your 30/27 and a higher high than your 52/12. It is slightly heavier and you'd probably need a new rear derailer but it does have the same range.

lineinthewater

Thx.

Yeah, I know certain extreme gears are never used (and many overlap). How many gears are typically usable with a compact double 9-speed?

Thanks for such a detailed breakdown. I generally knew the difference in "steps" was going to be a potential issue ... I'm also worried about spending more time shifting my FD (as compared to my triple) - I think that is kinda what you mean by two different 9-speed drivetrains - in addition to the odd stagger/overlap of gears. I will go make the calculations using Sheldon's info - thanks for the suggestion!! Maybe I'll post the results back over here.

lineinthewater

Here are the Gear Ratios:

Triple:

...............30.......40.0%......42......23.8%......52

12............4.8.....................6.7....................8.3
8.3%
13............4.4.....................6.2....................7.6
7.7%
14............4.1.....................5.7....................7.1
7.1%
15............3.8.....................5.3....................6.6
13.3%
17............3.4.....................4.7....................5.8
11.8%
19............3.0.....................4.2....................5.2
10.5%
21............2.7.....................3.8....................4.7
14.3%
24............2.4.....................3.3....................4.1
12.5%
27............2.1.....................3.0....................3.7


Compact double:

...............34.......47.1%......50

12............5.4.....................7.9
8.3%
13............5.0.....................7.3
7.7%
14............4.6.....................6.8
7.1%
15............4.3.....................6.4
13.3%
17............3.8.....................5.6
11.8%
19............3.4.....................5.0
10.5%
21............3.1.....................4.5
14.3%
24............2.7.....................4.0
12.5%
27............2.4.....................3.5

cyccommute 

On a 52/42, eleven or twelve are easy to get to with a minimum of double shifts (shifting rear and front). You can get more but some of the gears are isolated and much harder to get without some funky shifting. But a compact would suffer from a similar issue.

Look at the edit on my previous post. An 11-32 or 11-34 with a compact doesn't solve all the problems but it does offer some opportunities.

lineinthewater

cyccomute - 11-32/11-34?? I would have to replace the RD, and the cassette. Yikes. Too much $$. Not worth it to me.

I fixed the charts ... any comments?

cyccommute 

Better but you do have them backwards (high gear on the left) and gear ratios make my head hurt. I'm an old dog and gear inches make sense to me. Otherwise, look at the 34/19 to 50/19 transition to see what I'm talking about. To get the same gear ratio on the small ring you'd progress from a 3.4 gear ratio through four other steps to end up with the same gear. 3.4 to 5.0 is a very large step. Play with some of the other calculations like meter development and RPM to see what effect the gear change has.

Run the numbers on the 11-34 cassette too. Just keep it as an option for future reference.

DMF 

FALSE. The triple has better chainline. The most commonly used ring has perfect chainline; the outer rings are closer to the cogs most used with them, so have better chainline than the compact in practice.

FALSE. The distance between rings is less with a triple. With a compact, every front shift is like the granny-to-middle shift of a triple.

Huh? I have no idea what you mean. Stiffness? No difference.

FALSE. No difference.

FALSE. The triple has more gears, so you're more likely to be able to find and use that "perfect gear". Triples are commonly used with narrow cassettes; compacts need wide cassettes.

FALSE. Whatever you spend on this downgrade is that much more than the zero dollars it will cost you to leave your setup alone.

I rather suspect that there's another reason .. peer pressure?

lineinthewater

F-A-L-S-E. Double-fail bongo.

What is up with bike forums? Seriously. I belong to several message boards, and this one is the absolute top of wise-a$$ and rude comments.

Not that your rude and antagonistic post even deserves a response, but I don't even ride with other bikers (or hang out with any). I'm starting to understand why. I come on this forum to ask questions and many times correct my misunderstandings. And even when I phrase my question as admittedly somewhat naive on the topic, there is always someone like DMF who has nothing better to do but build himself up on the backs of others interested in learning.

joejack951

Call him rude but everything DMF said is true. Ignoring his post because of your assumption that he's being antagonistic is childish.

lineinthewater

And of course he has one of his many wingmen come in and defend his behavior. Mind boggling. This has nothing to do with the quality of his knowledge.

joejack951

Did you come here to receiving coddling or knowledge? I generally try to post with a smile but not everyone does. I agree that this forum could be better if people acted a little more cheery but it's nothing I lose sleep over. The knowledge is unaffected and that's what matters.

DMF 

Oooo. Cool. I always wanted to be a gang leader!



Unless tats are required...

lineinthewater

I knew this comment was coming. The whole "do you want someone to hold your hand" counter.

There was only one motive for the type of post DMF put up ... and here's a clue, it wasn't to impart any knowledge to me.

I've asked the Admin to close this thread, as it is only going downhill from here.

BTW, thanks to those that actually offered constructive advice - it helped out a lot!

joejack951

You're welcome, though my feelings are hurt that you never directly responded to my long-winded post

exRunner

Some people need the triple due to their abilities, and then use BF to try to make everyone believe that all of us need the same. The sad truth is that, although most of what they say is correct in a narrow range, it is not correct for most applications.

lineinthewater

I was reading backwards (up the thread), and I totally missed it. Sorry about that. I wanted to say thank you before the thread got locked. If I have any questions or comments, I will PM you. Thx again!!

lineinthewater

Assuming the thread isn't locked yet, I wanted to get a reply into joejack's post.

Believe it or not, for now, based on all the advice and input from my LBS, I decided against the compact double.

I'd really like to upgrade to a Shimano crankset - independent of the double/triple discussion.

Nope, not the 105 shifters. Unless I'm really missing something.

This issue came to me while riding yesterday ... I assumed that I would have to make the inner setting go to the inner ring, because of cable slack issue (as you mention).

I've never tried anything other than a 175mm, so I have nothing to compare it to.

IK_biker

[QUOTE=lineinthewater;10106883]

What is up with bike forums? Seriously. I belong to several message boards, and this one is the absolute top of wise-a$$ and rude comments.
[QUOTE]

lineinthewater,

DMF is spot-on.
And you, claiming experience with online forums, still need to learn how to post while having a thin skin: just ask the effing question and keep your reasons out of the discussion.
Either that, or develop thicker skin. Quick.

Cheers!

exRunner

No question about it, BF has more people who attempt to militantly force there opinion on others than anyother place I have been. Just your "DMF is Spot on" comment smacks of it.

Narrow mindedness seems to be running rampant on BF.