I have a compacts on my DL tri bike, and am a huge fan of them. They are great for climbing - the 34-23 is a great combo if you are hitting some really steep stuff. The 50-11 is also a lower combo than the 52-13 I was running when I wanted a climbing gear. All around, they are better than the 52/39 I was running.

re: your gearing selection - I would stick with an 11/23 - it's more versatile.

BTW: I will be running 52/39 on my steep tri bike - since most of my rides and races on this will be on flat to rolling courses and hey, I already own them...

Thanks John. I was also leaning to the 12-23 but the 11-23 for IM is to much for me. The 50-11 at 90rpm=32.2mph.If I am going down anything that steep I coast. I probably will buy a couple of cassettes. Might use an 11-23 for other riding. Thanks for thr response. Kenney

Wow, I say hats off to you for truly fine analysis of the gearing. It is an excellent plan. Well though out too. Pretty darn impressive.

Here's the one fly in the ointment though:

Sometimes people will desing gearing from a strictly physiological or "effort" point of view, as though any combination installed on the bike will work mechanically as well as any other.

Therein lies the problem. When you desing a gear spread or combination that appears perfect in the real world it remains to be seen if it mechnically feasible. New drivetrains and frames are increasingly cantancterous when it comes to anything other than a 53/42 with an 11-23 10 speed. That is what frame designers usually build around. They are positioning their bottom bracket shells, chainstays and front derailleur hangers (if its braze-on) for that combination, figuring it is the norm. Anything outside of that realm may amount to an experiment.

If you are willing to be the Guinea pig, it is a worthwhile project. It may work. Based on my expereince with my friends at FSA recently, they wouldn;t have released their compact crank if it had presented big problems on the majority of frames. But then again, they told me on the phone on Thrusday "None of the time trail chainrings we have now are 10 speed compatible based on the feedback we got form the CSC team". Hmmm, it would have been nice to know that before we bought them as an alternative for the still-missing Dura-Ace 10 speed 54 and 55 tooth chainrings.

So, it will boil down to a mechanical experiment, and an interesting one at that. Let us know what you discover. One note: If FSA is telling us their 54 and 55 tooth lenticular TT chainrings are not compatible with 10 speed, then are the reduced diameter compact chainrings compatible?

Hmmmmmmmm????????

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Tom Demerly
The Tri Shop.com

Tom

If it makes a difference,the bike I am doing this with is a Klein Q-Carb-Pro(53-39.......12-25 9 speed). So being a Road bike,the chain stays (compared to a Tri bike)would be longer and shouldn't pose as much a problem correct? It will be interesting.I will keep you informed. (fr der looks clamped on)

I bet that will work in your favor. How does the front derailleur mount? Clamp on or braze-on?

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Tom Demerly
The Tri Shop.com

I've been running the FSA compacts with an 11/25 rear cassette (bastardized 9sp). It's really, really hilly around here and I absolutely love the gearing combination, especially for early season base training (I can spin up 8 & 9% grades in the aero bars and keep my HR below 150 without any problem). In fact, for IM Canada, I'm even considering using a 12/27 cassette. You wouldn't believe how much different (better) your legs feel after a few hours when you've been able to spin easily up every hill nice as opposed to needing mash up them.

For what race are you considering making this purchase? Does it have some nasty hills? If not, then I don't think you'd gain ANY benefit from compact cranks (other than the weight savings).

On nine speed reports have been favorable with compact gearing.

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Tom Demerly
The Tri Shop.com

 I have had a 48/34 on one of my bikes for a long time now. Ritchey had a compact crank for the road 5 or six years ago that I got on sale.
I had to go to a wider BB width or the chain crossover draged on the big chain ring in the 34 / 12 and 13 gears. The Ritchey crank has a real low Q factor so that was not a problem. However on my bike with a braze on derailure cage it wouldn't fit. G

Considering I do not know what a braze on looks like..............Looking at it sure looks like a clamp on. (I thought "brazing"only had to do with brass?)

The race is Im CDA. The hills are not to bad,only a couple and pretty short relative to 112 miles. What interested me is the tighter gear ratio's. Basiclly it works that at you shift between 90 rpms and 85 rpms instead of the same speed differences of 90rpms and 80 rpms. The reason for the post was that over 112 would it help to have the ability to remain constant at close to the same rpms. In theory I like the idea of the tighter ratio of keeping the constant speed as compared to jumping between a 15,17,19 on the rear cassette,considering thats where I am always at.