Compact Crank Questions

jrprice

As part of the purchase of a new tri bike, the LBS is throwing in a new Dura Ace 50/34 compact crank.  (It came with a 53/39 172.5mm)  My question: For the new compact crank, should I stay with the 172.5mm or drop down to a 170mm?  Does it make a difference?  I was told to get the 170mm but I am not sure and would like to get the collective wisdom of the Haus. 

My plan is do change over to the compact while I train (pretty hilly terrain)  this summer and do several hilly Sprints/Olympics.  I am planning on switching back to my 53/39 when I start the Race Prep for IMFL.  However, if most of my training rides will be on hilly terrain, should I stay in the compact?  Looking at the bigger picture, will it make a difference during my training rides on the bike?  When would you suggest that I switch from the compact to the 53/39 during the 12 week Race Prep?  Before the race rehersal's?  Thank you for your advise!     

Scott Alexander

Once you go compact, you'll never go back. Isn't that the expression?

HayesSanborn

I don't see any reason to get a shorter crank arm if you're riding 172.5 now and it works.

Also, just stick with 50/34 Compacts.....At Florida just swap out the 12-25 for an 11-23 if you're worried. Cheaper than multiple cranks and even I can change a cassette.....

Paul Hough

I had a compact crank on my last road bike and raced my tri bike with regular cranks. New road bike this year has 53-39...so you can count me as one of those folks who did go back. I've read some posts online by folks that say it doesn't much matter and having ridden both, I'm in that category. Maybe the compact crank has some marginal value that I can't perceive, but either seem to get the job done. However, I will be using an easier cassette for my hilly races.

Nemo Brauch

What Hayes said- just swap the cassette if your worried. I went with shorter crank arms but that was due to fit issues. Unless you need the shorter cranks to help with the fitting I don't see a huge reason to swap them.

mgraffeo

A lot of the people who's opinion I trust re: bike fit seem to think that going for the shorter crank is an advantage on a tri bike. The reason is that it will serve to slightly open up your hip angle at the top of the pedal stroke. Intuitively, it makes sense to me, though I've always ridden 172.5's. Seems worth considering.

@ Paul, not all of us live in Tampa, bro! :-) Seriously, there's a balance between the 'it's personal', like whether or not you like wearing an aero helmet, and physics. No question that a compact will allow you to spin a higher cadence at the same watts on hilly terrain. If you never encounter that terrain, or if your FTP is sufficiently high that 65% of FTP gets you up most hills at 80 RPM, then I could see 'not seeing the advantage'. I just doubt that there's too many people in the tri world where the latter is the case.

Mike

Paul Hough

@ Mike - Tampa is pancake flat. But Florida is not as flat as you think...if you know where to go. Less than 1 hr from here are the hills of San Antonio/Dade City, FL...trust me, you wouldn't think you are in Florida, and bikers travel from a 100 mile radius to train there. Over in Clermont is Sugarloaf Mtn...17% grade for 1/2 mile climb...I've gone up many times and it's tough. There's a reason why it is one of the top winter training camps in the world. Last year, I took a 53-39 x 12-21 to the Boise 70.3 and only felt the effort on the Bird of Prey climb...a 23 cassette would have been nice there. My concession to IMCDA will be to buy a 12-27 for my regular cranks. I've got nothing against compact cranks...they worked great on my last bike (came stock). But when I upgraded to a new road bike, I didn't miss them at all...neither on the flats nor on the hills. But if I ever do IMSG I may have to reconsider!! In fact, I think I'll configure my back-up tri-bike to compact cranks - then I'll always have the option.