I drank the Kool Aid (switched to shorter cranks) (Page 2)

Oops, right!

Thanks for the good words guys and I'm glad I can help!  You guys are right, it's a relatively cheap trial so if It doesn't work for you, you can always pop in the old bottom bracket and arms and you're good to go.  In terms of the length of the bottom bracket, I guess you can measure the thickness or the width of the junction of the three tubes and go from there.  For Cervelo's it's 107mm and I went with that. 

Since I I decreased the crank length 3cm, I increased my saddle height 3cm as well and moved the saddle 1cm forward to compensate for the seat tube tapering back. 

I think this is the best and cheapest way to try the shorter crank without breaking the piggy bank (assuming you already have 110BCD chains and BB30 bottom bracket.

It took me all last season to get comfortable on my TT bike then I sold it at the end of the year- I did get all the important measurements prior to selling though. The cranks were 170. Over the winter I built up a B2 to the same specs but it came with 175 crank arms. I took it out Friday and OMG it sucked. I had a lot of problems basically because I had gotten acustomed to riding a more relaxed position on my road bike with clip ons over the winter but I couldn't get nearly the power i was getting last year with shorter cranks. I happened to find the identical cranks in a 165 on ebay for $70 so I'll try that before I go to 145-155.

I do worry about raising the seat more and increasing the drop. I had a hell of a time keeping my head up on the virgin ride. I know I just need to get used to it and HTFU but I'm still sore three days later.

@Bonafide: Embrace the pain bro!  That's why I incorporate spinning classes to my weekly bike training.  I'm always there gritting my teeth and forming a puddle...

175 to 165 is not a big drop though but since it's cheap might as well see how it is first.  I think m drop was pretty drastic wherein I went from 165 to 170 for 1 month and now I'm at 140!  Never felt better and more aero though.  I think it's time to ride it outside now...

if you reduce your crank arm length by 20%,

do you need to increase your gearing by 20%?

I'm gonna try to do a century ride on Friday (Cerritos - Dana Point) and I'll let you know how it goes.  Although I love hills so I don't think it would be a problem.  I love the uphills and hate the downhills... go figure... 

When you say enough gearing, what exactly do you mean?

 Yes they are tiny (not what she said by the way)...

Arkman...What really sucked was my neck pain. I like to suffer and sweat but I couldn't ride more than 1-2 miles aero. This was demoralizing because I was used to  doing 36 mile TTs on my road bike with clip ons averaging 21mph- comfortably. I had trouble hitting 21 at any time the other day and my avg was less than 20. This I attribute somewhat to the more closed hip angle/longer cranks.

Once I get the new BB/crankset I'll just switch arms and sell the 175 set on ebay. I think once my neck gets used to being low again I'll likely try even shorter cranks- of course depending on your updates

Please keep us posted.

I'll let you know how it goes although I don't think there would be a problem.  I'm already used to "turtling" in my head and I think that's more uncomfortable than "regular" neck position on TT bikes.

1 revolution of the pedals will take you just as far regardless what the crank length is.

Question, what was the difference in feel between the 145 that you did not like and the 165 (power/comfort/etc)? 

Also, height/torso length/etc (or is this not a factor in determining this)?

Have you been getting in a good deal of riding since the change? What have you found so far about the gearing you have?

I'm ashamed to say this but I have only ridden it indoors...  It rained last weekend here in SoCal and on the weekdays, I really don't think cycling with all the other cars at 1730 HRS is ideal either. 

I don't think I can answer your question about gearing right now but I sure will answer it on Friday afternoon after I get a long (70 mile) ride in with about 50% rolling hills.  I only installed it last week though but yeah.

All things being equal it should be harder to turn your cranks over in the same gear with shorter cranks- shorter lever. This however does not take your power and comfort band into account. I personally cannot generate as much power with a closed hip angle so If you're like me it may be a wash.

What chainrings are you using?

At only 5 feet 8 inches I have an inseam that is nearly 34 inches so I am all legs.   This might have been part of the problem because maybe my fit was so off at that point that 145 didn't feel right.   Yes I adjusted for saddle fore/aft/height but most bikes don't fit me that well to begin with. Truth be told both days I tried 145mm I had to ride in brutal gale force winds and that may have also contributed to the problem.  There was nothing wrong with them other than simply they felt off.   On the contrary I have always felt great on 165mm.  

I'm not saying I won't try 145mm again - just that with BB30 bottom bracket your crank options are even more limited and I want all my bikes the same and 165mm is kind of the lowest you can for the masses at this point.

When you move to shorter crank that affects your gain ratio.  You can look it up on Sheldon Brown's site.  It is a complicated topic, but I am of the opinion you should always be spinning up hills at 90 rpm opposed to mashing up them at 45-65 like I see many do.  With shorter cranks you may need that 12-28 cassette, I don't know for sure but you should definitely go out and try the setup outside on some hills to make sure you have enough gearing for Oceanside.  Please report back when you do

Cheers,

Thomas

No, crank arm length does NOT affect gear ratio. Gear ratio is only about revolutions, not the circumference or length of the lever arm.

However... The amount of force you can exert on the pedal does not change appreciably at peak (generally accepted to be at the 3 o'clock position), so with a shorter lever arm, you produce less torque. This means it'll be harder to turn the same gear over if you're at max. There's a reason that bike racers have tended to go to longer cranks for climbing.

I'd see how it goes first. You just made one noticeable change, a second could complicate it. If cost isn't much of an issue, you could get a lower range cassette and then install it if you find the ride a little tougher than you like.

Thanks for the advice guys.  I really appreciate all your input.  I'll test it out on the road first and go from there.  From my indoor rides I have noticed that it felt like as if I am mashing the pedals.  Maybe it's just the illusion since the cranks are much shorter thus resulting to a more efficient pedaling(?) 

I'm a spinner.  Never really counted my rpm but I know I pedal faster than most in my cycling club.  I guess I'll install my cadence sensor.  I already felt the running benefits of the shorter cranks since I was still able to bang out fast running miles after a sweat fest on the trainer.

I use 50/34T which I believe is compact.  It's the stock FSA rings that came with 2012 P3.

Yes, those chainrings only fit on a compact. You should be getting some idea on the trainer (as you indicated), but ultimately you want the outdoor rides to decide.