# Choosing The Right Crankset



## Spunjin (Nov 10, 2009)

Hello all,
I am 5' 9" and 150 lbs. I ride a 2008 Fuji Aloha and I am thinking of purchasing a carbon crankset as an upgrade from my stock FSA Gossamer crankset. I am looking to cut weight and increase power and efficiency since I mainly race in triathlons. I don't know what length crank to consider though, 170mm, 172.5mm, or 175mm. I believe my current crank is 175mm. I know that if I change the length of the crank I will be adjusting my saddle height and position but are there other variables to consider? Will I have to change my stem length as well if I get shorter cranks? What are the advantages of a standard or compact crankset besides the chainrings? 
I have been looking at the FSA K-Force Light and the SRAM Red cranksets. I would ultimately have a group of one brand on my bike so I am leaning toward SRAM Red components, just so you know about my bias opinion.
Thanks in advance for all the advice.


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## spade2you (May 12, 2009)

Get your bike fitted and they can tell you if you need longer or shorter cranks.


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## Hank Stamper (Sep 9, 2009)

There are a lot of formulas easily googled that will tell you something about crank length. They are based on leg measurments. Take them with a grain of salt because like anything they are just guidelines and should be trumped by personal preference. At 5 9, unless you're all legs....I might rule out 175s though. Then again, there are 25ish mm in an inch so that means each 2.5mm size difference is 1/10th of an inch (assuming my math is correct, which is not always a good assumption)....so "it doesn't matter" is an answer worthy of consideration. 

Presumably most of the the charts and formulas out there that I mention are derived with road bikers in mind. There might be something difference specific to tri bikes so you might want to check into that.

I can't imagine you'd need to change the stem. Even saddle really.


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## JCavilia (Sep 12, 2005)

> I am looking to cut weight and increase power and efficiency


A different crank might reduce weight slightly, but it won't increase power or efficiency. the stiffness differences between cranks are miniscule and insignificant.


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## PJ352 (Dec 5, 2007)

I agree with those that have said weight loss and efficiency gains will be insignificant. And if the weight loss is your primary goal, assuming you haven't already done so, going to a lighter wheelset would yield better results.

As far as crank lengths are concerned, IMO at 5'9" (and thinking in very general terms) I'd guess you'd probably be looking at 172.5 mm cranks, but I also agree with those that say it doesn't really matter, so the bottom line is that I wouldn't 'upgrade' the crankset based on weight, performance or crank length. 

Same goes for standard vs compact cranksets. Except for a very small weight advantage with compacts, you aren't going to see any difference in performance, assuming the standard chainrings suite your fitness level and terrain. And no, changing crank lengths won't require any other fit adjustments except saddle height and fore/ aft position.


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## kmunny19 (Aug 13, 2008)

while its true that you may not save a lot of wieght or have as big and noticeable efficiency gain as a new wheelset might give you, you will be rid of those annoyingly junky gossamer components, and you will have decreased some rotating mass. 

go for the red if you plan to eventually rebuild the whole gruppo.

i agree about determining crank length with a fitting as well.


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## Guest (Nov 11, 2009)

175 may be too long if you look at the formulas for those types of things, keep in mind though that those are generally based off leg length and don't take into account for example the size of your feet among others. I'm just over your height and ride 172.5's but I own or have owned bikes with longer and shorter cranks depending on the purpose and its never made much difference to me.


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## Mr. Versatile (Nov 24, 2005)

Crank length from 170 - 175mm makes very little to no difference. If those 3 lengths are your choices, get the one in the middle.


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## Spunjin (Nov 10, 2009)

Thanks for all the advice. I found that my arm length is 172.5mm.
I know the weight difference between my current crankset and a carbon crankset is little but it is the rotational mass I am looking at reducing. I would like to upgrade my wheelset but considering the price and my abilities on the bike, it may not be worth it for me at this moment.
I have been looking at the reviews for the SRAM red crankset and I see that it doesn't have that great of reviews. Are the chainrings really too flexible?
I have also been considering the FSA Neo Pro TT crankset (mainly because it is aesthetically pleasing).
Thoughts. The terrain I typically ride consists of long rolling hills to flat land.


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## wim (Feb 28, 2005)

Spunjin said:


> I have also been considering the FSA Neo Pro TT crankset (mainly because it is aesthetically pleasing).


I dunno—if I had $700 to spend on my bike and were purposefully racing triathlons, I would put the money toward some wheels instead of a crank. Forget the 'rotating weight' thing, it's meaningless. In a steady-speed event like a triathlon, aerodynamics trumps everything else as far as bike equipment is concerned.


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## Spunjin (Nov 10, 2009)

Super. I'll start comparing wheelsets. Any suggestions on weight and aerodynamics (i.e. 3-4 spoke, full disc, or deep dish)?


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## wim (Feb 28, 2005)

Spunjin said:


> Super. I'll start comparing wheelsets. Any suggestions on weight and aerodynamics (i.e. 3-4 spoke, full disc, or deep dish)?


Start a new thread or do a search over in "Racing, Training, Nutrition, Triathlons." I stopped racing some years ago and am no longer up on the latest wheel offerings.


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## Kerry Irons (Feb 25, 2002)

*Meaningless rotation*



Spunjin said:


> I know the weight difference between my current crankset and a carbon crankset is little but it is the rotational mass I am looking at reducing.


Given the speed of rotation and the length of a crank arm, rotational weight for a crank set is approximately 1/20 as meaningful as on a wheel. Plus, the only time rotational weight means anything is when you are accelerating, and since your cranks are normally spinning at about the same speed regardless of your road speed, the effect is essentially meaningless. Weight saved on cranksets is virtually the same as weight saved on water bottle cages. Save your money unless you just really want to spend it. There is no performance improvement to be had.


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