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Crank arm length and age? [some technical considerations]

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Joined: 08 Dec 2003
Posts: 17940
Location: Portland, OR

9/13/19 12:59 PM

Crank arm length and age? [some technical considerations]

I seem to have settled into a 172.5 preference. But used 175mm for forever.

I may need to consider a crank purchase for a change I am contemplating. Which would leave a 175mm Ultra Torque SR crankset out of the picture and in my ample part stores.

From a cheap ars and budgetary position, for 2.5mm this seems silly perhaps.

Points I am considering into the equation.:

With this frame, 67.5 BB drop maybe the 175mm will get a try before spending on Campy OT/UT cranks additionally. Bike has 172.5 now. Most of my bikes have 70+ BB drop. I know we are splitting m.m. hairs [thick hairs?] here. ;)

But again to the age issue, are hair splittings need a component of age is anyone finding?

It is a go fast bike for what that might bring to the fit formula.

One of my personal issues now is I find am a lot different with the weight loss, and want to further it.

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Brian Nystrom
Joined: 26 Jan 2004
Posts: 4720
Location: Nashua, NH

9/13/19 3:45 PM

Why are you going shorter? The only reason I can see to do so is if you've become less flexible, but if you've lost weight, the opposite should be true. Regardless, I'd say you're overthinking it, as BB drop shouldn't affect your crank length at all. Either a crank is the right length for you or it's not.

Funny, I couldn't tell you what the BB drop is on any of my bikes and it's not something I even consider when picking a frame. My off-road bikes all have higher BBs than my road bikes, but that's about all I know for sure. I have 175mm cranks on every bike I own and they work fine for me.

The BB drop/crank length combination would be a consideration if you're building a crit bike that has to corner sharply at high speeds without your pedals clipping the pavement as you pedal into the entrances and out of the exits of corners. Shorter cranks might allow you to spin a slightly higher cadence, which could also be beneficial for crit racing. Other than that, I don't see why anyone would be concerned about it on a road bike and I don't buy the idea that anyone can feel a difference in stability between bikes with small variations in BB drop. There are too many other factors that have a much larger influence.

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Joined: 08 Dec 2003
Posts: 17940
Location: Portland, OR

9/13/19 6:41 PM

"Regardless, I'd say you're overthinking it"

I expected to hear that, and from you as well. ;) But only because mostly this is a truism.

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Joined: 11 Jan 2004
Posts: 3310
Location: NorCal

9/14/19 11:54 AM

Shorter cranks always make the choice of saddle height less critical, so if one has any knee issues relating to saddle height then I vote for use of shorter cranks.

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Joined: 12 Jan 2004
Posts: 3073
Location: Midland, MI

9/15/19 10:38 AM

Spin cycle

Shorter cranks make it easier to spin. That's about all there is to this question. I rode 170 mm for several decades, then got swept up in the "longer is better" fad that came from mountain bikes. After nearly 20 years on 175s, I came back to 170 in 2014. Not much difference in the end, but I think I like the 170 better.

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