Fifty Plus (50+) - Sort of technical question

Okay, an actual bike question. One of my bikes has a Shimano FC-R700 compact crank with 172.5 mm crank arms and I might be interested in trying a shorter crank. Do I have to buy a whole new crank set or can I get just the sorter arms--and from where and is it easier (and/or cheaper) than getting a new crank set??

I fear you must get a new crankset.

You'll need the whole crankset. The drive side arm is attached to the spider arms to which the chainrings are connected.

I sure wish it was easier. I'd love to try 165mm crank arms. All of my bikes presently have 170mm.

Technically a 172.5mm arm should suffice unless your inseam is less than around 31".

Just swap the cranks themselves. You can reuse your bottom bracket, pedals, and chainrings. With luck, you might even find someone with whom to trade cranks.

Theoretically you could take the spider and rigs off of your current arm and replace just the arms. But in reality you will not likely be able to find the arms for lass than a whole crankset. Replacing a crankset is a 5 to 10 minute job. You won't even need a crank puller for the FC-R700.
http://www.parktool.com/repair/readhowto.asp?id=122#shimano

Now just a change of crankset and you may be lucky---BUT-- In my experience- even if you have the same type of bottom bracket (Splined or square Etc. ) You may need a different length bottom bracket. Found this a lot on the MTB's where you do an upgrade that is many grades of up. Shimano LX up to XT was fine as there was only 2mm difference but Once had to change a Cheap OE fitment to Deore and the Deore required a BB of 115 mm and the OE had a BB of 127mm. Didn't matter that much as The BB was shot- but just a warning that you may have to change the BB aswell.

Now just a change of crankset and you may be lucky---BUT-- In my experience- even if you have the same type of bottom bracket (Splined or square Etc. ) You may need a different length bottom bracket. Found this a lot on the MTB's where you do an upgrade that is many grades of up. Shimano LX up to XT was fine as there was only 2mm difference but Once had to change a Cheap OE fitment to Deore and the Deore required a BB of 115 mm and the OE had a BB of 127mm. Didn't matter that much as The BB was shot- but just a warning that you may have to change the BB aswell.

I think most of us are assuming he would be changing to a longer arm crank of the same model as the original, not an upgrade. At least that is what I took him to mean.

Bummer!
:)

Okay, an actual bike question. One of my bikes has a Shimano FC-R700 compact crank with 172.5 mm crank arms and I might be interested in trying a shorter crank.

Pricey crankset.

W/170mm crank arms:
http://www.niagaracycle.com/product_info.php?products_id=6755

w/165mm crank arms:
http://www.niagaracycle.com/product_info.php?products_id=6754

Pricey crankset.

W/170mm crank arms:
http://www.niagaracycle.com/product_info.php?products_id=6755

w/165mm crank arms:
http://www.niagaracycle.com/product_info.php?products_id=6754

No. THIS http://fairwheelbikes.com/index.php?main_page=product_info&cPath=9_41&products_id=64 is a pricey crankset. Only about $1,000 additional dollars!