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Crank arm length on Compact Crank

post #1 of 16
Thread Starter 
Hello,

Little by little I'm leaning towards getting a shimano compact crank on my Specialized Allez.

How can I find out what my OEM crank arm length is? I have no problems with it and would like to get the exact arm length.

Or - what is the standard length for a 56cm frame from MOST bike companies?

Thanks!
post #2 of 16

Re: Crank arm length on Compact Crank

Hi Cusp,

Many cranks have the length stamp at the end of the crank arm. Typically it's on the inside face of the crank arm. If you can't find it you can measure it yourself.

My guess is that most of the big manufacturers, like Trek and Specialized, put 172.5mm arms on when they come off the assembly line. If the customer wants to swap them shorter or longer it can be done at the point of sale or they can do it later on down the road (pun intended).

I have the Shimano compact and love it. It's really helped with the hills and seems to be about equal to the Ultegra in quality. Good luck!

Scott
post #3 of 16
Thread Starter 

Re: Crank arm length on Compact Crank

Quote:
Originally Posted by Pharaoh1
Hi Cusp,

Many cranks have the length stamp at the end of the crank arm. Typically it's on the inside face of the crank arm. If you can't find it you can measure it yourself.

My guess is that most of the big manufacturers, like Trek and Specialized, put 172.5mm arms on when they come off the assembly line. If the customer wants to swap them shorter or longer it can be done at the point of sale or they can do it later on down the road (pun intended).

I have the Shimano compact and love it. It's really helped with the hills and seems to be about equal to the Ultegra in quality. Good luck!

Scott
Scott,

Which Shimano compact did you purchase? R4550? R600? R700?

I have a 9-speed bike and apparently the R4550 is truly made for 9-speeds while the R600/R700 is 10-speed that 'works' with 9 speeds.
post #4 of 16

Re: Crank arm length on Compact Crank

Well, a 56x56 could also have a 175... check it on the inner arm! Or you can measure, with a caliber, the distance from the centre of the pedal-hole to the centre of the octalink hole (check only the left arm).

In Italy we say: if you are able to shift gears with your right hand and to put the right gear in the right situation, you can take a 53/39 everywhere
post #5 of 16
Thread Starter 

Re: Crank arm length on Compact Crank

Quote:
Originally Posted by Sikhandar
Well, a 56x56 could also have a 175... check it on the inner arm! Or you can measure, with a caliber, the distance from the centre of the pedal-hole to the centre of the octalink hole (check only the left arm).

In Italy we say: if you are able to shift gears with your right hand and to put the right gear in the right situation, you can take a 53/39 everywhere

Thanks for the heads up on where to check for the length.

I actually have a 170 length.
post #6 of 16

Re: Crank arm length on Compact Crank

Quite strange to have a 170 mm on a 56 centimeters frame... are you sure that your frame is a 56? I mean, 56 taken from: centre of crankset - centre of horizontal tube measured by following the seatpost-tube? Maybe it was a bike prepared for McEwen (sprinters love short cranksets)
post #7 of 16
Thread Starter 

Re: Crank arm length on Compact Crank

Quote:
Originally Posted by Sikhandar
Quite strange to have a 170 mm on a 56 centimeters frame... are you sure that your frame is a 56? I mean, 56 taken from: centre of crankset - centre of horizontal tube measured by following the seatpost-tube? Maybe it was a bike prepared for McEwen (sprinters love short cranksets)

56cm frame. Sticker is still on tube.

And 170 stamped on crank arm near where the pedal bolts are.
post #8 of 16

Re: Crank arm length on Compact Crank

Quote:
Originally Posted by Cusp
56cm frame. Sticker is still on tube.

And 170 stamped on crank arm near where the pedal bolts are.
Sounds like an "entry level" bike, they don't go proportional with individual components until you get up market a bit.
post #9 of 16
Thread Starter 

Re: Crank arm length on Compact Crank

Quote:
Originally Posted by gclark8
Sounds like an "entry level" bike, they don't go proportional with individual components until you get up market a bit.
haha. Heyyy now. 105 components. Be nice to my bike. j/k.
post #10 of 16

Re: Crank arm length on Compact Crank

Quote:
Originally Posted by Cusp
Scott,

Which Shimano compact did you purchase? R4550? R600? R700?

I have a 9-speed bike and apparently the R4550 is truly made for 9-speeds while the R600/R700 is 10-speed that 'works' with 9 speeds.
I've got the FC R700. I recently mated it with a 12-27 cassette. Not very macho, but I'm pushing 50 and am not too proud to use a little help!
post #11 of 16

Re: Crank arm length on Compact Crank

Same here Pharaoh, and I love it. I'm 53 and who cares about being macho when struggling up a hill.
Halcyon1
post #12 of 16

Re: Crank arm length on Compact Crank

Just got my Trek 2000 with an Ultegra compact crank. 170mm on a 52cm frame. Works flawlwssly (so far) with the new Ultegra groupset and the bike is a hell of a good climber. Previously had a stock 2300 which is the same bike with standard Ultegra parts. Very noticable difference accellerating and climbing with little loss of downhill speed. Try it. You'll like it
post #13 of 16

Re: Crank arm length on Compact Crank

Quote:
Originally Posted by Skittlebrau
Just got my Trek 2000 with an Ultegra compact crank. 170mm on a 52cm frame. Works flawlwssly (so far) with the new Ultegra groupset and the bike is a hell of a good climber. Previously had a stock 2300 which is the same bike with standard Ultegra parts. Very noticable difference accellerating and climbing with little loss of downhill speed. Try it. You'll like it
I have a "stock" '05 Trek 2100, it has a Brontrager Crank, SRAM rear cassette, 105 FD, and Ultegra RD.

I've been thinking about purchasing the R700 and have some questions:

1) Do I need to buy anything else to replace the crank? Bottom Bracket - Does one come with it (or integrated?) or will the one I have already work?

2) Will my 9-speed cassette, chain, etc... work fine with this crank?

3) Is it worth upgrading, possibly with lower gearing, my cassette to an Ultegra?

4) If replacing the rear cassette is an option for me, I can't go to a 10 can I? Not without getting new brifters, right?

Thanks for anyone that can help me out!
post #14 of 16

Re: Crank arm length on Compact Crank

1) Do I need to buy anything else to replace the crank? Bottom Bracket - Does one come with it (or integrated?) or will the one I have already work?

You will need the Shimano BB cups- The Truvativ (Bontrager ones won't work). The cups have to be purchased separately (about $35).

2) Will my 9-speed cassette, chain, etc... work fine with this crank?

Yes. You might need to shorten the chain a link or two, depending on the current length of the chain

3) Is it worth upgrading, possibly with lower gearing, my cassette to an Ultegra?

It is not worth the upgrade in and of itself. If you need lower gearing, then get a different cassette. SRAM 900 series cassettes (950,970,990) are comparable to Ultegra in quality.

4) If replacing the rear cassette is an option for me, I can't go to a 10 can I? Not without getting new brifters, right?

To go 10s, you WILL need new brifters (and a 10s chain, along with the 10s cassette). The crankset can go 9s or 10s. 9s derailleurs should work adequately with 10s, although a 10s front will work better than a 9s FD in the 10s drivetrain.
post #15 of 16

Re: Crank arm length on Compact Crank

Quote:
Originally Posted by Sikhandar
In Italy we say: if you are able to shift gears with your right hand and to put the right gear in the right situation, you can take a 53/39 everywhere
Certainly, if you can climb 2000m with a cadence of 30/min, you can take a standard crankset anywhere! But if you are wanting efficiency with big climbs, you may choose a different option.
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