Dura Ace Compact Crank choice!

[globaledge]

Hi. Here's a newbie question: Need to purchase a new set of cranks for my Cervelo R4 now that my FSA's have been damaged. Have been riding on 172.5 39/53. Am considering the Dura Ace 7900 but spotted the new compact crank. How does the new Dura Ace 7950 compact crank (which is essentially a 30/54) change the pedalling action and gearing. Have got a 12/29 cluster. i.e., would pedalling up Ou Kaapse Weg with a 29 on the small chain ring be easier or more difficult when compared to the 39. And would I have to pedal faster or slower coming down Ou Kaapse Weg with the 12 gear on the 54 or the 53. Can't get my head around it and need a techie to help clear the cobwebs! Thanks, Keith

[Tankman]

Hi Keith

 

First off, when looking at a compact crankset there are different options available. The normal setup on compact is 50/34 and then there are 52/36 or even the standard 53/39 chainrings blades can be found with a bit of effort.

 

Standard cranks have a BCD (bolt center diameter) of 130mm

and compact cranks BCD of 110mm

 

There will be a increase in cadence when going from standard 53/39 to compact 50/34 depending on your riding style.

If you are using a 12/29 with 50/34 the 29 will be a absolute overkill. You will be spinning so fast I doubt that youll be able to use that gear.

 

I would recommend using a 11/23 with 50/34. The 11 will come in handy when going downhill and will fair better than your current 12. I have used 52/36 with 11/21 (I like the close gearing) on my racing bike for quite some time. I wont go without the 11 and I dont need anyting more than 23.

 

What type of cadence you are comfortable with will also depend on what gearing you may choose but as you can see there are a lot of different options available.

 

For a more scientific approach look at Sheldon Browns Gear Calculator

Hope that helps!

[eggsovereasywithteandtoast]

So the term "compact crank" is indicative only of the BCD?

Please explain what BCD stands for.

[Spaceboy]

Cervelo R4? Never heard of this bike.

 

BCD = Bolt Circle Diameter

 

Compact cranks refer to the the chainrings....where 53/39 is considered standard, 50/34 and 52/36 etc are considered compact.

[globaledge]

Brilliant Tankman. That's exactly what I needed. Will take your advice on the 11 gearing. Makes sense. Much appreciated. Keith

[Tankman]

So the term "compact crank" is indicative only of the BCD?

Please explain what BCD stands for.

 

 

Thanks Spaceboy - Bolt Circle Diameter

[Wrigs]

Thanks guys, excellent discussion - do the same dimensions hold for Campy chain rings?

[Speed Devil]

Just remember, if you do decide to choose a compact crank and later decide that it's not your cup of tea and want upgrade to a 53 tooth blade, that you don't get a 53 for a compact crank, which means you will have get a new crank.

[Wrigs]

Just remember, if you do decide to choose a compact crank and later decide that it's not your cup of tea and want upgrade to a 53 tooth blade, that you don't get a 53 for a compact crank, which means you will have get a new crank.

Good advice Speed Devil - but just for the record, I dont believe your signature for even 1 moment

[Tankman]

Just remember, if you do decide to choose a compact crank and later decide that it's not your cup of tea and want upgrade to a 53 tooth blade, that you don't get a 53 for a compact crank, which means you will have get a new crank.

 

Not true Speed Devil - check out the photo - as I mentioned in my first reply 53/39 blades with a 110mm BCD can be found with a bit of effort. FSA and Controltech manufactures them.

 

[Tankman]

Thanks guys, excellent discussion - do the same dimensions hold for Campy chain rings?

 

Nope, Campy has a BCD of 135mm

[Tankman]

oh and most track bikes have a 144mm BCD

[Sharkie 2]

I use a 50/34 crank with a 11/23 casette on training and normal races here in Gauteng, when I go climbing I put on a 11/25 just works lekker for me

[Big J-WP]

Tankman, seeing that you are the wise one at the moment.

 

Can you have a BCD 110, 53/34 will the front der work?

[ANDYCAP]

Good advice Speed Devil - but just for the record, I dont believe your signature for even 1 moment

 

You better believe it..he's already got the 2nd child on the way.....

[Wrigs]

Nope, Campy has a BCD of 135mm

So if Shimano has 110 vs 130 Campy is 135 vs ?