globaledge Posted July 30, 2010 Share 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 Link to comment Share on other sites More sharing options...
Tankman Posted July 31, 2010 Share 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 130mmand 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 CalculatorHope that helps! Link to comment Share on other sites More sharing options...
eggsovereasywithteandtoast Posted July 31, 2010 Share So the term "compact crank" is indicative only of the BCD? Please explain what BCD stands for. Link to comment Share on other sites More sharing options...
Spaceboy Posted July 31, 2010 Share 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. Link to comment Share on other sites More sharing options...
globaledge Posted July 31, 2010 Share Brilliant Tankman. That's exactly what I needed. Will take your advice on the 11 gearing. Makes sense. Much appreciated. Keith Link to comment Share on other sites More sharing options...
Tankman Posted August 2, 2010 Share So the term "compact crank" is indicative only of the BCD? Please explain what BCD stands for. Thanks Spaceboy - Bolt Circle Diameter Link to comment Share on other sites More sharing options...
Wrigs Posted August 2, 2010 Share Thanks guys, excellent discussion - do the same dimensions hold for Campy chain rings? Link to comment Share on other sites More sharing options...
Speed Devil Posted August 2, 2010 Share 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. Link to comment Share on other sites More sharing options...
Wrigs Posted August 2, 2010 Share 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 Link to comment Share on other sites More sharing options...
Tankman Posted August 2, 2010 Share 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. Link to comment Share on other sites More sharing options...
Tankman Posted August 2, 2010 Share Thanks guys, excellent discussion - do the same dimensions hold for Campy chain rings? Nope, Campy has a BCD of 135mm Link to comment Share on other sites More sharing options...
Tankman Posted August 2, 2010 Share oh and most track bikes have a 144mm BCD Link to comment Share on other sites More sharing options...
Sharkie 2 Posted August 2, 2010 Share 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 Link to comment Share on other sites More sharing options...
Big J-WP Posted August 2, 2010 Share Tankman, seeing that you are the wise one at the moment. Can you have a BCD 110, 53/34 will the front der work? Link to comment Share on other sites More sharing options...
ANDYCAP Posted August 2, 2010 Share 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..... Link to comment Share on other sites More sharing options...
Wrigs Posted August 2, 2010 Share Nope, Campy has a BCD of 135mmSo if Shimano has 110 vs 130 Campy is 135 vs ? Link to comment Share on other sites More sharing options...
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