abshih

Hello,

I am fairly new to road cycling and I recently got a 2013 Cannondale Super Six Tiagra and I am getting the drivetrain changed out for an Ultegra.

When purchasing the Ultegra parts, it lets me pick the Chainring sizing? How do I pick the size?

" Choose from (170mm, 172.5mm and 175mm crank arms with 34/50 chainrings, 170, 172.5 or 175 with 39/53 chain rings or 170, 172.5 or 175 with 36/52 chain rings)"

And I know my crank arm is 172.5mm based on my height and inseam, but now I need to choose between 34/50, 39/53, 36/52.

Thanks for your help

Leisesturm

There is no formula. You pick 'gearing', you do not pick chainrings. 50/34 is nearly meaningless unless we also know the range of the cassette that you plan to use with it. In theory using smaller chainriings up front means using smaller cogs in the rear. The resulting gears are the same ones as if you used bigger rings up front and bigger cogs in the rear. The bigger cogs and chainrings apparently are somewhat more efficient and longer wearing, even if they are somewhat heavier. What are the gears on the bike you presently ride?

H

abshih

Hello Leisesturm,

Thank you for your response. I am not really sure what I use. I think I use the larger cog. Is there a general chainring size? I have been fine with whatever size that has been on my Cannondale CAAD8 54cm.

Thanks,
Alan

Leisesturm

These are some specs I pulled off a review of CAAD8, Cannondale's own site is not working for some reason. In 2013 at least, CAAD8's came like this:
Frame:
CAAD8, Optimized 6061 Alloy, SAVE
Fork:
Cannondale Ultra, carbon blades, 1-1/8 inch
Gears:
Shimano 2300 front and rear mech and shifters and compact crank with 50x34 tooth chainrings, SunRace 12-25, 8-speed cassette, 16 gears

The gears are the interesting bit. Ideally you don't use a gear, you use the entire range available. You asked about a "standard" gearing. For decades, a 52/42 chainring double with a 14-28 5sp freewheel was the standard default gearing of every bicycle sold in America. Even in 2014 a big ring of 52 (sometimes 53) teeth is "standard". The 42 tooth has become a 39 as front dérailleurs have gotten better. The 5sp became 6,7,8...10,11,??. For all practical purposes, the 52(3)/39 x 12-25/7 9sp is about as close to a standard gearing as anything in the 21st Century. But your bike is adopting a 'newer' standard. The 50/34 "compact double" aims to save weight and provide 'crisper' shifting over "standard" gearing. How did that work for you? Lots of people cruise in the big ring close to the middle of the rear cluster and others (me) cruise in the smaller ring close to the middle of the cluster. I'm guessing you're young. Enjoy it.

H

abshih

Hello Leisesturm,

Yea, I enjoyed it. I don't really have much to compare to, but I guess the 50x34 is good for getting me up some hills. I live in virginia and it can be quite hilly. Are you basically saying that 50/34 is becoming the newer standard? I was thinking of going 36/52, as a compromise.

Thanks,
Alan

Leisesturm

I meant enjoy your youth. And you are still missing my point about the gearing: 50/34 doesn't get you up hills any easier than 52/39, its what's in back that counts. The teeth in the rear are far more important than the teeth up front. What cassette do you intend to use in back? 52/36 might not shift properly with a standard front derrailleur. If you have a 12-25 now and the hills bother you, you could go to a 12-27. If you bump the big ring up to a 52 you might need to raise the 12 to a 13 or you might find that the 52x12 doesn't get enough use to be worth the weight. Look at some bikes online and see what gears they come with. Copy one. You can always change later.


H

abshih

I think I get your point. I am just going to copy the Ultegra builds on the 2014 Cannondales. It seems like they use 11-25 with 50/34.

I appreciate your help!

stephtu

11-25 may not be enough; you may well need 11-28 or 11-32. It depends on your weight, fitness level, and the steepness & length of the hills you plan to ride. Newer cyclist I would always recommend going as low gearing as possible (11-32, need the mid-cage rear derailleur). Better to have a gear back there even if you hardly ever need it, then to find yourself being forced to walk up a hill, or forced to stand & pedal more than you want. Especially with the 11 cogs on the new Ultegra, the jumps between cogs even on the wider cassette are not that bad; going smaller just gives you a few more one tooth jumps higher up. So what if you have to pedal at 95 rpm or 85 rpm instead of your preferred 90? Not a huge deal IMO. You can go smaller later if you find you really never need to use the big cog and those slightly bigger jumps between the smaller cogs really bother you. There's almost always a steeper hill somewhere where you'll be glad to have the bigger cog, especially towards the end of a long ride.

The back counts too, but given the same rear cluster, a 34 is going to be a large step lower than a 39. And there are limits to how big you can go on the back without changing out to a MTB derailleur. If one is a sub 155 pound lightweight racer, 39 may well be small enough to get up practically anything. Bigger people in less good shape better go for the compact 34, unless they live somewhere totally flat IMO. Even pros are often using compacts these days in mountain stages.

fietsbob

count teeth the number of teeth is what you use in math to get how big the combined number makes your drive ratio

say front is 50t, and rear is 20t ,then 1 crank rotation, turns the rear wheel 2.5 times..