chainrings

[bonj2]

my big chainring on my roadbike is 52t, and i have got a 12-25 cassette on the back.
I went for a ride yesterday and got the distinct impression my big ring isn't big enough. There were some stretches where I could easily have increased my power output, but my cadence was already high (at a rough guess, probalby about 100) and when i'm going fast downhill i don't feel quite as safe spinning my tits off like yenrod's avatar than pedalling at a slower cadence. So I was thinking of getting a 56t.
My questions are;
What does "A" type, "B" type, "E" type mean? And why is, say this one described as a "10sp" chainring - will it work with an 8sp cassette (and thus chain) - or is it 10sp because it will take UP TO 10sp chains but is also ok for 8sp and 9sp?
And how do I know what 'type' letter I need? It's just a 5-bolt fastening, so what's the difference between the types.

And what are people's opinions on how much difference it will make - has anyone else made this switch and what are your opinions, I don't want it to make too much difference...

 

[bonj2]

or alternatively, can you get an 11-23 8sp cassette?
i suppose 11/12 would make as much difference as 52/56

edit: oh you can get an 11-28... might try that...

 

[zimzum42]

u need to know the BCD of your chainset too......

 

[bonj2]

yeah... is the BCD what the "A" type, "B" type, etc. refers to?

 

[zimzum42]

Not sure about that.....

 

[zimzum42]

BCD is the diameter measurement of the diameter of the chainring bolts, or something like that.


Does Sheldon Brown not tell you?

 

[barq]

Yep. BCD = Bolt Circle Diameter.

 

[Smokin Joe]

Bonj,

if you can spin 52 x 12 at 100rpm and feel you are under-geared you should be writing to a few pro teams about a lucrative contract. Either that or your rough guess at your cadance is very rough.

 

[bonj2]

Bonj,

if you can spin 52 x 12 at 100rpm and feel you are under-geared you should be writing to a few pro teams about a lucrative contract. Either that or your rough guess at your cadance is very rough.

I would be trying to get a lucrative contract if i could do that on the flat, cleverdick, but where i've noticed the need for higher gearing is not on the flat, this is down a fairly steep hill... but the thing is there are quite a lot of fairly steep hills round where i live. The reason most people don't require it is either because they're happy trundling down at 25/30mph, rather than pushing it up to 35/40mph, or they don't live in such a hilly part of the world, OR they're happy wtih a ludicrous 3-figure cadence.
My estimate is just that it feels far too spinny.

edit: by my quick calculations, 100rpm by 52x12 on 700mm wheels is 60kph, or about 32/33 mph, not that hard!

 

[bonj2]

BCD is the diameter measurement of the diameter of the chainring bolts, or something like that.


Does Sheldon Brown not tell you?

i know what bcd is, but am unsure as to whether somebody has invented a lettering system to represent it, or whether the letters refer to something else.

 

[zimzum42]

Learn to spin, become like Lance.........

 

[SimonGalgut]

The letters, in the case of shimano, refer to the matching of the two rings - tooth profile and pick-up rivets are aligned to work best in matched sets. Try to match your new chainring to the existing inner, but it won't actually make that much difference to you.

BTW, 53x11 is a 'normal' combination for top riders even going downhill - I think you should change your cassette abd leave the chainrings alone.

 

[zimzum42]

Buy a moped.....

 

[Membrane]

The reason most people don't require it is either because they're happy trundling down at 25/30mph, rather than pushing it up to 35/40mph, or they don't live in such a hilly part of the world, OR they're happy wtih a ludicrous 3-figure cadence.

Most people stop pedalling when it becomes uncomfortable. This doesn't mean that they are trundling down at slow speeds. With my MTB style gearing I can only get up to 45km/h under pedal power, yet after my ride today the max speed logged by the computer was 84km/h.

 

[starseven]

Bonj

I replaced my shimano sora steel chainrings with some stronglight aluminuim ones, they were bought from ebay for under a fiver each including postage.
I think most shimano road chainrings are 130 bcd, theres loads on the net about how to measure it anyway.
The shimano rings than came off had pins and shapes presumably to ease gear change, the new ones are entirely flat, makes no diference though the stronglight change just as well if not better.
Another opttion though could be a sram 11/23 8 speed cassette this will give you a higher gear and the sram cassettes are readily availible I prefer them to the shimano equivilant.