chainrings

[mickle]

At 20mph 80% of your energy is being used to overcome wind resistance. At the kind of speed you claim to be descending, a change of gearing will have no discernable effect. Forget about changing your ratios and simply adopt an aero position.

 

[fossyant]

A 53 x 13 is good for 40 mph - you don't need to pedal to get to that.

I have a 53 x 39 front to a 8 speed 13 - 21 cassette on both road bikes. 39 x 21 will get me up anything, the 53 x 13 down anything.

 

[bonj2]

Hmmm, thanks for all the thoughtful replies...

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

yes, that's my thinking - but 53x11 is still 11% higher than 52x12.

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.

that's over 50mph! that must have been down some long, straight, steep road!

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.

Why what's the difference?

A 53 x 13 is good for 40 mph - you don't need to pedal to get to that.

what you mean just accelerating under gravity rather than pedalling?
I suppose you would go 40mph if it was a hill that was steep AND long, but they're rare compared to hills that are not so steep, but long - or steep and short. On the former, you're going to have to pedal to overcome wind resistance well before you get to 40mph, but on a steep hill, it's often short enough for you to have to slow down again not long after you've reached it, either for a bend, or an uphill section (or in the case of my ride yesterday, both )
... if that makes sense?

 

[starseven]

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.

Why what's the difference?

Im not much of a weight weenie but the sram are about 100g lighter, they shift very nicely and perhaps most important are very very shiny, considering there about the same price as Shimano thats enough for me. you could also get a sram chain at the same time which are also nice and bling and come with split link to ease removal.

 

[Membrane]

that's over 50mph! that must have been down some long, straight, steep road!

There are some nice gradients where I ride (Wicklow mountains, Ireland). Not really long, but speed builds up quickly. The most fun descends are the twisty ones. On yesterday's ride I crossed a small bridge which is immediatly followed by a sweeping bend. I didn't look at the speedo, but with the wind in my back it must have been around 80km/h. At least one wheel came off the ground after having gone over the bridge, which made it fun to then make the turn. I'm not much of a climber, so I try to get revenge on the way down

 

[HJ]

Have you tried consulting Ken Kifer's article on Cycling Cadence and Bicycle Gearing you might find something useful there.

 

[simoncc]

I'd like to know what the advantage of replaceable chainrings is when the chainrings cost more than a new chainset.

 

[Chuffy]

I'd like to know what the advantage of replaceable chainrings is when the chainrings cost more than a new chainset.

You're talking about a very cheap chainset there Simon. Decent chainrings are what, £25/£30 ish? You'd be hard pushed to find a decent chainset for that surely.

Hills are for freewheeling down. Customising your gearing just to get a tiny bit extra on the downhills is daft frankly. Buy some cheap aerobars, they'll scrape more speed out than an extra tooth on your chainring.
I bet all the knobs on your stereo go up to 11....

 

[itisaboutthebike]

Listen - if you're saying that you can comfartably get 52x12 round at 100 rpm on the flat(?) then you're in the wrong job.........you need to be riding for a Pro Tour team !

A 52 big ring is plenty big enough, especially with a 12 top sprocket - save your money.

 

[HJ]

Listen - if you're saying that you can comfartably

If you are cycling comfartably that should make you go fast enough....

 

[skwerl]

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...

changing the bottom end to 28 won't help. you shouldn't use the 28t on the big ring. It'll knacker the chain.
You're right though. Dropping the 12t for an 11t will be the same as going up to 56

 

[bonj2]

Listen - if you're saying that you can comfartably get 52x12 round at 100 rpm on the flat(?) then you're in the wrong job.........you need to be riding for a Pro Tour team !

Someone's already said that, and the response is that no I certainly can't do it on the flat, we're talking about down a hill.

 

[bonj2]

changing the bottom end to 28 won't help. you shouldn't use the 28t on the big ring. It'll knacker the chain.

I only use sprockets 5, 6, 7 and 8 on the big ring. So there'd never be a time when I'd be using the big ring with the 28.

 

[bonj2]

I think i might just get a cassette with an 11 tooth sprocket when it needs replacing, but in the meantime just heed the notion that 30mph's fast enough anyway, and just freewheel a bit more.

edit: is there any standard way of working out (or a lookup table published anywhere) that tells you what the number of teeth on all the intermediate sprockets of, say, a 12-25, or 11-28 cassette are?

 

[skwerl]

I think i might just get a cassette with an 11 tooth sprocket when it needs replacing, but in the meantime just heed the notion that 30mph's fast enough anyway, and just freewheel a bit more.

edit: is there any standard way of working out (or a lookup table published anywhere) that tells you what the number of teeth on all the intermediate sprockets of, say, a 12-25, or 11-28 cassette are?

look on the Shimano website. It lists the sprocket combinations for different cassettes