Help me understand gearing.

It seems to me that you have a pretty good set up and it all depends on your ability to mash or spin those pedals.
I guees you could go with a 12/27 set up but I still think this a question that only you can answer since you know your ability the best.

jhuskey said:

It seems to me that you have a pretty good set up and it all depends on your ability to mash or spin those pedals.
I guees you could go with a 12/27 set up but I still think this a question that only you can answer since you know your ability the best.

I was fine getting up the mountain with this setup but when the grades hit 18% around mile 5 my cadence really began to suffer. Would a 12/27 require extensive modifications or is it just a matter of changing out the cassette?? Thank you for your response.

I should mention in case someone did not know that Newton's Revenge is a race up Mount Washington at an average grade of 11.9% with extended sections of 18% on gravel..

I am not sure if I am correct but I think all Shimano rear derailleurs have the same cable pull; i.e. if you use the right shifter and cassette you can swap your rear derailleur for a long cage Deore. Then you could run an 11-34 cassette. Fortunately, you do not have a 10 speed setup because the MTB parts do not come in 10 speed, so no cassette.

twelvepercent said:

I was fine getting up the mountain with this setup but when the grades hit 18% around mile 5 my cadence really began to suffer. Would a 12/27 require extensive modifications or is it just a matter of changing out the cassette?? Thank you for your response.

I should mention in case someone did not know that Newton's Revenge is a race up Mount Washington at an average grade of 11.9% with extended sections of 18% on gravel..

You can change it out to a 12/27 cassette with no problem.I use the same set up with a double crank and have numerous 18% + grades but MT Washington is a ***** I hear.

Good to know, thanks. My only concern now is that I lose the 25 for the 24 on the 12-27 which means I'd be pushing a slightly more difficult gear in places where I pushed the 25 before.

twelvepercent said:

Good to know, thanks. My only concern now is that I lose the 25 for the 24 on the 12-27 which means I'd be pushing a slightly more difficult gear in places where I pushed the 25 before.

I think you can probably adjust this with your cadence.

Why not calculate what cadence you WOULD be spinning going from 25 to 27 at the same speed, and see if the difference is enough?

garage sale GT said:

Why not calculate what cadence you WOULD be spinning going from 25 to 27 at the same speed, and see if the difference is enough?

I don't know how to do that.. ?

twelvepercent said:

I don't know how to do that.. ?

You would need to take into account the gradient and your power output also.
I think I had a formula for that somewhere but I bet someone here has it on their desktop.

jhuskey said:

You would need to take into account the gradient and your power output also.
I think I had a formula for that somewhere but I bet someone here has it on their desktop.

You'd need those things to calculate if you had an adequate cadence to maintain a certain speed on a certain gradient.

I am simply suggesting calculating how much a switch from 25 to 27 would affect the cadence at the existing speed you made on the hard parts. To do that, you would simply estimate the cadence you were actually putting out during the difficult parts, divide by 25, and multiply by 27. Or, for the same cadence, the force required would be lower by a factor of 25/27.

Lets say for argument's sake you want to do 5mph on some of the really steep bits, and for the sake of this we'll ignore the power required and just look at the pedal revs in different gears. The rpm's shown are approximate and dependant on the actual diameter of the tire you're using and how worn it is but for a comparisons this'll work. I'm guestimating a 700x23ish tire.

So your 5mph will take.

30x25 = 54rpm
30x27 = 58rpm
30x30 = 64rpm

With most Shimano rear deuraillers you can get a 30 sprocket on there.

Harris Cyclery Century Special 13-30 9-speed Cassette - harriscyclery.net

It's not the lightest cassette but you'll not notice the slight extra weight when on the hills.

With that swap you'll just need a new cassette, if your chain is fairly new and in good condition. It's it's a year or so old and your ride regularly, get it changed too.

If you wanted any lower, you'd need a long cage rear mech - like an XT, XTR or LX (with a barrel adjuster) and a new chain in addition to the new cassette. The shimano mountain bike rear mechs will work with the road bike STI brake lever/shifters, whether you have 8, 9 or 10 speeds.

At 5mph with the lower gears:

30x32 = 69 rpm
30x34 = 73 rpm

incidentally, even a $9.99 nexave would work (but would be heavier)-anything with the same pull ratio in the derailleur.

IIRC, and if my secondhand knowledge was correct, all Shimano rear derailleurs have the same pull ratio.

So you just need to find one with a long cage to clear 34 teeth, and decide how much you want to spend in order for it to be light weight.

swampy1970 said:

Lets say for argument's sake you want to do 5mph on some of the really steep bits, and for the sake of this we'll ignore the power required and just look at the pedal revs in different gears. The rpm's shown are approximate and dependant on the actual diameter of the tire you're using and how worn it is but for a comparisons this'll work. I'm guestimating a 700x23ish tire.

So your 5mph will take.

30x25 = 54rpm
30x27 = 58rpm
30x30 = 64rpm

With most Shimano rear deuraillers you can get a 30 sprocket on there.

Harris Cyclery Century Special 13-30 9-speed Cassette - harriscyclery.net

It's not the lightest cassette but you'll not notice the slight extra weight when on the hills.

With that swap you'll just need a new cassette, if your chain is fairly new and in good condition. It's it's a year or so old and your ride regularly, get it changed too.

If you wanted any lower, you'd need a long cage rear mech - like an XT, XTR or LX (with a barrel adjuster) and a new chain in addition to the new cassette. The shimano mountain bike rear mechs will work with the road bike STI brake lever/shifters, whether you have 8, 9 or 10 speeds.

At 5mph with the lower gears:

30x32 = 69 rpm
30x34 = 73 rpm

This is excellent info, thank you. I think the 13-30 is MORE than sufficient for this event. I'm curious if you know how much it weighs, tho... ?

swampy1970 said:

Lets say for argument's sake you want to do 5mph on some of the really steep bits, and for the sake of this we'll ignore the power required and just look at the pedal revs in different gears. The rpm's shown are approximate and dependant on the actual diameter of the tire you're using and how worn it is but for a comparisons this'll work. I'm guestimating a 700x23ish tire.

So your 5mph will take.

30x25 = 54rpm
30x27 = 58rpm
30x30 = 64rpm

With most Shimano rear deuraillers you can get a 30 sprocket on there.

Harris Cyclery Century Special 13-30 9-speed Cassette - harriscyclery.net

It's not the lightest cassette but you'll not notice the slight extra weight when on the hills.

With that swap you'll just need a new cassette, if your chain is fairly new and in good condition. It's it's a year or so old and your ride regularly, get it changed too.

If you wanted any lower, you'd need a long cage rear mech - like an XT, XTR or LX (with a barrel adjuster) and a new chain in addition to the new cassette. The shimano mountain bike rear mechs will work with the road bike STI brake lever/shifters, whether you have 8, 9 or 10 speeds.

At 5mph with the lower gears:

30x32 = 69 rpm
30x34 = 73 rpm

Just an update: This is exactly what I did. So far so good. Look at that monster on the back wheel!

[IMG]media.dailymile.com989317c265fb53cd242161c783798e19.jpgOpen ↗[/IMG]

twelvepercent said:

Good to know, thanks. My only concern now is that I lose the 25 for the 24 on the 12-27 which means I'd be pushing a slightly more difficult gear in places where I pushed the 25 before.

Just add a 27T cog or 28T or 30T at the end (after your 25T) and remove one of the middle cogs... say... a 14T or 16T. One option to do this is to get a SRAM 9 speed cassette where all the cogs are loose and take one of the larger cogs and add it to the end of yours...

Alright, now here's another question.

I am configuring a new bike but I would like to run a double crankset this time.

If I ran a 50/34 could I still use my new 13-30 cassette on the back?? Or would I need to make some modifications??? Thanks!

twelvepercent said:

Alright, now here's another question.

I am configuring a new bike but I would like to run a double crankset this time.

If I ran a 50/34 could I still use my new 13-30 cassette on the back?? Or would I need to make some modifications??? Thanks!

I don't know your RD set up but I run a 11/30 cassette on a short cage 10 speed Ultegra RD and a 50/34 upfront. I can climb pretty much anything UNLESS I'm doing a century, in which case I still use my triple upfront (second bike).
I've tried a 32T cog on the short cage RD and it works... barely. You have to screw "B screw" all the way in and there is some slight noise from chain rubbing the cog. I've been told that getting a longer B screw will solve the problem OR replacing the RD top pulley (guide pulley) with a 10T pulley will do the trick but I have not tried it.
BTW, when you add the larger cog at the end, make sure the spacing between it and the next cog is exactly the same as the other cogs. Most shimano hubs actually fit and overlap into a small recess on the last cog (al least on 10 speeds) so if you just use the standard spacer, you end up with a narrower cog spacing at very end. You have to add the normal spacer PLUS a 1mm spacer to get it correctly. This MAY NOT be the case on 9 speeds though.

This is a pretty helpful site:

Bicycle Gear Inch & Shifting Pattern Calculator

it lets you input your current setup and look to see what the optimal shifting patterns are.