Looking for good gearing/grade/power calculator

[ruleof72]

I will be doing a very hilly century in September that has extended sections of 12%+ grades and total climbing of nearly 11,000 feet. I want to be able to decide which gearing I will need in order to stay within my power limits so I don't blow up on those climbs while maintaining a decent RPM.

Does something like this exist that is accurate and easy to use?

 

[daveryanwyoming]

...Does something like this exist that is accurate and easy to use?

Not really. You could use something like : http://www.analyticcycling.com/ForcesPower_Page.html but the big independant variable is speed, will you climb those 12% grades at 2 m/s or 5 m/s? And even if you know that answer it doesn't directly spit out cadence vs. gearing. Yeah you can back it out based on pedal force and rpm data but it's not a plug and chug solution.

I'd go ride some longer hills and pay attention to what it takes to get up them in the saddle without suffering. You've got a couple of months to do a few of these test climbs and figure out what you'll need for your long ride. Personally for sustained grades over 10% I like to have a compact up front (34 teeth) combined with at least a 25 tooth cog in the back. I currently weigh ~70 kg. If I'm doing a really long ride with a lot of climbing I like a 27 tooth cog in the back.

FWIW, I rode a compact with a 12-27 cassette in the Death Ride last summer and it was really comfy even on the steeps at the end of the day. I'm sure the folks riding it more competitively were riding tighter clusters but it was a fun ride with that bailout gear.

But YMMV and it depends in part on your climbing style. Go out and ride some steeper hills and you should find out quickly what you need in terms of gears.

-Dave

 

[ruleof72]

Ok, after posting the original question I found this site (the calculator is at the bottom of the page):

http://www.danenet.org/bcp2006/gearing.html

It appears like it might be what I am looking for. I plugged in some numbers based on my weight (191 me+bike etc.), cadence (60rpm), power (220 watts, 80% of my current FTP), and grade (10%). I hit the calculate button and it came back with:

"You'll need: 31.48 gear inches"
"You'll be moving at: 5.61 mph"

Then there is a spot to enter garing you have. I entered in 27.6 inch wheel (700c), chainring of 34, freewheel of 27 and it calculates gear inches of 34.75

So, based on that, it looks like I'll need a lower gear to stay at 80% of FTP or below on a 10% grade spinning at 60rpm.

Any thoughts on this calculator? Does it seem worthwhile?