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how low gear I need for 15% grade?(18 posts)

how low gear I need for 15% grade?cyclopathic
Mar 21, 2001 8:14 AM
I dont think I can cut it on doubles with 12-23 cass
I use a 53-11Retro
Mar 21, 2001 8:25 AM
But only going down...
Seriously, it varies with your fitness and climbing ability. That's triple territory for me, but I have friends who'd whip right up it. Go ride the thing and see.
Re:go ridecyclopathic
Mar 21, 2001 8:49 AM
I wish, but its in PA (300km brevet). 15% 1mi climb. I have nothing like this around, I mean road. Would be a piece of cake on mountain bike. I hate to walk in look cleats :-(
12-25 or 13-26look271
Mar 21, 2001 3:23 PM
Living in PA, I use the 12-25; however, there are days when I wish I had the 26! Where's this ride at? Is it the "Nightmare-ride?". Very close to me.
12-25 cassette+double OK for me on <20%(nm)Biking Viking
Mar 21, 2001 8:35 AM
re: how low gear I need for 15% grade?ScottV
Mar 21, 2001 9:41 AM
Really depends on factors such as

- Your ability
- Lenght of the climb
- Weight of bike
- Time of the year

I could do 15% with my 13-26 if it was a reasonable lenght climb.
re: how low gear I need for 15% grade?RobO
Mar 21, 2001 11:11 AM
I just got back from a training camp in NC, our cabin was placed on the top of a 200 meter 15% grade climb. I was able to that, with extreme pain, in a 41-21.
use a 12-27 to be safeDog
Mar 21, 2001 10:00 AM
I assume you want to be able do the climb without mashing and getting all anaerobic (the goal for most endurance events). Of course, your weight and climbing ability makes a huge difference.

Also, it matters alot how long the hill is, as well as where it occurs in the ride. 15% for 1/2 mile at mile 20 -- I'd just muscle it up and forget about lower gears. 15% for 2 miles at mile 175, I'd plan for some low gears.

Bottom line, use whatever gear you think you might need to get up the hill if you are totally bonked. If you've never truly bonked, it's hard to imagine what that's like, but put it this way, riding flat ground at 15 mph can be extraordinarily difficult and painful in a full bonk, even for someone who can timetrial at 25 mph. Riding up a 15% grade in a bonk can be impossible, unless you can sit and spin at 75 rpm or more.

totally agreeburnan
Mar 21, 2001 12:16 PM
Why not have a 12-27 on? If you can turn a higher gear then then its just a shift away. If you can't turn a 39/23 or 21 then you're screwed.

some calculationscyclopathic
Mar 21, 2001 1:47 PM
to maintain cadence 70RPM in 39/23 on 15% grade I will need to climb 125'/min. I don't know about you guys but this is what TDF can do, I can't do it and stay aerobic. It only requires 475 watts for my skin 140lbs arse.

This is what I am thinking: I am gonna borrow 11-34 cass and RD from my mountain bike, and if I never use it, so what? there's no better kill then overkill, are you with me?
How long is the hill?Dog
Mar 21, 2001 2:06 PM
If the hill is only 200 yards, it won't matter even if you do go anaerobic. That's not long enough to matter to anyone except someone who is in horrible shape.

If it's half a mile or longer, now it starts to matter.

Nonetheless, based upon my experience, unless this is a really long hill, a 27 cog should do just fine. There is an event here called Climb to Kaiser (C2K). This is over 150 miles, and goes from sea level to 9,300 feet and back. There is 12,000 feet of climbing in 65 miles. At around the 60 mile mark, there is a 20% climb for 2 whole miles! This is a monster son-of-a-b... climb, and it goes up to 7,000 feet. Many people climb this just fine in a 27 cog, but some do use a triple or the mountain bike gears. But the point is, this is about as bad as it gets, and a 39/27 worked for me. Incidentally, though, for training I have done the upper 100 miles of this course, including the big hill, with an 11-21 cassette, but it was brutal.

Bottom line, though, you're basically right. Better to have too broad a range than too narrow. Any way you can ride the hill first?

Nevermind - overlooked your other postDog
Mar 21, 2001 2:16 PM
1 mile - unknown territory - double century - take the low gears.

How long was your ride on C2K?Jon Muzilla
Mar 21, 2001 6:46 PM

How long was your ride on C2K? Also, what type of training did you use?

chain, tooDog
Mar 21, 2001 2:17 PM
Likely will need a longer chain, too. I'd just buy another for this.

some more calculationsDaveG
Mar 21, 2001 2:57 PM
Using a power formula I pulled off the internet somewhere, I'd need to maintain .69 horsepower to climb a 15% grade at 8 mph at my 180 lbs. Thats a cadence of 70rpm in a 39/27. That's why I have a triple on my bike.

This is based on:
P = (Vg*W*(K1+G) + K2*(Va)^3)/375)

P (horsepower)
Vg (ground speed mph)
W (rider+bike lbs)
K1 (mechanical loss) = 0.0053
G (Grade)
K2 (aero drag) = 0.0083
Va (air speed mph)
might be 27t maxburnan
Mar 21, 2001 4:28 PM
I read or heard some where that a Shimano standard cage length road derailleur has a max cog size of 27t. That is if you have a "standard" set up.
So MachoPing pong
Mar 22, 2001 4:47 AM
I think you have to consider your riding style as well. If you prefer to climb seated, keeping a 90 rpm cadence you will need some low gears.

I think that a lot of talk about gears gets a bit macho. People like to ride the gears of the pros. For example, in the alps most of the TDF riders will have a 39 25 available. A lot of people insist on limiting themselves to a double as if the couple of teeth a 27 gives is all that separates them from the pros. I have seen (and overtaken) many such riders in the alps. They are limited to riding in very ponderous styles, some even change up when the slope eases as if to convince themselves that this is how they like to ride.
True Ping Pong, most riders dont come close to the strength ofJimbob
Mar 22, 2001 7:58 AM
the pros yet they use gears that are just slightly lower. The strength/gearing ratio from pros to rec riders/racers is way out of wack if you ask me. People like to say they can push certain gears even if they have to struggle and ride in a less efficient manner.