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How do you calculate % grade using feet of elevation?(18 posts)

How do you calculate % grade using feet of elevation?Fausto
Sep 18, 2001 7:37 AM
Is is possible to calculate % grade on a hill if you know feet of elevation and distance? If so, is this an EZ computation?

Any info appreciated.

Thanks
It's simply rise over run ...Humma Hah
Sep 18, 2001 7:43 AM
... both dimensions in the same units. For example, if you climb 528 feet in a mile (5280 ft), the grade is 0.1, or 10%.
Curses! I got beat by a measley minute! (nm)RhodyRider
Sep 18, 2001 7:45 AM
It's simply rise over run ...Atombomber
Sep 18, 2001 10:45 AM
If you and your bike travel one mile of road and climb 528 feet, the actual grade is steeper than 10%. The horizonal distance is 5253.5 feet. Actual grade is 10.05%, which in the grand scheme is not that much different, but does if on eis nit picky.
If you will notice ...Humma Hah
Sep 18, 2001 11:37 AM
... I skirted that issue by stipulating "in a mile", rather than saying "travel one mile of road".

In the spirit of nit-pickyness, I do have a spreadsheet for calculating grade in which I do the actual trig to get the exact grade, when called for. That becomes a silly exercise even with my more precise odometer, which indicates distance to the nearest 0.01 mile. My altimeter computer displays tenths of a mile and 5 ft increments of altitude, so would be hard pressed to tell the difference.

My most frequent grade calculations are from computer topo-map data. In that case, you DO get horizontal distance, not road distance. Again, other sources of error are far worse (for example, the topo data never take into account that most roads are graded).
Rise over run.RhodyRider
Sep 18, 2001 7:44 AM
If you know the elevation gain over a fixed distance, just divide the two values. Example: subject road gains 1500 feet over 4 miles. Convert the miles into feet (@ 5280 ft per mile, 4 miles = 21120 ft) and divide the elevation gain by the distance. The answer to this example is approx 7.1% grade. That is an average, of course; certain pitches will be more or less, but this will give you a rough idea anyway. Other posters who are more technical engineering-types will no doubt give you more complicated alternatives to my layman's method. Have fun with it.
Rise over run.Empirion75
Sep 18, 2001 8:49 AM
I think the distance needs to be "how the crow flys" if you want to be accurate.
Or how the bike rides...RhodyRider
Sep 18, 2001 9:49 AM
...might also be appropriate. If I follow your drift, the assumption is that there will be substantial grade differences between a road that gains 1500 feet over 4 miles of switchbacks as opposed to a road that goes essentially in a straight line for 4 miles and gains 1500 feet. Maybe not? We need an engineer to chime in.
Its all rather moot on a geared bike, anyway ...Humma Hah
Sep 18, 2001 11:45 AM
... at least, until you run out of gears or are moving so slowly that you fall over, or the bike would rather wheelie than make forward progress. Basically, you shift gears to change the grade so it is more to your liking.

Once you have gears, on any kind of sane grade, the issues are: 1) how high is the climb (i.e. how much energy will you have to expend, and 2) how fast can you climb it (how much power can you produce). If you can sustain a 120 fpm climb indefinitely in the middle of a long ride, you're a TDF candidate.

Now, with us singlespeeders, its a different story. For us, there's a critical grade, depending on gearing and our strength, where climbing becomes more like weightlifting, and there are only so many reps we can do. On singlespeeds and fixies, knowing grade is critical.
Great, now we pick on the Gear Heads. nmMB1
Sep 18, 2001 11:51 AM
Pick on 'em?Humma Hah
Sep 18, 2001 11:55 AM
... Heck, get me about 70 miles into the typical century, where they typically have The Hill, get me halfway up the sucker, and I'm thinking of buying a gearie myself, and offering to trade bikes with anyone passing.
So, what percent is straight down? :-) nmDog
Sep 18, 2001 8:59 AM
I know you know, but for those who do not know...Cima Coppi
Sep 18, 2001 9:26 AM
A vertical line cannot have a percent representation of its slope since the "run" = 0. Anyone who understands simple division in math knows that you cannot divide a number by 0. Thus there is no percentage.

CC
you mean it's not 100%? ;-) nmDog
Sep 18, 2001 10:25 AM
InfintiyAtombomber
Sep 18, 2001 10:33 AM
How many times will zero go into any number?
Does anyone know the gradients of the climbs...Cima Coppi
Sep 18, 2001 9:33 AM
on the S.F. Grand Prix circuit? I know the climbs were short, but from the pictures, the riders appeared to have quite a struggle accending them.

Thanks

CC
Does anyone know the gradients of the climbs...moschika
Sep 18, 2001 10:46 AM
i think the fillmore climb was 18% and the taylor street climb was 16%. and each climb was i think 2-3 blocks long at it's steepest.
driving up fillmore is tough for a car. can't really imagine how hard it would be on a bike with a double crank.
There's no map, you're a techno-buff who's gotta know...like2bike
Sep 18, 2001 12:26 PM
...and can't tell from the burn that it's getting steep: You can get an inclinometer at
Nope, I don't have one and haven't tried them. I understand that the altimeters in cyclocomputers vary as much with the weather as they do with the altitude.