Wow, of all topics to get me to de-lurk, it's this one! I've always naively assumed that % grade was just a fraction of 90 degrees -- eg, a 45 degree slope would be a 50% grade.
If it is based on the sine of the angle (the ratio of vertical rise to distance along the road) as Patrick says, then a 45 degree slope would be about at 71% grade, and a 30 degree slope would be a 50% grade. But according to this Wikipedia page http://en.wikipedia.org/wiki/Grade_(slope)<http://en.m.wikipedia.org/wiki/Grade_(slope)> it's actually normally based on tangent of the angle (ie, ratio of vertical rise to flat horizontal distance). In this system, a 45% slope is actually a 100% grade and a sheer cliff is infinite grade. Weird. For small angles, like you find on actual roads, the tangent- and sine- based approaches are almost the same (because flat horizontal distance and distance along the road are almost the same). But they're still both pretty significantly different from my naive assumption of what grade meant. A 10-percent grade, for example, means a roughly 5.7-degree angle using either sin- or tan-based systems, and not a 9% angle (10% of 90) like I would have thought. -Eli Daniel Snowed in in Somerville, MA and not riding my Sam today On Jan 4, 2014, at 1:25 PM, Deacon Patrick <[email protected]> wrote: I'll let someone smarter than me delve into the details, but if you take the degree of a slope and get it's sin you have the percent of the grade. Since I'm (and most of us) more familiar with the % rather than the degree, I translate it. Yes, Theodolite is the app I used for the photo. It's very handy, and I feel a bit like Luke Skywalker scanning the horizon in Star Wars whenever I use it. With abandon, Patrick On Saturday, January 4, 2014 11:12:48 AM UTC-7, Patrick Moore wrote: > > Looks like fun (except for the cold). > > What is the difference between slope and grade? > > > On Sat, Jan 4, 2014 at 10:36 AM, Deacon Patrick <[email protected]<javascript:> > > wrote: > >> Slopes in pictures so rarely show how steep it actually is. Here is a >> study, using Theodolite to show the actual degree of the slope and a photo >> without it. >> >> Theodolite (reveals it’s a 7˚ slope, or 12% grade): >> http://www.flickr.com/photos/32311885@N07/11755929135/ >> >> Plain photo (looks like 4-6% grade): >> http://www.flickr.com/photos/32311885@N07/11756178903/in/photostream/ >> >> Oh, and the ride was wondrous! I did 7 miles in heavy snowfall and 15˚F >> and had a blast! >> >> With abandon, >> Patrick >> >> *www.MindYourHeadCoop.org <http://www.MindYourHeadCoop.org>* >> *www.OurHolyConception.org <http://www.OurHolyConception.org>* >> >> -- >> You received this message because you are subscribed to the Google Groups >> "RBW Owners Bunch" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected] <javascript:>. >> To post to this group, send email to >> [email protected]<javascript:> >> . >> Visit this group at http://groups.google.com/group/rbw-owners-bunch. >> For more options, visit https://groups.google.com/groups/opt_out. >> > > > > -- > Burque (NM) > > Resumes that get interviews: > http://www.resumespecialties.com/ > > -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/groups/opt_out. -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/rbw-owners-bunch. For more options, visit https://groups.google.com/groups/opt_out.
