% Grade Question

Quoted post said:

Originally posted by Pat Lee
I think this horse is dead now. Next?

Not at all. Let's talk about hills with curves and corners and (yikes!) switchbacks. 🙂

Quoted post said:

Originally posted by tanggoman
Sorry for the stupid question but how do u[sic] do an ArcSin in a calcuator? 😕

You want arctan, not arcsin. The road surface would the the hypotenuse with the rise as the opposite side and run as the adjacent side.

We're moving to Pittsburgh next summer, where one section of road is actually a 37% grade. Rise/Run=.37 --> 20.3 degrees (YIKES!)... I think maybe I'll have to work up to that one!!!

To find the inverse tangent on a calculator that only has sin, cos, and tan, just play a high low game. Start at say 22.5 (45/2) degrees and take the tangent (.41) double or half depending on which side this falls on... once you know one angle that is higher and one that is lower you can just go halfway between and then halfway between whichever two of those three work, and then halfway between whichever two of those three work, etc. Depending on how accurate you need to be, it shouldn't take long at all... 6 tries will get you the nearest degree (45/2 six times is .7)

Of course if your calculator doesn't have the sin/cos/tan functions then your best bet is to find an old (pre electronic gizmo) math book and look at the tables in the back... come to think of it this is probably a lot faster than using a calculator even if it DID have the inverse functions :-). Not to mention less likely to be wrong... I noticed that if I punch in Tan(45) in the calculator on my computer it gives me 1.000000000205103.

You absolutely CANNOT use the 45 degrees * percent slope as someone else suggested. If you graph the tangent function it is NOT a straight line!

For example, the tangent of 22.5 degrees is .41 or 41%
(already you can see that it won't work as 22.5 is half of 45 and its tangent is NOT .5)
.41 * 45 =18.45 degrees not the 22.5 degrees that we started with.

Ummm oops. If I had read further I would have seen that the horse was in fact killed long ago.

All appologies for any damage my beating has caused to its corpse, may it now rot in peace.

Quoted post said:

Originally posted by rollers hills with curves and corners and (yikes!) switchbacks. 🙂

Around here, that's all we have to choose from when riding hills. So, that's why I'd need to use the arcsine calculation. It's too tedious otherwise. In real life, you just open a book and the grades are posted there. When a graded road shows up on one of our rides, it goes into a file in the back of my head as a tough or not so tough climb and that's it. The numbers can be used to compare climbs later.

--Pat.