figuring grade steepness

[ndurbin]

I got into a discussion with a guy today about grade stepness. Either I am way off in how grades are figured or he's nuts. He was saying his truck could pull a 30% grade w/o loosing more than 5 mph pulling his trailer (I'd guess around 20,000 lbs when fully loaded). I know he's exceeding legal weight limits so lets not get into that can of worms.



So how do you figure grade steepness?



TIA

Nathan

 

[Thomas]

It's the slope you should have learned in your algebra class - Rise divided by Run. It's usually expressed as a percent.



Break your trip into vertical and horizontal components. If you gain 60 feet in elevation while moving horizontally 1000 feet, the slope is 60/1000 or . 06 - change to a percent and it's a 6% grade. Note that you actually travel farther than 1000 feet. You're unlikely to encounter any grades greater than 6% or 7% on our interstate system.

 

[JohnCooper]

I believe that if you travel 100 feet and climb or descend 30 feet that would be 30% grade (that is a really steep grade).

 

[SS]

Both John and Thomas are correct. For reference, Eisenhower Pass in Colorado is somewhere near a 6% grade. Of course he only loses 5mph on a 30% grade - 5mph at the bottom and 0mph at the top. There is no such grade on public roads to drive on, and any grade that steep (on a driveway for example) is likely very, VERY short. :-{}

 

[Thomas]

Fargo Street, a public road in Los Angeles, boasts a 32% grade - only a few blocks long.



Fargo Street Hill Climb.

 

[EarlKann]

It's the slope you should have learned in your algebra class - Rise divided by Run. It's usually expressed as a percent.



Break your trip into vertical and horizontal components. If you gain 60 feet in elevation while moving horizontally 1000 feet, the slope is 60/1000 or . 06 - change to a percent and it's a 6% grade.

I work as an engineering technician and this is the method we use. We try to keep public roads below 9% but will go as steep as 12% for short distances. An empty truck with no trailer is going to have a hard time going up a 30% grade, story might be believable at 3%, but that's not much.

 

[ndurbin]

I never paid attention in algebra class.



So if 60 feet in 1000 feet is a 6% grade. A 30% grade would be 300 feet every 1000 feet. Damn thats a steep grade. I think my assumption he's nuts is right on.





Thanks for filling me in.

Nathan

 

[GFritsch]

coming through !!!!

I never paid attention in algebra class.





Nathan

Me neither, but I can tell you for a fact that I would rather try going up a 30% grade with a 20k trailer than coming down.

:--) :--) :--)

 

[DPelletier]

Yes, you calculate the grade by rise over run, but I doubt you're buddy is running up a 30% grade. All the grades on our highways are marked for the truckers and a steep hill on the #97C, near here is 8%. My father works for a large roadbuilding company and he's indicated to me that the Ministry of Highways in B. C. has a mandate for a maximum 6% grade on any highway and a special variance is needed to design beyond 6%.



Dave

 

[DPelletier]

Wow, I got interrupted in the middle of posting my last reply and 5 people beat me to the punch.

Bottom line, your buddy is sniffin glue. There is no such grade on any highway, anywhere.



Dave

 

[klenger]

30% grade is serious jeep'n country, 4-low in 1st gear.

 

[SWendell]

Sonora Pass in California has some sections with 20+ percent grades and these were steep enough so that you couldnt see over your hood to the road.

 

[Jumbo Jet]

Try this for % grades -

#ad

 

[RCook]

Living in Utah, we tow all over western US and Canada. On the two-lane roads, there are a fair number of places in both countries with grades of 10 or 11%, and a few with 14 or 15%, but that's the max I recall seeing.



Taking even the 19-foot TT down one of those can be exciting if the brakes are not all up to snuff. We sure avoid those monster slopes towing the 12K lb boat. With the boat anything 5-6% or more can be a challenge to go down if it's long enough at that slope - gotta get slow and geared down before we start down.



Going up, however, the truck is amazing. Pulls the boat up a very long 6% grade at 50mph in fourth gear. Will do 8% easily in third. Don't think I'll tackle 30% any time soon.

 

[willyslover]

26% to be exact

 

[Ramtough]

I got into a discussion with a guy today about grade stepness. Either I am way off in how grades are figured or he's nuts. He was saying his truck could pull a 30% grade w/o loosing more than 5 mph pulling his trailer (I'd guess around 20,000 lbs when fully loaded). I know he's exceeding legal weight limits so lets not get into that can of worms.



So how do you figure grade steepness?



TIA

Nathan

:--) You can hardly walk on a 30% grade! That is steeper than the banking at Daytona or Talladega which are between 24% & 26%. I have tried backpacking on 30% grades and it is hand over hand climbing. I'd like to see this truck, can't be stock.

 

[ndurbin]

Well I live smack dab in the middle of chevy country. Do I need to say much more?

 

[Thomas]

You can hardly walk on a 30% grade! That is steeper than the banking at Daytona or Talladega which are between 24% & 26%...

I think you're mixing up angles measured in degrees and grades expressed as percents. The thirty-one degree banking of Daytona International Speedway translates to a more than 60% grade, while the thirty-three degree banking of Talladega Superspeedway is just under a 65% grade. If you will check the link I posted near the top of this thread you will see people walking and bicycling on a more than 30% grade.

 

[Ramtough]

You are exactly right Thomas - thank you for clarifiing this for me. How do you do the conversion from degrees of angle to degrees of grade?

 

[Thomas]

The short answer: express the tangent of the angle as a percent.



The tangent of 4 degrees is a bit more than . 0699 or 6. 99%. A road that forms a 4 degree angle with the horizontal has a grade of about 7%. Since percent means "per hundred", if one travels on a road with a 7% grade, their elevation will increase or decrease 7 feet "per hundred" feet of horizontal movement. Their actual distance traveled on the road during this 7 foot change in elevation would be slightly more than 100 feet.



A road (trail?) that forms a 45 degree angle with the horizontal has a grade of 100%.