Calculating Grades

[bcheever]

Hi, I have a total newb question. I spent about 30 minutes surfing the forums without any luck so I’m posting in the hope of getting some advice.

Is there a general rule of thumb or formula to calculate if a grade is too steep to tow my trailer up (and down)?

And any suggestions where I can find a highway’s grade and plan my safest route before I set out?

Here’s some specifics for us: Picking up a 22FB Caravel in February (5000 lb GVWR), towing w/ Audi Q7 with a tow package (7700 lb towing capacity). We will probably upgrade the TV at some point, but love the Audi and want to try it out for a season, avoiding mountain passes (we drove the spectacular Northern Cascades Highway over the weekend without a trailer and have seen Airstreams on that route, which seemed crazy).

I’ve been surfing these forums daily for the last few months and appreciate how generous everyone is with advice and guidance. Many thanks!

[mojo]

Get a copy of https://www.mountaindirectory.com/ which lists all of the mountain passes. There are western and eastern directories. Your engine and trans temps will let you know the rest of the story.

[GetawA-S]

Excellent advice from mojo. However, the Mountain Directory won’t cover every road, given the number of off highway routes out there.
It really is a matter of planning your driving as you go. Read the terrain ahead. If you are in the right gear at the start of a descent and use the brakes judiciously, you’ll be fine almost anywhere. If you miscalculate, there are usually places to pull over and cool your brakes.
It’s a skill you will develop. You won’t find many posts here about how “I lost my brakes and nearly died...”
There are so many hauling type vehicles out there more challenged than your rig, that the road crews post grade warning signs at almost every stretch that is cause for concern. Keep an eye out for those.
As far as calculating grade, the math doesn’t seem that productive to me. Your vehicle may have an “off road” display; if not, you can turn on the level app on your smartphone and set it on a flat surface next to the driver’s seat. Either way, I expect you’ll find the exercise more entertaining than useful pretty quickly, and then only if you are a “measurements junkie”.
Chill! It will be fine! Enjoy your trailer!.

[GetawA-S]

bcheever,
I did not mean to downplay your concerns. You obviously have a healthy degree of caution.
In fact, your post reminded me of the most exciting unexpected “pass’ i ever encountered while towing. At the time it was not in the mountain directory - the Doherty slide in SE Oregon. (See Blizzard Gap, Milepost 57 on Oregon Highway 140 when you get your directory) It is an absolutely steady 8% grade for 3 miles along a cliff face. No guardrails. We were pulling a moderately sized SOB up it with a 1 ton van (brand new transmission) and barely made it. But we did! Hopefully the signage is better now.
You can look it up on the “dangerousroads” website, for entertainment.
Happy travels!

[Lumatic]

Originally Posted by mojo

Get a copy of https://www.mountaindirectory.com/ which lists all of the mountain passes. There are western and eastern directories. Your engine and trans temps will let you know the rest of the story.

Don't forget the temperature of your brakes. I have a hand held temperature meter. Just point and pull the trigger. You can also carefully check the hub with your hand and your nose. If you smell asbestos you are too hot and may have glazed your brakes. Use your gears to control your speed.

[Lumatic]

Ever wonder what a particular grade means? I did so I looked it up. Take 5% grade for example. It is not exactly the angle in degrees but it is related. It is the difference in feet from level over a distance of 100 feet. So a 5% grade climbs or drops 5 feet in 100 feet of road. So if you didn't, l now you know.

[sirtate]

Also, remember highschool physics.

Energy is equal to the square of the velocity of the mass remains constant...

So, slowing from 70mph to 50mph puts as much heat (energy) into your brakes as *STOPPING* from 50mph...
(4900-2500=2400)

If you let your speed get to 70 before you snub your speed down to 50, you could overheat the brakes twice as fast as slowing from 50 to 30....

[BayouBiker]

All great advice about how to know how the combination is doing. But in this case it ia academic. The Q7 will easily handle anything out there and will own that trailer. It is a great combination. Drivetrain is great, brakes great. Get a brake controller, a nice gentle WD and sway hitch as insurance and it will be a pleasure to drive.

If you doubt me, there are some online horsepower calculators, and many other simulators, happy to show you how they work. All will show the Q7 is more than up to the task. Have a great time camping.

[CruizinDux]

Brian offers good advice. You should be fine, but also not be in a hurry. From OR, our Highlander/FC20/Equalizer hitch combo has been XC three times and with 53 k miles to the USA 4 corners nic Ak. Our rigs have the same weight and the Highlander has proven more than capable. You'll be more than fine. However my mountain rule is to go down in the same gear as the uphill.

You have great breaks on the Audi, but don't ride them...brake in short intervals and letm' cool in between.

Happy trails

[bcheever]

Really appreciate everyone's suggestions on this thead. Exactly what I was looking for!