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Old 02-20-2017, 11:41 AM   #1
Rich and Kat
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Virginia near , Washington, D.C.
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Ground Clearance: driveways, crowns, dips, angles, lions, tigers and bears

Hello all. I don't even know how to formulate this question so I hope you understand what I'm asking. We're considering building a new home. The home builder we're considering has a great reputation, but is not a custom builder so I don't have too much flexibility. The 1.7 acre lot that we like backs up to many acres of common space that can't be developed ... would be a nice home site.

This said, there's a gentle descending grade (enough for a walk-out basement). Given the driveway will slope down to the house, I'm concerned about the potential for high-siding the hitch coming out of the drive way, and potentially hitting the rear bumper on the surface of the driveway. Given it's completely undeveloped land, I have nothing to look at to determine whether or not I'll have an issue. I'd prefer to state my requirements to the builder so he can determine the possibility of accommodating my need before we sign a contract. Does anyone know if there's any literature published? Or calculations to determine what I need to spec in the contract to preclude there being a problem? Thanks so much!

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Old 02-20-2017, 12:52 PM   #2
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You can measure the wheel base, rear TV axle to ball, ball to coach front axle, and coach front/rear axle to low points and their elevation on the coach when level to model your rig and get a good idea of what transitions will work. Remember the pitch of the TV will minimize or maximize the clearance as it transitions a grade change. A good architect should be able to help you if the geometry is challenging.

Good luck with your analysis. I look forward to seeing the input you get. Pat

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Old 02-20-2017, 01:02 PM   #3
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What you do not want to happen is to create a valley, 2 adjacent slops without sufficient distant between them for the TV to run level. Not a likely hood if the ground has a continuous slop to it now.

You ca determine the max change you can traverse by measuring, on the ground, from where the rear wheel touches the ground to the low point at the rear of the trailer. Then measure the height to the low point. That will allow you to calculate the max angle of change that the trailer will clear.

You might stop in to the local township engineer and ask for standard they use in road construction.

You will be surprised at how great a change you can traverse. With my 34 fter. I have only dragged while loading onto several Canadian ferries and one church driveway in Md.
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Old 02-21-2017, 01:26 PM   #4
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Originally Posted by AIRHEDS View Post
Does anyone know if there's any literature published? Or calculations to determine what I need to spec in the contract to preclude there being a problem? Thanks so much!
There is a genuine possibility of a problem and you're doing well to be aware of it. I'm not aware of any specifications or formulas. It does depend on the tow vehicle geometry, hitch height, and the amount that the WD bars hang below the hitch.

Dips in the road, particularly low areas where the driveway meets the street gutter, are usually a more serious problem than peaks.
To learn to see below the surface, you must adjust your altitude
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Old 02-21-2017, 01:47 PM   #5
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Drive Drop off from Road


great question and good for planning. Wish I had measured my Dad's driveway drop off the county road, but I've got same truck, trailer, and hitch as you and his driveway was at least three feet lower than road top within 10 - 15 yards. Dad watched carefully as I drove in and again when I drove out seven weeks later, and no issues. I had planned to drop the tension on the ProPride jacks if I needed to raise the trailer tail, but no need.

Someday we plan the same property layout as you described. We hope to include the front circle driveway for visitors and the additional rear circle loop to park the trailer under the second floor deck, looking out over the wooded vista for the occasional AirBnB visitor to enjoy. Definitely need the circle drive part , horse barn, tool shed, etc., and of course, mountain views with lake access.
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Old 02-22-2017, 11:57 AM   #6
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One thing to be aware of is the use of surmountable curbs in some communities. Ours has caused me no end of issues both with my tow vehicle as well as my Parkit360 dolly.
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Old 02-22-2017, 12:53 PM   #7
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Howie has the right idea. With your TV and trailer hooked up on level ground, measure the longitudinal distance from the trailer's rear axle to the lowest point at the rear of the trailer. Also measure the height above ground of that low point. Then on a piece of graph paper you will make a scale drawing. Mark a point toward one side of the paper at the intersection of two lines. Then measure horizontally across the paper a scaled distance equal to your trailer's axle-to-low point measurement. Mark a 2nd point. Draw a line connecting point 1 and point 2. Measure up from the 2nd point a scaled distance equal to the trailer's low point-to-ground measurement. Mark a third point. Draw a sloping line connecting point 1 and point 3. Using a protractor, measure the angle between the horizontal line and the sloping line. That angle is the maximum up slope of your new driveway to the street, assuming the street itself is perfectly flat.
However, streets are not usually so flat. Most newer streets are going to have a crown in the middle to facilitate drainage. You will need to determine what the slope of that crown is where your new driveway will be. At that location, hold a yardstick on end and using a laser level hold it against the yardstick and aim at a small target you will place on top of crown in the middle of the street. I suggest looking both ways for cars on the street when placing the know, so they don't mess you up. Note the measurement on the yardstick where the laser level has to be raised in order for its beam to hit the target. Also measure the distance from the curb out to the target. Now you can make another scale drawing in a similar way as you did the previous drawing.
Now subtract the angle of the 2nd drawing from the angle of the first drawing. This is now the maximum slope of your new driveway. To be conservative, I'd subtract another degree or two just to be on the safe side.
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Old 02-22-2017, 03:28 PM   #8
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I just had a house built on 1 acre, with an RV garage. I really sweated the ground clearance, and I first tried USAtraveller's approach. Based on that method, I was right on the ragged edge of clearance. But I realized that was overly conservative. I have about 6 feet of elevation change over approximately 40 feet. My calculus skills abandoned me about three days after I completed that course in 1976, but I did conclude that the slope should be steepest in the middle, and taper out on each end. Over a long driveway, the middle section could exceed a 20% grade.

When our foundation was complete, and we had a gravel driveway, I made a test run and parked in the future RV garage. I was very relieved to find that I never came close to scraping either the bumper or the bars on our weight distribution hitch.

If I still had an issue, I would have tried with the WD bars removed - this would provide more clearance at both the bumper and the hitch. I had no choice but to place the RV garage door so near the street (we had to work around a septic system and such when laying out the lot.). But if you can design an 80' driveway with a 12 foot drop, I have to believe you will be fine.

My last ditch option would have been to install 3" riser blocks between the trailer and the axles, but I was happy that was unnecessary.
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Old 02-22-2017, 03:43 PM   #9
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Beware of steep slopes when backing up! The Airstream frames will snag on the higher surface. If you do that in a turn the frame end will not only stop any further movement. You will no longer be able back up and it will cause the corresponding quarter panel to be damaged when the frame pushes up. It may not damage it much to look at it, but the whole areas sealing can get compromised causing future leaks to ruin that corner's floor. Don't ask how I know. I wondered why my rub rail was bulging?
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Old 02-22-2017, 04:28 PM   #10
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One more to minimize or avoid altogether... short radius turn AND slope. Straight slope and gradual transitions okay, as mentioned previously. Take your rig out to an empty parking lot and make, then measure your tightest radius (and the added length to straighten out).Then add at least a 1/3 more radius - not really radius, rather the perpendicular distance between the inside trailer tire track and the outside TV front tire track at mid turn. Wet your tires on a dry parking lot or use a grassy field to see their tracks. Tight turns and climb or descents are bad news. Add slick surface and it becomes a disaster recipe. Good to plan now.
In the aviation world, it's referred to as observing 'The 6Ps' ('Prior Planning Prevents Piss Poor Performance'). Good luck.
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Old 02-23-2017, 08:08 AM   #11
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Rich Another solution is to construct a driveway slope that is not one slope from the garage to the street. Your driveway can vary in slope to meet both the grade at the garage and the street. Driveways are usually constructed after the structure. You can even construct the driveway subgrade test it and then add the wearing surface, concrete or asphalt. Many driveways are designed this way. For your contract get a price from your contractor on a per square yard price based on his estimate the number of square yards. Then adjust the final payment based on the measured yardage after the job is finished.
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Old 02-27-2017, 07:19 PM   #12
Rich and Kat
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I just wanted to get back to you all to say thank you for your time responding and the advice you provided on my request for assistance. As it turns out, we put the brakes on. The home plan/design we wanted to put on the lot I previously described didn't work for us. The house we wanted was too big for the lot given the the primary and secondary drain fields behind the house wouldn't allow it to be pushed back any further. So we're moving on.

You've all given me some really good things to think about when we find the next property... I especially like getting pricing/sq. yard and testing the sub-grade before it's poured or paved, but I've learned something from each of your posts - things to work through as contingencies and things to discuss with the site engineers ... Thanks again!

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