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Old 12-08-2020, 06:20 PM   #1
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Garmin RV 785 GPS low bridge routing analysis

Recently purchased a Garmin 785 RV GPS unit and wanted to learn more about the bridge height routing algorithm. Used a bridge on River Road near Farmville, VA which is signed as having 11’-5” clearance. We encountered it last year and had to back up.

So I set the RV height parameter to 11’-4” in the Garmin’s RV profile and specified a starting location and destination that straddled the low bridge. The default routing algorithm did not use River Road. It followed a series of more major roads. However, I set a shape point to force it to reroute along River Road and the route was updated to pass beneath the bridge. Given the artificially low RV height I entered, that is correct behavior.

Then I set the RV height parameter in the Garmin to be the correct Greyhawk height of 11’-6” or 1” higher than the bridge. When I set a shape point on River Road, the Garmin algorithm did indeed run the route through the shape point location — but it did so while avoiding the low 11’-5” bridge. Again, that is correct behavior.

I then wondered what the Garmin would do if I set the RV height parameter to be the exact bridge clearance of 11’-5”. When I placed the shape point on River Road, the routing algorithm ran beneath the bridge. So there is apparently no freeboard added in the algorithm. If your RV height is identical to the posted bridge clearance, it assumes you’ll squeak through. Better use a lot of WD-40 if you try that, though.

I think I’ll add 9” to my Greyhawk profile in the Garmin’s settings. I am not comfortable trying to pass beneath a structure less than 9” above my rooftop A/C unit.
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Old 12-08-2020, 07:29 PM   #2
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Very cool, thanks NC for that!
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Old 12-08-2020, 10:19 PM   #3
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My problem with one of their other RV models was avoidance of parkways in NY. Even after programing in the parameters for my truck and RV it still created routes that took my on parkways. I tried to setup manual avoidance but could get it to work.
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Old 12-09-2020, 04:29 PM   #4
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I think adding a few inches to the real height is a great idea. I suspect that, particularly on secondary roads, the height signs aren't changed after new pavement is added to the road. After a couple of times you might lose as much as 4" clearance.
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Old 01-14-2021, 08:50 AM   #5
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when driving a truck at work we would always set the truck GPS with 1 foot margin for safety, meaning our trucks were 12'6" and we would put them at 13'6" which is the minimum for standard bridges and we always seemed to avoid all low bridges and any issues. especially in NY when low bridges seem to pop up where you least expect them
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Old 01-14-2021, 09:08 AM   #6
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I've only been using my Garmin RV 785 for a week, but I am impressed by all of its features. Thanks for testing the Low Bridge feature. I'll add a foot to my trailers height just as a precaution.


I bought the one with the 7" screen that also has the built in Dash Cam, which is a great added feature. Amazing video quality and runs automatically when the vehicle is started. The voice activated features are also handy when driving in heavy traffic.
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Old 01-14-2021, 12:02 PM   #7
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Hope new Garmin is more up to date. Older version tried to send me down a walking path in Virginia and very 9’ high railway bridge. In pre trip planning I throughly check my route and Google Earth anything that looks suspicious.
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Old 05-21-2021, 05:16 PM   #8
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I just switched from a 24 foot 10' 8" motorhome to a 13' 1" 5th wheel. Never had to worry about clearances before, but I guess I'll need something better than Google maps now. Questions:
Is the Garmin 785 significantly better than the 780?
Are the trucker GPSes better or worse than the RV ones?
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Old 05-21-2021, 06:09 PM   #9
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I have the RV 890 and love it so far!
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Old 05-21-2021, 06:15 PM   #10
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I have the RV 890 and love it so far!
I'll second that.
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Old 05-21-2021, 08:25 PM   #11
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. Thanks for the info on the bridge routing. We also just purchased an RV785 and the touch screen functions aren't functioning. Just wondering if anyone else has had that issue? Thanks
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Old 05-21-2021, 08:26 PM   #12
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Quote:
Originally Posted by madsweeney View Post
I just switched from a 24 foot 10' 8" motorhome to a 13' 1" 5th wheel. Never had to worry about clearances before, but I guess I'll need something better than Google maps now. Questions:
Is the Garmin 785 significantly better than the 780?
Are the trucker GPSes better or worse than the RV ones?

I think that the only thing is different between the 785 and the 780 is the 785 have a dashcam.
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Old 06-14-2021, 12:37 PM   #13
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I have the Garmin RV 770 and its useless in NY. No commercial vehicles or RV's or trailers are allowed on parkways. When I got it I tested it in my truck without a camper. So it immediately took me on a forbidden parkway HOWEVER once driving on the parkway it did alert me to a low bridge coming up and I had to get off. Unfortunately it shouldn't have put me there in the first place. So they are taking into account the height of the trailer and bridges but ignoring the fact that you are not allowed on their in the first place.
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Old 06-14-2021, 05:48 PM   #14
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I have the Garmin RV 770 and its useless in NY. No commercial vehicles or RV's or trailers are allowed on parkways. When I got it I tested it in my truck without a camper. So it immediately took me on a forbidden parkway HOWEVER once driving on the parkway it did alert me to a low bridge coming up and I had to get off. Unfortunately it shouldn't have put me there in the first place. So they are taking into account the height of the trailer and bridges but ignoring the fact that you are not allowed on their in the first place.
Reach out to Garmin and report this issue. I noticed a problem and reported it. They got back to me a couple weeks later, acknowledged the issue and said the map would be corrected. It has worked well in the parts of NY that I’ve used it in.
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