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Old 07-15-2018, 02:51 AM   #1
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Any tail swing math wizards out there?

Hey folks, I have a Class A 31' Monaco Monarch on the Ford Chassis, with a 190" wheelbase.

I'm curious what is the actual distance of the backswing of the overhang of the back of the rig when making 90 degree turns.

Any math wizards better at me than trigonometry out there who could draw this up or have a rough calculation already?

Just wondering how much open clearance I need on the lane to the side of the rig when making 90 degree turns to avoid swiping other cars with the back end. It's a shorter Class A but it is still long.

I appreciate any feedback!

Thanks,
Jake
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Old 07-15-2018, 04:08 AM   #2
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Quote:
Originally Posted by ShantiJake View Post
Hey folks, I have a Class A 31' Monaco Monarch on the Ford Chassis, with a 190" wheelbase.

I'm curious what is the actual distance of the backswing of the overhang of the back of the rig when making 90 degree turns.

Any math wizards better at me than trigonometry out there who could draw this up or have a rough calculation already?

Just wondering how much open clearance I need on the lane to the side of the rig when making 90 degree turns to avoid swiping other cars with the back end. It's a shorter Class A but it is still long.

I appreciate any feedback!

Thanks,
Jake

Measure the distance from the center of the rear axel to the farthest point on the rear of the MH. Or what ever the rear overhang is. That will be the maximum.

Since the MH is moving forward when turning the rear will be moving away from any objects at its side.

It dosent matter how long or short the rig is it is the overhang. The big worry is "cheating" where the back axel makes a tighter turn that the front. This allows the MH to remove telephone poles, fireplugs and people from the corner.

Now go back to bed and get some rest you are posting too early in the morning.
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Old 07-15-2018, 05:27 AM   #3
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I believe I understand your question which is to prevent damage to other vehicles in the lane to your left while making a sharp right turn.

My suggestion would be to practice right turns while checking the amount of rear bumper swing you are concerned about. To do that, I would choose a road with a stripe on it at an intersection and have someone follow me to watch for the swing. I would line up just to the inside of the stripe and make the turn. My follower can watch from his/her vehicle for the anticipated swing. Maybe even photograph it. Do this 3 or 4 times to get comfortable with turns. If you have a large parking lot nearby, that would work as well. This should answer your basic question of how does a tight right turn affect the rear bumper swing.

Good luck on your quest.
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Old 07-15-2018, 06:10 AM   #4
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I inadvertently “measured” my own tail swing by hitting a large plastic trash can in my driveway. With a bit of pre-collision setup, I think you could get a pretty close measurement.
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Old 07-15-2018, 06:21 AM   #5
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I will attempt to answer this. Basically, there are two variables that affect the swing distance. One being the angle of the swing, and the other is the overhang distance. Use the table below for an overhang distance of 10 feet, and the swing angle of 5 to 45 degrees:

Degrees of swing, Multiplier, Swing Dist.
5 degrees, 0.087, 0.87 Ft
10, 0.176, 1.76
15, 0.268, 2.68
20, 0.364, 3.64
25, 0.466, 4.66
30, 0.577, 5.77
35, 0.700, 7.00
40, 0.839, 8.39
45, 1.000, 10.00

For another than 10-foot overhang distance, just multiply it by the multiplier corresponding to the swing angle. The multiplier is the Tangent of the angle. So, you simply multiply the swing distance by the Tangent of the swing angle.

Sorry, the columns do not lineup real well, hopefully it will make sense!

I hope this helps!
Happy trails.
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Old 07-15-2018, 06:41 AM   #6
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Quote:
Originally Posted by txcpl View Post
I believe I understand your question which is to prevent damage to other vehicles in the lane to your left while making a sharp right turn.

My suggestion would be to practice right turns while checking the amount of rear bumper swing you are concerned about. To do that, I would choose a road with a stripe on it at an intersection and have someone follow me to watch for the swing. I would line up just to the inside of the stripe and make the turn. My follower can watch from his/her vehicle for the anticipated swing. Maybe even photograph it. Do this 3 or 4 times to get comfortable with turns. If you have a large parking lot nearby, that would work as well. This should answer your basic question of how does a tight right turn affect the rear bumper swing.

Good luck on your quest.
Good post

We once met friends on a big empty parking lot, and while waiting I parked with the left side of the rig aligned with a long painted line. The I turned right as tight as I could while my wife watched to demonstrate to how how far left the rear turns. We didn't actually measure it, but I wanted her to understand what happens so she wouldn't take out a gas pump or something.
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Old 07-15-2018, 06:57 AM   #7
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My steering is 50 degrees, newer ones are around 60 degree capability.

I don't know what the backswing is but I know I can stick the Toad in the next lane of traffic and wake up those driving over there!

Being farm raised there were lots of opportunities to learn the hard way as an 11 year old and beyond driving all that long stuff. You farm boys know what I mean If you can reach the pedals you can drive it.
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Old 07-15-2018, 07:04 AM   #8
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Quote:
Originally Posted by ShantiJake View Post
Hey folks, I have a Class A 31' Monaco Monarch on the Ford Chassis, with a 190" wheelbase.

I'm curious what is the actual distance of the backswing of the overhang of the back of the rig when making 90 degree turns.

Any math wizards better at me than trigonometry out there who could draw this up or have a rough calculation already?

Just wondering how much open clearance I need on the lane to the side of the rig when making 90 degree turns to avoid swiping other cars with the back end. It's a shorter Class A but it is still long.

I appreciate any feedback!

Thanks,
Jake
We've used the formula...for every 3 ft of overhang...it will swing 1 ft out on a turn

If the overhang from the center of the rear wheel is 12 ft,then the coach will swing 4 ft out ....Now if the the overhang is 13 ft....you need 5 ft of clearance....C
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Old 07-15-2018, 08:34 AM   #9
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The backswing is determined by the amount of overhang and the turning radius and the wheel base.
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Old 07-15-2018, 08:37 AM   #10
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They told me there would be no math involved after I purchased the motorhome. I just use my mirrors.
I have a 31' Holiday Rambler, probably very similar to yours. The only situations I have been in where I really have to watch the tail very closely is in tight campgrounds.
I do like the fact that when towing my trailer, the tail swing makes the off-tracking of the trailer less severe, than in my pickup, by swinging the tongue of the trailer away from the turn slightly when first starting the turn.
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Old 07-15-2018, 02:04 PM   #11
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These responses are awesome! Thank you so much everybody!

I feel confident now in what I'm dealing with.
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Old 07-15-2018, 10:05 PM   #12
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Why not do the obvious? Go to an empty parking lot on a weekend, align the two left wheels with a line, then turn hard right. Have someone walk beside the rear bumper with a stick. Use that to mark the most extreme left point during the turn. Then you will know. Not all coaches have the same steering cut angle. 3' is certainly not uncommon.
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Old 07-15-2018, 10:18 PM   #13
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Here is a nice video about rear overhang turns.
https://youtu.be/y5MSGqfh8z0
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Old 07-16-2018, 06:55 PM   #14
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Tail Swing 101

IggyTech, great vid but I believe the OP will get better use from the following:

https://youtu.be/0jrMaziuamg
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