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Old 01-21-2020, 09:02 PM   #1
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Adding a bike rack when using a dolly? "The physics don't allow it"?

We tow a car on a dolly using an 8" drop hitch. I was thinking we could use a dual receiver drop hitch, use the dropped part for the dolly and the other receiver for the bike rack. We want to carry two 61 lb ebikes.

But the answer I received from eTrailer is:

Unfortunately, there isn't a bike rack that you'll be able to use for electric bikes as well as use a tow dolly for your car. The physics of the bike rack and bikes as well as the vehicle don't allow for it to happen.

I asked them if they can point me at a link or something to explain this limitation but haven't heard back yet. Clearly they would like to sell me the equipment if they could so there must be some truth to it.

What is different about pulling a dolly with a dual receiver drop hitch and pulling a car as a flat tow?

I would think that as long as the tongue weight limit of the adapter and hitch was not exceeded and the maximum towing weight limit was not exceeded there would be no difference but apparently there is.

Would someone please explain it or point me at an article?

Thanks,

Ray
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Old 01-22-2020, 07:16 AM   #2
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They could possably be talking about the clearance between the RV and toad, in a tight turn.

You could load the car on the dolly, and head for an area where you can make a tight turn, stop and check the clearance and where the bikes would need to be placed.

I plan on doing the same this summer and see if I can locate my bike rack in the space between them. I have a hitch adaptor that can be clamped to the dolly tongue, so I can possably place it where it clears.

For now, I use the toads hitch and an adaptor with a 7° up angle, so the bikes are level, with the toad on the dolly.Click image for larger version

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Old 01-22-2020, 08:15 AM   #3
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Have you seen these dollys before. You can get them to carry motorcycles, atvs, golf carts etc.
https://tandem-tow.com/Models.htm
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Old 01-22-2020, 08:33 AM   #4
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I’ll guess, just a guess.
Say you have a hitch with 500# tongue weight rating.
You add the dual drop hitch which is approx 1foot extended derates hitch combination to 250#
You add a very stout bike rack that weighs 50# and load 122# of bike approximately another foot extended so the combination is now rated 125# and you have loaded 172# with just the bike rack.
Add the dolly with brakes (I hope) and you will add some amount of derating to the combination again (due to torque). I don’t know how much due to differences in brake systems but estimate it could be a lot!

Your tongue rating is based on two forces, vertical force and torque, the torque is what possibly makes the combination a no go

I’m not a physicist and don’t play one on tv, didn’t stay at a Holiday Inn last night, so don’t flame me, just guessing
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Old 01-22-2020, 08:34 AM   #5
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Quote:
Originally Posted by winniman View Post
Have you seen these dollys before. You can get them to carry motorcycles, atvs, golf carts etc.
https://tandem-tow.com/Models.htm
No, I had not. That would be ideal if I didn't already have one.

Ray
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Old 01-22-2020, 08:45 AM   #6
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sell the dolly you dont need and buy the dolly you do need(tandem-tow dolly) before your ebikes fall off of your bike rack and kills somebody on the interstate!!
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Old 01-22-2020, 08:48 AM   #7
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I made a modification to one of my hitches so now I can put my bike rack on and still pull either my Ranger or dolly with the surge brakes.

I just welded a short piece of 2x3 1/4 thick wall tubing to the top of the hitch and then a short receiver tube on that.

Happy Glamping.
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Old 01-22-2020, 09:55 AM   #8
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Doesn’t just having to use an 8” drop alter the max tongue weight? Then add the weight of the bike rack plus 120 lbs of e-bikes bouncing around going down the road. I can see where all that plus the dolly could put a lot of stress on the MH hitch. Just my thoughts.

ON edit, I thought you would find this helpful. Take note “they” don’t seem to support the use of dual drop down for ball hitch.

https://www.etrailer.com/Hitch-Adapt.../RM-077-8.html
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Old 01-22-2020, 10:17 AM   #9
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Quote:
Originally Posted by twinboat View Post
They could possably be talking about the clearance between the RV and toad, in a tight turn.

You could load the car on the dolly, and head for an area where you can make a tight turn, stop and check the clearance and where the bikes would need to be placed.

I plan on doing the same this summer and see if I can locate my bike rack in the space between them. I have a hitch adaptor that can be clamped to the dolly tongue, so I can possibly place it where it clears.

For now, I use the toads hitch and an adaptor with a 7° up angle, so the bikes are level, with the toad on the dolly.Attachment 272943
OK, good thoughts. Thinking out loud follows:
  • The RM-077-8 dual hitch adapter adds ten inches horizontally to the hitch, placing the bike rack 10" further back from the RV, which is irrelevant because the dolly is also pushed back 10". So there actually is less chance of the car hitting the motorhome. I may need to replace the safety chains on the dolly, though.

  • When the Thule EasyFold XT 2 rack is set in the hitch, per the videos, it actually is angled up and then out. Please see the attached picture. I do not know how much height that angle adds but a guess would be 4" to 6".

  • The upper dual hitch adapter is a 2" rise (hole to hole) which, along with the bike rack angle, will raise the bike rack relative to the front of the car.

  • Adding up the 8" drop hitch for the dolly, the 2" lift for the top of the dual adapter, and the 6" of angled rise on the bile rack itself, the bike rack bottom should be raised about 16" above the dolly. Please check this math and assumption for me.

  • The car hood is about 36" off the ground or the bottom of the dolly.

  • The car front is about 30" from the dolly coupler.

  • The rear of the Thule EasyFold XT 2 bike rack I'm looking at is 35" from the pin hole in the hitch, or dual receiver adapter in this instance. That means the rear of the bike rack is 35" closer to the front of the car.

Uh oh. If the car front is 30" from the dolly coupler and the Thule rack rear is 33.5" from the adapter edge (subtracting the 1.5" hole setback) I think the bike rack will be right up to the front of the car. Is that correct?

So in any turn the car would strike the bike rack.

The only way that would not happen is if the bottom of the bike rack was several inches above the car hood but it won't be unless my math is way off.

If I'm missing something on this or figured something wrong, please point it out.

Qwap.


Gator8, all of the materials I've read say that adding one adapter is not a problem, as long as you stay within the tongue and total weight limits of the adapter and the hitch itself.

All adapter manufacturers I read have said that if you put an adapter in an adapter you will experience a failure from torque or leverage.

Most adapters do caution that they derate the hitch by 50% but the RoadMaster is one that does not. eTrailer "confirms" that on their web site, for whatever that is worth.

So normally the 5,000 hitch would handle 500 lbs of tongue weight and each adapter could only handle 2,500 lbs and 250 lbs respectively. But the RoadMaster 077-8 says it is 10,000 tow weight rated but only 400 lbs tongue weight.

(sigh)

twinboat, what is this hitch adapter of which you speak? I was thinking if I could somehow clamp a hitch receiver to the 3" dolly frame then I might be able to attach the bike hitch to the dolly so it could not strike the car. (This could be a condition where the bike would strike the motorhome in a tight turn, though.)

Even if I could put a hitch on my car (or another car), I could not use the Thule EasyFold XT 2 because it is not certified for going on the rear of a towed vehicle, trailer, fifth wheel or whatever. This apparently is because a towed vehicle experiences a lot more bounce and movement that attaching the bike rack directly to the tow vehicle itself.

I like that bike rack because it has a ramp for pushing heavy bikes on to and off of the rack.

Ray
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Old 01-22-2020, 11:23 AM   #10
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Why not use a bike rack on the rear of your towed car?

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Old 01-22-2020, 11:50 AM   #11
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Quote:
Why not use a bike rack on the rear of your towed car?
There's no hitch on the car and many bike racks, including the Thule EasyFold XT 2, specifically say they cannot be used on the back of a vehicle being towed whether it is on a trailer, fifth wheel, or whatever.

The issue apparently is that the bouncing and jolting on the back of whatever is being towed are significantly stronger than when attached directly to the tow vehicle itself.

Ray
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Old 01-22-2020, 12:07 PM   #12
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I received a response from RoadMaster as to whether their dual receiver adapter can be used with a dolly. I had read here that someone called them and they said it was OK. eTrailer says it cannot be used with a dolly. The RoadMaster web site and PDFs are silent on using it with a dolly.

But:

Our Hi-lo hitches are not meant for any type of trailer use. These are strictly for flat towing vehicle using tow bars only. Your tow dolly will most likely bend the 077-8 hi-lo hitch. A company like Reese or curt manufacturing might have something that can handle that set up.

Best regards,

Technical Service Dept.
Roadmaster Inc


I asked them if they could point me at an explanation of why towing on a dolly seems to impart much greater forces than flat towing. If I get a response I'll post it.

I am somewhat stunned by that response. A dolly can bend a 10,000 lb rated hitch adapter but bend not the 5,000 hitch itself? Or maybe both would go. And then I could install a bigger hitch just for the margin.

So this may be a total non-starter for us. The smaller foldables that we could barely fit in the back seat of the car and in the trunk really do not meet our intended need and my wife must use a step-through. (sigh)

Ray
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Old 01-22-2020, 01:03 PM   #13
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Quote:
Originally Posted by NXR View Post
There's no hitch on the car and many bike racks, including the Thule EasyFold XT 2, specifically say they cannot be used on the back of a vehicle being towed whether it is on a trailer, fifth wheel, or whatever.

The issue apparently is that the bouncing and jolting on the back of whatever is being towed are significantly stronger than when attached directly to the tow vehicle itself.

Ray
I think you will find the bouncing on the rear of a motorhome is much worse that that on the rear of vehicle like a car or SUV. The auto suspension is much softer on a auto than a motorhome as well as the distance from the pivot point (rear axle) is much shorter on the auto,

I do not buy that assessment.

Ken
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Old 01-22-2020, 01:52 PM   #14
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I could understand the bounce on the rear bumper of a 5th wheel or travel trailer but as mentioned, a car on a dolly will not bounce much at all.
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