Good Sam Club Open Roads Forum: Adding Hitch for Bike carrier on rear??
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 > Adding Hitch for Bike carrier on rear??

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4x4ord

Alberta

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Posted: 01/28/21 06:32am Link  |  Quote  |  Print  |  Notify Moderator

I think I would get a carrier for two or three bikes to be carried on the front of your trailer and carry two on the back. Here’s a pic of a simple rear mount carrier:

[image]

If your bumper is too flimsy you might need to cut your bumper off and have a piece of square tubing welded on in its place.


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Sjm9911

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Posted: 01/28/21 06:36am Link  |  Quote  |  Print  |  Notify Moderator

Not a great idea, the bikes will also cause sway on a smaller TT as well as take away fromt the tongue weight. What is your TV? Some use a front hitch on the TV to carry a few bikes or the double hotch bike carrier. Those options need a big TV. Can you put some in the TT? Or get smaller bikes, like fold up. Not really a good way to do this.


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APT

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Posted: 01/28/21 06:55am Link  |  Quote  |  Print  |  Notify Moderator

For me there have been far too many lightweight TT owners use some form of bumper mount camps and report failures and damage to whatever it is they want to carry. Get the Curt Adjustable receiver.


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GrandpaKip

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Posted: 01/28/21 08:46am Link  |  Quote  |  Print  |  Notify Moderator

I added a frame mounted cargo tray to our camper. When 100 pounds was added the tongue weight decreased by only 20 pounds or so. Don’t remember exactly, but was less than 25 pounds. I think that 4 bikes “could” reside there if loaded creatively.
The problem with most bike racks is the bounce from a receiver mount. Someone on this forum had a double receiver built for their trailer mounted to the frame.


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jukes

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Posted: 01/28/21 09:38am Link  |  Quote  |  Print  |  Notify Moderator

Our TV is the 7.3 diesel excursion..
we’ve been putting them in the TT a pain dragging bikes in and out, made our last trip kind of annoying and the next trip we plan to stop at about 5 diff locations so would involve lots of dragging them in and out... fold up bikes won’t work for my family of mountain bikers....
Ideally a toy hauler would be useful! But soon our teens will be gone and we will downsize....
This is one of those simple but not not simple issues lol.

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Posted: 01/28/21 09:40am Link  |  Quote  |  Print  |  Notify Moderator

Sjm9911 wrote:

Not a great idea, the bikes will also cause sway on a smaller TT as well as take away fromt the tongue weight. What is your TV? Some use a front hitch on the TV to carry a few bikes or the double hotch bike carrier. Those options need a big TV. Can you put some in the TT? Or get smaller bikes, like fold up. Not really a good way to do this.

I’ll look into a front hitch perhaps for the diesel excursion we tow with...
Or even a roof rack one but they look awkward,?

valhalla360

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Posted: 01/28/21 10:34am Link  |  Quote  |  Print  |  Notify Moderator

GrandpaKip wrote:

I added a frame mounted cargo tray to our camper. When 100 pounds was added the tongue weight decreased by only 20 pounds or so. Don’t remember exactly, but was less than 25 pounds. I think that 4 bikes “could” reside there if loaded creatively.
The problem with most bike racks is the bounce from a receiver mount. Someone on this forum had a double receiver built for their trailer mounted to the frame.


Not sure what you did but something is off with this. Should be more like 60-80lb off the hitch depending on the exact lengths involved.

Let's run some numbers on the OP's case.

He didn't provide the exact model, but let's say he has the 30U model.
- GVWR 7500
- 13% hitch weight (975lb)
- Based on pictures, the center of the axles sit approximately 60% of the overall length from the hitch. 33ft total length with a-frame.
- Let's assume 5 bikes at 30lb each plus the hitch weighs 200lb total and the center of gravity of the combined mass is 3ft behind the back of the trailer.

The moment arm created around the center of the axles by the bikes/rack:
- Back of trailer is 13.2ft behind the axles, plus an additional for the rack 3 ft (16.2ft total)
- 200lb * 16.2 = 3240 ft-lb applied to the axles.
- Hitch is 19.8ft ahead of the axles.
- 3240/19.8 = 163lb off the hitch.

975lb - 163 lb = 811lb (10.8% hitch weight)

This is around the lower limit recommended but likely will be OK but presumes you are starting at 13% hitch weight. If you start at say 11%, you will drop to 8.8%...that's getting into the range where trailers often become unstable. Minimum hitch weight is usually suggested at 10-12% minimum with 15% desirable.

Now if you have the ability to repack some of the gear inside the trailer to move heavy items toward the front, you can compensate but it would be a good idea to swing by a CAT scale and get the real numbers before bolting on and hoping for the best.

With the CAT numbers, you should be able to take accurate measurements and rerun the same calculations for a more accurate estimate based on your specific trailer.

PS: 5th wheels are more tolerant of weight hung off the back. The wheels tend to sit further back with the goal of 20-25% hitch weight. The result is for every pound on the rear, less weight comes off the hitch plus you have a much higher hitch weight to begin with, so the percentage loss is smaller. But even with 5th wheels, something like a full size motorcycle gets questionable. A few months back, someone was asking about putting lead shot as ballast into the front to compensate for it getting squirrely after adding a large rack with full size motorcycle on the back.


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GrandpaKip

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Posted: 01/29/21 08:19am Link  |  Quote  |  Print  |  Notify Moderator

valhalla360 wrote:

GrandpaKip wrote:

I added a frame mounted cargo tray to our camper. When 100 pounds was added the tongue weight decreased by only 20 pounds or so. Don’t remember exactly, but was less than 25 pounds. I think that 4 bikes “could” reside there if loaded creatively.
The problem with most bike racks is the bounce from a receiver mount. Someone on this forum had a double receiver built for their trailer mounted to the frame.


Not sure what you did but something is off with this. Should be more like 60-80lb off the hitch depending on the exact lengths involved.

Let's run some numbers on the OP's case.

He didn't provide the exact model, but let's say he has the 30U model.
- GVWR 7500
- 13% hitch weight (975lb)
- Based on pictures, the center of the axles sit approximately 60% of the overall length from the hitch. 33ft total length with a-frame.
- Let's assume 5 bikes at 30lb each plus the hitch weighs 200lb total and the center of gravity of the combined mass is 3ft behind the back of the trailer.

The moment arm created around the center of the axles by the bikes/rack:
- Back of trailer is 13.2ft behind the axles, plus an additional for the rack 3 ft (16.2ft total)
- 200lb * 16.2 = 3240 ft-lb applied to the axles.
- Hitch is 19.8ft ahead of the axles.
- 3240/19.8 = 163lb off the hitch.

975lb - 163 lb = 811lb (10.8% hitch weight)

This is around the lower limit recommended but likely will be OK but presumes you are starting at 13% hitch weight. If you start at say 11%, you will drop to 8.8%...that's getting into the range where trailers often become unstable. Minimum hitch weight is usually suggested at 10-12% minimum with 15% desirable.

Now if you have the ability to repack some of the gear inside the trailer to move heavy items toward the front, you can compensate but it would be a good idea to swing by a CAT scale and get the real numbers before bolting on and hoping for the best.

With the CAT numbers, you should be able to take accurate measurements and rerun the same calculations for a more accurate estimate based on your specific trailer.

PS: 5th wheels are more tolerant of weight hung off the back. The wheels tend to sit further back with the goal of 20-25% hitch weight. The result is for every pound on the rear, less weight comes off the hitch plus you have a much higher hitch weight to begin with, so the percentage loss is smaller. But even with 5th wheels, something like a full size motorcycle gets questionable. A few months back, someone was asking about putting lead shot as ballast into the front to compensate for it getting squirrely after adding a large rack with full size motorcycle on the back.

Well, I simply added 100 pounds to the cargo tray while the tongue was on a scale and then noted the difference. Sure, it’s basic physics, but why go to all that bother when really basic math will give you a real world answer?

valhalla360

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Posted: 01/29/21 10:53am Link  |  Quote  |  Print  |  Notify Moderator

GrandpaKip wrote:

Well, I simply added 100 pounds to the cargo tray while the tongue was on a scale and then noted the difference. Sure, it’s basic physics, but why go to all that bother when really basic math will give you a real world answer?


Still say something isn't adding up with your measurements. Not having been there for the measurements, I can only speculate on what you did to get those measurements. As you say, it's basic physics and your measurements don't match up with the physics.

If I'm doing it for myself, I can run the calcs in 2 min. The writeup was longer so some else could follow it and replicate with actual numbers.

blaczero

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Posted: 01/29/21 03:41pm Link  |  Quote  |  Print  |  Notify Moderator

Bottom line, don't do it. I had a 5 bike Thule rack on my 37' TT hitch and the bike rack itself broke.

The distance from the last axle to the hitch is greater than most bike racks are rated for, the bouncing is too much torque on the rack. Forget the bumper/hitch/mount itself, the rack will break.

Either get a rack on the front of your truck or top of the truck. Or this for a couple bikes: https://www.amazon.com/Swagman-80503-The-Straddler/dp/B07DVZML5X

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