Weight Calculations

At most you are going to get some guesses on this one. To mathematically figure it out you would need exact length from the coupler to the center pivot point of the axles and from the pivot point of the axles to where the bike will be hanging on the rear. You will also need the weight of whatever apparatus will be used to hold the bike.
I would also question the frame strength of the camper to have that weight bouncing around back there.

Was the trailer built for an additional 300+ pounds at the rear? Tongue weight decrease isn’t the only consideration. How much weight will the rack add to the 300 pounds?

schlep1967 wrote:
I would also question the frame strength of the camper to have that weight bouncing around back there.

Strongly concur. He’ll need some significant frame/bumper reinforcement. Best to haul the motorcycle in the truck bed, if possible.
There are many tales of bumper to frame weld breaks destroying a 3 to 4 bicycle rack load.

I throw some ballpark numbers around. Update them based on your specifics and you will get a fairly good approximation.

Let's say total current length is 25ft and the center of the axles is 15ft behind the hitch. The center of gravity of the bike and rack will sit 13ft behind the center of the axles. The rack will weigh 200lb.

Assuming the starting hitch weight is a healthy 15% and loaded for travel it weighs in at around 6500lb (assuming 4500 is the empty weight) results in a hitch weight of 975lb to start.

You are adding 500lb (bike and rack) should take about 433lb off the hitch leaving a hitch weight of 541lb which is around 7.7% hitch weight. That's way below the 12-15% recommended.

PS: This ignores the question if if the frame can even handle the weight. If it takes a lot of beefing up, it could easily result in the rack being 300-400lb. You also have to consider if the axles are spec'd to handle the load. In the original situation, if the weight = 6500lb with a 975lb hitch weight, the axles only have to carry 5525lb. If they put a pair 3000lb axles on that's fine. But with the bike on the back, the axles are now expected to carry 6658lb out of the now 7000lb loaded trailer. That would mean overloaded axles.

Assuming he is towing with a capable pickup, a better option would be to put the bike into the truck bed. Obviously, he would need an extra 300lb of payload but it would only require some straps/blocks to hold it in place and the trailer itself would never be compromised.

Excellent analysis.

Plus the added moment of inertia added to the yaw or "sway" axis.

Weight added to the ass end of a RV trailer is always A Bad Thing because they are already built like a teeter totter / weather vane with their little wheels halfway up the frame.

Back of a TT??? NOPE...tell son to forget that idea! Best look at other options.

Jerry

MFL wrote:
Back of a TT??? NOPE...tell son to forget that idea! Best look at other options.

Jerry

I agree.

I've loaded several hundred GN/pintle hitch flatdeck and stock trailers and was always surprised how small the percentage was of adding a load on the azz end of the trailer and changes hitch weight.
First off the center of the axles doesn't work like a teeter totter #1 because one end sits on the trucks hitch. #2 can be distance behind the last axle spring hanger and #3 is the distance from the hitch to the first axle spring hanger. Without seeing the trailer I wouldn't guess a weight.

Loading a 21000 lb 38' GN tri axle stock trailer with young stuff....cows...and big mature bulls is a guessing game. I know adding the 2200 lb bull in the last stall didn't change the weight on the ball by a quarter of a inch = approx 200+ lbs.

Adding 300 lbs on the rear bumper of a small TT IMO can make a ill handling combo.

JIMNLIN wrote:
I've loaded several hundred GN/pintle hitch flatdeck and stock trailers and was always surprised how small the percentage was of adding a load on the azz end of the trailer and changes hitch weight.
First off the center of the axles doesn't work like a teeter totter #1 because one end sits on the trucks hitch. #2 can be distance behind the last axle spring hanger and #3 is the distance from the hitch to the first axle spring hanger. Without seeing the trailer I wouldn't guess a weight.

Loading a 21000 lb 38' GN tri axle stock trailer with young stuff....cows...and big mature bulls is a guessing game. I know adding the 2200 lb bull in the last stall didn't change the weight on the ball by a quarter of a inch = approx 200+ lbs.

Adding 300 lbs on the rear bumper of a small TT IMO can make a ill handling combo.

Assuming you keep the trailer reasonably close to level, the weights do transfer like a teeter totter:

#1 The teeter totter is purposely out of balance with the front end longer than the back end. This would be like putting a 10ft arm on one side and a 5ft arm on the other end...to keep the teeter totter level, you would need a lifting force (ie: hitch weight) under the rider on the long end.
#2 & #3 Unless The trailer is wildly out of level, this won't have an impact as the springs will give pretty closely approximating a central pivot point.

Gooseneck & 5th Wheel trailers have a different geometry from bumper pulls as they are shooting for 20-50% of the weight on the hitch (semis are typically around 50%). This means the trailer wheels are set much further back typically. As a result, the moment created by a weight put way at the back has far less impact on the pin weight.
- Bumper pulls travel trailers tend to have the wheels centered 55-60% of the length back from the hitch. So weight placed a few feet behind the rear bumper will tend to remove 80-100% of that weight from the hitch.
- 5th Wheels tend to be 65-75% back from the hitch. This will result in a similar weight removing 30-60% of the weight from the hitch. Add in that the hitch weight is much higher to begin with and you can absorb more weight without significant impact on the handling. On a lot of commercial GN trailers, the trailer axles may be 80-90% back and it may only remove 5-20% off the hitch (hence your 2000lb bull example)