Cracks in the Aft SubFrame

[gbrmksmith]

While getting bike ready for addition of trailer hitch, I notice cracks in the aft frame supporting the top bag. I believe this is a common problem. I'll TIG weld these up and lighten the load on the top bag. Fortunately, I've purchased a CM-1000 motorcycle trailer, so I am adding a trailer hitch. I may end up not using the top bag for longer trips. The cardboard and blue painters tape in the top photos are the start of hitch fabrication.

 

[gbrmksmith]

Here are some photos of trailer hitch fabrication. Still need to disassemble, fully weld and paint, but gives a rough idea of the structure.

 

[gbrmksmith]

Getting the vertical supports to clearing the side bags and rear tire has been the most time consuming part.

 

[Whooshka]

Is that support along the inside of the muffler going to interfere with the pumpkin when it travels up and down with the suspension?

 

[Kelvin]

That is some nice fab work there

 

[Ignacio]

That's the subframe, not the frame. Tweaked your title as admin.

That said, it's happened to a bunch of us including me on a Gen 1. Remove it, weld it, fix whatever you did to overstress it, maybe add a gusset here in there.

....Or, we'll see how your McGyver design works. Looks stout certainly.

 

[torch]

While getting bike ready for addition of trailer hitch, I notice cracks in the aft frame supporting the top bag.

Hard to tell from the profile pic, but is that an aftermarket case on an adapter plate to the OEM rack?

Givi makes replacement racks for their top boxes that eliminate the stress on that subframe. Worth the extra $$$, IMHO. I've never had a frame crack issue with hundreds of thousands of miles on the Gen1, and tens of thousands on the Gen2.

 

[gbrmksmith]

Is that support along the inside of the muffler going to interfere with the pumpkin when it travels up and down with the suspension?

No, the angle of the photos don't show the clearance.

 

[gbrmksmith]

Hard to tell from the profile pic, but is that an aftermarket case on an adapter plate to the OEM rack?

Givi makes replacement racks for their top boxes that eliminate the stress on that subframe. Worth the extra $$$, IMHO. I've never had a frame crack issue with hundreds of thousands of miles on the Gen1, and tens of thousands on the Gen2.

Yeah, didn't know about those until recently. That GIVI design is clever and certainly solves the issue by increasing the bending stiffness of the tail.

 

[Mihalis fjr]

Did you overloaded the top box?What caused the crack on the subframe?

 

[Fontanaman]

I really hope pulling a trailer with the FJR works out for you better than it did for me. I bought a Bushtec trailer and hitch. No matter how I loaded the trailer when riding solo the trailer pushed the bike around. I remember riding on a downhill slope off Rainy Pass in Washington where it was raining, on a chip seal surface. Just rolling off the throttle was a pucker moment. I had a few of those types of experiences. If my wife joined me it might have helped keeping the rear tire planted but camping isn't her thing.

I sold the trailer and hitch as a significant loss.

Best wishes.

 

[Oldjeep]

I really hope pulling a trailer with the FJR works out for you better than it did for me. I bought a Bushtec trailer and hitch. No matter how I loaded the trailer when riding solo the trailer pushed the bike around. I remember riding on a downhill slope off Rainy Pass in Washington where it was raining, on a chip seal surface. Just rolling off the throttle was a pucker moment. I had a few of those types of experiences. If my wife joined me it might have helped keeping the rear tire planted but camping isn't her thing.

I sold the trailer and hitch as a significant loss.

Best wishes.

Sounds like ball on bike was too high and/or not enough tongue weight. Same thing happens on a truck if your trailer tongue is uphill or the trailer weight is not biased towards tow vehicle.

 

[RossKean]

Sounds like ball on bike was too high and/or not enough tongue weight. Same thing happens on a truck if your trailer tongue is uphill or the trailer weight is not biased towards tow vehicle.

Consequence of which is insufficient tongue weight. Same if the trailer has too much cargo weight aft of the wheels. Sometimes a nice heavy cooler on a platform in front of the trailer box is the answer.
Edit: The upward tilt is especially bad when braking. The weight pushes forward and reduces the weight on the bike's rear wheel even further by "lifting" at the hitch.

 

[Fontanaman]

This was the setup using the Bushtec hitch with a cooler and all cargo loaded forward.

 

[Oldjeep]

This was the setup using the Bushtec hitch with a cooler and all cargo loaded forward.

Hard to say for sure, but doesn't look good - looks tipped back- meaning that the flat part of tongue looks uphill. The physics on the single wheel trailer I built are a little different, but the main thing when building it was keeping the weight axis centered on the hitch and the weight biased forward. Stable to 100mph loaded, which is as fast as I have gone with it.

 

[escapefjrtist]

Yeah, didn't know about those until recently. That GIVI design is clever and certainly solves the issue by increasing the bending stiffness of the tail.

Probably too late now, but Yamaha also makes a heavy duty replacement rack for their OE 50L trunk. Nice rack, larger than stock and solves the trunk support issue.

~G

 

[harper]

Nice rack,

George! And the day before mother's day. This is a family forum.

 

[gbrmksmith]

Did you overloaded the top box?What caused the crack on the subframe?

At least a couple of times, I've taken short trips with lots of weight in the top box. Generally, on the longer road trips, it's just clothes and laptop.

 

[gbrmksmith]

Here's the "finished" hitch. Short test ride with all suspension on soft and not interferences. Tested with bike on side stand and weighting the back (and bouncing), no issues.

Using a 1 7/8" ball for now, since need to ride to pickup the trailer and it currently has a ball coupler. I'll switch to Heim coupler once I get it home.

 

[gbrmksmith]

Wiring under the seat is complete, just need to split loom and tidy up the wires running down to the coupler.