FJR Unsuitable for Passenger with Top Box Fitted?

[wfooshee]

On my bike the grb bars have separated from the piece that goes under the seat on both sides. It has me concerned.

I would stop whatever you're doing and pull some bodywork off the bike and have a really good look at the rear bulkhead. If the grab handles have popped, something else is already moving, and as stated before, the grab handles are loaded in tension by any weight on the rear rack, and without that tension, there is no reinforcement for the rear bulkhead. (Unless you're in the habit of lifting the bike by the grab handles, which would be a Bad Thing....)

 

[Auburn]

On my bike the grb bars have separated from the piece that goes under the seat on both sides. It has me concerned.

I would stop whatever you're doing and pull some bodywork off the bike and have a really good look at the rear bulkhead. If the grab handles have popped, something else is already moving, and as stated before, the grab handles are loaded in tension by any weight on the rear rack, and without that tension, there is no reinforcement for the rear bulkhead. (Unless you're in the habit of lifting the bike by the grab handles, which would be a Bad Thing....)

Already did with this winter's maintenance and upkeep. No damage to subframe found. That is when I saw the breaks in the grab bars to the piece under the seat. . Switching to Givi so it has steel bars that are welded and not the POS composite that the grab handles are.

 

[Enn]

I assume that you have one of these mounts now?

You could use the Givi frame under this, but it will not be simple. You'd have to remove the big plastic Givi trunk plate and then make or buy a flat adapter plate that would mount on the Givi frame and the HB mount would fasten to. That would have the advantage of being able to adjust forward and backward position of the HB mount and trunk position to get the best backrest position for your passengers.

Yes, I have the mount like on that pic. Many thanks for advice, I just have no clue where to get the flat adapter from

 

[Fred W]

What you would want is something like this guy did to mount a pelican case, only different.

Get the same flat aluminum plate like this:

But instead of mounting the plate to the three standoffs supported by the weak subframe (which would surely cause it to crack) you'd use 4 screws to attach it to the Givi frame. Then drill the three holes for the HB mount in this plate.

This PDF file shows Givi SR357 Frame.

 

[mferriter]

Unfortunately, in this scenario, the Givi rack is also supported by the rear subframe.

I agree that the Givi SR357 frame looks much more robust than the POS Yamaha plat and grab (and snap off) rails, keep in mind that it doesn't remove much of the weight from the rear subframe. The part that bolts under the seat is effectively only the front pivot point for the load.

To prove this, think about mounting this rack using only the under-seat mounting bolts. The rear-most part would easily flex up and down, until it too is bolted down.

Most of the weight is still supported by the rear subframe. You'd need another, even further forward, point of attachment to remove most of the load from the rear.

It's fizix.

 

[mferriter]

So, who can build something to mount to, and be more or less fully supported by, the green part?

 

[Fontanaman]

I have a SW Motech Alu rack and a Givi adapter with a Givi 46 liter case. After a recent sub-frame crack report I installed the case and pushed on it quickly. I did not like the result. The rack move up and down slightly as I applied pressure and released pressure. I can imagine the work hardening going on over time, then one day crack there goes the sub-frame.

Due to sub-frame cracking concerns I have ordered a Givi SR357 top case rack.

Are there any reports of sub-frame failures when using Givi SR357?

 

[Fred W]

Unfortunately, in this scenario, the Givi rack is also supported by the rear subframe.
I agree that the Givi SR357 frame looks much more robust than the POS Yamaha plat and grab (and snap off) rails, keep in mind that it doesn't remove much of the weight from the rear subframe. The part that bolts under the seat is effectively only the front pivot point for the load.

To prove this, think about mounting this rack using only the under-seat mounting bolts. The rear-most part would easily flex up and down, until it too is bolted down.

Most of the weight is still supported by the rear subframe. You'd need another, even further forward, point of attachment to remove most of the load from the rear.

It's fizix.

That is true. The weight is still borne primarily on the three rearmost mounting points. But what the arms do provide is a triangulation of the structure so that the cast rear part of the subframe isn't allowed to flex around with the trunk out there bouncing around. That is what causes the cast piece to break, not sheer downward force of the weight.

Look where these subframes usually crack

The Givi rack ties the top piece (that is broken off in this picture) to the tubular steel part of the subframe keeping it from flexing under the cantilevered force of the trunk, which is what shatters that casting.

I do not recall anyone having a broken sub-frame casting who had a (healthy) Givi trunk mount installed. There were some Givi racks that cracked welds when severely overloaded, but I do not know what happened to the sub-frames in those cases if anything.

 

[mferriter]

there are probably a couple ways to move the weight distribution forward onto the frame and off the rear par of the subframe.

If the under-seat roughly 1" wide mounting strap on the Givi was made more into a rectangular plate-like configuration that mounted both in the normal location and further forward, like under the part that holds the rear seat lock mechanism, than very little weight would need to be supported by the rear-most piece that is prone to cracking. This also assumes that the tubular frame structure of the Givi could support the weight of a loaded trunk without this support in the rear. It would be sort of like a diving board arrangement.

 

[Fred W]

there are probably a couple ways to move the weight distribution forward onto the frame and off the rear par of the subframe.
If the under-seat roughly 1" wide mounting strap on the Givi was made more into a rectangular plate-like configuration that mounted both in the normal location and further forward, like under the part that holds the rear seat lock mechanism, than very little weight would need to be supported by the rear-most piece that is prone to cracking. This also assumes that the tubular frame structure of the Givi could support the weight of a loaded trunk without this support in the rear. It would be sort of like a diving board arrangement.

Ummm... the green part already supports the entire red part of the subframe. There ain't nothin' else there that can.

 

[wfooshee]

Unfortunately, in this scenario, the Givi rack is also supported by the rear subframe.

I agree that the Givi SR357 frame looks much more robust than the POS Yamaha plat and grab (and snap off) rails, keep in mind that it doesn't remove much of the weight from the rear subframe. The part that bolts under the seat is effectively only the front pivot point for the load.

To prove this, think about mounting this rack using only the under-seat mounting bolts. The rear-most part would easily flex up and down, until it too is bolted down.

Most of the weight is still supported by the rear subframe. You'd need another, even further forward, point of attachment to remove most of the load from the rear.

It's fizix.

As already stated, it's not the weight itself that cracks the rear bulkhead piece, it's the flexing. Weight applied downward cause the top of the bulkhead to torque away from the bike. The grab handles take that torque load in tension, and the Givi rack (steel) does a better job of taking that load.

Keep in mind that the entire load of the top case is behind the rear bulkhead. Structurally, it's hanging out there in space. The load would twist the rear bulkhead off the back of the bike if not restrained by the grab handles. Givi's grab handles are steel, not plastic, and much stronger. The grab handles do move the load forward, by taking it up in tension.

Look at my drawing, below:

Without the grab handles, the top case load can twist the rear right off the frame. That's where the cracks occur. With the grab handles, that twisting force is pulled forward into the steel tubing of the seat area.

In my own experience, I have carried somewhere between 20 and 25 pounds in my E52 case. Not just around the corner or to work, but from here to Sebring. I've carried heavier loads on short in-town jaunts.

 

[Fontanaman]

My Givi 357 toprack is on back order. I am thinking of making a video to record what happens when I push to the case to demonstrate the flex before and after Givi 357 installation.

I agree with Fred. The flexing of the sub-frame is the cause of the busted sub-frame. I think over time the flexing sub-frame work hardens until catastrophic failure occurs.

Additionally in my less the humble opinion this is an Achilles heal on an otherwise great motorcycle. I don't ride two up or use my Givi topcase often so no big deal - yet. Yamaha needs to address this design issue.

 

[Fred W]

Yup, look at these functional (though not professional) schematic diagrams of the sub-frame and the Givi rack:

And now when the Givi (or similar) is installed to "triangulate" the torsional load:

Yeah, in case anyone was wondering, I'm not a draftsman. But hopefully you can get the idea. Even if the forward mounting of the steel rack wasn't solid, even if it was a hinge, it would cause the bouncing vertical force to be transferred into being a more lateral one that the red part of the rack could better withstand.

 

[Auburn]

Unfortunately, in this scenario, the Givi rack is also supported by the rear subframe.
I agree that the Givi SR357 frame looks much more robust than the POS Yamaha plat and grab (and snap off) rails, keep in mind that it doesn't remove much of the weight from the rear subframe. The part that bolts under the seat is effectively only the front pivot point for the load.

To prove this, think about mounting this rack using only the under-seat mounting bolts. The rear-most part would easily flex up and down, until it too is bolted down.

Most of the weight is still supported by the rear subframe. You'd need another, even further forward, point of attachment to remove most of the load from the rear.

It's fizix.

That is true. The weight is still borne primarily on the three rearmost mounting points. But what the arms do provide is a triangulation of the structure so that the cast rear part of the subframe isn't allowed to flex around with the trunk out there bouncing around. That is what causes the cast piece to break, not sheer downward force of the weight.

Look where these subframes usually crack

The Givi rack ties the top piece (that is broken off in this picture) to the tubular steel part of the subframe keeping it from flexing under the cantilevered force of the trunk, which is what shatters that casting.

I do not recall anyone having a broken sub-frame casting who had a (healthy) Givi trunk mount installed. There were some Givi racks that cracked welds when severely overloaded, but I do not know what happened to the sub-frames in those cases if anything.

After i put the givi bracket on, I will weld a tab to it so I can support it from the trailer hitch and prevent the top case from rocking it and give my wife more support to lean against the box. That should tie everything together and make it very strong. The vertical bars from the hitch tie into the bolt that holds the inner fender in place.

You can see teh gap in the grab bar. It is the same on both sides.

 

[someguy]

So, who can build something to mount to, and be more or less fully supported by, the green part?

theres this guy on here, builds some good shizzle

Garauld

he could so rock this and it would look good and we'd all buy it.

i have his rack on mine and wish it was additionally braced like the Givi rack...

i'd gladly send it to him if he want to play around with some ideas...

I think the Garauld rack, either in it's current form or with a plate along with the addition of the braces would be ideal.

I don't want a Givi box, or even the FJR factory trunk. I prefer a wrack as it's the most versatile for me, and allows me to throw whatever size TNF duffel or MotoFizz bag on there i'm using... and it will still look good with nothing on it.

and frankly, i think the Givi SR357 mount is ugly as piss... all except for the grab bars/braces of course.

and i'm sure "braces" or "Struts" is probably not the correct term but, i'm sure you get what i mean.

 

[wfooshee]

There's a perception here that the rear subframe bulkhead should not be carrying the weight, but the seat-area subframe should.

That's not necessarily correct.

What has to happen is that the rear subframe bulkhead has to be well enough braced that it can't twist away from the back of the bike.

The factory rack doea this with plastic grab handles. The Givi rack does this by using steel. The rear bulkhead does not support the Givi rack, the rear bulkhead is braced by the the Givi rack. It's also braced by the factory rack, but not nearly as well.

You could hang a hundred pounds of weight from the rear bulkhead, and it wouldn't care, as long as it was a purely vertical load. You can't cantilever a hundred, or even 50 or 30 pounds from the rear bulkhead and hang the weight out a few inches behind it. The top of the bulkhead will twist out, resulting in cracks and breaks at the base of the bulkhead where it attaches to the seating frame.

Enter one set of grab handles. There's your load transfer to the seating frame. The handles support the rear bulkhead. The bolts attching the grab handles, or the Givi rack, are right at the rear bulkhead. The rack itself handles the moment arm of the top case's weight as long as the grab handles are intact. A load doesn't have to be supported from underneath. If you don't think the load can be transferred in tension, then you'd better stay off suspension bridges as you drive around.

The very first subframe issues I read about on the forum were from someone who intentionally removed the grab handles to make room for an auxiliary fuel tank in the pillion space.

As for additional struts from other places on the bike to support under the top case, they are unnecessary and almost certainly will interfere with bodywork, lights, and side cases.

I asked once years ago, and I think I got one responder, but I can't find it now. Anybody with the Givi rack have this subframe failure?

 

[Fred W]

I asked once years ago, and I think I got one responder, but I can't find it now. Anybody with the Givi rack have this subframe failure?

Yes, exactly! I don't think there is any need to do anything more than what the Givi SR racks do to reinforce the rear subframe. I do understand that not everyone wants to use a Givi trunk, and many folks dislike the clunky appearance of the Givi adapter plate when there is no bag on it. I happen to agree with that sentiment, just as of yet haven't done anything about improving it.

It is pretty easy to just remove the plastic Givi trunk adapter and replace it with your choice of flat luggage rack, other brand trunk plate, or whatever, then sell off the plastic Givi adapter to someone else. Though it would be really convenient if one of our resident metal fabricators cloned and manufactured a tubular metal grab rails/rack similar to the Givi SR's.

There are some features that could even be improved upon, like getting the passenger handles up a little higher and a tad wider so they do not rub against the sides of a Russell seat, and maybe installing some sort of grip material for the passenger to hang on to? Also having slotted (or drill your own) holes to allow fore and aft adjustment of the trunk position (within reason)

Seems like with all of the various (non-Givi) trunks in use on FJRs there would be a pretty healthy market for just the reinforcing grab rails. And as for what you could charge, well the SR357 street price is $160, so take it from there.

edit - BTW, I happened to see that Twisted Throttle makes an adapter plate to use the SR rack with their Trax brand rear trunks. So someone out there is thinking along these same lines...

 

[Pepperell]

Note to self: Check tightness of grab handles, inspect subframe.

 

[SoCalFJR1300]

Unfortunately, in this scenario, the Givi rack is also supported by the rear subframe.
I agree that the Givi SR357 frame looks much more robust than the POS Yamaha plat and grab (and snap off) rails, keep in mind that it doesn't remove much of the weight from the rear subframe. The part that bolts under the seat is effectively only the front pivot point for the load.

To prove this, think about mounting this rack using only the under-seat mounting bolts. The rear-most part would easily flex up and down, until it too is bolted down.

Most of the weight is still supported by the rear subframe. You'd need another, even further forward, point of attachment to remove most of the load from the rear.

It's fizix.

That is true. The weight is still borne primarily on the three rearmost mounting points. But what the arms do provide is a triangulation of the structure so that the cast rear part of the subframe isn't allowed to flex around with the trunk out there bouncing around. That is what causes the cast piece to break, not sheer downward force of the weight.

Look where these subframes usually crack

The Givi rack ties the top piece (that is broken off in this picture) to the tubular steel part of the subframe keeping it from flexing under the cantilevered force of the trunk, which is what shatters that casting.

I do not recall anyone having a broken sub-frame casting who had a (healthy) Givi trunk mount installed. There were some Givi racks that cracked welds when severely overloaded, but I do not know what happened to the sub-frames in those cases if anything.

After i put the givi bracket on, I will weld a tab to it so I can support it from the trailer hitch and prevent the top case from rocking it and give my wife more support to lean against the box. That should tie everything together and make it very strong. The vertical bars from the hitch tie into the bolt that holds the inner fender in place.

You can see teh gap in the grab bar. It is the same on both sides.

Can you post a few more pics of your RED FJR??

Reds my favorite color next to Black.

 

[Auburn]

Unfortunately, in this scenario, the Givi rack is also supported by the rear subframe.
I agree that the Givi SR357 frame looks much more robust than the POS Yamaha plat and grab (and snap off) rails, keep in mind that it doesn't remove much of the weight from the rear subframe. The part that bolts under the seat is effectively only the front pivot point for the load.

To prove this, think about mounting this rack using only the under-seat mounting bolts. The rear-most part would easily flex up and down, until it too is bolted down.

Most of the weight is still supported by the rear subframe. You'd need another, even further forward, point of attachment to remove most of the load from the rear.

It's fizix.

That is true. The weight is still borne primarily on the three rearmost mounting points. But what the arms do provide is a triangulation of the structure so that the cast rear part of the subframe isn't allowed to flex around with the trunk out there bouncing around. That is what causes the cast piece to break, not sheer downward force of the weight.

Look where these subframes usually crack

The Givi rack ties the top piece (that is broken off in this picture) to the tubular steel part of the subframe keeping it from flexing under the cantilevered force of the trunk, which is what shatters that casting.

I do not recall anyone having a broken sub-frame casting who had a (healthy) Givi trunk mount installed. There were some Givi racks that cracked welds when severely overloaded, but I do not know what happened to the sub-frames in those cases if anything.

After i put the givi bracket on, I will weld a tab to it so I can support it from the trailer hitch and prevent the top case from rocking it and give my wife more support to lean against the box. That should tie everything together and make it very strong. The vertical bars from the hitch tie into the bolt that holds the inner fender in place.

You can see teh gap in the grab bar. It is the same on both sides.

Can you post a few more pics of your RED FJR??

Reds my favorite color next to Black.

Here is a few in another thread

and here with the canyon cage installed

and here on a trip