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Rear frame reinforcement?

Started by musicweb, July 02, 2019, 03:54:20 PM

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musicweb

Has anyone tried to reinforce the rear of their Vision so it would accomodate a larger trunk/backrest? I tried installing one with a backrest, but it tends to shake a bit when riding.  I put a homemade bracket under from 1/4 inch steel but still wobbly. Also used a pair of large hinges so if I needed to get under the seat. Pictures attached....
1982 XZ550 Vision
Most upgrades done... and a large pizza paint job!

injuhneer

Is the top box and back rest connected to the rack? It looks like the hinges are bolted to that rack.

It isn't clear to me how your gear is connected to the bike but reinforce the rear subframe may not help the rack itself.

Can you add some shots from down low showing how the rack is attached to the rear frame?
- Mike O
1982 Yamaha XZ550RJ

musicweb

Yeah... the trunk is attached to the rack mounting points and the hinges are also attached to the rack. The only frame connection I can see is ehwere the rack bolts on near the tailights. I'll get more pics up in a couple hours....
1982 XZ550 Vision
Most upgrades done... and a large pizza paint job!

musicweb

Found a photo of an old frame for reference, and added a few more pics of how I have the new trunk mounted. I'm beginning to think it's too flimsy in that frame area, or the old luggage rack mounts are not that great either. Or.... I have about 25 pounds of stuff in my trunk.....
Maybe reinforce the frame going across over the wheel, or a couple more brackets to the tailight mount?
1982 XZ550 Vision
Most upgrades done... and a large pizza paint job!

jefferson

The biggest problem I see is with the flat strap that is used for the mounts. There is nothing to keep things from swaying side to side as angle iron would do, but the flat strap is a lot easier to fabricate.

musicweb

I see that happening when I hit the trunk. It will move side to side a bit. I'm adding a few more braces from the top of the tail light bracket to the luggage rack and from the bottom of the passenger grab handles out to the luggage rack. We'll see what happens in the morning....
1982 XZ550 Vision
Most upgrades done... and a large pizza paint job!

injuhneer

Just remember that triangulation is what will immobilize it. Parallel brackets tend to flex together.
- Mike O
1982 Yamaha XZ550RJ

fret not

One important point to consider is the weight (inertia) so far from the center of gravity, and so high above the road.  Weight high and back so far can easily induce instability, in particular a 'weave' pattern.  We ran into this very aspect at the Bonneville salt flats with a Suzuki T500 with a home designed and made fairing for the 'partially streamlined' classification.  One fellow land speed racer mentioned the CG/CP (Center of Gravity / Center of Pressure).  The 'rule' is to have the Center of Gravity in front of the Center of Pressure.  So we weighed both wheels and took some measurements, then scratched our heads and came up with the solution: we had to add weight as far forward as we could and lengthened the swing arm and then moved the pivot point back another inch.  The weaving stopped and now the bike is very stable at speed.  It has been to 161.xx mph.

Also, when sissy bars were so popular folks found that you could strap a bunch of your stuff to the sissy bar like for a trip, and find that the weight so far up and back made for instability, especially at low speed or when trying to wrestle the bike into sport mode.
Retired, on the downhill slide. . . . . . . . still feels like going uphill!

musicweb

I kinda figured it would be like carrying a passenger the way I set it up. I'm almost done with extra braces and will post some pics later today after a test run. I still think the vision frame lacks stability going up over the rear wheel....
1982 XZ550 Vision
Most upgrades done... and a large pizza paint job!

musicweb

So I ended up putting extra supports at bottom of passenger handles, and at top of tailight bracket to the luggage rack. This helped a lot.... but still not satisfied.
So.... to stop the new trunk from the little bit of sway that was left, I put 2 long braces from the passenger foot peg mounts to the bottom of the new trunk, in the front corners.  I used new longer flange bolts and nuts through the foot pegs. Plenty of clearance around the wheel. Now it hardly moves at all, so I think I'm done with this project for now. Looks a little weird, but doesn't interfere with my riding....
1982 XZ550 Vision
Most upgrades done... and a large pizza paint job!

injuhneer

- Mike O
1982 Yamaha XZ550RJ

musicweb

Result of a short test run was good....
Sorry, I fractured a lower vertebrae in my spine 7 weeks ago, so not riding much yet.
I'll post more about it when I'm up for a longer run....
1982 XZ550 Vision
Most upgrades done... and a large pizza paint job!