Lets Talk About Handling

[Ramblin Man]

You all know how much I love my FJR, as much as you do or more. But one thing I have never been a fan of is using the engine as a stressesd member. That just seems wrong, even if it works. So I've been toying with the idea of frame connectors in the same vein of the frame connectors you can get for fox body mustangs and others, obviously with a design to fit the FJR. Just something to help tie things together.

Now I've got no real complaints with the bike's handling, but this is America where we fix things until they break so I figure talking about it can't hurt.

I've got two locations in mind for cross members. One is where the upper rear sub frame connects to the main frame, and the other would be a spar runnung in front of the frame between the block and the headers. I was thinking about a modified version of a moko bracket that would also extend forward and let you connect a cross member. So you would have a cross bar roughly the same hight as the bottom edge of the radiator.

None of that looks like it would help much as far as reducing twisting forces applied to the engine by the frame in a chicane type of situation, but then again maybe it would.

topic open for discussion.

 

[sparky3008]

Don't understand your connection between handling and the engine being directly connected to the frame. Many of the all out sport bikes today do exactly the same thing. Reason being that they are smooth enough and strong enough to handle it and allows for a narrow body. As allows for a lighter frame.

I assume also that you are comfortable with welding on aluminum?

Twisting forces then are going to be applied to that weld and not the engineered engine.

Why would it be bad?

 

[slapnpop]

I've got one of these sitting in my garage, and not with the rest of the bike attached. Belive me when I say it is STIFF all on it's own.

I think the only real dangers of bending lie in 2 directions. Left to right, or tortionally front to back (both as your are sitting on the bike). In both situations the engine block is stiffening the frame in this manner, but the engine is never bearing any direct "load" of the motorcycle.The tree's axle, the rear subframe mount, and the swingarm are all attached to and connected by the frame. The engine's mount is all below that in a seperate protrution of the frame. There's also the T brace above the engine. The only real benificial place I could see to add a tie would be the front motor mounts as you mentioned. But, even if you do this, you've still got the engine already tied in there doing more than enough stiffening already. How do you propose to non-stressed-memberize the engine, if this was the original qualm?

As for a rear tie at the subframe: It's really close to the BEEFY braces where the subframe attaches. I doubt it would add much benifit.

I think that you're just going to end up adding weight. Better forks/trees and swingarm would be where the handling improvements would come. A beefier rear subframe might be helpful towards higher load carrying capacity.

Please keep in mind this whole rant comes from a total modernjackass. (for a defenition of modern *******, please listen to This Real Audio Clip of a radio program with a good explanation)

oh yeah... I did get t-boned by the front corner of an s-10 directly on the right lower engine mount. I was lucky it wasn't 6" back of that, or it would have been my knee, and I wouldn't have walked away. I DID have to replace the frame, hence the extra one sitting in my garage. It was replaced because a cracked pinch-bolt on on the engine mount. It still drove straight, but I replaced it anyway. That's 25% of the engine's support, didn't feel comfortable without it.

 

[markjenn]

Interesting idea, but probably ill-advised.

First, I don't agree that using the engine as a stressed member is a bad idea to begin with. In fact, it is generally considered to be a very good thing for handling as it takes the inherent strength of engine (which must be very strong to support the crank, pistons, etc.) and uses this strength to enhance the frame rigidity. Without doing this, the frame would have to be much heavier.

You seem to be worried that the engine is stressing the frame - that engine loads are causing the frame to flex and cause handing problems. Actually, I think it works the other way around - road loads govern the required frame rigidity and that any engine that can contain it's crank, pistons, etc. and live a long time is not going to introduce any significant flexing in the chassis. I've never heard of worrying about the engine torque or engine flexing causing poor handling.

The trade-off using the engine as a stressed member designs is the issues of heat, vibration control, and serviceability. So if the goal was to reduce heat and vibration transfer from the engine to the frame, then you could consider a design to mount the engine in rubber mounts and beef up the frame to provide the rigidity that was lost. This would be a huge engineering exercise requiring a great deal of work.

As to simply beefing up the frame just so that it is more rigid in general, you'd be adding weight for rigidity that may not be required or even desirable. Many of the new motorcycles are being designed to be "controlled flex" so they are relatively compliant in one direction but not in another. I don't know about the FJR, but you might make the frame more rigid in an undesirable way which might manifest itself as wheel chatter over rough surfaces or poor suspension performance. More rigid isn't always better. And there is a huge risk you'd introduce new vibration modes that would make the engine vibration quite uncomfortable.

I think you have to go back to the problem you're trying to solve. You want the FJR to handle better? Well, there's really nothing to indicate that the frame currently contirbutes to poor handling characteristics at all. So I think you have to identify the handling problem and find the cause before you just assume it is a lack of frame rigidity and start beefing it up. Of course, the first place to start is suspension, then perhaps unspring weight control, then chassis weight, then perhaps steering geometry. There is a long list of things to work through before you start welding in braces to the frame.

This just feels to me like it is something that the home DIY'er is much more likely to make things worse rather than better.

- Mark

 

[Ramblin Man]

No, I'm worried that with my fat *** on the bike and riding it like a sport bike, which is what I do most, is putting unecassary strain on the engine block. I know it's plenty strong, and as I said, I don't have any real complaints. this is more conjecture.

Anything I would add would be a bolt on like the T bar under the gas tank.

I'm on my way out and just skimmed the replies so far and I'll try to give a better response later but I just wanted to adress those points now.

I'm thinking strut tower brace in car speak. And maybe I can't ride an FJR hard enough that the bracing I have in mind would make a difference. Thats why were having this discussion.

More thoughtful reply later

 

[slapnpop]

I'm thinking strut tower brace in car speak. And maybe I can't ride an FJR hard enough that the bracing I have in mind would make a difference. Thats why were having this discussion.

more to the point, I don't think we have traction that these kind of modifications would benifit. The fjr wasn't subject to such weight saving tradeoffs as bikes that could benifit from this type of mod.

Then again, you could get one of those trick polished tubular aftermarket frames the brits tout, if you can find a fjr one.

 

[markjenn]

No, I'm worried that with my fat *** on the bike and riding it like a sport bike, which is what I do most, is putting unecassary strain on the engine block.

Never heard of this being any concern whatsoever on a stressed engine bike. Ever. And there have been literally hundreds and hundreds of designs over the years, some which use engines in much more fundamental ways than the FJR. From what I've read, the strength requirements of any engine block that can keep a hot crank, pistons, cams, cylinder jacket, head, etc. all aligned within a thousandth of an inch or less are orders of magnitude larger than any stress you can feed in via the chassis, no matter how hard you ride.

Heck, most oilhead BMWs have virtually no frames to speak off - you bolt the rear subframe and the front telelever mounts to the engine block - that's it- there is no connection whatsoever between the steering head and the rear swingarm other than the engine. And these bikes are ridden just as hard as an FJR. There are literally thousands of these bikes now rolling with 100K+ miles and I've never heard of any engine block issues.

If the FJR was a monocoque/unibody construction with welded together sheet metal forming the structure, I'd agree that there might be more of an issue here.

- Mark

 

[nusman68]

As to simply beefing up the frame just so that it is more rigid in general, you'd be adding weight for rigidity that may not be required or even desirable. Many of the new motorcycles are being designed to be "controlled flex" so they are relatively compliant in one direction but not in another. I don't know about the FJR, but you might make the frame more rigid in an undesirable way which might manifest itself as wheel chatter over rough surfaces or poor suspension performance. More rigid isn't always better. And there is a huge risk you'd introduce new vibration modes that would make the engine vibration quite uncomfortable.

Concur with Mark...Kevin Cameron had an excellent explanation of this (as it applies to racebikes) in an issue of Cycle World a few months ago...(would need to research which issue); the upshot of the article was that the various teams (years back) would actually cut parts of the frame to induce a desirable flex to enhance handling...sorry, not giving his article justice here...now the teams experiment with 'variable wall thickness' of the frame, etc.

However, I do recall seeing some tricked out V-Maxes? (I believe) that had a bolt on frame brace designed not unlike a strut tower brace that Ramblin referenced. We're comparing apples & oranges now, though since we all know the V-Max is a 20 yr. old platform and handling was (so I was told) not its strong suit. No, I've never ridden one...no offense to any V-Max owners out there....just brainstorming.........

 

[BrunDog]

The idea of this is absolutely ridiculous. You are questioning the integrity of this system without any engineering data or factual basis?!?

By all means, weld and bolt away, but like stated above, you will: likely make no improvement, possibly make it worse, and certainly make it heavier.

Why not start out with some measurements? Put some strain gauges at various points on the frame and quantify the deflections first? Then you can decide if there is really any problem to try to solve.

Don't get me wrong, I like the idea of improving this bike further, too!! But this is resources wasted if you go about it the wrong way.

-BD

 

[Ramblin Man]

Damn, BrunDog!?! Ridiculous is kind of harsh don't you think? :blink:

Like I said I don't have any real complaints, but I do have the 03 brocure on my wall at work and when I look at that point where the upper rear sub frame bolts on it just LOOKS weak. I'm not saying that it is weak. I also thought that a brace running between the front spars would help spread out the force of impact and maybe keep it out of the block during a tip over. The idea there was to fasion a moko style slider mount in such a way that you could tie the two together. That way when the slider takes a hit the energy is transfered through the bar to the other side of the frame instead of through the block.

I just brought up the topic to get some discussion. I don't have access to an Instron or laser alignment/measurment systems but isn't trial and error what people did before they had all of the new stuff?

Seems like the concensus is that the block is plenty strong. And I'd never hear of the controlled flex argument before. I always thought you wanted to make the frame as rigid as possible and let the suspension do the work. But if the frame can soak up some of that duty then why not. OK, now that I have some learned opinions I can shelve the whole idea.

And I just realized something. There is already a cross brace, actually there are two at the rear sub frame. I just forgot about them because thay aren't in the picture in the brocure. One is the rear gas tank mounting bolt, and the other is the steel brace that the shock hard/soft selector mounts to.

So the frame gets left alone. What about the battery? Would moving it under the seat behind the air box be a good thing? That foil bubble wrap would make the perfect battery box liner.

 

[markjenn]

Now you're talking. A lot of people have raised their eyebrows over the battery location. That's a heavy lump to be situating so far forward and up with a huge lever arm with respect to the bike's center of mass. Some journalists have pointed to this location as a possibly reason for the FJR's somewhat odd handling feel.

As I understand it, the ABS bikes don't have room for the battery under the seat, but the space is open on the non-ABS'ers. It would be an interesting, modification to relocate it, albeit messy what with having to reroute some major wiring bundles.

- Mark

 

[madmike2]

I suppose you could move the battery and leave the bundles, etc., under the fairing by running the cables from the battery's new location to the fairing area.

 

[BrunDog]

Damn, BrunDog!?! Ridiculous is kind of harsh don't you think? :blink:

Sorry. Crazy fingers on the keyboard.

Moving the battery may make sense, but as noted above, for ABS bikes: WHERE?

-BD

 

[FJRMGM]

Formula 1 cars use the engine as a stressed member of the frame and the suspension. Seems good enough for the cutting-edge technology guys.

 

[markjenn]

I'm not sure about the new ST1300, but I recall on my ST1100 that they put the battery and fuel under the seat and put all the ABS stuff under the false tank and and in the front fairing. While ABS pumps and computers aren't light, they're not as heavy as fuel and batteries. While the bike was no great handler, it had a very honest and sure-footed feel and seemed more willing than the FJR to make quick side-to-side transitions.

Of course, all bikes are compromises and any solution in one area begats a new problem.

- Mark

 

[panthercity]

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Do not be mislead by the unbelievers who might urge you to take a variety of riding courses to improve the handling of your machine when you can avail yourself of the benefits of moderne technology.

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[deanw]

As I understand it, the ABS bikes don't have room for the battery under the seat, but the space is open on the non-ABS'ers. It would be an interesting, modification to relocate it, albeit messy what with having to reroute some major wiring bundles.

Put the ABS unit up inside the front part of the fairing where the battery is, put the battery under the seat. QED.

(Not that I'd expect this to be a casual owner mod; something I'd have thought Yamaha should have done in the first place.)

 

[markjenn]

The battery re-location, especially if you just ran big cables and didn't bother optimizing the wiring for the new location would be fairly easy, but I shudder to think what would be involved in relocating the ABS unit, which sits in a rat's nest of hoses and wiring.

- Mark