Stiffening up Swingarm?

[fredintoon]

Don't do that and ride solo

TC posts:-
I've been told that if I were to put the Standard's Triple tree on, that it would increase the rake angle, would that increase the stability of the front wheel, sorta like a long forked chopper and how they have the tree angled further out vs. a standard bike!?
Hi TC,
yes, the Standard & Special have identical rake & trail. The Special's forward axle is countered by it's shorter 'trees to keep the trail the same as a Standard's. I put Standard 'trees on my Special to reduce the trail for sidecar use and that works really well to lighten the steering. If you do that on a solo bike your steering will perhaps be more responsive than you'd like it to be.
The Standard onto Special 'tree swap moves the axle forward to reduce trail.
If you wanted to increase trail, swap in Standard fork legs onto your Special 'trees. The only way to increase the rake is to cut'n'weld the frame to increase the steering head tilt angle.
Fred Hill, S'toon.

[TopCatGr58]

Hey Dick,

Well, it's a good thing I'm not an engineer!

Fred, I followed your train of thought until the statement about the "longer" trees of the Standard reducing your trail on your Special!?

We've had this discussion before, and the farther away the axle is from the steering head pivot line, the more increased the trail which increases the stability, but also increases the heavyness or difficulty of steering. So...can't explain why you got a lighter steering feel from your Standard TT's on your Special since the fork line and axle was placed farther forward away from the steering pivot line??

But now onto the Ride Report:
I opened up the garage door, and had a little surprise waiting for me! I left the antifreeze jugs there for scale, it was just a little rat snake, caught it and released it into the back yard!

I got the SA installed this morning, all buttoned up, regreased everything since I had it apart. Here are a few photos.

As mentioned earlier, made sure there was room for the rear brake lever.

Also room for the exhaust collector that comes from between the centerstand and to the right side!


Here you can see enough room between it and the frame crossbeam, the SA is already at it's lowest position of travel with the shocks mounted and rear tire raise, and YES I KNOW that little hose is supposed to go inside that wire loop in front of the crossbeam!!



Okay, seat of the pants feel, it did feel more taught and stable thru corners. The wobbles I had talked about before were not just thru some bumpy curves, but also just a nice fast straight highway run!

There is a nice stretch of highway just a couple of miles from where I live, took a run heading away from the house, was a slight head wind. Got up to 90 but then started to experience a slight wobbling action! Turned around and came back with the wind, got to 95-100mph before starting to get the rhythmic wobble! Got me to thinking........scary stuff!!

A new word for my vocabulary....AERODYNAMICS! I took off the saddlebags....appx. a pair of 1 square foot of FLAT surface sticking out on both sides of the rear of the bike, and did another run. Got up to 100-105mph against the wind before wobble started, and 105-110mph with the wind return run. I also have a simply curved handlebar mounted windscreen, and that may also be contributing to this wobble. I didn't try taking it off for a run.

So....in my conclusion, this mod is probably not really necessary for every rider, but folks like DennyZ that like to push the envelope in the twisties "might" appreciate a bit more stability. I just have to realize that I can't push it to the "Bug 2.0" speeds with my full dress gear! I can live with that.
I may still play with the steering geometry later?
T.C.

[fredintoon]

draw a new diagram

TC posts:-

Fred, I followed your train of thought until the statement about the "longer" trees of the Standard reducing your trail on your Special!?

We've had this discussion before, and the farther away the axle is from the steering head pivot line, the more increased the trail which increases the stability, but also increases the heavyness or difficulty of steering. So...can't explain why you got a lighter steering feel from your Standard TT's on your Special since the fork line and axle was placed farther forward away from the steering pivot line??

Hi TC,
regretfully, your concept and your diagram are flawed. Go back to the drawing program and start over. Draw a line down the axis of the steering head until it hits the road. This is the theoretical point where the steering acts from. Draw another line from the axle that goes straight down. This is where the centre of the tire contact patch hits the road.
Where the tire patch hits the road is behind where the steering head centreline hits the road. That distance is the trail. The greater the trail, the more the front wheel acts like a caster and the heavier the steering is. Conversely, moving the axle forward, (by swapping in longer 'trees for instance) will lessen the trail and lighten the steering.
Fred Hill, S'toon.

[TopCatGr58]

I admit it when I'm wrong!

Hey Fred,

Thanks for rattling the brain cells in my skull!! My diagram is actually correct, because I was comparing the change that occured with the reduction in steering head angle which reduced the trail to allow easier steering, that occured with my front end collision some 20 years ago

What IS flawed is my thinking about the effect of the Standard TT in place of the Special TT, when the steering angle is the same. You are correct, the longer TT's position the axle more forward putting the vertical plumb line closer to the steering centerline which in deed reduces the trail size/length.

As I've said before, I'm no TRUE GURU, just a shadetree survivalist and enthusiast, and happy to admit my mistakes, and also hopefully learn from them!

At least now I realize I don't need to put on the Standard TT's on my Special thinking that I would get more stability, in fact it would be even MORE TWITCHIER . I enjoy the ease of steering that my reduced rake angle has gotten me, so I just won't try doing 100+mph with my square saddlebags in place!
T.C.

[snowdog51]

swingarm

my 76 bmw 90s usa super champ that year, sides by battry and behind were braced welded abar in the shape of a u on the swingarm then i could corner at hi speed.before that the bike was unsafe at over 60.
as ever bill