Hey kpke. I remember your dogbones, and will have to be careful when I measure mine.
The wide brace on the FZR swingarm is going to be my biggest challenge.
(since this pic, the FZR arm has been modified, so that it has the same dogbone pivot locations, as the FZ600 arm).
I'm hoping I can shorten the dogbones (maybe 1/4" or more), and see if I can get 1/2" or 1" ride height increase.
The current temperature is -15C, and being outside right now, is unpleasant.
That means I'm sitting indoors, with too many vices, an internet connection, and not enough parental supervision.
Probably not a good idea.
So, why would a person spend a ridiculous amount of time, calculating some numbers on a piece of paper?
As usual, there's a long story, and a short story. Which one do you want first?
Too late. You get the long story.
The big obsession started when I saw the tires on my FZR rims.
I suspected the huge rear tire, & tiny front tire, were going to affect the steering geometry,
and I wanted to know if the bike was going to be safe.
I started looking into rake & trail, then made calculations for my setup, and it looked like it was going to be good.
Spring arrived, I started riding the bike, and I was not impressed. The handling sucked.
The front end got really hard under braking, the bike wouldn't turn in to the corners, and it drifted wide on exit.
I started looking into suspension setup. Sag, spring rate, fork oil, compression & rebound damping.
During this search, I read 2 statements that have stuck with me.
"Handling is arguably one of the most important aspects of motorcycling. The entire time you are on the motorcycle, you are using it's handling capabilities".
"The best you've ridden is the best you know." Until you've ridden something better, the best you've ridden is the best you can compare it to".
Well, ain't that the truth. One of our city streets has an awesome set of S's.
Back in the day, when I was still 10 feet tall and bulletproof, I used to take them a more than twice the speed limit.
One day, I'm flying through them on an old Kawi KZ1000, (80+ HP with a bad suspension).
A left, a right, a left, but the bike wouldn't turn left.
The bars started shake really bad, and the bike drifted wide, and the curb kept getting closer, and I could see the sidewalk, and the fence beside it.
And nothing I did seemed to make any difference. I was just along for the ride, which looked like it was about to end, at any second.
Somehow, I didn't hit the curb, and didn't crash. But it was close. Too close.
Then I got the 81LC, and that bike handled much better than the Kawi.
Then I got the RZ, and it handled even better than the LC.
Then I got a 90 RZ, and the 2 piston front calipers are way better, than the brakes on the early bike.
Then I put the FZR400 bakes on my RZ, and they're a huge improvement over the 90 RZ.
Over the Summer, I made some adjustments to sag, fork oil, and damping, and the bike definitely handles much better now.
Then I saw RZResurection's project, using an R1 front end, and a longer swingarm.
I was just curious about how the R1 parts would affect the RZ's geometry.
This started a search for R1 specs and info, and how Yamaha changed swingarm angle to improve traction out of corners.
When I finally got around to calculating Specs for the R1 components, I found that I'd made incorrect assumptions, and math errors, when doing the FZR calculations.
Then pride and ego took over. If I was calculating numbers, I wanted the right numbers.
Finally finished the R1 calculations
Then started to use my new information to re-evaluate the modifications done to my bike.
What have I changed? How did it affect the bike? Can I improve it?
Which got me thinking about a motorcycle "with springs", then re-evaluating the affects on rake & trail, by changing sag and/or ride height, all over again.
So, did I learn anything, other than a couple of new terms, and few definitions.
Sure. First off, the numbers that I calculated for rake & trail, are pretty much irrelevant.
It doesn't matter whether my "calculations" say that the rake is 24* or 26*,
the bike is what it is.
When you ride it on the road, it will have certain handling characteristics, no matter what the "calculated" numbers are.
Changes and adjustments will be needed, in order to optimize the handling.
The best part of going through this exercise, is that it has given me a much better understanding of how, and why motorcycles react in the way that they do.
And learning how certain changes affect the bike, and what adjustments can be made to improve the handling, has been very useful.
For instance, my bike with the FZR400 suspension, has awesome high speed stability.
My calculations say that it has a slightly steeper rake, and a bit more trail, than a stock RZ.
The bike also has a pretty small amount of front sag, which will increase the rider-on-board rake & trail.
In addition, the swing-arm angle has been reduced, witch will also increase rake & trail.
I want to try less rake & trail, to see if I can quicken the steering, without upsetting the stability.
First step will be to make shorter preload spacers, and increase rider sag by 10 mm (1/2").
Next mod will be shorter dogbones, to increase the rear ride height.
This will also steepen the swing-arm angle, and increase antisquat.
Stay tuned, I'll post the results of this experiment as soon as the snow melts, in about 6 months.
Now the short version on why I spent all this time looking at suspension tuning.
1- I find the subject fascinating. It seems that every part on the bike, affects its handling, including whether or not, the rider farted before getting on.
2- I'm one of those sick puppies that like to brake late for the corners, turn in quick, be able to change my line if I have to, and then accelerate sooner and harder on exit.
And I prefer to do this without the bike trying to throw me off, and/or scaring the shit out of me.
I'm just funny that way.
3- My bike handles pretty good, but "The best I've ridden is the best I know". Can I make it better? After all, better is...well,...its better.
4- The previously mentioned KZ1000. That moment in time happened over 30 years ago, and I remember it like it was yesterday.
I doubt I'll ever forget it, and I really, really, really, don't want any more memories like that, running through my mind for the rest of my life.