Chassis set up notes.

[8541Hawk]

A little more info to share with your guy and my reasoning and thingking that got me to the set up I run now.



When I still had the stock suspension I was running the forks up 10mm, a .250" or 6.35mm ride height spacer and 16\43 gearing.

This worked pretty good. The major draw back is that it is rather easy to touch down the header in right hand turns. Also, IMHO, the ride always felt a little harsh with this set up.

So when I did the front end swap, one of the first goals was to get more ground clearance.

Buy my calculations, the SP2 forks with the cut top out springs end up to be around 3-5mm shorter then the stock forks (or equal to the stock forks pulled up 3-5mm)

I then went to a 10mm ride height spacer in the rear to get the rake and trail numbers around where I wanted them.

I also changed gearing,which lengthened the wheel base, which moves the CG forward.

Now the first step would be to look at what each set of changes does to the stock geometry.

I did cheat a little here as I had worked out all the numbers while setting up a friends Duc but as it had a rake of 24.3 with a trail of 97mm and the SH is 24.5 with 97mm of trail, I figured close enough.

Keep in mind that lowering the front ride height, or raising the rear ride height, are not equivalent adjustments. Lowering the front serves to lower the bike's center of gravity. With a higher front, raising the rear, raises the C.G.

So this is what you get:

for every 1mm increase in rear ride height:
Trail decreases 0.4mm
Wheelbase decreases 0.2mm
Height of the bike’s center of gravity increases 0.8mm
Percent of the bike’s weight on the front wheel increases 0.03 percent

The adjustment can be felt most in trailbraking - The bike stands up less on the brakes, which can be a benefit on backroads where you never quite know what might be coming up around the next bend. Also, some feel that the steering is more neutral at large lean angles.



Every 1mm that you raise the forks in the triple clamps (lowering the front end):

Trail decreases 0.2mm
Wheelbase decreases 0.5mm
Height of the bike’s center of gravity decreases 0.4mm
Percent of the bike’s weight on the front wheel increases 0.06 percent

So with this I was able to see that with the stock suspension I was running a set up that gave me a:

Trail decrease of 4.54mm
Wheel Base decrease of 6.27mm
The CG raised 1.08mm
and a .7905% increase in weight on the front end.

While setting up the new stuff, along with added ground clearance, I also wanted to raise the CG of the bike as I felt this might improve the ride quality and also add stability in turns.

The old (late '90s) Ducati factory race bike setup manual recommended raising the front 10mm to increase "flickability" in turns. Yes, I said raise, not lower. Raising the front end raises C.G., and a higher C.G. makes the bike go to the tire edge quicker.

Familiar with the Mille SP? It has the capability to raise the engine in the frame to increase C.G. to improve flickability. Same effect. Even the Mille R has the engine mounted higher in the frame to do the same thing.

Once in a turn, a higher C.G. biases the weight more to the inside of the corner which helps the bike turn.

So with this in mind, I left the forks as high as possible (I used -3mm for my calculations) and then raised the rear 10mm, like I stated earlier.
At this time I also went back to 16\41 gearing

Which gave me these numbers:

Trail decrease 4.6mm
Wheel Base decrease 3.5mm
CG raised 6.8mm
and a .48% increase in weight on the front end.

So what do these numbers mean while riding?
With similar trail numbers the steering is still quick and light but with the higher CG the bike transitions from side to side quicker.

Add to this the longer wheel base, which increases stability and you have a bike that is very neutral when leaned over. In other words the bike holds it line until you tell it to do something else.

Now the difference in weight on the front wheel does look rather small but it was much bigger that I expected. In fact it took 5 turns of preload on the Ohlins shock and I had to lower the oil in the forks 30mm to get the sag numbers and bottoming correct.

The first thing I noticed was yes the front end will come up quicker but also most of the vibrations I had through the bars was gone.

The other unexpected thing I have seen is longer rear tire life.
This is opposite of what I expected with more weight on it. About the only thing I have come up with so far is that the added traction, due to the increased weight, causes less tire slip at speed.

Well that is enough for now.....

[8541Hawk]

And reading the rest of my notes I realized I forgot something so before I get corrected:
The RC triples I'm running have 5mm less offset so my numbers now are really:

for every 1mm decrease in fork offset:

Trail increases 1.1mm
Wheelbase decreases 0.9mm
Height of the bike’s center of gravity increases 0.2mm
Percent of the bike’s weight on the front wheel increases 0.05 percent

So add this forgotten bit to the mix and I end up with these numbers:

Trail- increase by .9mm for a total of 97.9mm

Wheel base- decrease of 8mm for a total of 1422mm

CG raised 7.8mm

% of weight transfer to the front wheel -.73%

[seb421]

I ran a full 954 front end and 6mm shock spacer on the rear, that felt fantastic for me

Its all fairly simple stuff re what its going to do which way you raise or lower both ends and how it moves weight bias and CG but the numbers although technical and interesting are just numbers at the end of the day, just got to see what feels best for each individual and take it from a factory setting and adjust it a little at a time to suit

[lloydie]

My head hurts :-(
I will read this again when I've woken up lol

[VTRDark]

I must admit I couldn't get my head around all the numbers. I agree with Seb, it's all about trial and error and going with what feels right. But there is going to be a point where one could go to far where it becomes dangerous.

(:-})

[8541Hawk]

I understand where you guys are coming from as yes it can make my head hurt at times also but there is a reason for all of it.

The first is it shows that if you make an adjustment (raise the forks or add a ride height spacer), you are actually are changing a number of chassis setting.
Which is why you want to make small changes and test the bike after each one.

Second it allows you to keep track of the one number that is very important IMHO for a street bikes (well all bikes really but trying to keep it simple) which is trail.
From what I have learned, you want to keep a minimum of 100mm of trail or you can end up with issues and usually need to fit a steering damper to keep the front end in check with anything less than 100mm of trail.

Though nothing is set in stone as I am running a touch less than 100mm of trail but I knew I'm was close enough to really test the bike out with no real "surprises" waiting to catch me out.

So it is not all really necessary, you can just slowly adjust things to make the bike work the way that fits your riding style, it is just I'm one of those guys that ask "why"?