[desmo_pt]

Originally Posted by doorsdude

cheers for the feedback! quick question though, how is the swingarm angle measured?

With the back wheel just touching the ground, to take out the sag from the rear.

Measure the height of the swingarm axle to the ground, call it A.

Measure the height of the wheel axle to the ground, call it B.

Measure the swingarm lenght.

Now you have the two values to use in here.

Calculate Angle and Sides opposite, hypotenuse, adjacent of right angled triangle calculator

A-B = Adjacent side
Swingarm lenght = Hypotenuse

[doorsdude]

sweet!

[Woopy]

The magic number (swingarm angle) on gsxr's etc seems to be 12-13 degrees.

Are we looking at 10-11 for the Ducati SSA and the linear rocker?

Cheers

[1fast750ss]

A general consensus is that most people have the best feel and control of the bike with the angle at 10-11*. That said, there are other variables to consider, swingarm length for example.

You should not look for the question, rather the answer, and the degree is just an equation. The upward force versus the TQ required to compress the spring in a "linear"(you asked about the linear link) movement is your answer, at a force amount to ensure enough anti-squat of the chassis during acceleration so that the longitudinal force doesn't transfer too much weight to the rear.

So does the "answer" require the same equation from an 848 versus the 1198?

[Woopy]

Fair enough.... not just swingarm angle
So you are saying that the torque from the 1198 is considerably more than the 848 in causing the anti-squat under power and the swingarm length (which will also have an effect on the swingarm angle) will determine the balance in weight transfer (pro-squat) versus the anti-squat?

So.. if I was running 14/38 gearing on my 1198 (505mm swingarm length) and I had a DU714 ttx shock (shorter clavis) with a linear rocker.... what do I need to complete the equation?

Surely the subjective nature of rider style/experience getting on the gas (hard/soft) would get in the way of all of this objectivity?

[1fast750ss]

Originally Posted by Woopy

Fair enough.... not just swingarm angle
So you are saying that the torque from the 1198 is considerably more than the 848 in causing the anti-squat under power and the swingarm length (which will also have an effect on the swingarm angle) will determine the balance in weight transfer (pro-squat) versus the anti-squat?

So.. if I was running 14/38 gearing on my 1198 (505mm swingarm length) and I had a DU714 ttx shock (shorter clavis) with a linear rocker.... what do I need to complete the equation?

Surely the subjective nature of rider style/experience getting on the gas (hard/soft) would get in the way of all of this objectivity?

Think of the TQ of either motor as the leverage necessary to create Squat Effect. However it is just one variable. Swingarm length, angle and spring rate have similar affects on the sum you are looking for.

Invariably, its in how you set the bike up that will create anti-squat though. Think as in Newtons' third law of motion regarding equal and opposite action(force) theory. You need to balance the components within their own regard to summarily control squat.

Does that mean the angle will always be the same on every bike? Will the swingarm length be identical? Even to make it more finite, how about an 848 versus and EVO 848 with different TQ characteristics? In this case you deal with increased motion versus peak TQ at a given distance, so equalled out to a lower result in TQ at any given RPM. This will affect your development too.

How about different TQ values and contact patch area between all of the bikes at lean angles and their relative cosign? Tire size and pressure levels as a variable, not to forget compound.

The subjective nature of rider style/experience getting on the gas is truly a variable, but don't forget electronics. Does the bike have TC? What level do you run it at? How does it affect your riding?

FYI, instead of running 14/38 gearing, I would recommend a change it to a 15/40, and the reasons are as follows: 1. decreasing angle between both radius' aiding in anti-squat. 2. (not as big a deal)opposite tooth counts aid in chain durability by decreasing the percentage of a given link hitting the same tooth, resulting in premature wear. 3. The difference in ratio is only .04, so not going to be a huge difference.

A 505mm swingarm length is recommended simply because the swingarm is inherently short for race purposes, otherwise Checa's or Zemke's bike would have a stock unit on it.

Having a baseline number is good, but never the answer, as you will find. You may notice the bike handles better with an angle of 9.5* and more preload but a softer spring and compression because you run the throttle very smooth through the turns. Another issue is the rod position in relation to the shock position. This will position the rocker at a specific angle causing premature radius movement of the rocker/rod/shock points of contact, which may increase or decrease your overall rate.

Just FYI, if you put that last statement together with ride height and swingarm angle, a little light should come on. Bink!

I know I'm splitting hairs here guys, and I'm not acting like I'm into loop versus string theory but I bring this out to let you guys open up to all of the variables of developing your bikes. It's not a finite answer, only an infinite question.

[Woopy]

Oh Brian, I think I'm just going to buy a fixed frame push bike and sell the Duke!
It's doing my head in. I understand the variables at play, but am never going to be able to analyse it all in the detail you described.

I will throw a new rear tyre on and find out what my baseline measurements are and work from there.

Cheers

[1fast750ss]

LMAO!

I was splitting hairs! I get a bit nerdy sometimes.

Start at around 10* unloaded swingarm angle and work from there. So get the bike off of the ground when measuring and set the ride height to get you in the area.

Measure your heights F&R to determine the angle. If you need help, give me a holler or an email.

[Soz]

Brian, that's a pretty awesome write up. I have a couple of questions though, as I tend to simplify things a lot.

Once you have installed your components, eg: triples, shocks, springs etc - then set your sags up to your weights, then aren't things such as swing arm angles and rakes going to be determined by any changes you make to fork height and ride height anyway? Why is it really necessary to know these dimensions? If you treat your trail measurement as the starting point target measurement, and for argument sake lets call it 100mm, then by starting at your fork height, the only way to then change your trail is by adjusting ride height, correct? This will change all the other dimensions, but practically, do you really need to know them?

If you are not happy with the result of your starting point fork height, you can either raise or lower them and adjust your trail back by re-adjusting ride height, correct?

Please forgive my ignorance here, I am trying to understand if there is something I am missing myself.

[Woopy]

Hey Soz
I was working on the same principal initially, then I started to realise that you need to start at the back of the bike and then move forward. If you get your swingarm angle/wheelbase etc correct (thru your ride height adjustment) then you will get the bike driving forward out of the turns. Then you approach the front end for turn in/stability etc.

I found this really long link from Dave Moss who explains it in basic detail.


Measuring swing arm angle, interrelationships of shock length, and axle position, How to measure swing arm angle cheaply and quickly, how shock length and ...