[desmo_pt]

Originally Posted by Duc_L_over_V

26mm is a ridiculously small amount of offset. Why not 28mm and eccentric head bearings to change the rake to 23.5 degrees? You may want to turn your damper in a few clicks...

I bought the bike like that.

I don't think that reducing the trail will resolve the problem. But is another thing to try.

[STOPPIE]

Originally Posted by desmo_pt

Is really scary, on the big straight you just grind you teeth and go for it.

In the back straight with the kink i can't manage it. For you to see i can't be faster with the 1098 as a was with my 748R...

Do you leave little drops of pee on the track? LOL

[desmo_pt]

Originally Posted by STOPPIE

Do you leave little drops of pee on the track? LOL

[1fast750ss]

Originally Posted by desmo_pt

Hi Frank,

Great article!

I'm also going around the geometry of my bike!

My bike is a 1098S track preped, with a tuned engine. The chassis has a 26mm offset triple.

I'm having a problem with wobble on the straights at WOT even in 6th.

One of the causes of my problem and a thing to watch when putting a lower offset triple is the wheelbase, as each millimetre of offset you take you roughly get out the same in the wheelbase. And that causes all the sort problems stability wise.
The problem is worse in the 1098 bike as the swing arm doesn't have the range of the 999 bikes. I'm at the longest position and have 505mm of swingarm length, that with a brutal engine, get's me the wobble.

Other cause that i will study in the next track day is a COG height, high in my case, the forks are flushed with the triples, and coupled with a very high speed, acceleration track like Estoril, this might be another cause for the wobble.

Here is a video of a bike with the same problem, mine is a little worse, but you get the point.

Mugello_20120407_Session2.wmv - YouTube

After the trackday i will have a idea of the problem.

I'm already considering a SF swingarm as will get me the lost wheelbase, and give more front weight.

If you have more solutions for me to try...

If you are having issues with stability in straights, it would seem your problem is with load transfer, resulting in your front getting too light. It's not a wheelbase issue. If that were the case, every Japanese bike would be doing that, as they are all under 56" wheelbases.

I wouldn't worry about the 26mm offset triples. I run 27mm on my street bike. That is probably the one factor saving your skin right now.

This may be due to your swingarm being too flat. Back when the 1098 came out, everyone "assumed" that you had to lower the rear end to get it around the track. Not so much.

It could be many things. Feel free to contact me and let's see if we can sort it our for you.

[desmo_pt]

Originally Posted by 1fast750ss

If you are having issues with stability in straights, it would seem your problem is with load transfer, resulting in your front getting too light. It's not a wheelbase issue. If that were the case, every Japanese bike would be doing that, as they are all under 56" wheelbases.

I wouldn't worry about the 26mm offset triples. I run 27mm on my street bike. That is probably the one factor saving your skin right now.

This may be due to your swingarm being too flat. Back when the 1098 came out, everyone "assumed" that you had to lower the rear end to get it around the track. Not so much.

It could be many things. Feel free to contact me and let's see if we can sort it our for you.

Hi Brian,

The load transfer is what i think also and why i want to try reducing the front height, to reduce the CoG.

About the swingarm angle, i don't think that is the problem. I'm using measured with the ducati height tool 248mm.

I bought an inclinometer so i can take measures and see what is the geometry, them i will ask for your help with numbers.

[doorsdude]

interesting discussion guys. would you mind explaining the measuring technique in a bit more detail for those of us that don't know enough about the subject. for instance, when you say the swingarm length is x, from where to where is the measurement taken, and what tools are used. also, with today's superbikes, what are good geometry settings to start off with?

[desmo_pt]

Originally Posted by doorsdude

interesting discussion guys. would you mind explaining the measuring technique in a bit more detail for those of us that don't know enough about the subject. for instance, when you say the swingarm length is x, from where to where is the measurement taken, and what tools are used. also, with today's superbikes, what are good geometry settings to start off with?

I will try and explain the principal measurements.

Front

For the front you need to get 3 values.

Fork Offset - Distance between the centre of the forks and the centre of the headstock
Headstock angle
Radius of the front tyre

Rear

Swingarm angle
Swingarm length - From the pivot of the swingarm in the frame to the centre of the wheel. A bigger length improves traction and transfers weight to the front.

General Measures

Wheel base - Centre front wheel to centre back wheel
Weight distribution F an R

Some general rules

The measurements are taken without sag, with wheels off the ground, except weight distribution.

The geometry we are aiming is:

Trail - 100mm
Swingarm angle - 10 to 12%
Weight distribution - 52F 48R

There is also another variable that i think important , CoG position, but i don't know values for this.

Now, this values and the way to get them are very different from bike to bike and each change is diferent for each bike. Also the setting must be adaptable to each rider.

Brian will surelly complement my information, as he studied more this geometry stuff.

[1fast750ss]

Originally Posted by desmo_pt

Hi Frank,

The load transfer is what i think also and why i want to try reducing the front height, to reduce the CoG.

About the swingarm angle, i don't think that is the problem. I'm using measured with the ducati height tool 248mm.

I bought an inclinometer so i can take measures and see what is the geometry, them i will ask for your help with numbers.

Knowing is half the battle, starting with my name(Brian). No worries there.

Here's what you should focus on PT. If you are using a DP ride height tool, are you measuring at the top or the middle? The DP is taken from the middle, so you may be running lower than you think. If the rear has not been touched in the past, the ride height is closer to 238mm.

The second point of focus; has the front been increased? What is the fork height measurement from the top of the triple clamps to the center axle..... You can do this with the front off of the ground or on the ground, that won't matter as I know stock numbers.

Most importantly, do "NOT" lower the front end(at least not yet)..... Lowering CofG will put your bike at a disadvantage, in turning and transitions. Not only that, your swingarm will flatten, making your problem worse than it is now.

I think we can cure your straight speed "ills" with just a few minor tweeks, but feel free to PM me. Let's get your bike safe to ride at speed.

[doorsdude]

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

[desmo_pt]

Originally Posted by 1fast750ss

Knowing is half the battle, starting with my name(Brian). No worries there.

Sorry, don't know were Frank came from...

Originally Posted by 1fast750ss

Here's what you should focus on PT. If you are using a DP ride height tool, are you measuring at the top or the middle? The DP is taken from the middle, so you may be running lower than you think. If the rear has not been touched in the past, the ride height is closer to 238mm.

I'm measuring to the top of the tool. But to help, the height adjuster is with 7 threads showing.

The bike is an ex race bike, it has been changed..

Originally Posted by 1fast750ss

The second point of focus; has the front been increased? What is the fork height measurement from the top of the triple clamps to the center axle..... You can do this with the front off of the ground or on the ground, that won't matter as I know stock numbers.

Most importantly, do "NOT" lower the front end(at least not yet)..... Lowering CofG will put your bike at a disadvantage, in turning and transitions. Not only that, your swingarm will flatten, making your problem worse than it is now.

The front is flushed with the triples. The forks are the 1098S original Ohlins.

Originally Posted by 1fast750ss

I think we can cure your straight speed "ills" with just a few minor tweeks, but feel free to PM me. Let's get your bike safe to ride at speed.

Let me take the measurements. Then i will get in touch with you.
Thank for your help.