A complex question about front end geometry

[robtg]

With the axle it the center of the leg and less offset in the triple clamp you would have more trail.
The shorter fork will increase steering head angle a bit and reduce trail, but not by much.
Overall trail should be increased.

So, like this, right ?

The axle is in the center of the fork, whereas the BMW axle is on the front of the fork leg, so further forward.

The Duc increases trail by virtue of a lesser ("0") axle offset.

The Ducati fork has less overall offset. In other words, it does not end up as far forward.

Also the Duc increases trail by virtue of a lesser fork offset.

Anything that changes the the tire contact patch point on the ground in relation to steering axis changes the trail.
Less T/C offset, moving the axle to the center of the slider, move the wheel to the rear increasing trail.

[Chuey]

As I said in the last sentence of my original post, I'm going to measure everything out that I can think of. I started and then it got too dark. Tomorrow.

Chuey

[Deleted User 61]

One of my favorite bikes I never owned:

[Duane Ausherman]

Rob, I completely ignored that model and shame on me. It is worthy of being chosen to not own, or own.

[Chuey]

I measured the trail as well as I could. On the stock BMW I came up with 4" of trail. On the one with the Ducati fork and a 19" BMW wheel, it is 5 1/4".

What are modern bikes running for trail?

Chuey

[robtg]

I measured the trail as well as I could. On the stock BMW I came up with 4" of trail. On the one with the Ducati fork and a 19" BMW wheel, it is 5 1/4".

What are modern bikes running for trail?

Chuey

R100 trail from the factory shop manual--3.74"

[vanzen]

...R100 trail from the factory shop manual--3.74"

FWIW: I have planned for a trail # of @ 3.69 inches – not too far from stock ,
but a good balance in terms of stability and curve-ability .... IMO.

... and a well considered choice.

[Major Softie]

Sorry I missed this for a bit, Chuey, but there's something VERY important that you are not considering here.

There's a reason that fork is available and (very) affordable. The Ducati Sport Classic fork is generally considered to be the absolute worst fork on any modern motorcycle, and CERTAINLY the worst fork on any Ducati from (at least) the past 20 years. The fork is the first thing changed on almost every SC I knew about. On top of this, the SC is nearly 100 lbs. lighter than an airhead, and the SC fork is horribly undersprung. So, it would be inconceivable to consider this change without first making sure that someone is making a spring heavy enough for this application.

Also, the Ducati SS fork, was a fully adjustable fork and is about an inch longer than the SC fork. This fork fits into the same triple clamps, so it would also work on your bike without the height issues you are currently facing (although the trail change issues would still exist).

SO, in case you haven't noticed, I think you might want to adjust your current plan.

[Chuey]

Thanks, I was thinking of checking into fork lengths used by Ducati. I was figuring on using an 18" rim so having to go to the 19" was only for measuring, to see if I could get the figures somewhere in the ball park.

Chuey