Frame geometry questions

[wcorey]

I noticed on the Seattle craigslist ad posted here for the 450 R/T that the seller states .. "the frame is original not modified as many were for high speed stability...".
Anyone know why there's a stability issue and what this modification entails? These obviously have a rearward weight bias compared to other models, the rear tire looks closer to the motor and the fork much further forward. My impression looking at the low rear ride height and tall front end would be that the rake/trail is greater. Anyone have numbers for the wheelbase, swingarm length, rake/trail for the scrambler/mk3 frames?

[Teckhardt]

I noticed on the Seattle craigslist ad posted here for the 450 R/T that the seller states .. "the frame is original not modified as many were for high speed stability...".
Anyone know why there's a stability issue and what this modification entails? These obviously have a rearward weight bias compared to other models, the rear tire looks closer to the motor and the fork much further forward. My impression looking at the low rear ride height and tall front end would be that the rake/trail is greater. Anyone have numbers for the wheelbase, swingarm length, rake/trail for the scrambler/mk3 frames?

Wheelbase is shown here in the 450 Owners Manual. R/T is not listed.

http://www.bevelheaven.com/manuals/450_ ... p38-39.htm

[wcorey]

I can barely make out those manual numbers, even blowing them up and using a magnifier, lol.

I have Ian Falloon's 'The Ducati Story' and realized the wheelbase specs are in there, haven't been able to find any of the other numbers though.
Seems the R/T is 1490mm, the mk3's and most others 1360mm, that's over 5". Some of the extra wheelbase is probably due to the taller fork but there is obviously some significant additional length sticking out in front, some of which was to clear the 21" wheel I would think.

I got out the protractor and put it up against some pictures for a general reference. Looks like the rake on both the stock R/T and Mk3 is at about 26 degrees, but a 19" wheel and 'street length' fork brings the R/T in 4 or 5 degrees and the trail at somewhere around 2". Considering a typical sport bike is 24 degrees and upwards of 4" of trail that could certainly make things more than a bit twitchy. I have to assume the frame mod involves at minimum changing the rake of the steering head.
When I first decided to do a street conversion on it I suspected that moving the steering head back and lengthening the swing arm might be an improvement but I hadn't got as far as to figure out the change in rake. I wanted to avoid altering the frame but in light of this I guess I'll have to, I've owned it for twenty years now and I doubt I'll ever sell it anyway. Won't have to bother keeping all the original equipment around either. There doesn't seen to be a lot of interest in collecting this model anyway.
Is this 'morally wrong'...?

[Teckhardt]

There doesn't seen to be a lot of interest in collecting this model anyway.

Think the R/T is a love it or hate it kinda thing. I grew up on dirt bikes so I love it. Someday I would like to have one to go with my SCR.

Is this 'morally wrong'...?

It's your bike - do what you want with it. If someone wants to buy it from you to "save it" then they could do what they want.