Boxerworks.com

gspd wrote:There is no OPTIMUM setup.
Tuners have been experimenting with rake/trail variations since the first motorcycle was built.
All are a compromise between stability and flickability.

Exactly true as evidenced by Tony Foale's experiments
and the current trend to decrease rake & trail from the old world "golden standard".
Improved chassis design, and (yes, Major) tire technology
have raised the bar to allow a level of "flickability" & "stability"
unknown even in the recent past.
The temporal nature of the march of changing standards and engineering
will not preclude the judicious application of this technology
to revise the handling characteristics of an old mc.

An "old school" technique for solo-spirited riding on a relatively stock box
was to crank up the rear shock preload to max.
This decreased effective rake & trail
and allowed for lighter handling in the twisties.
Best used on smooth roads,
the down-side of this technique was loss of suspension compliance and road holding ability.
Ken Whitehawk has proposed a better scenario – longer shocks.
This accomplishes the same goal of a slightly quickened geometry
but with the advantage of an optimally tuned suspension.
Even a small change = felt results !

Experimentation with rake & trail is either limited or expensive on a twin-shock stock boxer chassis.
Any experimentation should be approached with the strategy of making one minute change
followed by cautious riding to witness the difference.
A whole concert of physics is at play in an mc chassis –
surpassing a critical threshold can be either dangerous or disastrous !

IMO: Consider the importance of that legendary balance called "neutral handling" –
and not just the solitary goal of quicker steering

vanzen@rockerboxer.com wrote:Did I even suggest that the rake & trail #s of an R12S are suitable for an airhead chassis with a K-fork ?
I think not, Major !
Please note that I am trying to learn something here, and not simply argue irrelevant details ...

My apologies. It seemed that you were using the comparison with the 1200's geometry to support a statement that the older design's numbers yielded "lethargic" handling vs. the handling of the 1200: old numbers = lethargic, 1200 numbers = good handling. That was the way I was reading it, thus my question. I did not realize that the comparison was an irrelevant detail.

vanzen@rockerboxer.com wrote:Have there been any triangular profile tires on the market since the mid '70s ?
They were a disaster !

Oh yeah, they were still around in the 80's and maybe even into the 90's. I don't know about track tires, but Dunlop was still selling something with a triangular profile. I have no idea if there are any left today, although some current tires are still described as being "more triangular" than their predecessors (such as Pirelli Diablo Supercorsas and Dunlop Qualifiers), but there's "more triangular" and then there's "triangular."

Here are two shots to show the front end and the geometry of the bike. I didn't have time to measure rake, wheelbase and calculate trail, but the forks are now up through the yokes by the same amount as before installing the gaiters.

Jean: Thanks for your advice about buying non stock gaiters, after much thinking, I went for these Triumph scrambler ones (modern Triumph).

Vanzen: I pulled them further over the tops of the forks and down to reduce the amount of rubber in the way at full compression (note flat section above the second corrugation: That is where the fork seal is)

The idea is to have the fork tubes shortened (by an engineering firm) once I have found the ideal length, as I don't like seeing them projecting through the top yoke.

Pipes are not straight through, the rear section came that way from the tube bender. I have cut up some Keihan mufflers and will install perforated tubes with glass packing.

Mmmmmm, you got some brakes now.

It's funny how massive those lower castings look. I guess it's partly because we've now gotten used to "upside-down" forks.

Are you going to use the airbox or go to pods?

Major Softie wrote: I guess it's partly because we've now gotten used to "upside-down" forks.

Mine have only been upside down a few times, it's not something I really want to get used to.

Major Softie,

I've had this front end on the bike since about 2002, the brakes calipers are great and work with the under-tank master cylinder so I was able to keep the 1974 handlebar controls.

Sam

Major - I'll keep the airbox.

Major Softie wrote:...
Oh yeah, they were still around in the 80's and maybe even into the 90's. I don't know about track tires, but Dunlop was still selling something with a triangular profile. I have no idea if there are any left today, although some current tires are still described as being "more triangular" than their predecessors (such as Pirelli Diablo Supercorsas and Dunlop Qualifiers), but there's "more triangular" and then there's "triangular."

Yes, tires, particularly track tires, having what could be described as a "triangular-ish profile" ...
I also remember one VERY triangular tire marketed by Dunlop back in the day, maybe a K81 ? –
Scary business. The K81 profile made turn-in an effortless "non-event"
with a transition that felt extremely vague & awkward !
Rounding a curve with those tires could best be described as:
"Falling ... and then catching yourself from falling"
(with apologies to Laurie Anderson)

Sam, you've been busy ! A radical departure from what I remember of the mc.
The updated works & classic styling is nothing less than elegant.

Just my opinion, of course, but I will think that you took the right path with the gaitor-fitment solution !

What would be the measured distance from the top of the yoke casting to the top of a stanchion tube ?
This simple measurement is a good general clue / indication of the resulting geometry.

vanzen@rockerboxer.com wrote:Yes, tires, particularly track tires, having what could be described as a "triangular-ish profile" ...
I also remember one VERY triangular tire marketed by Dunlop back in the day, maybe a K81 ? –

Yeah, I remembered it was a "K" with some numbers. 81 may be correct.