--- In KOG@yahoogroups.com, "Kogswell Cycles" <kogswellcycles@>
> wrote:
> >
> > At 145, I think you should be using no more than a 30 in
> > the back and about a 28 in front, unloaded or a 30 in front
> > loaded. And the 28 will naturally need to be pumped
> > up to above 80psi. And the 30 could be used at right
> > around 80. And since tires that are inflated to higher
> > pressures have less pneumatic trail, then 41 is right
> > for -high-side- trail.


OK. I just consulted my copy of Bicycle Quarterly, Volume 5 Number 3. Quoting
from the
article "How To Design a Well-Handling Bicycle" on page 45:

+++
MODERATE LOAD, MEDIUM TIRES

Bike #4, RH No.148 51 Randonneuse (1951).
700Cx30mm (dia.:690mm). f=10.9mm.
[my note, Bike #4 has 39mm trail]

"...The Singer is close to perfect for riding with a moderately loaded handlebar
bag. It
rides straight with little concentration, corners with ease and precision, and
climbs without
excessive wheel flop. It is stable at speeds of 80km/h (50mph) and more."

"However this geometry relies on the pneumatic trail of relatively wide tires
for its stability.
__With 30mm tires at 5.2 bar (75psi)__[emphasis mine], the Singer is close to
perfect,
whereas with 21mm tires at 8.3bar (120psi), it lacks directional stability."

MODERATE LOAD, WIDE TIRES

Bike #5. RH 2 52 Randonneuse (1952). Tires:
650Bx39mm (dia.: 669mm). f=7.2mm.
[my note, Bike #5 hs 26mm trail]

"The wider tires of the 650B bike (No. 5) add significant pneumatic trail, so
the geometric
trail hs ben reduced to 26mm. The bike's handling is very similar to that of
the 700C
Randonneur bike (No. 4), with perhaps a slightly lighter steering and more
low-speed
stability due to its decreased wheel flop factor. Despite its low geometric
trail, this bike is
very stable at high speeds of 80km/h (50 mph) and more."

+++


So, Matthew recommending 700x30 tires at 75-80psi for a ~40mm trail bike does
agree
with what Jan wrote.

What I'm taking away from this is that I should either switch to a narrower 30mm
tire @
75psi on my bike, or swap the 40mm trail fork for the 30mm version, and keep the
tires
as is. Unfortunately Jan doesn't report on the tire pressure used for Bike #5
above, but
since it's a 650B tire I think we can safely assume that they're lower.

-Jim G