Road Bike Geometry: Traditional vs. Comfort (eg. Trek 1000 vs. Trek Pilot 1.0)

* * Chas wrote:
I
had a 1954 Hetchins with a 44" wheelbase and 46cm chainstays. I could
ride over a speed bump and hardly feel it.

This is not because the rear triangle flexed, but because the
chainstays were a super-long 46cm and the overall wheelbase a
super-long 44". The extra-long chainstays move the contact patch back
away from under the arse, resulting in a much smoother ride, regardless
of flexibility. This well-known effect is geometric, not elastic.
Overall wheelbase, bottom bracket height, and wheel size are similarly
involved:

http://www.classicrendezvous.com/British/cycling_old_articles.htm
¿

"* * Chas" wrote:

Every test I've found on the web or seen quoted here are static tests.
The flexing that I'm talking about comes from road shock and impact
caused by bumps, pot holes, rough road surfaces, and so on.

The characteristics of the material in a static test are a very good
indicator of the characteristics at the frequencies we're talking
about (low audio range).

I agree, the horse is dead. BTW, I like the geometries that you use on
your frames.

Thanks - I haven't found anything that works better. ;-)

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

Gray wrote:
FWIW... a comparision of the geometries of the 2007 Trek 1000 and Pilot
1.0 taken from:

1000: http://www2.trekbikes.com/bikes/bike...id=1413000&f=3
Pilot: http://www2.trekbikes.com/bikes/bike...id=1402000&f=4

and the 1983 Trek 620 taken from
http://www.vintage-trek.com/images/t...churePart1.pdf

Frame Size
1000: 58cm
Pilot: 58cm
620: 22.5in (57.15cm)

Head Angle
1000: 73.0°
Pilot: 72.5°
620: 73.0°

Seat Angle
1000: 73.5°
Pilot: 73.0°
620: 73.0°

Effective Top Tube
1000: 57.3cm / 22.6in
Pilot: 57.0cm / 22.4in
620: 56cm

Actual Top Tube
1000: 56.9 / 22.4
Pilot: 54.8 / 21.6
620: 56cm

Chain Stay
1000: 41.7 / 16.4
Pilot: 41.7 / 16.4
620: 44.0cm

Bottom Bracket (ground clearance? center of BB to ground?)
1000: 26.8 / 10.6
Pilot: 27.2 / 10.7
620: 7.2 (called "drop" in 620 brochure; same?)

Offset (fork offset)
1000: 4.5 / 1.8
Pilot: 5.0 / 2.0
620: 5.5cm

Wheelbase
1000: 100.4 / 39.5 (1.3% than Pilot; 2.3% than old 620)
Pilot: 101.7 / 40.0
620: 102.8

Trail (defined at
http://www.slowtwitch.com/mainheadin.../geometry.html)
1000: 5.7 / 2.2
Pilot: 5.5 / 2.2

Stand Over
1000: 80.8 / 31.8
P ilot: 78.6 / 30.9

Seat Tube
1000: 58.0 / 22.8
Pilot: 53.0 / 20.9 (9.4% shorter than 1000; 5.6% than old 620)
620: 56cm

Head Tube
1000: 14.0 / 5.5 (36% longer than Pilot)
Pilot: 19.0 / 7.5

There are some significant differences from your ideal (620) here, most
significant being chainstay length, bottom bracket height/drop,
effective/real top tube length, and it would seem, handlebar height and
trail. The first three affect the response over bumps (see the article
by Davision I linked in my previous post), while the fourth is of
course rather a direct question of fit (as is effective top tube
length) and the last affects handling.

You can calculate bottom bracket height in inches from bottom bracket
drop in centimetres (7.2) if you know the wheel diameter, which
requires knowing exactly what size tire they used when referencing that
bottom bracket height.

Obviously the best solution would be to find a 620 used on eBay. It's
hard to say how big the differences above are, but I do believe they
are significant. I can't guaranteed the geomtries are similar, but you
might try looking at old Centurions, Raleighs, some others. Of course,
the best solution really is to find a 620. If after a quick check, I
were to find one available now on eBay, I wouldn't broadcast it here,
but really you should check for yourself.
ú

Gray wrote:
In the last 3
months, I've put about 500 miles on a borrowed vintage (1983) Trek 620
touring bike, which obviously has a very traditional geometry. In all
that time, I've never experienced any discomfort or body pain while or
riding (despite not owning any padded bike shorts and the 620 being
equiped with its original seat).

You found something you like? Good deal. If you haven't already,
measure the heck out of that bike, including "repeating" the factory
spec sheet for the frame. Record, incl. handlebar brand, model, width,
stem length, crank length, saddle brand, model, height and "setback",
whatever.

I know someone whose son (sent on a recon mission?) found an old steel
Trek at a yard sale for less than $30. Rideable with a little work.

(Understanding "children, budget"): I found a local-sale Ti Litespeed
on ebay recently. Was looking for a Trek or similar, for a sacrificial
(only if unavoidable) crit bike, but the L-d Catalyst wasn't much of a
budget stretch once a repaint was figured in. I got to look at it,
money in hand, and it indeed was very nice, low miles. "Decals already
removed", no worries about rust or disfigurement in normal use. Parts
scrounged successfully and economically, rides great.

Craigslist might be an excellent resource for local items, too. Happy
hunting! --D-y

"41" wrote in message
oups.com...

* * Chas wrote:
I
had a 1954 Hetchins with a 44" wheelbase and 46cm chainstays. I could
ride over a speed bump and hardly feel it.

This is not because the rear triangle flexed, but because the
chainstays were a super-long 46cm and the overall wheelbase a
super-long 44". The extra-long chainstays move the contact patch back
away from under the arse, resulting in a much smoother ride, regardless
of flexibility. This well-known effect is geometric, not elastic.
Overall wheelbase, bottom bracket height, and wheel size are similarly
involved:

http://www.classicrendezvous.com/British/cycling_old_articles.htm
¿

Interesting article.

In the mid 1970's I built a number of very large frames, 66cm to 83cm. I
was concerned about stiffness vs. flexibility and did a number of static
tests myself. We later had several European bike manufacturers build
frames and complete bikes for us which we sold both retail and
wholesale.

I obtained some special long tube sets and could build a 70cm all
Reynolds 531 (metric only) and a 67cm all Columbus frame.

I've never built a bike with curly stays but I've ridden a number of
them. The idea behind the design was that they were supposed to act as
rear "springs" and flex up and down to absorb road shock and impact.

A bicycle frame is not as rigid as many people think!

Chas.

* * Chas wrote:
"41" wrote in message
oups.com...

* * Chas wrote:
I
had a 1954 Hetchins with a 44" wheelbase and 46cm chainstays. I could
ride over a speed bu mp and hardly feel it.

This is not because the rear triangle flexed, but because the
chainstays were a super-long 46cm and the overall wheelbase a
super-long 44". The extra-long chainstays move the contact patch back
away from under the arse, r esulting in a much smoother ride, regardless
of flexibility. This well-known effect is geometric, not elastic.
Overall wheelbase, bottom bracket height, and wheel size are similarly
involved:

http://www.classicrendezvous.com/British/cycling_ol d_articles.htm
¿

Interesting article.


I've never built a bike wi th curly stays but I've ridden a number of
them. The idea behind the design was that they were supposed to act as
rear "springs" and flex up and down to absorb road shock and impact.

Alf Hetchin and his builders knew bicycles, so I don't think they
actually believed that marketing ploy, although I don't know if anyone
knows for sure. The real reason though was that at the time, no logos
of any kind were allowed on the bicycles used for six day races and so
on, so they came up with this as a brilliant way of making their
bicycles identifiable. Also, the aesthetic matches the Hetchin's lugs
very well.

A bicycle frame is not as rigid as many people think!

The rear triangle (tetrahedron), made out of somewhat flexible but
effectively incompressible tubes that are triangulated, is effectively
completely rigid. The front triangle is not a triangle and therefore
has some compliance, especially at the head tube/steerer, and depending
too on the size of the frame. But it still pales in comparison with
that of the tires. You might notice that no automotive springs are ever
made out of comparable tubes of steel.

Bicycles have much more compliance laterally. Some work (at Trek) seems
to show that lateral stiffness does indeed have something to do with
perceived ride comfort, although how exactly this works is not clear.
This was reported in the Velo News article on frame stiffness testing
that I mentioned some time ago. I believe it was the May issue.
‡

Mark Hickey wrote:
"* * Chas" wrote:

...BTW, I like the geometries that you use on
your frames.

Thanks - I haven't found anything that works better. ;-)

See http://www.ransbikes.com/images06/F5XP/7F5XP.jpg for an example
of a better frame geometry.

--
Tom Sherman - Here, not there.

"Johnny Sunset aka Tom Sherman" wrote:

Mark Hickey wrote:
"* * Chas" wrote:

...BTW, I like the geometries that you use on
your frames.

Thanks - I haven't found anything that works better. ;-)

See http://www.ransbikes.com/images06/F5XP/7F5XP.jpg for an example
of a better frame geometry.

Wait, I was talking about bikes... ;-)

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

"41" wrote in message
ups.com...
snip
The rear triangle (tetrahedron), made out of somewhat flexible but
effectively incompressible tubes that are triangulated, is effectively
completely rigid. The front triangle is not a triangle and therefore
has some compliance, especially at the head tube/steerer, and depending
too on the size of the frame. But it still pales in comparison with
that of the tires. You might notice that no automotive springs are ever
made out of comparable tubes of steel.

Some cars us hollow torsion bars which are springs of sorts.

There a special tape used to measure stress and movement. I've never
seen this material applied to testing bicycle frames. I'm going to try
and get some of this tape and prove a point.

Chas.

* * Chas wrote:
"41" wrote in message
ups.com...
snip
The rear triangle (tetrahedron), made out of somewhat flexible but
effectively incompressible tubes that are tria ngulated, is effectively
completely rigid. The front triangle is not a triangle and therefore
has some compliance, especially at the head tube/steerer, and depending
too on the size of the frame. But it still pales in comparison with
that of the t ires. You might notice that no automotive springs are ever
made out of comparable tubes of steel.

Some cars us hollow torsion bars which are springs of sorts.

There a special tape used to measure stress and movement. I've never
seen this material applied to testing bicycle frames. I'm going to try
and get some of this tape and prove a point.

If you can manage it, it might be instructive. Before doing so, you
might want to dig up the, May issue I believe it was, where they had an
extensive article on frame stiffness testing as done by various
manufacturers. You may note that according to the article, only one of
them (Specialized) even goes to the trouble to test vertical
compliance, and even they are yet to make use of the data in any
production bicycle, zerts or not.