Frame Stiffness - What Does It Affect

One frame laterally deflects 2.5 mm and another 5 mm .....what does this
mean? For me the bottom line is handling. I've ridden the whole spectrum
from a Trek Carbon that was really stiff and tracked through high speed
turns like it was on rails to a lightweight steel track frame (now
relegated to my stationary trainer as a permanent fixture) that becomes
unrideable in the turns at 30 mph on the track.

What exactly is going on to make one frame handle better than another.
IMO its the lateral deflection resulting in the rear wheel
alignment/tracking going out of sync with the front wheel. Smaller sized
and compact frames, even with longer seatposts and stems, tend to track
better because the lateral deflection within the frame is proportionally
less so the wheels stay aligned better.

I also rode a Softride for a couple of seasons where lateral deflection
of the seat was huge yet it had no affect on the handling
characteristics of the bike (which were pretty good).

My 2 cents

Phil H

Phil Holman wrote:
One frame laterally deflects 2.5 mm and another 5 mm .....what does this
mean? For me the bottom line is handling. I've ridden the whole spectrum
from a Trek Carbon that was really stiff and tracked through high speed
turns like it was on rails to a lightweight steel track frame (now
relegated to my stationary trainer as a permanent fixture) that becomes
unrideable in the turns at 30 mph on the track.

it's not fluke that steel isn't a feature with elite riders any more.
r.b.t retrogrouches still cling to it, and it can be very pretty, but to
get it light enough, it gets too flexy to make a good ride.




What exactly is going on to make one frame handle better than another.
IMO its the lateral deflection resulting in the rear wheel
alignment/tracking going out of sync with the front wheel. Smaller sized
and compact frames, even with longer seatposts and stems, tend to track
better because the lateral deflection within the frame is proportionally
less so the wheels stay aligned better.

call it torsional stiffness, and you'll be dead-on. and yes, torsional
stiffness does mean the wheels stay aligned as intended.



I also rode a Softride for a couple of seasons where lateral deflection
of the seat was huge yet it had no affect on the handling
characteristics of the bike (which were pretty good).

right. the torsional stiffness on the softride is not a function of the
seating beam.



My 2 cents

Phil H

On Sat, 19 Jan 2008 09:33:21 -0800, "Phil Holman"
piholmanc@yourservice wrote:

One frame laterally deflects 2.5 mm and another 5 mm .....what does this
mean? For me the bottom line is handling. I've ridden the whole spectrum
from a Trek Carbon that was really stiff and tracked through high speed
turns like it was on rails to a lightweight steel track frame (now
relegated to my stationary trainer as a permanent fixture) that becomes
unrideable in the turns at 30 mph on the track.

What exactly is going on to make one frame handle better than another.
IMO its the lateral deflection resulting in the rear wheel
alignment/tracking going out of sync with the front wheel. Smaller sized
and compact frames, even with longer seatposts and stems, tend to track
better because the lateral deflection within the frame is proportionally
less so the wheels stay aligned better.


This all makes sense to me.

still just me wrote:
On Sat, 19 Jan 2008 09:40:21 -0800, jim beam
wrote:

it's not fluke that steel isn't a feature with elite riders any more.
r.b.t retrogrouches still cling to it, and it can be very pretty, but to
get it light enough, it gets too flexy to make a good ride.

My experience as a retro-grouch steel rider is that the flex results
in the bottom bracket moving side to side. The worst effect I notice
is that when you are humping you can have some chain /gear alignment
issues....

What does connecting railroad cars (humping) have to do with the
discussion?

--
Tom Sherman - Holstein-Friesland Bovinia
"And never forget, life ultimately makes failures of all people."
- A. Derleth

On Jan 19, 12:33 pm, "Phil Holman" piholmanc@yourservice wrote:
One frame laterally deflects 2.5 mm and another 5 mm .....what does this
mean? For me the bottom line is handling.

If you carry a significant touring load on the bike, lateral
deflection can mean a lot. I've ridden with two people whose bikes
shimmied terribly with loaded panniers, to the point they were
unrideable under certain conditions. Frames that are stiffer
laterally are much less likely to suffer that problem.

- Frank Krygowski

On Jan 19, 6:12*pm, wrote:
On Jan 19, 12:33 pm, "Phil Holman" piholmanc@yourservice wrote:

One frame laterally deflects 2.5 mm and another 5 mm .....what does this
mean? For me the bottom line is handling.

If you carry a significant touring load on the bike, lateral
deflection can mean a lot. *I've ridden with two people whose bikes
shimmied terribly with loaded panniers, to the point they were
unrideable under certain conditions. *Frames that are stiffer
laterally are much less likely to suffer that problem.

I had that (shimmy, loaded touring bike) happen on the first downhill
of a Rockies tour. On a stop, I noticed my front panniers' mounting
cords had "rotted" (the rubber strands inside had turned into knotty
lumps) over the winter previous and had lost the stretch they had when
put on shortly before. Problem cured, didn't return, when I wrapped
each pack tightly to the carrying rack with spare bungee cords. That
was a new frame that I thought was at fault. Not a nice feeling but
this at least was an easy fix. --D-y

On Jan 19, 4:29*pm, Tom Sherman
wrote:
What does connecting railroad cars (humping) have to do with the
discussion?

You are both confused:
http://video.google.com/videoplay?do...arch&plindex=1

Ron Ruff wrote:
On Jan 19, 4:29 pm, Tom Sherman
wrote:
What does connecting railroad cars (humping) have to do with the
discussion?

You are both confused:
http://video.google.com/videoplay?do...arch&plindex=1

That is about as annoying as the sound the "retarders" make at a hump yard.

--
Tom Sherman - Holstein-Friesland Bovinia
"And never forget, life ultimately makes failures of all people."
- A. Derleth

Phil Holman wrote:
One frame laterally deflects 2.5 mm and another 5 mm .....what does this
mean? For me the bottom line is handling. I've ridden the whole spectrum
from a Trek Carbon that was really stiff and tracked through high speed
turns like it was on rails to a lightweight steel track frame (now
relegated to my stationary trainer as a permanent fixture) that becomes
unrideable in the turns at 30 mph on the track.

What exactly is going on to make one frame handle better than another.
IMO its the lateral deflection resulting in the rear wheel
alignment/tracking going out of sync with the front wheel. Smaller sized
and compact frames, even with longer seatposts and stems, tend to track
better because the lateral deflection within the frame is proportionally
less so the wheels stay aligned better.

The biggest problem arising from a flexy frame is probably tyre scrub at
the rear wheel. I don't think it affects handling greatly, at least for
a conventional diamond frame.

Things like twin-lateral mixte frames, and some folders, are supposed to
be woeful if you get out of the saddle and stomp.

On Sat, 19 Jan 2008 09:33:21 -0800, "Phil Holman"
piholmanc@yourservice may have said:

One frame laterally deflects 2.5 mm and another 5 mm .....what does this
mean?

In some cases, it might mean the difference between the chain clearing
vs. rubbing on the der cage. It could mean the difference between the
chain riding down onto the next sprocket during a downshift on a hard
climb, or riding over it onto the BB shell. It might mean the
difference between the slightly too fat tire rubbing on the chainstay,
or not. It might mean any number of things having to do with
clearance issues.

For me the bottom line is handling. I've ridden the whole spectrum
from a Trek Carbon that was really stiff and tracked through high speed
turns like it was on rails to a lightweight steel track frame (now
relegated to my stationary trainer as a permanent fixture) that becomes
unrideable in the turns at 30 mph on the track.

That's far more likely to be a matter of angular geometry than frame
stiffness, IMO.

What exactly is going on to make one frame handle better than another.
IMO its the lateral deflection resulting in the rear wheel
alignment/tracking going out of sync with the front wheel. Smaller sized
and compact frames, even with longer seatposts and stems, tend to track
better because the lateral deflection within the frame is proportionally
less so the wheels stay aligned better.

Your logic is inverted from the physics involved. The *longer*
wheelbase should be the one that is more resistant to variance under
load.

I also rode a Softride for a couple of seasons where lateral deflection
of the seat was huge yet it had no affect on the handling
characteristics of the bike (which were pretty good).

Ponder on that.

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