Frame Stiffness - What Does It Affect

[Phil Holman]

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

 

[jim beam]

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
>
>

 

[jim beam]

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
>
>

 

[John Forrest Tomlinson]

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]

On Sat, 19 Jan 2008 09:40:21 -0800, jim beam
<[email protected]> 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. It's easy to see the BB swing with the bike on a trainer and
the same issue show up on the road.

Whether additional flex is causing the wheels to mis-align, it's hard
to say. I'd have to assume that as the BB swings that the stays swing
too.

 

[Tom Sherman]

still just me wrote:
> On Sat, 19 Jan 2008 09:40:21 -0800, jim beam
> <[email protected]> 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

 

[[email protected]]

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

 

[[email protected]]

On Jan 19, 6:12 pm, [email protected] 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

 

[Ron Ruff]

On Jan 19, 4:29 pm, Tom Sherman <[email protected]>
wrote:
> What does connecting railroad cars (humping) have to do with the
> discussion?

You are both confused:
http://video.google.com/videoplay?d...072&start=0&num=10&so=0&type=search&plindex=1

 

[Tom Sherman]

Ron Ruff wrote:
> On Jan 19, 4:29 pm, Tom Sherman <[email protected]>
> wrote:
>> What does connecting railroad cars (humping) have to do with the
>> discussion?
>
> You are both confused:
> http://video.google.com/videoplay?d...072&start=0&num=10&so=0&type=search&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

 

[Zog The Undeniable]

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.

 

[Werehatrack]

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.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

 

[jim beam]

Werehatrack wrote:
> 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.

that's not right - all other dimensions being equal, the long tube will
be more flexible than the short one. you can't build a frame with a
longer wheelbase without using longer tube.


>
>> 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.
>

 

[Phil Holman]

"Werehatrack" <[email protected]> wrote in message
news:[email protected]...
> 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.

Not really, it can be adjusted out or eliminated with a tweak of the
cage.

>It could mean the difference between the
> chain riding down onto the next sprocket during a downshift on a hard
> climb. Yes, ghost shifting is a possibility on flexy frames but not
> the biggest problem if its that flexy.

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.

No, even with BB deflection, the wheel still tends to be centered.
Lateral wheel stiffness is much more of a factor here.

>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.

No, it's a factor of trying to create a 16lb steel track bike.

>
>>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.

That's backwards; longer tubes of similar gauge and load deflect more in
bending and torsion.

>
>>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.

Your point is.....?

Phil H

 

[still just me]

On Sun, 20 Jan 2008 19:36:37 -0800, "Phil Holman"
<piholmanc@yourservice> wrote:

>
>"Werehatrack" <[email protected]> wrote in message
>news:[email protected]...
>> 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.
>
>Not really, it can be adjusted out or eliminated with a tweak of the
>cage.


I'd disagree - if you adjust the derailleur to clear for frame flex,
you might be taking it far enough that it throws the chain when you
shift either extreme.

 

[still just me]

On Sat, 19 Jan 2008 17:29:09 -0600, Tom Sherman
<[email protected]> wrote:

>still just me wrote:
>> On Sat, 19 Jan 2008 09:40:21 -0800, jim beam
>> <[email protected]> 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?

It's more like Marine humping - you know, when you are riding with the
50 cal strapped on your back.