Compact frame vs Traditional Frame geometry

[James Thomson]

"David L. Johnson" <[email protected]> wrote:

> what makes you think that the wheelbase makes the response quicker?

Assuming that the tyres aren't slipping, the bike moves on an arc centred approximately at the
intersection of two lines extended from the hub axles. For a given angular displacement of the front
wheel, the radius of this arc is proportional to the wheelbase. This could reasonably be interpreted
as a measure of responsiveness.

I agree that whether or not a frame is 'compact' has no bearing on its wheelbase.

James Thomson

 

[Robin Hubert]

"David L. Johnson" <[email protected]> wrote in message
news:[email protected]...
> On Sat, 30 Aug 2003 06:29:29 +0000, Tim McTeague wrote:
>
> > David L. Johnson wrote:
> >
> >
> >>> On the other hand, you see a great many custom builders going to sloping top tubes to deal
> >>> with the limited height adjustability afforded by threadless headsets and carbon steerers.
> >>
> >> One bad technology driving another.
> >
> > I don't know why so many are still attached to old headsets. I LOVE the threadless design. Yes,
> > I miss the easy adjustability of quill stems
>
> Enough for me, there. A minor spill -- pushes your bars out of alignment, then you have to
> re-adjust the headset?
>
> > And, while I did not have to adjust it often, I hated having to use those huge wrenchs. More
> > than once over the years my headset became lose on a ride and I had to keep trying to tighten it
> > with my hands, as who carries the proper tools for that?
>
> My headset has been quietly doing its job for two years. No adjustment. Meanwhile, I move the bars
> to accomodate my aging back, no trouble, and to re-align after falling in the rain.
>
> Threadless can be adjusted with just about any mini-tool.
> > Alligning the stem does not require me to "pound" the center bolt to
free
> > the wedge as with quills.
>
> "Pound"?

You've never had to pound a cone-style quill stem bolt/binder system to get the cone outa the quill?

--
Robin Hubert <[email protected]

 

[Steven M. Schar]

"ajames54" <[email protected]> wrote in message
news[email protected]...

> Much of the attraction is a marketing ply that allows the retailer to lie about fit and carry only
> three frame sizes rather than five or six...

This is the crux of it. Just as the reason for threadless headsets is for the benefit of the
manufacturer and retailer, and leaves the consumer to purchase those ridiculous looking extensions.

Many of the "advances," alumimum versus chromolly, threadless versus threaded, compact versus
traditional, are done to save money, then reasons are invented for them to sound plausible to people
that don't know any better.

Even though you can still buy a bicycle with a chromolloy frame, threaded headset, and normal frame
geometry, the mass market has gone to aluminum, threadless, and compact, raising prices
significantly for the enthusiasts that don't appreciate the decontenting.

 

[Bruce]

Assuming similar tubing, a compact frame is stiffer in the area where stiffness matters - the BB.
Whether this stiffness is measurable is another story, but if you compare the traditional diamond
design with that of a typical compact with a shorter seat tube and use the same tube set, then the
smaller triangle will be stiffer and lighter.

And the longer seatpost (if it is the same material & dimenions) will have more flex in the
direction you might like - to give you a softer ride. But you may have to have a stiffer seatpost to
handle the longer extension.

Now if you don't like the appearance then that's another story. But the shape gives a lighter and
stiffer frame.

-Bruce my road bikes: horizontal TT my mtbikes: sloping TT

"H. Guy" <[email protected]> wrote in message
news:[email protected]...
> In article <[email protected]>, [email protected]
> (Chris Zacho "The Wheelman") wrote:
>
> > Basically, the shorter the tubes, the stiffer the frame. And lighter, quicker response due to
> > the shorter wheelbase.
>
> nice theory, but when you've got a foot of unsupported seatpost hanging out of the "size L" frame,
> how stiff is that going to be? and is the wheelbase really shorter? (not being a smart aleck
> here...just don't know.)
>
> while the compact frame will probably be lighter, i'll put my money on the traditional design for
> stiffness.
>
> hg

 

[H. Guy]

In article <[email protected]>, "Steven M. Scharf"
<[email protected]> wrote:

> > Much of the attraction is a marketing ply that allows the retailer to lie about fit and carry
> > only three frame sizes rather than five or six...
>
> This is the crux of it. Just as the reason for threadless headsets is for the benefit of the
> manufacturer and retailer, and leaves the consumer to purchase those ridiculous looking
> extensions.

well, i'm going to give the manufacturers the benefit of the doubt here, and theorize that cheaper
manufacturing leads to cheaper prices, which puts more bikes between the legs of customers. if a
decent alu-framed bike costs you almost $2K, i'm betting you could add another $.5K to get a nice
handmade, lugged steel frame on there. and a price increase of 25% OR MORE might tend to shrink the
market a bit.

and as far as alu not being an advance, i remember the first time i climbed aboard a cannondale and
sprinted up a hill (i'm not going to tell you when, exactly, but let's just say that klein was still
doing its damndest to sue cannondale back into the stone age). it was AMAZING. i LOVED it. no brake
rub, no derailleur cage rub, no mushy feeling.

of course, over the years that no flex ride got real old, and the cannondale ended up on the junk
heap and there's a nice solid piece of japanese steel between the wheels right now. but if i were
still racing, there'd be no doubt about what i'd be on: stronger, lighter, stiffer aluminum.

 

[David L. Johnso]

On Sun, 31 Aug 2003 14:53:19 +0000, Robin Hubert wrote:

> You've never had to pound a cone-style quill stem bolt/binder system to get the cone outa
> the quill?

Pound, no. Tap, yes.

--

David L. Johnson

__o | A foolish consistency is the hobgoblin of little minds, adored _`\(,_ | by little statesmen
and philosophers and divines. --Ralph Waldo (_)/ (_) | Emerson

 

[Mark Hickey]

[email protected] (Chris Zacho "The Wheelman") wrote:

>Basically, the shorter the tubes, the stiffer the frame.

Not really - this was discussed ad nauseum here many moons ago, and there was no one who could make
a case for that theory based on the physics of the matter. In the end, the differences are going to
be absolutely miniscule one way or the other.

>And lighter, quicker response due to the shorter wheelbase.

No difference in wheelbase. And not lighter - we worked that one out as well. The difference in
tubing weight was almost exactly offset by the extra long seat post. And that doesn't take into
account the strengthening you have to do to the compact frame's top tube / seat tube / seat stay
junction to handle the higher stresses from the longer seat post (which effectively act as a longer
lever arm).

'Course, all that doesn't mean the opposite won't appear in glossy ads in your favorite cycling
magazines (and in the "tech articles"). Sigh...

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame

 

[Mark Hickey]

"David L. Johnson" <[email protected]> wrote:

>On Sat, 30 Aug 2003 06:29:29 +0000, Tim McTeague wrote:

>> I don't know why so many are still attached to old headsets. I LOVE the threadless design. Yes, I
>> miss the easy adjustability of quill stems
>
>Enough for me, there. A minor spill -- pushes your bars out of alignment, then you have to
>re-adjust the headset?

Worse, due to the fact the threadless design grips the steer tube more than is necessary, very
likely the crash will bend your bars. Worse yet, if your soft middle is what's doing the bending,
the damage could be painful.

With a threaded stem, the stem simply slips a bit. You stand the bike up, twist it back and ride.

If you pack the bike for shipment with a threadless stem, the fork is no longer held in. When you
reassemble the bike, you'll have to futz around with the headset preload. Oh, and did you remember
to tape all those spacers to the bike, or do you have to drive to the LBS to get some more?

With a threaded stem, drop it in, set the height, twist the allen wrench and ride. If you decide to
raise the bars a bit in the middle of a ride, it's a 30 second adjustment. With a threaded stem, you
get to pull the stem off, juggle washers, and reset your headset preload (unless you drop one of the
washers or bolts, in which case you get to ride in the sag).

>> And, while I did not have to adjust it often, I hated having to use those huge wrenchs. More than
>> once over the years my headset became lose on a ride and I had to keep trying to tighten it with
>> my hands, as who carries the proper tools for that?
>
>My headset has been quietly doing its job for two years. No adjustment. Meanwhile, I move the bars
>to accomodate my aging back, no trouble, and to re-align after falling in the rain.

I NEVER have to tighten my threaded headsets. Just get 'em right the first time and ride until you
decide to repack.

> Threadless can be adjusted with just about any mini-tool.
>> Alligning the stem does not require me to "pound" the center bolt to free the wedge as with
>> quills.
>
>"Pound"?

A love tap, maybe. With a bit of grease and an absolute minimal amount of maintenance, you're not
going to have any problems with a threaded stem.

Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $695 ti frame

 

[Doug Kaye]

> What is the main difference between the two bike geometries?

The most rational answer I've seen for this question was posted by Gerard Vroomen of Cervelo, on the
slowtwitch forum: "The differences are actually very easy to measure and understand, unfortunately
few people in the industry are interested in the actual differences or in testing and rather just
make up stuff for their brochure.

The differences between sloping and horizontal are small, but if you use the same tubeset for both
frames, the following differences will occur:

1) slightly higher bottom bracker stiffness for the sloping frame
2) slightly higher torsional stiffness for the horizontal toptube frame
3) slightly lighter frame with the sloping toptube
4) slightly lighter seatpost wit the horizontal toptube frame
5) slightly more seatpost compliance with the sloping frame.

issues 3 and 4 are a wash, and for us at Cervelo the choice between sloping and horizontal depends
on whatcombination we are looking for out of 1, 2 and 5. For our Alu bikes, which have plenty of bb
and torsional stiffness anyway, we go with a sloping toptube (or a dropped toptube on the tri bikes
which has the same effect) to get a bit more seatpost compliance.

For the steel frames, this is not necessary and so we can increase the torsional stiffness by
keeping the toptube horizontal, especially nice for the twisting and turning on rough roads.

For the new carbon frame, the seatpost compliance wasn't an issue but we did want to get the highest
possible bb stiffness, so we opted for a sloping frame."