Compact cons?

[Ryan Cousineau]

In article <[email protected]>, Mark Hickey <[email protected]> wrote:

> Ryan Cousineau <[email protected]> wrote:
>
> >Compact geometry and its associated availability of long seat tubes and varied stem lengths means
> >that the chances a used bike will fit a given person have gone from roughly 1 in 8 to 1 in 4. It
> >also greatly eases the inventory issues a bike shop faces, which ought to be reason for rejoicing
> >in their ranks and ours.
> >
> >I'm a little surprised that nobody else seems to have noticed this particular
> >good-for-the-consumer side effect. It's not a bad thing when one size fits more, at least without
> >causing issues for the rest of the bike (for those that fit them, I gather the only real
> >objections to compact geometry are aesthetic).
>
> To take that to its logical conclusion, you could fit 100% of the riders in the world onto a
> single size frame if you don't put any limitations on the stem and seat post design. Sure, a
> lot of them (the vast majority actually) would be riding an evil-handling pig of a bike, but
> they'd "fit".

Mark, first your four-speed wide-range gearing a few months ago, now this. You're on a one-man
crusade to build the ur-bike!

How bad is too bad? That's really the compact quandry. We can agree that custom is perfect,
conventional sizing is good enough, and compact, well...compact geometry hasn't slowed down the
several pro teams that use it, though I stand corrected if a lot of those guys are sneaking off and
getting custom-built compact-look frames.

> Then there's the problem of getting the bar height correct. With standard frames built in 2cm
> increments, there is overlap between the sizes in terms of handlebar height. If you try to cover
> the same range with only four sizes of frames (compact or not), you're going to have gaps.
> Specifically those who like to ride with their bars low will likely find they can't do so on the
> compact frame that "fits" them, since it's designed with a taller head tube to accomodate those
> riders who would normally be riding a larger frame.

You think that stems don't come in sufficiently sloped forms? I thought one of the fun things about
threadless stems (oh no, it's like Godwin's Law for rbt) was that you could flip them over and gain
an extra couple of centimetres of drop.

Maybe I'm misunderstanding. If so, assume I have an excuse that suggests my brain fade is temporary
rather than persistent.

--
Ryan Cousineau, [email protected] http://www.sfu.ca/~rcousine President, Fabrizio Mazzoleni Fan Club

 

[Ryan Cousineau]

In article <[email protected]>, ajames54 <[email protected]> wrote:

> On Fri, 14 Feb 2003 07:39:55 -0800, Ryan Cousineau <[email protected]> wrote:
>
> >In article <[email protected]>, ajames54 <[email protected]> wrote:
> >
> >> On Thu, 13 Feb 2003 18:58:31 -0800, Ryan Cousineau <[email protected]> wrote:
> >>
> >> >In article <[email protected]>, [email protected] ([email protected])
> >> >wrote:
>
> >
> >Well, I'm probably not the best to ask that rhetorical question, since my current bike is SunTour
> >PowerShift, and my next bike probably won't be better than Tiagra. The differences between Sora
> >and 600, according to people I respect like Sheldon Brown, are one cog, some grams, the shifter
> >button, general finish, and lots of money.
>
> This is more than a bit over simplified... I can list stacks of differences in materials and
> production differences that may or may not make a difference depending on what is important to you

Oh sure, but I assume that barring aesthetics and snob appeal, we can agree that the key factors in
choosing components are price, weight, and function differences (whether one shifts better, or has
more gears, or breaks more often). The steel stampings of Sora make it cheaper and heavier than the
forged aluminum bits in Ultegra.

In other words, we can account for materials and production differences by noting how they affect
the price, weight, and function. I largely discounted function because the only guy here who admits
to a lot of experience with Sora and other lower-order groups (Sheldon Brown) says that they are
quite reliable, and shift as well as any other STI system.

The differences also make Ultegra look prettier, but if I want my gruppo to look pretty, I'll get my
brother to paint it.

> Snip
> >
> >That's because the myths surrounding a frame's contribution to handling and feel are fading.
>
> Myths? What else contributes the handle and feel? Tire selection? bar wrap? Colour? handling and
> feel are 98% frame related.

Tire selection and--even more importantly--inflation is responsible for about almost all of the
"feel" (perceived stiffness variation) of a road frame. That figure Handling differences come down
to the very minor geometry variances between frames, and a lot of those have as much to do with
which fork is specified as they do with tube angles.

If a frame maker tells you that the dimensions (and here I'm talking about things like head-tube
angles, seat-stay lengths, BB heights, etc.) make his frame handle specially, he may be close to the
truth, though a quick stroll through a catalogue of various road frames will show that most
non-touring bikes differ by very small amounts in the geometry department. A hundred years of racing
bicycles, 69 years of UCI frame regulations, and 20 years of near-universal selection of the 700c
(aka ISO 622) have brought everyone to a concensus on what a road bike is, plus or minus .5 cm and 1
degree in all dimensions.

If, on the other hand, a frame maker tells you that hourglass seat stays make his bike ride better,
or that his nice steel frame is better than that nasty, stiff aluminum for your tired joints, then
he may still be a good framebuilder, but he doesn't know what he's talking about. That's okay, I'm
sure Bicycling Magazine will listen to him.

> hell those one size fits all beach cruisers handle .....

But they're heavy. And they don't put the BB in the right place.

> >No. But I don't think you've proven your claim that compact bikes fit fewer people than
> >conventionally sized bikes.
>
> OK then couple of quick examples ...

Now we're getting to something!

> 1) Head tube angle and fork rake greatly affect steering response and handling... your stem length
> should be optimized to fit the geometry of the bike within fairly tight parameters governed by
> comfort... using a stem that is significantly longer or shorter than what the head-tube / fork
> rake demand will result in steering that is "twitchy and unstable" or "sluggish". In the case
> of a stem that is at the absolute limit of the available "long" sizes you even end up with body
> positioning issues...(see note)

It is, to my mind, an interesting question whether the stem lengths on compact bikes are outside of
the optimal to any serious degree. I can see that with longer stems there are effects you have
pointed out.

I went and did some calculations. JensonUSA (picked as the vendor du jour because I could remember
their name) lists a Thompson road stem available in 10mm increments from 90-130mm. I ran the
numbers: assuming a 90-degree sweep of normal necessary bar movement (very generous numbers for a
race bike, which is probably going to see actual usage in something like a 10-degree sweep under use
above a walking pace), the difference from the smallest to largest stem is 14-20 cm of swept
circumference, which is a lot.

But this is worst case scenario. Confining it to the 20 cm range that is fairly common among stems,
and probably all most riders need to size to a compact frame, the differences get interesting. I
also pushed it out to about a 20 degree sweep, which is, at a good guess, where real at-speed
handling effects happen (if you care about bike handling effects for road racing bikes outside of 20
degree ranges, I'd like to see the crit course you ride!)

It's very interesting. I recommend doing a drawing of it to give you an idea of what kind of sweep
differences this causes over normal stem sizes. The answer is that over a 20 degree range, stems
from 100-120 mm make a difference of about 4 mm in the amount you have to move the bars from side
to side. That is, if you are stuck on a small frame and have to use a 120 mm stem, and I get a
nice big frame and use a 100 mm stem, your normal bar sweep will take you 4 mm more from side to
side. Drawing the diagram of the arcs in question, though, gives you an idea of how small this
difference is.

> 2) Seat tube angle affects the way your body pushes the pedals... (as a very general rule of
> thumb) steeper angles like 76-78 (specialist tri bikes) are considered more efficient but less
> comfortable while shallower angles 74 (standard road) are more comfortable and angles like 71
> are pretty much only found in touring frames when comfort is the key issue. The seat tube
> angles given assume a seat positioned in the center of its rails... sliding the seat all the
> way back or all the way forward on the rails changes the effective seat tube angle.. which in
> turn also changes how your legs reach the pedals.

Yes, plus you can also change the effective angle using offset seat posts. This is a standard fit
adjustment: first you choose a frame that's close to the right reach range, then you get the seat
height and distance aft of BB correct, and then you adjust reach with the stem height, length,
and angle.

> NOTE You say you body only touches the bike in three places, while broadly true this is a massive
> oversimplification .. bike and bike fit really need to be considered a dynamic thing, after all
> it's not a chair. Think more of the bike and rider combo as a unit, while moving the stability of
> that unit is dependant on the riders positions. Using the stem length as an example, a longer stem
> will do two different and important things. First it moves the riders centroid (center of mass)
> further forward on the bike weighting the front wheel more lessening the amount of lean the rider
> can put into a corner and generally lessening the stability. Second, because the stem is longer
> there is more body motion (chest shoulders and arms) required to turn the wheel, this motion also
> moves the centroid, lessening stability.

That extra motion is 4 mm for normal stem ranges, slightly more if you have a really freaky stem.
Stems don't change Cg relative to BB and seat, and I think fork rake changes can move the front
wheel back to where you want it. This does change some geometry elements in interesting ways, but
where are the riders complaining about funny-handling compact bikes?

> It is possible to get a perfect fit in a compact frame, but NOT by screwing with things like seat
> post and stem... if you want a good fit look rather at some builder like Pinerello or Colnago each
> of them makes something like 15 or 16 frame sizes.
>
> A couple of final comments...
>
> If an LBS can't fit a traditional road frame they sure as hell wont be fitting a compact.

Well this is certainly true. This could go around and around, and is sure to turn into a pity-party
about how the rise of mountain bikes has destroyed road bike knowledge at most shops. But for a shop
with the knowledge but not the inventory cushion, a four-size model gives them half a chance of
carrying a stock and maybe even demo models. Nobody will do 19 demo models, so you're stuck at best
with a knowledgeable staff fitting you and specifying your bike without you ever riding the thing
until they present you with the finished product. Which is exactly what one of the biggest road
shops in Vancouver does....

> Mountain Bike riders would also benefit from proper fit if stores new how to do it and they were
> smart enough to demand it. the whole large medium small thing is only slightly less ******** off
> road than on.

Can't comment on that...

--
Ryan Cousineau, [email protected] http://www.sfu.ca/~rcousine President, Fabrizio Mazzoleni Fan Club

 

[Bruce]

> I guess I'm missing something. What does seat angle have to do with top tube length? I can see
> where the two are related in terms of hamstring flexibility.
>
> Jay Wenner

compare a 73 versus 74 degree angle on a 56cm c-c frame (center to center = 56 from BB center to
seat joint center)

( cosine(73) - cosine(74) ) * 56 = (0.2923 - 0.2756) * 56 = 0.937 cm

so it's about one centimeter for each degree.

That's assuming you adjust your saddle fore-aft via the saddle rails to achieve the same horizontal
position relative to the BB.

-Bruce

 

[Mark Hickey]

Ryan Cousineau <[email protected]> wrote:
> Mark Hickey <[email protected]> wrote:

>> To take that to its logical conclusion, you could fit 100% of the riders in the world onto a
>> single size frame if you don't put any limitations on the stem and seat post design. Sure, a
>> lot of them (the vast majority actually) would be riding an evil-handling pig of a bike, but
>> they'd "fit".
>
>Mark, first your four-speed wide-range gearing a few months ago, now this. You're on a one-man
>crusade to build the ur-bike!

One size fits all - get 'em while they're hot!

>How bad is too bad? That's really the compact quandry. We can agree that custom is perfect,
>conventional sizing is good enough, and compact, well...compact geometry hasn't slowed down the
>several pro teams that use it, though I stand corrected if a lot of those guys are sneaking off and
>getting custom-built compact-look frames.

A lot of pros have always ridden "non-standard standard" bikes - I haven't been trying to find out
but I can't imagine that would be LESS likely on a team riding compact bikes.

>> Then there's the problem of getting the bar height correct. With standard frames built in 2cm
>> increments, there is overlap between the sizes in terms of handlebar height. If you try to cover
>> the same range with only four sizes of frames (compact or not), you're going to have gaps.
>> Specifically those who like to ride with their bars low will likely find they can't do so on the
>> compact frame that "fits" them, since it's designed with a taller head tube to accomodate those
>> riders who would normally be riding a larger frame.
>
>You think that stems don't come in sufficiently sloped forms? I thought one of the fun things about
>threadless stems (oh no, it's like Godwin's Law for rbt) was that you could flip them over and gain
>an extra couple of centimetres of drop.

I guess you could (ala the Cannondale headshock MTB stems that droop toward the dirt). Maybe I'm
just too much of a retrogrouch, but the results would be "less than pretty".

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

 

[Andrew Lee]

"Mark Hickey" <[email protected]> wrote in message
news:[email protected]...
> There are other reasons why we do it this way, but the bottom line is that there's only about a
> 1cm difference in seatpost clamp position between my 73.5 and a 72.5 degree frame - easily within
> the "normal distribution" of the vast majority of the riders. That's factored into the cockpit
> length as well.

I've looked at your website before since I'm kind of looking to get a 'cross bike some day, and the
thing that struck me was that the seat tube angles didn't seem within the "normal" range at 74.6
degrees. This puts the seat clamp at about 2 cm forward of a 73 degree frame for me - a probable no
fit for me, and I haven't had problems fitting any off the shelf bike before. I was wondering why
you do it that way, since 74.5+ degrees seems as high as any frame that I have ever seen specs for.