In article said:Ryan Cousineau said:In article said:On Thu, 13 Feb 2003 18:58:31 -0800, Ryan Cousineau <[email hidden]> wrote:
>In article <[email hidden]>, [email hidden] ([email hidden])
>wrote:
Quoted message said:
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.
Quoted message said:Snip
Quoted message said:
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.
Quoted message said:hell those one size fits all beach cruisers handle .....
But they're heavy. And they don't put the BB in the right place.
Quoted message said:Quoted message said: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!
Quoted message said: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.
Quoted message said: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.
Quoted message said: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?
Quoted message said: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....
Quoted message said: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 [censored] off
road than on.
Can't comment on that...
--
Ryan Cousineau, [email hidden] sfu.ca~rcousineOpen ↗ President, Fabrizio Mazzoleni Fan Club
