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URT sucks?



 
 
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  #1  
Old June 24th 03, 11:34 PM
Dave Stocker
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Default URT sucks?

Puts on flame retardant suit.

So after all of the URT bashing in the Giant Warp thread, I was wondering
what everyone's beef is with URT anyway. It is a design with advantages and
disadvantages, just like any other suspension design. It seemed to be a fad
a few years ago to build URT designs (Trek Y-bikes, Klein Mantra, etc) and
that it has fallen out of favor because it did not deliver on it's hype. At
one time URT was considered a great thing (
http://www.cycletech.com/TechTips/body.htm and look at the bottom). Now is
seems to be hated. In a recent Velo News article, the author seems to sneer
at somebody he meets on the trail because that rider liked his URT bike.
http://www.velonews.com/tech/report/...es/4082.0.html So the mags say it
is fashionable to hate URT, but a few years ago they were touting it. Does
it really suck that bad?

From googling a bit, I can say that the generally accepted behavior traits
of the URT a
- It is immune to bob on out of saddle sprints. good
- Supposedly they bob (especially low pivot designs) bad
- It has no pedal kickback. good
- Prone to brake jack bad
- BB-seat distance varies bad
- Only active if rider remains seated (rider stands on swing arm when out of
saddle) bad?

I have a mid-90's Katraga Proto Winner in my garage that I have logged a lot
of miles on. FYI, a little background- Katarga is an Austrian bike maker
that I would not call boutique. They are a small maker of low to mid end
bikes, inhabiting the same ecological niche as e.g. GT. The Proto Winner
was a URT design that they sold in the mid to late 90's. It is not a high
pivot design like the Mantra. The BB sits about 2" directly behind the
pivot. If you are interested in what it looks like, I could photograph it,
but I do not have a web page at the moment to post it to.

From my experience on this bike I can report:
- It does bob a little bit if you pedal very badly, but bob is easy to
completely eliminate with a seated spin (easier than with 4-bar). I do not
know where the low pivot URT bikes developed the reputation for bobbing. It
really does behave like a hardtail on out of saddle sprints. On steep
climbs this is a good thing or a bad thing, depending on your perspective.
I tend to pull hard on the upstroke and climb better on a more
"conventional" FS design than on a URT.
- Never experienced pedal kickback. Hell, I could run this bike as an SS.
- Brake Jack. I hate that term. This bike has a low pivot and this is not
really an issue. I have heard that it can be quite severe on a high pivot
bike.
- BB-Seat distance only varies by about a half an inch at full travel on
this bike. No biggie.
- The not active part I can attest to. I recently bought a four bar bike
and now the old URT bikes seems quite harsh and inactive. It is still
taking the edge off of hits. In this respect, it behaves a bit like a heavy
(13kg) Giant NRS.

There is no suspension design that is the Holy Grail. Path Analysis makes
interesting reading if you have the proper background:
http://www.mtbcomprador.com/pa/english/ IMHO- URT does quite well in a
couple of applications:
1) The lightest FS frames are single pivot. URT is basically single pivot
with the BB on the rear triangle. It follows that a URT frame could make it
into the 4lb range. One good application would be XC marathon bike where
big travel was not an issue and the suspension is mostly there to take the
edge off and delay the onset of fatigue. The NRS works this way. My old
low pivot URT bike is too heavy to be considered for racing, but it is great
on epic rides. Too bad URT is unfashionable. It could in principle be used
for a great XC marathon bike.
2) Touring bikes and Walgooses. Wallgoose buyers want the FS look and
tourers want to take the edge off, but both are ridden by people who
probably have never (and never will) practiced a clean spin. I do not buy
the "URT bobs like crazy" line. The FSR bobs like crazy if I do not spin
smoothly. The URT bike is very forgiving.

In short, it URT has shortcomings, but the vilification of URT has more to
do with fashion than anything else. Remenber, the macstrut is making a
comback.

Runs for cover.

-Dave



Ads
  #2  
Old June 25th 03, 12:53 AM
P e t e F a g e r l i n
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Posts: n/a
Default URT sucks?

On Wed, 25 Jun 2003 00:34:30 +0200, "Dave Stocker"
wrote:

|From googling a bit, I can say that the generally accepted behavior traits
|of the URT a
|- It is immune to bob on out of saddle sprints. good

Bull****.

|- Supposedly they bob (especially low pivot designs) bad

All FS bikes bob to some extent.

|- It has no pedal kickback. good
|- Prone to brake jack bad
|- BB-seat distance varies bad

Very bad.

|- Only active if rider remains seated (rider stands on swing arm when out of
|saddle) bad?

Not necceessarily.

huge snip

|In short, it URT has shortcomings, but the vilification of URT has more to
|do with fashion than anything else.

URTs have many shortcomings when compared to four bar bikes.

The "vilification" isn't always based upon fashion issues. Many times
it is based upon the fact that there are much better full suspension
designs available.
  #3  
Old June 25th 03, 07:37 AM
Dave Stocker
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Posts: n/a
Default URT sucks?

"P e t e F a g e r l i n" schrieb im Newsbeitrag
...
On Wed, 25 Jun 2003 00:34:30 +0200, "Dave Stocker"
wrote:

|From googling a bit, I can say that the generally accepted behavior

traits
|of the URT a
|- It is immune to bob on out of saddle sprints. good

Bull****.


Perhaps "immune" is a strong word, but standing does act as a lockout.


|- Supposedly they bob (especially low pivot designs) bad

All FS bikes bob to some extent.


Yup. What I should have said was the "URT bikes are especially prone to
bob". My four bar is far more prone to bobbing than my URT.

|- It has no pedal kickback. good
|- Prone to brake jack bad
|- BB-seat distance varies bad

Very bad.

|- Only active if rider remains seated (rider stands on swing arm when out

of
|saddle) bad?

Not necceessarily.


Actually true. I have never ridden a Mantra, but from what I have heard
about its behavior, this is a prominent feature. Some like it, some hate
it.

huge snip

|In short, it URT has shortcomings, but the vilification of URT has more

to
|do with fashion than anything else.

URTs have many shortcomings when compared to four bar bikes.

The "vilification" isn't always based upon fashion issues. Many times
it is based upon the fact that there are much better full suspension
designs available.


But Pete, what I am trying to say is that many of the supposed problems of
URT stem from specific implementations of it, not the principle itself. Is
my FSR a better trail bike than the Katarga? You betcha. It is smoother
and faster over the rough stuff and I do steep technical climbs better with
it than with the URT bike or with a hardtail.



But- if I were entering a race, I would have to think long and hard about
which bike to use, even though the Katarga weighs 5lb more. The FSR climbs
and descends better, but the Katarga sprints better and bobs less. Also
smoother and more active is not necessarily better. There are people in
this NG who advocate rigid. After riding the FSR for a couple of months now
I can see how it can lull me into bad habits and I understand this rigid
advocacy much more.



What I tried to say in my original post was that URT, like any other
suspension type, has its pros and cons and it has its niche. When people
say URT sucks, they are usually extrapolating the shortfalls of a particular
design to the principle.

-Dave


  #4  
Old June 25th 03, 06:09 PM
P e t e F a g e r l i n
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Posts: n/a
Default URT sucks?

On Wed, 25 Jun 2003 08:37:46 +0200, "Dave Stocker"
wrote:

"P e t e F a g e r l i n" schrieb im Newsbeitrag
.. .
On Wed, 25 Jun 2003 00:34:30 +0200, "Dave Stocker"
wrote:

|From googling a bit, I can say that the generally accepted behavior

traits
|of the URT a
|- It is immune to bob on out of saddle sprints. good

Bull****.


Perhaps "immune" is a strong word, but standing does act as a lockout.


Not on all URTs.

|- Supposedly they bob (especially low pivot designs) bad

All FS bikes bob to some extent.


Yup. What I should have said was the "URT bikes are especially prone to
bob". My four bar is far more prone to bobbing than my URT.

|- It has no pedal kickback. good
|- Prone to brake jack bad
|- BB-seat distance varies bad

Very bad.

|- Only active if rider remains seated (rider stands on swing arm when out

of
|saddle) bad?

Not necceessarily.


Actually true.


Actually false. The Ibis Bow Ti is active when you are out of the
saddle. Less active than when you are seated, but active nonetheless.

I have never ridden a Mantra, but from what I have heard
about its behavior, this is a prominent feature.


So because you've heard that this is a characteristic of one flavor of
URTs, it follows that all URTs are only active when the rider is
seated?

Some like it, some hate
it.

huge snip

|In short, it URT has shortcomings, but the vilification of URT has more

to
|do with fashion than anything else.

URTs have many shortcomings when compared to four bar bikes.

The "vilification" isn't always based upon fashion issues. Many times
it is based upon the fact that there are much better full suspension
designs available.


But Pete, what I am trying to say is that many of the supposed problems of
URT stem from specific implementations of it, not the principle itself.


That sounds like double speak.

The "suppsed" problems associated with URTs (principle) aren't
"supposed," they are very real.

snip

What I tried to say in my original post was that URT, like any other
suspension type, has its pros and cons and it has its niche. When people
say URT sucks, they are usually extrapolating the shortfalls of a particular
design to the principle.


You seem to be hung up on creating a difference between design and
principle.

For example, the URT principle involves a constantly changing BB to
saddle distance. This is not specific to a particular design, but
rather to all URTs..




  #5  
Old June 25th 03, 08:03 PM
Dave Stocker
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Posts: n/a
Default URT sucks?

"P e t e F a g e r l i n" schrieb im Newsbeitrag
...
|- Only active if rider remains seated (rider stands on swing arm when

out
of
|saddle) bad?

Not necceessarily.


Actually true.


Actually false. The Ibis Bow Ti is active when you are out of the
saddle. Less active than when you are seated, but active nonetheless.


Holy Cow! That monstrosity is a URT? I have never seen this thing in real
life, but I found this picture. http://www.soresaddle.com/ibisbowbi.jpeg



OK, lets define URT before we go any further. If you defined it as variable
BB-saddle distance, then yes, it would be a URT. But titanium monstrosities
are not comparable to pivot based bikes made with relatively inflexible
materials. From the fact that it is ti and a look at the layout, I think I
get the basic principal of how it works*. Calling this bike a URT would be
like cutting the seatstay out of a Scalpel or Unicoi (or most hardtails for
that matter) and redefining them as URT bikes. I would define unified rear
triangle as a pivot based bike with the BB on the rear triangle. In this
definition of URT, when you get out of the saddle, you are standing on the
rear triangle and holding on to (in a roundabout way) the front triangle.



*It appears to be a big leaf spring. When you sit on it, you add a
considerable preload and thus it is not very active. When you stand, you
are unloading that preload. It looks clever. Has anyone here ever ridden
one? Nevertheless, IMHO, it is inappropriate to label this thing URT.

-Dave


  #6  
Old June 25th 03, 11:01 PM
external usenet poster
 
Posts: n/a
Default URT sucks?

"Dave Stocker" wrote in message ...
"P e t e F a g e r l i n" schrieb im Newsbeitrag
...
On Wed, 25 Jun 2003 00:34:30 +0200, "Dave Stocker"
wrote:

|From googling a bit, I can say that the generally accepted behavior

traits
|of the URT a
|- It is immune to bob on out of saddle sprints. good

Bull****.


Perhaps "immune" is a strong word, but standing does act as a lockout.


|- Supposedly they bob (especially low pivot designs) bad

All FS bikes bob to some extent.


Yup. What I should have said was the "URT bikes are especially prone to
bob". My four bar is far more prone to bobbing than my URT.

|- It has no pedal kickback. good
|- Prone to brake jack bad
|- BB-seat distance varies bad

Very bad.

|- Only active if rider remains seated (rider stands on swing arm when out

of
|saddle) bad?

Not necceessarily.


Actually true. I have never ridden a Mantra, but from what I have heard
about its behavior, this is a prominent feature. Some like it, some hate
it.

huge snip

|In short, it URT has shortcomings, but the vilification of URT has more

to
|do with fashion than anything else.

URTs have many shortcomings when compared to four bar bikes.

The "vilification" isn't always based upon fashion issues. Many times
it is based upon the fact that there are much better full suspension
designs available.


But Pete, what I am trying to say is that many of the supposed problems of
URT stem from specific implementations of it, not the principle itself. Is
my FSR a better trail bike than the Katarga? You betcha. It is smoother
and faster over the rough stuff and I do steep technical climbs better with
it than with the URT bike or with a hardtail.



But- if I were entering a race, I would have to think long and hard about
which bike to use, even though the Katarga weighs 5lb more. The FSR climbs
and descends better, but the Katarga sprints better and bobs less. Also
smoother and more active is not necessarily better. There are people in
this NG who advocate rigid. After riding the FSR for a couple of months now
I can see how it can lull me into bad habits and I understand this rigid
advocacy much more.



What I tried to say in my original post was that URT, like any other
suspension type, has its pros and cons and it has its niche. When people
say URT sucks, they are usually extrapolating the shortfalls of a particular
design to the principle.

-Dave



Thanks for the informative post Dave
  #7  
Old June 26th 03, 03:08 AM
P e t e F a g e r l i n
external usenet poster
 
Posts: n/a
Default URT sucks?

On Wed, 25 Jun 2003 21:03:53 +0200, "Dave Stocker"
wrote:

|"P e t e F a g e r l i n" schrieb im Newsbeitrag
.. .
| |- Only active if rider remains seated (rider stands on swing arm when
|out
| of
| |saddle) bad?
|
| Not necceessarily.
|
|
| Actually true.
|
| Actually false. The Ibis Bow Ti is active when you are out of the
| saddle. Less active than when you are seated, but active nonetheless.
|
|
|Holy Cow! That monstrosity is a URT? I have never seen this thing in real
|life, but I found this picture. http://www.soresaddle.com/ibisbowbi.jpeg
|
|
|
|OK, lets define URT before we go any further.

How can you define something when you apparently don't understand what
bikes are URTs?

If you defined it as variable
|BB-saddle distance, then yes, it would be a URT. But titanium monstrosities
|are not comparable to pivot based bikes made with relatively inflexible
|materials.

Again, you are discussing things that you apparently have no
experience with.

From the fact that it is ti and a look at the layout, I think I
|get the basic principal of how it works*. Calling this bike a URT would be
|like cutting the seatstay out of a Scalpel or Unicoi (or most hardtails for
|that matter) and redefining them as URT bikes.

Uh, you're just digging yourself deeper and deeper.


I would define unified rear
|triangle as a pivot based bike with the BB on the rear triangle. In this
|definition of URT, when you get out of the saddle, you are standing on the
|rear triangle and holding on to (in a roundabout way) the front triangle.
|
|
|
|*It appears to be a big leaf spring. When you sit on it, you add a
|considerable preload and thus it is not very active.

Uh, again, you're just digging yourself deeper and deeper.

When you stand, you
|are unloading that preload. It looks clever. Has anyone here ever ridden
|one? Nevertheless, IMHO, it is inappropriate to label this thing URT.

LOL.

Educate yourself:

http://www.math.chalmers.se/~olahe/Bike/Rear/urt.html

http://www.titusti.com/techtalk.html

http://www.geocities.com/MotorCity/F...7/fullsus.html

To answer your question, yes, I'm pretty sure that someone in this NG
has ridden a Bow Ti.






  #8  
Old June 26th 03, 07:57 AM
Dave Stocker
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Posts: n/a
Default URT sucks?

"P e t e F a g e r l i n" schrieb im Newsbeitrag
...

When you stand, you
|are unloading that preload. It looks clever. Has anyone here ever

ridden
|one? Nevertheless, IMHO, it is inappropriate to label this thing URT.

LOL.

Educate yourself:

http://www.math.chalmers.se/~olahe/Bike/Rear/urt.html


Says:
"This category of bikes is, or at least used to be, characterised by the
fact that the rear triangle and the bottom bracket is one unit, connected to
the main triangle via one pivot point. I say used to be since there are some
newer designs (like Kona) that still puts the bottom bracket on the swingarm
but also uses a linkage between the swingarm and the shock. I will call this
new design "linked URT" and the old design just URT. URT's are also called
"floating drivetrain"."


http://www.titusti.com/techtalk.html

Says:
"The basic idea behind all unified rear triangle designs is to isolate the
drivetrain from the forces of the suspension. There are two basic types of
unifieds: Sweet Spots and low pivots. Sweet Spot designs do a good job of
eliminating any pedal or rider induced suspension movement. On Sweet Spot
Unifieds, the suspension is fully-active while the rider is seated and
becomes less active when the rider stands up. Most builders of unified
designs focus their design towards cross-country rather than down hill. On
Sweet Spot designs, there is a large change in seat to pedal distance as the
suspension goes through its travel. This occurs because the seat and cranks
are on separate moving parts of the frame and the pivot is approximately
midway between these two points. You will not experience any Bio-pace or
DISC on a Sweet Spot unified design."


http://www.geocities.com/MotorCity/F...7/fullsus.html

Says:
"The unified rear triangle (URT), or floating drivetrain, is a rear
suspension design whose popularity is waning in the current climate of
downhill and freeriding.

The basic premise of this type of design is to isolate the rear suspension's
effect on the drivetrain by placing the entire drivetrain on the swingarm
itself. Thus, the various components of the drivetrain move together as the
suspension compresses and extends. This eliminates any chain reaction and
can also allow for a very clean, simple suspension configuration consisting
of a single large pivot and a directly driven shock.

The inherent problem with this design is that the rider is in effect
standing on the swingarm. This is less of a problem when the rider is
seated, but the natural tendency when going over larger obstacles, rough
terrain, or technical sections is to stand up, rendering the rear suspension
almost useless. The flip side to this effect is that during sprinted or
climbing out of the saddle, the suspension's lack of movement is considered
a bonus, as less energy is wasted in suspension movement.

There have been several very popular URT bikes in the past, most notably the
Klein Mantra, the Trek/Gary Fisher Y-bikes, and the Ibis Sweet Spot. There
have also been twists on the URT design in the form of the GT iDrive and the
Paul Turner desiged Maverick."

LOL! This is all consistent with what I said.

but from http://www.castellanodesigns.com/diff.html
"While developing the Sweet Spot suspension, John became intrigued by the
idea of incorporating spacecraft-style pivotless flexures into his
long-travel suspension system, and began modeling and testing pivotless
prototypes. This work culminated in the Ibis BowTi, the ultimate expression
of his Sweet Spot Suspension. With 5" of travel and no pivots, the titanium
BowTi is in a class by itself. Castellano's next inspiration led to the
SilkTi and Ripley softails, also built by Ibis, featuring John's pivotless
Flat-Plate chainstays and Critically Damped Elastomer shock."

So the bow tie is considered a variant of URT. More importantly, the guy
who designed it did so with the intention of building a pivotless high pivot
bike.

So I stand corrected about the Bow Ti. But I still maintain that it is a
titanium monstrosity! ;-)

-Dave



  #9  
Old June 26th 03, 10:21 AM
Dave Stocker
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Posts: n/a
Default URT sucks?

"P e t e F a g e r l i n" schrieb im Newsbeitrag
...
|
|*It appears to be a big leaf spring. When you sit on it, you add a
|considerable preload and thus it is not very active.

Uh, again, you're just digging yourself deeper and deeper.

When you stand, you
|are unloading that preload. It looks clever. Has anyone here ever

ridden
|one? Nevertheless, IMHO, it is inappropriate to label this thing URT.

LOL.

Educate yourself:


My finite element analysis is a bit rusty and I do not know the relative
elastic properties of the stays that run from the head tube to the rear hub
(what would they be called on this bike?), the chainstays and the "seat
tube", but I still think this is a reasonable approximation unless I am
missing some secret ingredient.

So if I am wrong in my assumptions about how this thing works, then I ask
you: How does it work?

-Dave


  #10  
Old June 26th 03, 03:14 PM
Dave Stocker
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Posts: n/a
Default URT sucks?

I wrote:
Standing on the swingarm does essentially causes the rear to have two
spring rates where the difference in k is proportional to the distance

from
BB to pivot.


Sorry, this is a mistake. If the hub moves x0, the BB moves x1, the shock
compresses x2, the shock has spring constant k a the rider wieghs R, then
the work done would be:

W=x1*r+k*x2^2

This is not delta k, nor is it preload. It is more like additional unsprung
wieght.

-Dave


 




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