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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 |
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#2
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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
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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
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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
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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
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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
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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
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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
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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
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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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