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  1. #1
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    Tested the rear triangle stiffness on 4 FSR bikes

    I test road the following XL Specialized FSR bikes back to back up a steep hill yesterday: 06 Epic Disc, 07 FSR XC Comp, 07 SJ FSR Comp and 07 SJ FSR Elite, which was my favorite. The hill was a sidewalk that was inclined by about 2+% and about 1/2 mile long. Riding these bikes up this hill with the chain on the middle chain-ring yielded the stiffest rear triangle out of the bunch, which I subjectively measured by the ease of peddling. Both of the 07 SJ FSR's were noticeably easier to peddle up the incline than the 06 Epic, which came in third followed by the 07 FSR XC. The SJ Elite for some unknown reason was the easiest to peddle up the hill-I did not have to shift down to a lower gear (the forth largest cassette cog) on this hill, which I road up 5 times on this bike. The SJ Comp needed to be shifted to the next lower gear, the 06 Epic required two gear shifts and the FSR XC needed to be shifted up three gears to the largest cog and really needed the to be down shifted into the smallest chain-ring to match the peddling pressure of the other bikes up the hill.

    All of the bikes were locked out (front and rear), had the same air pressure in the rear shocks and the front forks, with the exception of the FSR XC, which has a coil spring fork.

    The SJ FSR Elite was the smoothest and stiffest out of the bunch because it has large diameter a-symmetric chain stays and (4) 6800 RS bearings (two bearings in each dropout) with M10 bolts in the dropout pivots. I surmise that it made it up the hill easier than the SJ Comp because it is equipped with stiffer cranks-Shimano XT Hollow Tech II. The bike did not creak with the Triad locked-out like the SJ Comp and the FSR XC. And counter to popular believe, the bike seemed to climb easier with the Fork set to 140mm (creating a more slack ST angle) than it did when set to 120 or 100mm.

    The SJ Comp is somewhat summarized above.

    The Epic: I though this would be the best climber out of the bunch because it has the steepest seat tube, flat handlebars and a Fox F100 fork and Brain shock that are locked-out and make the bike feel like a hard tail. The bike was easy to peddle on flat and slightly inclined surfaces; however the flexy rear triangle zapped away pedal energy on when climbing up the steep hill. Most of this flex is from the single 6800 RS bearing in each dropout, which are sandwiched by plastic bushings and held together with a M10 bolt. Like the SJs, the Epic also has asymmetrical chain stays.

    The FSR XC rear triangle had the most flex out of all of the bikes tested because 1) the chain stays are small and are symmetrical and the four 688 RS dropout bearings (two in each dropout) with M8 pivot bolts are the smallest out of the bunch. Unfortunately, the X-Fusion rear shock bobbed and made a lot of noise when locked out, so this shock skewed the data. Technically, the double 688 bearings should be stiffer than a single 6800 in the Epic.

  2. #2
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    You lost me at "test road".

  3. #3
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    sounds like you had a defective XC, my 07 XC comp doesnt bob creak flex etc, locked out the x fusion is stiff as a hardtail and it doesnt make any noise whatsoever

  4. #4
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    1) Dusty Bottoms I test drove the bikes.
    2) darkest_fugue the X-Fusion perfomed well on flat surfaces when locked-out but was overloaded when I climbed the hill. I wish the bike shop had an FSR XC pro with a Fox Triad on hand to test as well so I could eliminate the shock from the equation.

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    that x fusion was still faulty in my opinion, i do a lot of road riding with mine up down you name it, locked out, its hardtail stiff, it doesnt budge

  6. #6
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    I may be skewing the data or overloading the shock because of my weight, which is 215 pounds, but this is the second FSR XC to perform this way up a steep incline for me. The first one I tested was a 08 FSR XC expert back to back with an FSR XC Pro with a Triad. Both of the rear shocks were aired up to yield 25% sag and when I climbed a very steep short hill the X-Fusion fizzed out-this made the bike very hard to peddle where as the FSR XC Pro's Triad was a lot stiffer and as a consequence much easier to peddle up the steep hill. Like I said earlier on flat smooth terrain the FSR XC equipped with an X-Fusion feels pretty good and is easy to peddle.

  7. #7
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    Quote Originally Posted by bwalton
    1) Dusty Bottoms I test drove the bikes.
    2) darkest_fugue the X-Fusion perfomed well on flat surfaces when locked-out but was overloaded when I climbed the hill. I wish the bike shop had an FSR XC pro with a Fox Triad on hand to test as well so I could eliminate the shock from the equation.


    I believe DB means you used "road" and not "rode" (http://dictionary.reference.com/browse/ride). And, while we're at it, you might want to use "pedal" and not "peddle" as you are not trying to sell something. These tend to detract from the meaning of your post.

    http://dictionary.reference.com/browse/pedal

    http://dictionary.reference.com/browse/peddle
    1997 Specialized Stumpy Pro
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  8. #8
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    Quote Originally Posted by bwalton
    And counter to popular believe, the bike seemed to climb easier with the Fork set to 140mm (creating a more slack ST angle) than it did when set to 120 or 100mm.
    What was the grade of the climb (I see 2+% but that seems awful low)? What gearing were you using? How much sprung weight (rider, chassis, gear, etc.) was involved? How much torsional flex could be observed, measured, and repeated?

    The reason I ask is not to be argumentative, but rather point out that this is subjective. And, as being subjective, it's hard to state that "contrary to popular belief..." in that manner. Now, for you to observe this makes sense, and the feelings you have are reasonable. But, you seem focused on the bearings (as you have been since your earlier posts about your own SJ FSR) and chainstay measurements without taking material, pivot placement, or construction technique into account (well, at least as far as I can tell). Also, if you used a steep gear and have a fair amount of sprung weight, you can create a significant amount of chainline force (applied torque) to make the rear axle "suck up" into the travel. When this is combined with the fully extended fork, it will shift the weight back dramatically and unload the front end. While I am a Specialized and Horst link/FSR fan, this is something that cannot be ignored and is easily reproducible.

    This is not meant to start any fights, nor am I picking on your results; this is merely criticism of the case you are presenting. Take it with a grain of salt if you wish.
    1997 Specialized Stumpy Pro
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  9. #9
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    Quantitative data! No test report is complete without it!

  10. #10
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    Student Driver, you are absolutely right about my test(s) being completely subjective. That said, I have test ridden (12) 07 Specialized FSRs, (2) 08 FSRs to date in pursuit of purchasing a durable bike that fits me and my style of riding. With gearing, rear hubs, count of rear spokes and similar rims all being more or less equal and ignoring the drive train differences, all of the bikes I tested yesterday should peddle somewhat equally up a steep incline. They didn’t, the SJ Elite was the easiest, followed by the SJ Comp, followed by the Epic and last place goes to the FSR XC Comp. So that means that the only other factors involves are 1) the rear shocks, which were all locked-out, pivot placement-again the rear shocks were all locked-out and lastly frame flex induced by the drive-train-note I kept my tail planted on the seat during every climb. Frame flex is broken down into the pivots and surrounding frame material and the frame sections themselves-specifically the seat stays, which take the brunt of the load. My subjective tests basically confirmed that the 07 SJ with the beefiest asymmetrical stain stays and the largest double dropout bearings was the easiest to peddle up a steep incline because it has the stiffest rear triangle out of the bunch. The Epic has a less beefy asymmetrical chain stays than the SJs with single dropout bearings and the FSR XC has the smallest chain stays that are symmetrical with the smallest double dropout bearings. Where else can the peddle energy be going if it is not being absorbed by lateral frame flex in the rear triangle?

    Lastly, the frame geometry is what really blew my socks off-I was planning on buying the 06 Epic because it really seemed like the best bike for my type of riding-with 100mm of travel the Fox F100RL fork and the Fox Float R shock with adjustable brain (i.e. inertia valve) are completely locked-out. On paper the bike should have been the best climber out of the bunch with its steep seat tube, which is angled very close to the new 08 SJ’s at about 73.5 degrees (effective) and its flat handle bars; however it lost out to both SJs with their beefier chain-stays and dropout bearings.

    PS; thanks for the spelling check.

  11. #11
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    bwalton. Unless you can provide test data with measurements that are traceable with calibrated equipment in a lab environment, your comparing apples to oranges. When you write an "Engineering Test Report", it's imperative to include little things like "Traceability"

  12. #12
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    I am a Licensed Engineer, and agree with your scientific test method, which in an ideal world must be repeatable (hopefully in different environments) and statistically significant. However, as a bicycle consumer, I am not prepared to shell out thousands of dollars to a testing agency to prove my theory-this is a bicycle club not a science or engineering journal where professionals scrutinize theories and test results.

    As I mentioned in my previous posts, all of my test results are SUBJECTIVE-QUALITATIVE not quantitative and are solely based on the pedal force I felt through my legs while climbing the hill. Maintaining a somewhat consistent cadence in a pre-selected gear, some of the test bikes boggled down and required that I change gears in order to maintain my cadence up the hill while other bikes did not. One of the possible explanations for the different pedal forces between the bikes is frame flex.

    I rented a Gary Fisher HiFi on the Thanksgiving holiday and rode it up a very steep gravel road that I normally ride up on with my 04 SJ FSR and hands down the HiFi is much easier to pedal on an incline than my SJ. One of the reasons for this is because the HiF is not taxed with a drop-out pivot inline with the drive train like all of the Specialized Horse FSR designs are. The GF HiFi gives up some of the active suspension that the Specialized FSRs have and in its place yields a noticeably stiffer rear end that pedals like a hard tail.
    Last edited by bwalton; 12-03-2007 at 06:24 PM.

  13. #13
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    I think Student Driver must be an engineer of some sorts by his dialogue...

  14. #14
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    So I am looking at a new Epic myself and here's what I wanna know bwalton; you pumped the rear shocks all up to the same air pressure and used the same rebound setting and dampening settings and you liked the Stumpjumper best? My understanding was the same as you mentioned: that the Epic is the climbing-FS-bike to have.
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  15. #15
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    Here is another point of reference to consider: hard tail pedal efficiency. It’s been so long since I have ridden a hard tail mountain bike that I have forgotten how easy or efficient they are to pedal-especially up a steep incline.
    So to get back to my test rides, what variable would cause one dual suspension bike to have better pedal efficiency than another dual suspension bike if both were locked-out?

    Remember, the four Specialized bikes I tested were all new, they all have very similar rear Shimano hubs, 32 spokes, heavy walled rims, HG-50 cassettes with the same gears, 30.9 mm seat posts, seats, main pivot bearings 6802 RS orientated behind the BB and chain ring gear ratios. The component differences between the bikes are as follows: Crank sets with their respective BBs-two pieced with outboard bearings vs. three pieced with a cartridge bearing, SRAM vs. Shimano chains, Shimano SP-505 vs. SP-520 pedals, all of the bikes weighed 30 pounds +/- one pound, all of the tires were pumped up the 45 psi, all of the rear shocks and front forks were adjusted to 25% sag and SRAM vs. Shimano rear derailleurs. None of these components other than the cranks would have any effect on peddle efficiency. The crank setup would have very little impact on the peddle efficiency because the relative stiffness between them is probably within 10% or less.

    Again this line of deductive thinking brings you back to the relative stiffness of the rear triangle as a major contributor to pedal efficiency. All I can say is that my hybrid road bike, with different gearing, tires and sized wheels can be peddled up a very steep hill at 10 MPH, while my SJ FSR travels up the same hill (fully locked-out) at 4 MPH and is noticeably harder to pedal as well.

  16. #16
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    kersh13, no one was more surprised by my findings then I was because I intended to purchase the Epic that day. After all it is advertised as a climber-race bike with hard tail pedal efficiency. I dialed all of the rebounds to the center settings on all of the rear shocks before I rode them up the hill. All of the bikes I tested pedaled quite efficiently on flat surfaces and slight inclines. They all felt stable down hill and felt very similar except when pedaled up the steep hill. It could be that my weight of 215 pounds coupled with my height of 6’-3”, which positions my saddle above the average height, puts addition stress on the rear suspension that may be maxing-out the frame components and causing them to flex beyond their design parameters.
    All I can say is test ride the Epic over as many different surfaces and slopes as the bike shop will allow-better yet find a shop that will rent one to you so you can try it on your trails. Remember you will ride a bike that fits you and that is tuned to match your trails more than a bike that is not.

  17. #17
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    I test rode one just this weekend and I really loved it. But I'm coming from a HT Stumpjumper so obviously the difference is night and day there. Too, where I'm from, is all the North Georgia Mountains XC riding so the amount of travel from a Stumpy FSR is a bit much for the type of terrain here. I was just wondering if you had used the same air pressure and everything from bike to bike. When I first got on the Epic, it felt entirely too plush for my likings. Until, one of my friends recommended that I change the rebound settings and that made all the difference. Just one click on that red rebound knob made a very, very noticeable change in the way the suspension reacted. Maybe if someone else knows this, but are the median settings on all these bikes going to react differently?
    - Just livin' the dream -

  18. #18
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    I'm not an engineer, but I am in engineering. I'm the guy who tells the engineers whats wrong with their designs. I'm a Lab Rat! So, help me through this. I dont understand how you concluded that bike "A" was harder to ride uphill because of rear triangle flex? Why not the weight of the different bikes as the major factor? Or one rotor was dragging on the pads etc? Or change in wind direction?

    Nothing wrong with a good "Feel by the seat of your pants" theory, but that would make it just a theory and not a true test that should be published IMO. You could be 100% correct, but without data to support your theory, it's just a theory and not a true test.

    Interesting stuff though!

  19. #19
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    Kersh13, my ride on Sunday was the second time tested the Epic Disc-the first time was in August on the way back home from a camping trip. The first time I rode the bike the rear end bobbed like a pogo stick because there was not enough air pressure in the shock. Last Sunday I made sure that the Mechanic aired up the shock correctly and the bike did not bob at all in the front or the rear-it felt like a hard tail with a locked-out fork. The Epic's shock and fork did not bob what so ever when I climbed the steep hill either, so it surprised me to learn that both of the SJ's, which felt softer when fully locked-out then the Epic, were noticeably easier to pedal up the hill. I tested all of the bikes back-to-back at least four times each. That is, I would ride the Epic up the hill on one run then the SJ Comp on a run, next the SJ Elite on one run and finally the FSR XC. Then I would start another round of runs. As far as the rebound adjustment goes, I dialed both the rear shock and fork to the middle settings on all of the bikes.

    I would recommend that you rent a Stumpjumper and a Gary Fisher HiFi, so you can get good feel for all three the bikes on your trail before you fork over $2K+.

  20. #20
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    Quote Originally Posted by mtbikernc69
    I think Student Driver must be an engineer of some sorts by his dialogue...
    1997 Specialized Stumpy Pro
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  21. #21
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    Gary H, as young engineering student I have three bits of advise for you 1) Study hard and don't blowout all of your brain cells at parties. 2) Relax when you are taking a test-remember its not life and death only one extra semester of retakes at worst. And 3) there is a different reality out there other then what your course work is exposing you to. Aside from the abstract world of language and theorems, a human being relies on his five primary senses to understand the world around him and any concept that is beyond the reaches of his senses must be related back to an actual experience (which at some level involved your senses). In other words, your core education will be dwarfed by real world experiences that you expose yourself to-and with that you will eventually develop a feel and much deeper understanding of the essence of your education. In less abstract terms, you will develop a feel for the mechanics behind the engineering principles and formulas that you are learning in school today. And that feel will transcend all the numbers and methodologies that you see today into a real understanding of how and why things work.

    So to get back on the subject, a number of members have posted that they can actually see their rear seat stays and chain stays laterally flex when their bike is mounted in a trainer and a friend is pedaling on the saddle. Specifically, I remember a few large Epic riders posting this observation on older frames. None of these observations are surprising given the eccentric chain load, which is transverse to the riders and suspension loads all acting on the rear axel and small frame section members and pivots that make up the rear triangle.

  22. #22
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    I'm not a young engineering student. I'm an old guy who works in an engineering lab. lol Testing is what I do for a living!
    Last edited by Gary H; 12-05-2007 at 03:50 AM.

  23. #23
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    I'm new here, but this sounds weird. Where you testing mountian bikes for "climbing ability" on a 2% grade on pavement?

  24. #24
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    Quote Originally Posted by xxforeverfallenxx
    I'm new here, but this sounds weird. Where you testing mountian bikes for "climbing ability" on a 2% grade on pavement?
    Yes, you're new however you are correct in that it's weird; this is a typical bwalton post with respect to Specialized bikes. You will get used to it though. To know bwalton is to think "what the hell just happened?" after reading one.

    j/k, but seriously, it's weird.
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  25. #25
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    Unfortunately, that was the steepest grade available in the bike shop’s area and I would like to amend my original estimate of 2% to about 3+% (i.e. 3’-0 of rise with 100’-0 of run or 2.3 degrees slope). The hill I tested the bikes on was approximately 500 yards long
    with total rise of about 50 feet. I can not find a bike shop in my area that rents 07 SJ FSR’s, so I can test it on my trails, which comprises of steep gravel roads and single track trails covered in clay with large out crops of rocks and grades in the upwards of 15%. I did however rent a Gary Fisher HiFi, which handled my trails very well.

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