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GT IT-1 and Nexus?

Discussion in 'Downhill & Freeride' started by revmonkey, Nov 11, 2005.

  1. revmonkey

    revmonkey Monkey

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    shimano lists nexus as a commuter system... can the system handle the abuse a DH/FR bike is put through?
     

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  2. Thrillkil

    Thrillkil Monkey

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    There was a guy on this forum who bought a IT-1 a while back, and he has had no problems with the nexus-gearbox as far as I know
     
  3. bballe336

    bballe336 Turbo Monkey

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    It's inside the frame so it should not be experiencing any of the harm a hub normally would.
     
  4. vitox

    vitox Turbo Monkey

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    you mean like pedalling forces and that stufff?
     
  5. vitox

    vitox Turbo Monkey

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    im wondering about that too, guess we'll just have to wait and see.
     
  6. trialsmasta

    trialsmasta Monkey

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    They only concern I would have would be torque. The killer of all hubs. I belive they changed the ratios, and internals a bit to add durabilty. There also isn't nearly as much torque seen on a DH bike as you would XC, but a DH bike ratio spread is wide enought that if used for the wrong application it could do some damage to the internals. Either way I don't think the overall speed ratio drops below 1.3 or so. Still low but nothing like a .7 of a XC rig.
     
  7. AusRottenVirus

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    i was the one with the IT-1. Still no real problems yet but havent ridden it enough still to give a real report.
     
  8. revmonkey

    revmonkey Monkey

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    you have any more pretty picutres of your bike other than those previously posted?
     
  9. mack

    mack Turbo Monkey

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    If its a commuter hub then why wouldnt it handle the stress? A commuter bike gets pedaled the whole time, and it has to be built to withstand all the strain that commuter bikes are put through, no maitnence, shifting while putting the hammer down, and not to mention all the miles. I would think that a hub like that would last longer in a down hill bike than on a commuter bike as long as the dirt is kept out.
     
  10. AusRottenVirus

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    sorry, no pics right now. I'll get some when the bike is nice and dirty for ya.:p
     
  11. revmonkey

    revmonkey Monkey

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    actually, i like clean bikes... :P
     
  12. Sir_Crackien

    Sir_Crackien Turbo Monkey

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    the hub will be fine. the hub being in the frame keeps it from the forces that it not designed to handle and makes it only handle the forces of pedaling which is much less than what is was designed for
     
  13. .:Jeenyus:.

    .:Jeenyus:. Turbo Monkey

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    Brilliant. Just brilliant. :p
     
  14. Zutroy

    Zutroy Turbo Monkey

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    I'd have to disagree with that, most DH riders are bigger and stronger than most XC guys, who sprint and full power alot of the time, and shift under full power sometimes, all of which are harder on a hub than XC riding.
     
  15. maxyedor

    maxyedor <b>TOOL PRO</b>

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    personaly I think the nicoli is a safer albeit more expensive option for the gearbox nuts out there, plus its got more gears for about the same weight
     
  16. ragin-sagin

    ragin-sagin Monkey

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    I will pipe in a few thoughts here based on some past usage of the Nexus hub...about 8-10 years ago when Shimano first introduced the Nexus I was in high school, and in one of my classes we built human powered vehicles for that great Arcada to Ferndale Kinetic sculpture race.

    Being more technical minded, opposed to the shroom chewing-patchouli oil smelling-psychedelic sculpture oriented crowd, we focused on a well engineered, light weight bike. One of the local parts reps told us about the Nexus and gave us three of them to try out on our vehicles.

    The larger vehicle was a tandem, 3-wheeler, both riders recumbent, and weighed around 100 lbs, less rider and gear. It usually carried around 150lb of gear (inflatable pontoons, tracks for sand&#8230;etc).

    We put the hubs through lots of abuse&#8230;before we upgraded to the Nexus we had actually twisted the body of other hubs into two pieces&#8230;they were submerged in salt water while we crossed a bay, spackled with sand on the dunes, and worked hard to get two riders and loads of gear up some rather steep climbs. Under these conditions they shifted great, and never showed any signs of wear.

    I thought were onto the future of biking&#8230;apart from the weight, they were amazing&#8230;but in the past 10 years little has changed, they still weigh a ton, the shifters still sucks and they have not marketed it as anything other than an option for grandmas bike.

    Two thumbs up&#8230;Joe-bob says check it out!
     
  17. ioscope

    ioscope Turbo Monkey

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    Double disagree. I think that xc riders are harder on hubs, torsionally at least. It is rare that you pedal as hard as you can on a DH bike, but the wheel just shoots up and under your bike. Happens all the time on shorter-chainstayed xc bikes, especially on techy climbs.
     
  18. Rik

    Rik Turbo Monkey

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    I'd be in on the idea that XC would smash a hub around more (pedalling-wise) than DH would. There's always a but... One thing I could imagine would give the hub hell is a trials-style drop to rear wheel, with the rear brake pretty much locked. Such an action would probably torque the hub more than any pedalling could. That said, you'd have to be an absolute fool to do such a move on a long travel dually.
     
  19. vitox

    vitox Turbo Monkey

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    what ive seen atleast is that while dh riding clearly doesnt put so many miles or shifts on drivetrains, the combination of shifting mostly ALWAYS under torque and the general disregard towards drivetrain happiness that is mandatory in dh racing makes for a "drivetrain time accelerator" when compared to xc racing or riding.

    maybe this isnt true for an internally geared hub, i dont know, but for normal drivetrains to me atleast the evidence is clear.
     
  20. zedro

    zedro Turbo Monkey

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    regardless of who is stronger (because in light of the following engineering aspect those differences would be negligable), there is one gaping reason why XC use would put alot more stress and thats because of gearing. If you used a baseline max force input of the riders mass (ie. not wearing clips, he can only exert his own body weight down on the pedals), between two equal guys it'll be the gearing that determines the torque. So that guy hammering up the hill with a 32/32 will be dishing twice the torque as the guy spinning across the flats with a 42/21 combo. Now add in the fact the guy climbing is clipped in and pulling more than his body weights worth in force (on longer cranks and smaller rubber most likely for an even lower overall gearing), he's putting gobs more torque in.

    I'm guessing that hub comes with a chainring size limit just like the Rohloff does to limit torque.

    And besides, roadies would probably destroy it way quicker than anyone.
     
  21. bikenweed

    bikenweed Turbo Monkey

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    I ripped a sealed bearing, house brand GT hub in half doing sprints a few months back on my slalom bike. The freewheel mechanism decided to become a fixed gear, and it was half-fixie, half-sketchy going for a few minutes until it died. Not sure on the exact series of events, but the shell is in two pieces and the freewheel mechanism is gone. This hub has seen tons of miles with a single chain ring sprinting and climbing up hill fast. I am willing to guess torque has nothing to do with hubs failing, but this is a valid example of a failed hub.

    Who puts more force on a hub, XC or DH? Easy, a DH rider. Many downhill runs have climbing sections on them. In addition, a lot of us just ride XC all day on our DH bikes to stay in shape and have more fun going down. A heavier bike, with a larger front chainring, and probably a smaller rear cassette, will require more torque to move up the hill. I do not understand the subject of torque very well, (all I know is force x sin theta of the lever arm= torque, high school physics stuff) but I do understand that it is a lot more difficult to ride this heavy bike up a hill than my light little hardtail.

    Why do people just assume this hub is the downfall of the world and will fail instantly when put on a DH rig? Marketing sure does work wonders...
     
  22. zedro

    zedro Turbo Monkey

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    if you did, you wouldnt come to that conclusion (if you dont understand torque, how can you say which creates more???). The weight of the bike has little to do with it, that only means you will have lower acceleration for the same given force.

    It's simple really, the torque input to the hub is equal to the torque output by the rider multiplied by the total gear ratio. If the DH and XC rider of are equal strength (output) and are both trying to go the fastest they physically can, both will produce the same maximum torque regardless of climbing or decending. But if the climber is using half the gearing, he is contributing twice the torque. It's not hard to see the harder/steeper the climb, the more torque will be required.
     
  23. bikenweed

    bikenweed Turbo Monkey

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    That´s what I wanted to get at. A DH bike with a 38t chainring and a 32t or 26t rear cog will need more torque to climb than an XC bike with a 22t chainring and a 34t rear cog. XC guys can put it in a higher gear and push, but with them narrow bars and small tires, standing and pushing on the super steep stuff sucks. Therefore, DH bikes should be prepared to handle plenty of torque. That would be hilarious if a GT couldn´t be ridden up a hill. I´m pretty confident that the Nexus will do alright, but we´ll just have to wait and see. Don´t all kinds of pedi-cabs and several person bicycles, tandems, etc, use the Nexus all the time?
     
  24. zedro

    zedro Turbo Monkey

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    no, you still dont understand, and you are confusing 'needing' more torque with 'providing' more torque. In that situation (gearing), the XC guy will be (and be capable of) producing more torque at the wheel. You seem to be assuming that the XC guy is taking a leisurely time up the hill in his granny gear when really he may be pounding as hard as the under-geared DH guy. The DH guy is struggling because he needs more torque, because he is not actually producing as much as the properly geared XC guy.

    Dont confuse the ease of pedalling; just because it feels harder to pedal with a 42t doesnt mean you are producing more torque. The reality is the opposite: you arent producing enough torque at the wheel therefore the effort seems higher. Also if you are heavier you will accelerate slower, the net force is the same if you were lighter and accelerating faster (Force = mass x acceleration)

    Another example: a car in 1st gear can easily start from a stop, another in 4th will stall the engine. The 1st gear (xc setup) is producing more torque at the wheel (ie our hub) than the other guy in 4th (DH setup) struggling to get going. The fact that he's struggling means he needs more torque at the wheel (the engine is producing the same amount of torque in both cases) which is the whole basis of gearing.

    To see how mass doesnt matter, if car A weighs 1 ton and car B weighs 2 tons, and both have the same engine (torque), car A will accelerate twice as fast as car B, yet both are producing the same amount of torque. So the DH rider could have an elephant on his back and it would only make him slower, it wont allow him to produce more torque through his legs, he'll just be slower.

    Anyways you can pick up a 101 physics book if you like, it's all there.
     
  25. MMike

    MMike A fowl peckerwood.

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    Where the HECK am I supposed to find an elephant this time of year??


     
  26. zedro

    zedro Turbo Monkey

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    well the elephant was really metaphorical so any present life-burden will do, like say...really expensive diningroom furniture bills for instance.....
     
  27. MMike

    MMike A fowl peckerwood.

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    A metaphor??? Oh GREAT!! Now I have to RETURN my elephant?? I just spent the last hour haggling over shipping costs with the "Off-Season Elephant Emporiam and Muffler shop". This is just GREAT....

     
  28. vitox

    vitox Turbo Monkey

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    zed


    just to tease ya

    ever though of the "peak torque" theory at work here.

    see, when a dher that you calculated would have just half of the torque (dont think so but ill give it to ya just because) gets on the pedals and sprints or whatever, he will be putting an uneven chaintension on the system because the bike will be traversing rough terrain and the chain will be tensioned and slackened by the effect of inertia thru his pedals when the bike moves up and down.
    this would mean the resulting peak torque might be a lot more than what his own weight could produce.
    so i could now further speculate that since the hub designers probably knew full well what sort of max torque to expect from a rider on smooth ground, namely torque resulting from the rider weight or muscle (if he uses clips like you say) they have this level of torque resistance built into the design. whereas, the thousands of split second "torque peaks" would not, and could potentially be harmful to the design, and these would only occur when pedalling through rough terrain and with "square edged bumps".
     
  29. zedro

    zedro Turbo Monkey

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    oh of course, but it's a big assumption that XC bikes wouldnt generate those spikes as well, and i'm sure this is a concern with any heavy use factor (imagine trials riders without suspension even). But if torque spikes were the only issue then slip-clutch plates could easily be used for thos anomalous spikes. But as far as the continuous torque demands are concerned, the only factors are the input force of the rider and the gearing (ie. the output torque). With top riders at their peak performance, the climbers in low gearing are out torquing the descenders in higher gearing without a doubt.
     
  30. trialsmasta

    trialsmasta Monkey

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    Thats an interesting point Vitox, but the human legs arn't rigid members so assuming that we have an efficient supension design would this be somthing to be concerned about? To generate torque you have to have a reaction i.e. resistance to rolling. If the guy is sprinting, resistance to rolling would most likely be low, and he is in a high gear, so if he hits a large bump creating chain growth that then turns into torque at the hub, considering the damping properties of the human body, and rolling resistance would this really be a spike or more of a blip? Inertia would have to play a really large part. I guess thats where that elephant comes in. I'm not completely sold on that theory yet, but interesting none the less.
     
  31. Trigger

    Trigger Chimp

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    I'm also one of the guys that actually have one of the IT-1's. I havn't had any trouble with the Nexus.

    It's well protected under it's plastic covers, and you see that the hub itself is sealed with different rubbersolutions if you take a close look.

    I think the way the stress is on the hub is more like a mix between a bottom bracket and a hub, just less than both. Like the RaceLink's upper hub as well. No problemo.

    The only thing I've had to pay attention to is adjusting the dropouts correctly to get the chain tight enough.

    So no matter how much stress an XC rider puts on a rear hub, the second BB Nexus hub on the IT-1 does just fine, and I've ridden it ALOT now. :)