1. The most important thing about buying a new bike is to make sure it fits. The only way you'll know if the bike is right for you is to size up the bike and make sure that the bike's geometry matches your body's geometry. Ask questions and do some research.
mtn. biking 101
2. If possible, try to find a shop that will let you demo the bike on real dirt. Five minutes in a parking lot won't cut it. You wouldn't buy a car without a real world test drive, and a bike should be no different.
3. Don't belive the hype. Just because your favorite rider or best friend rides a certain bike, that doesn't mean that's the best one for you. Have an open mind and be realistic about your needs and ability.
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  1. #1
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    Idea! Trek 3900--Shifting Help!!!

    Hi everyone! First off I like to say im new to this site and semi new to the sport. About two years ago I took a Law Enforcement Bicycle Association Mt. Bike course and loved the sport. I recently got a new bike and have been experiencing some problems with the shifting. My Trek has shimano shifters.

    My bike has a shifter on the left and a shifter on the right. The shifter on the left only has 3 different gears. The shifter on the right contains 8.
    I have noticed that when I shift the left shifter to 1 it seems peddling does nothing. It is so easy to peddle I dont even move. It is like this for every combination on the other shifter (1-8). Is that a problem?

    When my left shifter is on 2 it seems too run smoother and harder. Usually I peddle at 2 and 6. When on 3 on the left, 6 - 8 feels good on the right.

    I hope I didnt confuse you yet but I want to know if there seems to be a problem or am I just not setting the right combination???



    The biggest question and problem other then what I posted above is how the shifter is shifting. It keeps getting stuck and sounding scratchy then dropping into gear hard. Its like my chain keeps slipping in between gears. Is there something that could be causing this or does my entry level bike just have crappy shifters?


    If I confused any of you please let me know and I'll try and re word something. I dont remember all the terms so bare with me .

    Thanks in advance guys and girls and I look forward to using this site for all the valuable info its worth/sharing my hobby with other people!!!

    Im going to the Tigers game... Ill be back later ha ha

  2. #2
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    Junky Derailleur?

    Not really a fan of the Tigers, but I hope they do well anyways, considering there isn't much to root for in the Bay Area.

    Anyways, the cog labeled "1" on your left shifter is meant to make pedaling extremely easy. It's used on climbs that are just too long to complete in the gear labeled "2" on your left shifter (1 is the easiest to pedal in, 2 is a little tougher (most people stay in this gear), and 3 is the toughest). As for your rear derailleur, the mechanism that switches your gears in the rear, it's understandable that the components may be junky, so your shifting might not be quite up to par. Take it to your Local Bike Shop, LBS for future reference, and have your rear and front derailleur adjusted. Also, as for gear combinations, you don't want to excessively cross up your chain. In other words, you wouldn't want to put your bike in 1st gear in the front and 8th gear in the back. Doing this can stretch your chain and bend the teeth in your freewheel (the gears in the back of your bike). So, keep your chain as straight as possible. Suggested gear combinations might be 1 in the front and 1-4 on the back, 2 and 3-6, 3 and 5-8. Don't pressure yourself to stay within these guidelines 100% of the time, especially if you aren't that hardcore. Happy shifting

  3. #3
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    Your shifter on the left side is for your FRONT derailleur as you see your cranks have 3 gears. The right shifter is for the REAR derailleur as it has 8 gears. 1st gear up front is for climbing, it's extremely east to pedal on flat ground and you have to spin really fast to get anywhere. 2nd gear is the one you should be in most of the time, your "cruising" gear. 3rd many people never use on an MTB. It is your top end gear. Most of you gear selection should be done in the rear, only shifting your front in preparation for a steep climb or back when you're done.I really hope you didn't think that shifting gears would have no effect on pedalling effort.

    Anyway, it's tough to say why your bike is shifting noisy and hard, could be because you are pedalling while shifting. That's a no no, especially while going uphill and shifting to higher gears. Could also be you derailleur needs to be fine tuned and adjusted. The derailleur on your bike is a bit clunky from its design but should still be able to shift smooth when properly tuned.

  4. #4
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    Go tigers... you in michigan?? I assume baseball right? I LOVE THE TIGERS.

    anyhow, down to business. to answer the questions. the chainrings (gears on the front) are easier to pedal at the smallest one and get harder as the size increases. (the word is pedal). The smaller gears on the rear are harder to pedal. so with the little gear in front and the biggest gear in the rear will be the easiest to pedal. that is called your granny gear. rule of thumb gears that are easier to pedal are for climbing. gears that are harder to pedal are for flat lands where you want to carry fair amounts of speed.

    now, with the sloppy shifting. your bike may be in need of a tune up. after riding for some time, your shifters and brakes settle in and need adjustment. that may be what you are experienceing. without researching the 3900 and not being aware of the components on it, i suggest you take the bike to your local shop and have them adjust the derailleurs and brakes for you. and then... get out and ride..

  5. #5
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    I really hope you didn't think that shifting gears would have no effect on pedalling effort.
    No I am not that dumb. I just wanted more knowledge on what the shifters did and what I should be at when peddling.

    Thanks for the help guys who did post.

    For some reason I thought you peddled while shifting I dont know why I thought that but I will stop that asap and see how it works.

    And Tigers lost today :-(.........but I was 1 of 10,000 fans who got a free vintage jersey ;-)

  6. #6
    Cheezy Rider
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    Quote Originally Posted by BlurredVision
    ...could be because you are pedalling while shifting. That's a no no, .
    You have to pedal while shifting, or your bike won't shift. I think what you mean is pedaling UNDER LOAD while shifting, such as while climbing a steep hill. You can usually get away with shifting your back gears under load, though it's better not to. Shifting the front under load can cause real problems. So make sure you shift down a little before you actually need to.

  7. #7
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    Quote Originally Posted by BlurredVision

    Anyway, it's tough to say why your bike is shifting noisy and hard, could be because you are pedalling while shifting. That's a no no, especially while going uphill and shifting to higher gears. .
    i do have a question for ya blurred.. I have been riding multispeed bikes for many years and have yet to find one that will shift gears when you are not pedaling.

    i agree with you on the uphill portion. very hard on a drivetrain but hell, i do it.. i will always do it when i approach a hill that i underestimate. i will reap the consequences when they arise.

    just need to play the devil's advocate for a minute.

  8. #8
    Hey! Watch This!
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    Quote Originally Posted by Fenech627
    For some reason I thought you peddled while shifting I dont know why I thought that but I will stop that asap and see how it works.
    NO!! No no no. I think what he meant was don't be pedaling hardcore standing up hammerfest when you shift. You must be pedaling while you shift, but pedal easy. If you do not pedal, it will put stress on your components/chain and will not shift nearly as smoothly.

  9. #9
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    NO!! No no no
    You have to pedal while shifting, or your bike won't shift.
    I knew you peddled while shifting. I guess if I would of tried what blurry suggested I would of found out real quick you have to pedal while shifting because it wouldn't work.

    Hopefully it does not rain tomorrow because I was planning on taking the bike out for another test run. I did not know about crossing the chains thanks for letting me know that helps out alot.
    Go tigers... you in michigan?? I assume baseball right? I LOVE THE TIGERS.
    ^ Ya I'm from Downriver......You?

  10. #10
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    Ok, perhaps i stated it wrong, obviously you need to pedal for the derailleurs to shift but you should be anticipating your downshifts before hand and on the downhills when you're not pedalling you and downshift in advance for the gear you need on the next incline. Sometime you will have to shift under load but with experience to can learn what gear you mey need in advance and minimize the strain on your drive train.

  11. #11
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    i knew what you meant blurred. . I was just giving you a hard time from somewhere in cyberspace. hehe.

  12. #12
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    to the OP, rest assured your drivetrain is perfectly OK for someone starting to ride mtn bikes or returning to the sport. i've got a 3900 with Shimano Acera derailleurs and they're fine. like all derailleurs they need adjusting after the initial break-in period (up to a month) so get your bike shop to check them out. as the other replies say, avoid extremes of gearing eg 1-8 and 3-1 because chains are designed to take stress in a straight line and cross-gearing puts the stress in the wrong places. i ride a fair bit of tarmac and fast, flat trails on this bike so i'm often in top gear (3-8) but can drop to 3-4 no problem.

    ease off the pedalling when triggering a gear change, then put some load back on and the gear shifts smoothly. putting load on the pedals while hitting the gear trigger can cause your chain or derailleur to bend or break, or break off a tooth on the gear cogs.

    enjoy your 3900. i've had mine for 3 years and it still rides great and looks bad@ss.

  13. #13
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    Thanks Qatarbhoy good info right there.

    Im glad to hear your 3900 has done so well for you.

  14. #14
    responsible zombie owner
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    yup i've fallen in love with it again after putting clipless pedals on it, which turned it from feeling a bit tanklike to giving it a turbo boost. the stock nylon pedals are feeble and look it but you may as well wear them out while you think what you'd like to replace them with. IMO the 3900 is a decent enough frame to add a few minor upgrades to, although i wouldn't bother sinking big money into this level of bike.

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