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  1. #1
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    Stem change from 100mm to 120mm...handling difference?

    I have been riding my Mojo for 2 months now and loving every minute of it. Just in case I was missing out on any mojo goodness I took the bike to an expert on setting people up on bikes and he made a few changes in my position on the bike.

    He moved the seat forward 1cm or so and changed the stem to a 120mm (I had a 100mm on there).

    The bike feels great as usual but I was wondering if the 120mm stem will affect my handling in any way????

    I love to do long hard climbs and fast descents.

    Will I have as much control on the ascent / descent?? Is there much of a tradeoff?

    Thanks for any info.

  2. #2
    Founder: Dirty3hirties
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    The longer stem should make the front end twitchier on the descents, quicker on twisty singletrack and easier to keep the nose down on steep climbs. Since you moved the seat fwd as well, you're gonna have more a fwd weight bias.

    My preference is to have the shortest stem possible to clean all the climbs because on the descents which is wear all the fun is, is much better with a shorter stem. I think most people run a 90 mm stem for "trailbike" riding. Some even have shorter 60-70 mm stems, especially if they're running 160 forks.

    If you haven't ridden the bike yet with this set up, try it....maybe you might like it. If you find that it's a little too sketchy on the DH's but you like the 120 stem for overall "fit", then you can also try raising the handlebar a little higher to change your weight bias, and/or get a wider bar (i like 27") to help slow down the steering a bit on the descents.

  3. #3
    Anytime. Anywhere.
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    IMO a 120 has no place on a mtb. Get the shortest that you feel comfortable with. Long stem = otb.

    http://forums.mtbr.com/showthread.php?t=311026
    I got some bad ideas in my head.

  4. #4
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    Actually the moj frame designer that did most of the design of the bike is a tall guy that rides a large with a 120 on his Moj as he likes a more xcountry feel. His comment to me was that his buddy likes the feel to be more downhill oriented and rides with a 90mm. There are some goods threads around here on Moj positioning and ergonomics that can be found via search engine. Doing slight positioning changes is fun and insightful. Keep of quiver of diff length and rise stems to experiment with. There should not be too many absolutes with this amazing bike.
    I know there is allot of focus on being positioned for bicycle suspension performance. Honestly, I don't beleive enough empahasis is put on positioning for what is right for your particular ergonomics. I am a little further back with my seat position than optimal for Dw link but it is correct for my body. I give up a little suspension performance but not body positioning ergonomics.
    Last edited by ghawk; 07-28-2008 at 03:30 AM.

  5. #5
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    The Mojo is such a centered and balanced design that I find it much LESS reliant on stem length for the overall feel of the bike as compared to other bikes I've ridden. I have a small frame for my medium size and run a 12mm set back seatpost and have run 90-120mm stems without issue. I've never come close to OTB with the long stem. I do ride very steep terrain and find it no problem keeping my weight back and the bike controlled with the longer stem. Switchbacks and climbing are grounded and controlled as well. So I think it is worth a try to see how you like it.

    "I must not be crazy because I'm seriously questioning my sanity"

  6. #6
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    Stem length and seat position on a new bike is very individual, and comfort and confidence is mostly relative to what you were riding before. If coming from road or smoother trail riding, using a long stem stabilizes steering and handling, but reduces braking power and downhill and drop off confidence.

    Shorter stems are quicker turning and can be twitchy handling, and can be slowed and stabilized using a slightly wider handlebar. For rougher trails a shorter stem is easier to lift the front up step rocks and then get ride weight further rearward while dropping off similar step downs, and rider weight can be shifted rearward further before braking harder. Some climbing power is lost, but seated climbing ease is mostly dependant on seat position to put your rider weight center over the pedals.

    I've found the Mojo to be the easiest climbing bike I've every ridden, so I'm biasing my handling for difficult trail conditions, after starting with an 80mm stem going to a 50mm stem with more precise control and quicker handling responce riding technically difficult trail. With the short stem it still climbs very easily on all but the steepest sections just bending my elbos a little more. Iím riding with bent elbos more full time, better ready to react to whatever surprises the trail has to knock me off.

  7. #7
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    I am riding a 120mm stem to get my weight over the front wheel when climbing - at my size (6'6"), the rearward saddle position puts a lot of weight on the rear wheel and lets the front wheel wander. This is true for all bikes, the Ibis is actually surprisingly good at avoiding it.

    On downhills, I sometimes wish my stem was shorter, to be able to get further back on steep descents. Might try a shorter stem (90mm), if I switch to a fork that can be travelled significantly, such as the Manitou Minute IT to preserve the weight balance. Generally, I would estimate that taller people need slightly longer stems, to remain balanced, given their saddles are further over the rear wheel that is the case for shorter people.

    My impression is also that the long stem = slower steering, as Derby says.

    Cheers
    Jever

  8. #8
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    Again, not nearly that simple and forget about it anyway what is most important...

    I suspect the stem length/steering feel was already addressed fairly well in this thread.
    http://forums.mtbr.com/search.php?searchid=7004924
    Quoting Tom at Ibis,
    "To a certain extent, I think riders have been influenced to go with shorter stems over the past few years because of the prevailing trends and not necessarily because of the relationship with the bike's overall design. Quite a few bikes with similar travel to the Mojo have longer top tubes and consequently the rider is probably better off with a shorter stem, but - as I mentioned in my previous post - that is not without its downside. The point being that stem length, steering geometry and top tube length need to be considered as a whole.
    ...........
    The shorter stem will mute your steering input creating a sort of understeer which may be desirable. The weight balance I described as a result of using the longer stem can still be achieved with the shorter stem by simply lowering your shoulders (mimicking the longer stem position) as needed because the top tube length and head tube angle are the same."

    I know there are allot of experts on bike design and suspension on mtbr but I go back to the frame designers for best advise for me personally.
    Still, much too overlooked is.........................................
    I will make a bike quicker handling slower handling...what-ever if it feels correct for my body type. Longer torso, shorter legs vs versa, longer forearms, shorter shins, etc.
    There is not nearly enough discussion on what feels right for positioning of arms, legs, back, shoulders; that is the most important, your "frame" positioning.....thing.
    I'm working through some hand positioning issues myself, and am now pretty set on trying a straighter bar than the easton monkey-lite riser bars (too much sweep). I also have a 110 in the mail from Ibis--it will probably take some tinkering and will always be a compromise.
    Things faced by many elder long time mountain bikers. HVS (hand vibration syndrome),UNE (ulmar nerve entrapment) and the big daddy, CPS (carpal tunnel syndrome.)
    Work for good core [your suspension system] support (do you supplementary training flexibility.) Maintain lumbar curve (whole nother subject, pm me if interested.) Arm, forearm, wrist strengthening. (weight training). Work to lengthen and straighten the wrist to bar interface. Ergo grips and Ergo bar ends for position change depending on riding "conditions." There is too much more for a thread. A common misconception is more upright protects your back in mountain biking. The reasoning behind this rash generalization and why it's not necessarily the case many times are to long to go into via this format.
    Last edited by glovemtb; 07-30-2008 at 03:58 AM.

  9. #9
    No Tail-Just a Nub
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    don't forget those bars

    I'm working through some hand positioning issues myself, and am now pretty set on trying a straighter bar than the easton monkey-lite riser bars (too much sweep). I also have a 110 in the mail from Ibis--it will probably take some tinkering and will always be a compromise.

    I'd say try it out--for the price and weight (and lengths up to 130mm), the Ibis stems make it pretty easy.

    Another nice topic to call out those that totally over-generalize ('A 120mm stem has no place on a mtb' ...that is, unless that works for you...).
    (insert favorite Ed Abbey quote here)

  10. #10
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    I just had a professional bike fitting done at my LBS and they recommended that switch my 105mm stem to a 135mm. I made the switch and my position does feel better (at least on the indoor trainer -I have not been able to ride it outside yet as we still have lots of snow). Will the 135mm stem make it impossible to handle downhill (in the Alps)? I'm 6'1" (185cm) with a 32" inseam so I have a fairly long torso. My Mojo SL is a Large and my seat is now set as far back as the seat post allows. The new set-up just does not look right -very old school! Even with 105mm I felt like I was OTB when going downhill in the Alps!

  11. #11
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    I used to run a 120mm stem on my XL (am 2m), and bought a 90mm stem to experiment. This will shorten my position and shift my weight back, which will not be so good for climbs, but I will try and compensate with the travel adjust of my fork to shift the weight forward again.

    The reason I changed is that I also feel too far forward on technical descents when the Mojo starts shining.

    Ludwig, if you need to shift the seat that far back and have such a long stem, then I think the frame might be a bit small? My feeling is that if I put the seat too far back, I can't get as much pressure on the pedals as in my preferred position.

    Of course, it oculd maybe also be that the bike fitter just favours very stretched-out positions on the bike. I heard there are some significant differences between how people ride-some very upright, some very low.

  12. #12
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    R. Cunningham of MBA says and there is nothing to add:

    What is funny is that a slack head angle kicks the axle forward, which takes weight off the front tire, and increases the amount of force transferred from the trail through the steering to the handlebars. So stem length makes a big difference. Presently, the super slack all-mountain bikes also have the shortest stems, so they feel cramped when climbing, corner marginally on flat ground unless you weight the front wheel, and feel unstable through rock gardens unless the handlebars are wide.
    What has evolved to fix it are super-wide handlebars.
    Super wide bars:
    -force the rider to move forward over the front wheel
    -add leverage to compensate for the boost in trail feedback
    -effectively lengthens the cockpit by straightening out the arms

    What all-mountain and XC trailbikes need is, a combination of a slightly longer stem and medium-width bars. Adding a half inch in the stem has about the same effect as adding an inch on either side of the bars. Slightly narrower bars give the rider more freedom of movement fore and aft and laterally, when balancing in the saddle. This, however, is contrary to present fashion, so we'll have to wait a while for bike designers to figure the head-angle/stem relationship on their own.

  13. #13
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    A 135 stem is way too long IMO. Unless you ride on flat trails, you will be OTB in no time. I've never even heard of anyone using a stem that long.

  14. #14
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    Quote Originally Posted by ludwig1
    I just had a professional bike fitting done at my LBS and they recommended that switch my 105mm stem to a 135mm. I made the switch and my position does feel better (at least on the indoor trainer -I have not been able to ride it outside yet as we still have lots of snow). Will the 135mm stem make it impossible to handle downhill (in the Alps)? I'm 6'1" (185cm) with a 32" inseam so I have a fairly long torso. My Mojo SL is a Large and my seat is now set as far back as the seat post allows. The new set-up just does not look right -very old school! Even with 105mm I felt like I was OTB when going downhill in the Alps!
    What seatpost do you have, straight or offset. If straight one, than I would recommend to you the setback Thomson a change the stem into 110 mm. What bar do you have. If they are at the narrow side, you can add an inch at both sides and shorten the stem by 15 mm, as R.C. says.

  15. #15
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    I am not sure that the professional fitters are the right fit for a lot of modern mountain bikes. They are great for road bikes!

    135mm was for a old school world from a couple of decades ago!

    My current findings:

    It is a very personal thing, I started out riding on bikes when everything was old school and 120-135 stems were the norm.

    I have been doing a long term test with a 80, 90, 100 and 110. I am 5'8.5" on a medium frame.

    Currently my fave is the 90mm, good on downhills and climbs.

    80 is to short for me, just a bit to twitchy and hard to climb, not enough lever arm for my taste.

    100 is a good compromise and what I have used for a long time.

    110 is old school and is good for climbs but a bit long on descents.

  16. #16
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    These "fitting experts" come from road racing have no place in real MTBing. I used to work at a shop that had one (in the 90s) and everything they know is based on getting the best efficiency on a road bike. They aren't thinking about handling or dynamic shifts caused by steep terrain. If all you care about is biometrics and pedaling efficiency you are missing the real fun of carving up a trail and hitting jumps.
    Look at a bike that makes no concesions to pedaling efficiency and is setup purely for handling (DH, FR, DJ, 4X). They have 50mm stems and 26"+ bars. Try riding one and you'll be blown away at how fun they feel and how naturally they take to the air.
    Now of course AM bikes have to make some compromises to be more enjoyable for climbing but consider what you are giving up before you go to a full XC setup. If you need a 120mm stem to get comfortably stretched out for climbing I suggest you try riding the next frame size up.
    Next time you see this "fitting expert" ask to see him do a manual or hit a small jump with style. Do you want to ride like him or like Lopes?

    P.S. I'm 6'2" and ride an XL Mojo SL, 6" fork, 70mm stem, and 26" bar. My DH and FR bikes use 50mm and 28".
    P.P.S. As for saddle fore/aft, when you are climbing ask youself, "Do I feel like I'm hanging over the back wheel or nicely positioned above the pedals?" Then on the flats do you feel properly balanced between the wheels or too far forward? My point is that a forward saddle position is better for climbing and a more rearward position feels better when powering the flats and downhills. Roadbikes don't see such drastic differences in terrain pitch. You have to reach a compromise and part of that is deciding what is a greater priority. I don't see how a stranger looking at you on flat ground can do that for you.
    Last edited by Lelandjt; 03-01-2009 at 01:30 AM.
    Keep the Country country.

  17. #17
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    This is an interesting thread. I ride a 100mm stem on a large and stand 179 or 80cm. Bars are Race Face carbon and fairly wide. No dropper seat, so I should be really flat and forward ala XC. I prefer single track and trail in general, but ride what might be called modified street as well - you know, shortcuts through parks, tracks, beach, stairs, whatever. I like speed and the with my setup it seems the faster the speed the more stable going downhill and I never feel I can't get back far enough. It amazes me how verstile the longer stem is, but that asks more questions than it answers. Maybe this should be in another thread to look at the way we ride our bikes.

    I always feel better seated, but that can mean on the very tip of the nose of the saddle on a steep climb. I find being seated tends to keep me over the rear wheel most of the time. This seems to maintain the bike's geometry both on downhill and uphills.

    I wonder if stand-up climbers prefer shorter stems (regardless of whether they XC, FR or just plain ride) and maybe longer fork travel? Not because they get more forward by standing going uphill, but because they maintain their bike's individual geometry by standing more both downhill and uphill? ie: long fork, short stem, drop seat and more weight over the pedals vrs longer stem, more weight over the rear wheel and a relatively "longer" fork travel with less sag at the front end???

  18. #18
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    Great feedback! I think mtb set-up is so dependent on your individual riding style and terrain and advice is only useful in general and you will have to experiment.

    I switched back to the 105mm stem but also changed my seat to one with longer rails and was able to put the seat back some 2cm more. I was going to change my seat anyway for a wider one as it turns out I have been riding on far to narrow seats (SLR) and the new Specialized Phenon 143 is sooo much more comfortable!

    I'm off to Spain in a couple of weeks so I will report on how the new set-up has worked!

  19. #19
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    Exactly, due the variance in trails and riding styles MTB fit is too personal for a "fitting expert" to decide for you. You just have to try a bunch of settings out and decide what you like best.
    Keep the Country country.

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