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  1. #1
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    Stem length and spacers and the effects they have on bike feel and fit

    I recently got a new Santa Cruz Chameleon, and I've been slowly modifying the fit to be more like my old bike. I immediately noticed the new bike was more playful, and I could turn around corners quicker. I assumed it was due to wider bars and a 45mm stem vs 60mm stem.

    One difference between the two bikes is that the handlebars are 1cm higher on the new bike than they are on the old bike. So I experimented with that and lowered it on the new bike by 1cm by moving the spacers around. As soon as I did that the new bike lost a lot of playfulness and I couldn't lean the bike over and turn as quickly. Makes a lot of sense, since the "lever" to lean the bike is closer to the ground therefore not as easy to push.

    After that experience, I decided to test out the longer stem from my old bike on the new one. It was only a parking lot test, but apart from more of a "truck driver" steering/feel when turning the bars, I still felt like I could lean the bike over as much as the shorter stem.

    So what are your strategies in modifying the cockpit when buying a new bike? What are the typical changes in feel when changing stem length? On my new bike I'll be keeper the spacers to the higher position. This new playfulness I've experienced is just so much more fun, even if it feels less "stable". I'm probably sitting more upright too, don't know if that's good or bad. I'm curious to try a 50mm stem too just to see if that might make the bike more stable but still keep the playfulness.

  2. #2
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    Quote Originally Posted by nemesis256 View Post
    One difference between the two bikes is that the handlebars are 1cm higher on the new bike than they are on the old bike.
    are you sure about this? how are you measuring the height? if you're basing it on height from the ground, that's bunk because you're not standing on the ground when you ride the bike. unless your old bike had identical geometry to the old one, you need to go deeper. Bottom bracket drop, reach and stack, angles, etc play into this bigtime.

    measure the effective reach and stack on your old bike and transfer those measurements to the new bike. then adjust as needed.

    by "effective reach and stack" I mean the horizontal and vertical distance from the bottom bracket to the grips. Lee McCormack calls this RAD, Rider Area Distance. the bottom bracket is the center, the point of reference by which to measure everything else on the bike.

    Stem length and spacers and the effects they have on bike feel and fit-rad.jpg

    don't waste your time measuring the bar height from the ground, because you're not standing on the ground when you ride your bike. don't waste time comparing the distance and height of your saddle to your bars, they are only secondarily important to how the bike handles.

    start here- measure from the center of your old bike's BB to an imaginary spot between the grips. because your handlebar has some upsweep, backsweep, maybe some rise, and also some length that results in that spot being 20-60 mm behind and probably above where your handlebar is clamped in the stem. for example, I am 5'9" and I shoot for 77-78 cm when I change anything on my bike.

    if you want to know more specifically what your effective reach and stack are, try this:
    get your bike standing perfectly upright and measure from the ground to the center of your cranks (A). measure from the ground to the center of your grip (B). subtract A from B and you have your effective stack.

    now push your back tire against a wall and measure from the wall to your BB (C). now measure from the wall to your grip (this part will be tricky, try a few times and get an average) (D). subtract C from D and you have your effective reach.

    to confirm, check your RAD measurement against your e-reach and e-stack measurements using Pythagorean Theorem. if you don't know how to apply Pythagorean Theorem, look that up. That was basic geometry that I remember from when I was 13.

    the other helpful tool would be to plug in the numbers from your old and new bikes here: Stack and reach calculator. keep in mind that your new bike might have different shaped bars, but see what you would need to do to get the number similar within a centimeter or so and make small adjustments from there.

    what size is your Chameleon and what brand/model/size is your old bike?

  3. #3
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    Wow, great post, thanks for that. I'll make some measurements. My method to measure the difference between saddle and handlebars was using the ground.

    Chameleon is size medium. Old bike is Specialized Fuse size small. I was on the big side of a size small and put on a longer stem for a better fit.
    https://www.specialized.com/us/en/fu...attie/p/106977

    My primary interest in this thread though is finding out other people's experiences with stem length and spacer height and their effects on handling and what they do when buying a new bike.

  4. #4
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    your measurement method could get you close, but it could also end up being off by a significant amount. if the BB drop is different, the measurement will not be equivalent. the bike's reach will also throw off the measurement because a grip position at the same height of but not the same horizontal distance will handle and fit differently. start with setting up the bike so it fits the same as the old one regarding the BB-grip relationship. adjusting spacers and stem length don't mean much, but where those put your hands does.

    I could build two bikes, one with 5 inches of spacers, 40 mm rise bar, and a 120 mm stem, and the other with no spacers and a 35 mm stem slammed on top of the headset with a flat bar, and have them fit exactly the same way. they would handle completely different though because of where the rider's center of mass would be and how the steering would be affected.

    I don't know if this is universally applicable, but I am starting to think that, at least on a modern bike, you want your hands to be about even with the steering axis of the bike. if that results in a bike that is too long or too short, you need a frame with more reach/ less reach.

    in general, getting your bars closer to you (shorter stem, higher bar) makes the bike more flickable and getting lower and further away makes it more stable. that's a very broad generalization though.

  5. #5
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    If you liked the feel of the old bike, why'd ya sell it?? ;-P

    If you've only recently bought the bike, give it a chance to feel 'normal' before making - possibly unnecessary mods ^^

    Usually, if you shorten the stem - you should widen the bars...

    Although, you may find - as I have a number that works for you i.e. 50mm stem w/ 785mm bars.

    I run the above setup on both my mules.

    One is a 29er AM HT, the other is a 27.5 Enduro rig.

    PS - to get a more familiar feel, you could try moving your saddle - backwards/forwards as well.

    'Born to ride!'
    "Mountain biking: the under-rated and drug-free antidepressant"

  6. #6
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    Quote Originally Posted by nemesis256 View Post
    My primary interest in this thread though is finding out other people's experiences with stem length and spacer height and their effects on handling and what they do when buying a new bike.
    These things are fit considerations. They aren't really something that you mess with on a bike you already have, with the sole purpose of changing the handling. Because as soon as you change something, they change the way the bike FITS as well as how it will handle. The two go hand-in-hand. This is why when you buy a bike, you want to buy the bike that lets you achieve the fit you need with the least amount of deviation from "stock" setup, to minimize unwanted changes to handling. Deviate too much from that "stock" arrangement, and the bike will wind up handling SIGNIFICANTLY different. If that's what you have to do to make the bike fit, then you probably bought the wrong bike.

    There are a few generalities you can say. Longer stem slows handling, shorter stem quickens it. Wider bars slow handling, narrower bars quicken it. This is why the current trend of short stems is also combined with wider bars, and why mtb's in the 90's with super long stems came with super narrow bars. Raising the bars is going to take some weight off the front of the bike, for better or worse. The key for each rider is to find the grip position (fore-aft, up-down, width, and angle) that is comfortable and allows the bike to handle well.

    There are only a few things you can do to change handling without affecting fit. Better suspension setup, changing the fork offset, changing wheel/tire size (say between 29 and 27.5+, for example), changing tire width/tread, that sort of stuff.

  7. #7
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    after you have set up the BB-grip position to your liking, check the saddle offset. it's not as important as some make it out to be, but if you want to set up the bike so it fits identical to the old one, do the same measurement that i described above, but measure from the wall to the nose of the saddle and from the wall to the center of the BB. subtract the saddle distance from the BB distance and you get your saddle offset. set the saddle to the same height from the BB and try to mimic that on your new bike to start.

    then compare the distance from the nose of the saddle to some point on both bikes. the Chameleon likely has a longer reach, so it will be longer. it might not matter, but you may want to adjust the saddle fore/aft position to make up the difference. then again, with different saddle designs, the sweet spot where you sit might be in a different place relative to the overall length of the saddle, so that measurement might be irrelevant. see if you can get it within a ballpark of the old bike, but don't fret about it if you can't.

  8. #8
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    Quote Originally Posted by targnik View Post
    If you've only recently bought the bike, give it a chance to feel 'normal' before making - possibly unnecessary mods ^^
    It already has become the new normal actually, I've got about 40 miles on it. Now when I get on my old bike it feels small and cramped. It has narrower bars (720 I think vs 750) which is probably the primary reason. I'm keeping it to try winter riding with studded tires, and I get a feeling I might make cockpit changes to it now.

    I tried making the measurements from the wall and ground mack_turtle mentioned and get different results every time. I would probably need a solid ruler to get anything useful. The RAD measurement is 2 cm longer on my new bike though. My issue with relying on only that one measurement is that the angle is different so there's no way knowing where the difference is.

    As far as saddle position, I did get the height the exact same. As far as fore aft, I just adjusted it so it would be in the right place when I sit down after standing for a while. Going by what feels natural instead of measuring.

  9. #9
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    Quote Originally Posted by nemesis256 View Post
    Going by what feels natural instead of measuring.
    in the end, that's all that matters. but you have to try different things to know the difference between cramped and stretched out and just right. a lot of people get a bike set up one way and just keep it that way and ride in ignorance. the fact that the new bike is 2 cm bigger and does not feel "cramped" is informative.

    have you tried plugging the numbers from your two bikes into the bikegeo site? it's not perfect, but it gives you some sort of idea with numbers and a visualization that will help.

  10. #10
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    For me measuring the difference between the seat height and bar height works pretty well, a good starting point anyway.
    I brake for stinkbugs

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