• 09-04-2019
    nobody special
    Trek "Dialed" component weights
    I'm looking at upgrading my 8YO's (~55", ~71lbs) 2004-ish Trek MT220. I honestly don't know what year it is, but I suspect it's an older bike, since it has the threaded fork and quill stem.

    I weighed the bike this week and it was 29.66 lbs. Sorry, my shipping scale has better resolution when measuring in pounds, so that is what it is. He has been riding it for about a year and likes it, but a month ago we bought some new tires for it from the Giant store (Kenda K849), and he complained that it actually got heavier and slower. The old tires were dry rotted in the sidewalls so we were in a "we just need some tires now" situation.

    Among other weight savings options, I would like to swap the fork for a 26" Manitou Markhor since it is 1656g and 456mm AC (80mm travel). The SR Suntour on the bike is 424.3mm AC and I believe over 2200g. The AC measurement for the OEM fork came from here:
    http://www.vintage-trek.com/Trek-Fis...manualTrek.pdf

    I considered the F1RST and JUnit, but the F1RST is expensive and mostly unavailable, and the JUnit is expensive and tapered headset only. I am aware that the extra AC height will bring the head tube angle from 70deg to about 68.3 deg, and extend the wheelbase from 985mm to 996mm. I don't really see these as terrible, and also with the front end going up, it will put his weight farther back on the rear tire, which I don't necessarily see as bad.

    I am trying to figure out specifically how much the OEM Dialed angle adjustable quill stem and steel handlebars might be so I can make my weight estimates more accurate. I cannot find this online, so I appreciate any input if you all have actually measured these components. Measurements of the Dialed cranks, steel chain rings, and square taper BB would be appreciated as well.

    He rides the bike every day, so I don't want to tear it apart to measure at the moment.

    Thanks.
  • 09-04-2019
    TimTucker
    Lots of old threads around here that have builds detailed if you do a search of this forum for MT220.

    Here's an example:
    https://forums.mtbr.com/families-rid...ld-844138.html

    Note that HTML has been disabled for forum posts since that was written, so the table of weights that they included is kind of a mess as-is -- here's the table copied into JS bin for viewing:
    https://output.jsbin.com/cafafopite/
  • 09-04-2019
    svinyard
    I'm not familiar with any of this...but kids bikes in general are pretty bad, aside from a select few. Upgrades are usually expensive as well. Fitment is key but its like many bike engineers have never seen a kid ride.

    You might be better off just getting a new bike. The Vitus Nucleus 24" might be in stock again. Decent geo, right crank length, hydraulic disk brakes and a decent air fork. 480$. Itd be worth the extra cash over finding new air forks and other stuff aftermarket. Odds are you might even save some money.
  • 09-10-2019
    nobody special
    Quote:

    Originally Posted by TimTucker View Post
    Lots of old threads around here that have builds detailed if you do a search of this forum for MT220.

    Here's an example:
    https://forums.mtbr.com/families-rid...ld-844138.html

    Note that HTML has been disabled for forum posts since that was written, so the table of weights that they included is kind of a mess as-is -- here's the table copied into JS bin for viewing:
    https://output.jsbin.com/cafafopite/

    Thanks. I actually had seen several of the MT220 builds on the forum, but I never saw that one, or if I did I never realized that was a table. It has some good info in it.
  • 09-10-2019
    nobody special
    1 Attachment(s)
    Quote:

    Originally Posted by svinyard View Post
    I'm not familiar with any of this...but kids bikes in general are pretty bad, aside from a select few. Upgrades are usually expensive as well. Fitment is key but its like many bike engineers have never seen a kid ride.

    You might be better off just getting a new bike. The Vitus Nucleus 24" might be in stock again. Decent geo, right crank length, hydraulic disk brakes and a decent air fork. 480$. Itd be worth the extra cash over finding new air forks and other stuff aftermarket. Odds are you might even save some money.

    I have considered the newer bike, but every time I look for something better, I come back to the question of why that bike actually better? I understand the geometry is supposed to be better, and the weight is supposed to be less, but what makes good geometry? Obviously less weight is better.

    When I did my spreadsheet of the new purchase alternatives I can find on the web (this website, bikedads, rascalrides, twowheelingtots, etc) The MT220 really doesn't fall far outside of the "best" geometry and seems competitive with the "good" geometry. I believe the primary drivers of "better" geometry are wheelbase, chainstay length, head angle and seat angle. In my opinion, changing the fork to go from 424 AC to 456 AC actually improves the geometry. Also, if I put the frame in my milling machine and move the rear dropouts/tire forward 15mm, the geometry gets better again. This also requires making a bracket to put a disc brake on the rear, which is doable.

    If I assume that the Trailcraft Pineridge 24 is the top of mountain for the best geometry, an MT220 with a 456 AC height, and the OEM wheelbase and chainstays are within 1% of the chainstay to wheelbase ratio of the Pineridge 24. Yes the overall wheelbase and chainstays on the MT220 are longer, but is the absolute dimension more important or the ratio? I really don't know. If I move the rear tire forward 15mm, then the ratio of the MT220 is within 0.1% of a Pineridge 24. I am ignoring head and seat angle because since wheelbase is fixed, head angle and seat angle affect the reach, and reach is adjustable to some extent using different offset stems and seat posts. Also with the higher AC the head angle of the MT220 becomes so close to all the others it's practically the same, so I didn't bother comparing it.

    This all gets me back to:
    1) new fork which is transferable to a different frame in the future
    2) reduce some weight as done in other MT220 projects

    Given that I can buy the aluminum MT220s for anywhere between $30-$100 used, I really don't care if I screw one up and buy a replacement frame as a second try. I specify aluminum because the original MT220s in the late 90's were steel, and those I would not buy.

    Last year we swapped out the derailleurs and shifters and seat on his MT220 so it is actually a pretty good riding bike at this point. Just heavy.

    I don't know, what am I missing?

    Attachment 1278169
  • 09-10-2019
    TimTucker
    The other ratio that I'd be looking at is chainstay to outer tire diameter rather than just chainstay to wheelbase.

    380mm on the Commencal Meta HT 24 with 2.6" tires is likely to feel quite a bit shorter than the MT220 with smaller wheels.

    Meta HT 24 w/ 2.6" tires: 0.565
    672mm tire diameter

    Yama Jama 24 w/ 2.2" tires: 0.583
    652mm tire diameter

    Pineridge 24 w/ 2.1" tires: 0.596
    646mm tire diameter

    Orbea MX 24 w/ 1.95" tires: 0.606
    639mm tire diameter

    Zulu Four Heir (2.35" tires): 0.607
    659mm tire diameter

    MT220 w/ 2.0" tires: 0.637
    642mm tire diameter

    Nucleus 24 w/ 2.0" tires: 0.646
    642mm tire diameter

    Frog MTB 62 w/ 1.95" tires: 0.645
    639mm tire diameter


    Looking at some adult sizes:
    Big Honzo ST with 27.5x3.0" tires: 0.577
    425mm chainstay
    736mm tire diameter

    Niner EMD 9 with 29x2.2" tires: 0.598
    439mm chainstay
    734mm tire diameter

    Trek Stache with 29x3.0" tires: 0.543
    420mm chainstay (only 11mm more than the MT220 / 5mm more than the Vitus!)
    774mm tire diameter

    Here's what I was using to calculate tire sizes:
    Berkshire Sports - Bike Computer Tire Size Calculator
  • 09-10-2019
    nobody special
    I understand the calculation you are doing but I don't understand how the ratio of tire outer diameter vs chainstay length affects the frame geometry. If the bike sits on flat ground then (theoretically) the wheelbase is the same as the distance from the center of the front tire contact patch to the center of the rear tire contact patch. So when designing the frame the tire size that fits should determine the required chainstay length, bottom bracket location, and the seat tube design and angle. If I put a smaller diameter tire on the MT220, IE a Donnelley MXP 24x1.25, then the ratio of tire diameter to chainstay length changes, but the frame geometry does not.

    I believe that the shorter chainstay effectively moves rider mass rearward so a larger percentage is on the rear tire. The loading of the rear tire is compounded by seat location which is a function of seat tube angle and seat height and post offset, and seat tube angle is likely a function of tire size, tire clearance, and chainstay length. More load on the rear tire allows the front end to yaw faster during steering inputs. This is why I'm suspecting that the absolute numbers are less critical than the relative ratios. However, I'm speculating, I've not designed a bike before, I'm just trying to look at it from an engineering / systems perspective. Granted, a bike with a shorter wheelbase, that has the same ratio of chainstay/wheelbase, as a bike with longer wheelbase, should feel like it yaws faster, because the same linear displacement results in a larger yaw angle. This angle delta is likely very small though, but again, feel is very subjective so some people may notice it and others may not.

    I do appreciate the input though, I'm definitely interested in the conversation. I'd like to understand the kinetics of the system.

    I really don't want to go spend big bucks on a bike that my son will outgrow quickly and my daughter likely won't want, because it's the wrong color...