How short a chainstay is too short?- Mtbr.com
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  1. #1
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    How short a chainstay is too short?

    So I am starting to draw out a project I have wanted to have built for a while. I have wanted to build up a 26in "play" bike. Basically something that felt a bit like a big BMX that could handle some pump track, skate park, 4X and dirt jump action but could be taken on the trails to pedal to places to session so a longer seatpost and more reach then a typical dj. Been looking at bikes like the Transition PBJ, NS Surge Evo and BTR Ignitor for inspiration.

    Been thinking somewhere around 405-410mm slammed with horizontal dropouts.
    Ragley Big Wig, Sunday Soundwave (BMX), 91 Schwinn High Plain (single speed "gravel" bike), Nashbar CXSS (on trainer)

  2. #2
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    Reputation: mack_turtle's Avatar
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    when you can't fit a tire behind the seat tube and the BB, it's too short. the rest is subjective.

  3. #3
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    Once again mack_turtle whips out his hammer and strikes the nail directly on the head.

    Back in the early 90’s my friend Tim took a frame building class and whipped up a 26/24” wheeled bike with chainstays somewhere between 14-15” IIRC. He named the bike “Sketch” and referred to it as his 2-wheeled unicycle. To say it was a handful to ride is an understatement.

    I think today Tim would say 14+ inches is too short. YMMV
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  4. #4
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    I'm 6'3" and have a PBJ. 388mm chainstays. Bike feels dialed, for it's intended purpose.

    I've not tried riding it on normal trails because the saddle is slammed and the SS gear ratio is not ideal for trails but great for pump tracks and jump lines.

    I would guess if I was building a hybrid 26" DJ/hardtail MTB I would want something with 400-410mm ish chainstays. It wouldn't hold you back on the pump track and would definitely track better on singletrack.
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  5. #5
    pvd
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    I'm 5'10" and do a 410mm rear center on 622-64. It's pretty awesome. 420 is maybe better if I were to do stupid steep climbing.

    For anyone shorter than me, 410mm is great everywhere.

    Long rear centers are garbage for performance mtb.

  6. #6
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  7. #7
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    And did you break 2:40?

  8. #8
    pvd
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    2:42.79. Terrifyingly fast but not quite enough to brake the wall. Flow racing is very different from other dirt events where the in a good run for a rider and their average run can be less than a second.

    I'm too old to race these days. I focus more on design than training.

    Grudgematch 2. Flow trail boogaloo. 2015 | Peter Verdone Designs

  9. #9
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    I have a bike with 385mm Chainstays. It is 2x, so I have a front derailleur to catch the chain when running at extreme gear selection. I would feel that I am more likely to have issues with a 1x if I had a shorter Chainstay. There are limitations other than just axle location. With my bike, if I had constructed it with a slider dropout, I could have reduced a further 20mm, but the chain would have been stressed too much. My wheel size is 700c x 35 - gravelgrinder.

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  10. #10
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    Depends on the wheelbase (or front center, as WB = FC + horz CS length).

    If the WB is 1150mm, I'd hope for 415mm CS. Enduro FS bike, for reference: 1250mm WB, and I'd hope for 440mm CS. For a DJ bike with 1050mm WB, 390mm CS maybe.

    All about getting that weight distro right, precisely 60% weight on the rear and 40% on the front or whatever your preferred ratio is. Lengthen CS if you want more weight % on the front, shorten if you want more on the rear. Or think about it vice versa, lengthening the front center for less weight % on the front.

    405-410 CS would maybe go with a 1100 to 1130mm WB depending on HA and fork travel, to account for my pref weight balance under sag.

    Long CS is made to compensate for riders who do a vast majority of riding in the saddle--keeps enough weight on the front so they don't wash out and keeps the front wheel on the ground when climbing while seated (esp on slack STA bikes). When out of the saddle, there's a bit too much weight on the front so you tend to need momentum and need to get back so the front doesn't get planted on obstacles and send you over the bars. Also, tend to need speed and technique to keep the front from diving when in the air, and making jumps and drops feel dangerous, bucking your ass up and over your shoulders. Jumps only work safely if they basically are "bump jumps" or hucks that are not too picky about landing skill. If drops don't have clear run-ins long enough to allow for speed, they're pretty much lawn dart hazards for these bikes. Sad/sketchy to watch a rider with long CS (e.g. 440mm on a 1150mm WB bike, like a typical XC entry level HT) brake check a jump before rolling off it, and have given early 29ers their reputation for being bad at jumps.

    Too short CS and you're forced to compensate by riding over the fork to make up for lack of front wheel traction, due to understeering and continuing to continue going straight when you want to corner. Rad for riding like 50:01 (love back wheel), but you'll likely be dabbing and falling a lot.
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  11. #11
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    Quote Originally Posted by *OneSpeed* View Post
    I would guess if I was building a hybrid 26" DJ/hardtail MTB I would want something with 400-410mm ish chainstays. It wouldn't hold you back on the pump track and would definitely track better on singletrack.
    That is kind of the realm I was thinking. I figured with a horizontal dropout maybe go slightly under 400 like maybe 395 and that gives me room to have a longer chainstay if the wheel isn't slammed.
    Ragley Big Wig, Sunday Soundwave (BMX), 91 Schwinn High Plain (single speed "gravel" bike), Nashbar CXSS (on trainer)

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