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Thread: Tire damping

  1. #1
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    Tire damping

    I've heard a lot about the problem of fat bikes getting uncontrollable and bouncy at high speeds. Would it be possible to have half of the tire filled with an impact absorbing foam to mimic the damping of regular mtb suspension? (assuming that a light weight impact absorbing foam exists)
    The outer part of the tire wouldn't have any foam to minimize resistance to the tire deformation when rolling. The inner part of the tire would have the foam to dampen the big impacts.

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    I'm not sure what other people consider high speeds, but since my 29er has been out of commission for about a month I've done all my group rides on my Fatback. After a few rides I have not had any problem keeping up with all the front suspension bikes on the down hills and our trails are fairly rocky. Overall, whether it's ascending, descending, or on the flats, you have to adapt your technique a bit. Some of it is the big tire, some is that most fat bikes are rigid fork, but you do have to be a little more conscious of avoiding rocks that might knock you off your line. A rock that might knock a suspended bike off a little will knock you off more, but the big tire also eats up small chatter, so you keep rolling with momentum when everyone else gets bogged down. Once you get your tire pressure adjusted for your trails you can stop most of the bouncing. Even on the trails around RI that are littered with small fist sized rocks I run 7.5 lbs in the front and 9.5 lbs in the rear.

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    Waaaay back in 1990 or so, when I was racing MX in high school, there was a device called a "tire shock". It was a 6" rigid plastic tube with a male schrader valve on one end and a female schrader thread with a different valve on the other end.

    You removed the valve guts from the MX tire tube, threaded the tire shock on and filled the tire. It supposedly worked by having a flow restriction between the tire inner tube and short external tube.

    Under a hard hit, the pressure would force air out of the tire and into the compensation tube. The valve would restrict flow of the air back into the tire but would still equalize the pressure over a longer than normal time.

    It was intended to help on square edged hits and whoops. I don't remember how well they worked in that application, but I sure wish I had them to play around with on my fatty today. It is an interesting concept at least.

  4. #4
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    That sounds cool! My biggest issue with the fatbike is the lack of damping. I am definitely faster on my Enduro for the trails I ride, techy, New England singletrack.

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    This is because it's a rigid bike. Just because it's a fatbike doesn't offset that it's a rigid bike. I think people see the tires and they get the idea that it's going to be like 4" of suspension. It's not, it's mostly like riding a rigid bike. Now on snow it does react significantly different, but if you lower the pressure enough so that it starts reacting similar on dirt it's nearly unridable due to the wallow and squirm, not to mention with that low pressure sharp rocks will be a threat to the tube/rim. They work very differently on snow/snow trails vs. summer trails. They are plenty ridable in the summer or in non-winter conditions, it's just that it's a rigid bike.
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    Yes, I should have stated that I do not like rigid forks. I can handle the hardtail, but I need a suspension fork for the way I want to ride when it's not snow conditions.

    That's why I'm putting together an old Marzocchi Z1 for my Pugs. It will give a few inches of damped suspension. I can't wait to ride it!

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    Quote Originally Posted by bausscog View Post
    I've heard a lot about the problem of fat bikes getting uncontrollable and bouncy at high speeds.
    What you have heard are stories from people who aren't used to rigid bikes or who have not yet dialed in their air pressure. I have bombed down some fairly rocky stuff with a pack of full squish guys and never had an issue keeping pace or control.

  8. #8
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    I ride with a guy who is on a fully rigid SS bike (not fat), he can keep up to anyone on any FS bike. I know that sounds like BS, but this guy rides so active, it looks like someone turned off the gravity.

    You don't have to ride quite like that on a Fat bike, but that's kind of the idea, you have to read the terrain and position your body for whatever is coming up, pick good lines, you know really ride your bike, not just sit on the saddle. You can't get on a fat bike and plow through things like you can on a FS bike, totally different animals.

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    Am I wrong in saying when a fat tire bounces off an object it is actually a function of "rebound", not "compression"? Potentially the foam could offer a form of 2 stage compression dampening but would have no effect on rebound.

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    That is correct. The foam idea would not really affect rebound significantly.

    That's why I mentioned the old tire shocks. I have my brother looking to see if he still has the ones we used to have. If he finds them, I will post pics and give them a shot.

  11. #11
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    Quote Originally Posted by jonshonda View Post
    What you have heard are stories from people who aren't used to rigid bikes or who have not yet dialed in their air pressure. I have bombed down some fairly rocky stuff with a pack of full squish guys and never had an issue keeping pace or control.
    And there you have it. Rigid bikes are indeed just as fast as FS.

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    I 2nd a lot of what has been said already

    It's rigid...fat... but still rigid - you have to adapt. Remember your first suspension is your arms and legs. Aim to be smoother and use 'em!
    PSI - adjust till you find what's just right. I also typically ride techy NE style trails and found 9r/7.5f, or so works for me.

    Also take note, if you also ride a FS - once you adapt to fat then get back on your FS - that thing will feel funny and you might not even like it anymore

  13. #13
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    The first few minutes back on the FS bike are strange that's for sure, especially seeing that impossibly narrow 2.3" tire out front.

  14. #14
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    Quote Originally Posted by 69tr6r View Post
    And there you have it. Rigid bikes are indeed just as fast as FS.
    Yeah, if you're strong enough and a good enough rider. I know when I first had my Karate Monkey (rigid 29er) some folks were amazed that I could ride it thru places. I know that after riding rigid, I could ride FS faster/better both from driving skill improvements and physical conditioning.

    But, back on topic: If you're bouncing at speed, your tire pressure is too high! Tire pressure is important for fats, balancing rolling resistance, flotation, and bounce.

    I would love to have one of the adaptrac tire pressure control systems. Then I could dial in the perfect pressure for a specific situation.


    They have the gageset for fatbikes (0-15 or 0-30psi), but not the fathubs. {sigh}
    This isn't a "you're doing it wrong" topic.

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    If you run low enough pressure that the tire doesn't bounce, does denting the rim become a problem during the summer?

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    Quote Originally Posted by bausscog View Post
    If you run low enough pressure that the tire doesn't bounce, does denting the rim become a problem during the summer?
    Yes, but actually I've never dented a rim, but pinch flatted a few times.

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    Talking to my son about how increasing the tire pressures on my Bud and Lou to reduce drag had increased bounce, he surprised me by saying that on his On One Fatty he increases the tire pressures when they are too bouncy when riding fast on rough gravel ground.

    This took me aback somewhat. It works for him, and guess he is changing the harmonics. Lots to try and learn with tire pressures.

    Brian

  18. #18
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    this is the right response. it is a rigid bike.

    admittedly, it's a rigid bike with lots of tire volume meaning you can ride it on summer singletrack at 12psi without pinch flatting, and at 4psi on snowy winter trails with tons of grip without ripping the bead off the rim.

    all good stuff. and a recipe for some real good fun. but ultimately, a rigid bike it is.

    Quote Originally Posted by Jayem View Post
    This is because it's a rigid bike. Just because it's a fatbike doesn't offset that it's a rigid bike. I think people see the tires and they get the idea that it's going to be like 4" of suspension. It's not, it's mostly like riding a rigid bike. Now on snow it does react significantly different, but if you lower the pressure enough so that it starts reacting similar on dirt it's nearly unridable due to the wallow and squirm, not to mention with that low pressure sharp rocks will be a threat to the tube/rim. They work very differently on snow/snow trails vs. summer trails. They are plenty ridable in the summer or in non-winter conditions, it's just that it's a rigid bike.
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  19. #19
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    I was riding my rigid Karate Monkey almost elusively before I got my Fatty. While I get away with things on the fatty that I wouldn't do with the monkey, doubles, jumps, etc, if my 6" AM rig was a 0 on an arbitrary scale and the KM was a 100, the fatty would be like a 95, in terms of how close the ride is to the rigid 29er. I commute on a fatbike every day and after a short while it just seems like your "normal" bike. Wheels don't feel heavy, you pre-jump for curbs and lean back and absorb drops, etc. Riding a rigid bike though is so extremely different from having a suspension fork. It's a quantum shift that many these days have never really experienced. I'm not talking about riding a short ride or lap around the block, I'm talking about extensive time and extensive epic rides. Many people never ride a rigid in conditions and terrain they have "graduated" to over time on FS bikes. Fatbikes may make that a little more accessible, in terms of doing it on a rigid bike, with a little more control and roll-over, but once again, it's a rigid bike and it acts like one.

    Downhill on semi-packed snow trails on the other hand, holy crap that's fun and sooooo different than bouncing to and fro down the hardpack in the summertime...
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    Does anyone know of a way that a tire could have increased rebound damping without affecting the compression damping too much? of course while also not adding too much weight.

  21. #21
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    If riding a 4-4.8" tire on soft snow isn't damped enough, you probably need a suspension fork. Many of us are riding fatbikes on packed to semi-packed winter singletrack trails where the snow absorbs a good deal of impact, in addition to the tire. I think a lot of people are riding fatbikes now in summertime conditions, on rocks, roots, in places where only 5" of snow is on the ground or has sunken down to much less in compressed depth and ice has formed, in areas that don't get complete snow-coverage and different kinds of traffic to pack it down, and in those cases, a suspension fork probably IS needed to maintain any kind of sanity. What kind of tires, terrain and speeds are you riding that is causing the issue, and what PSI are you at approximately?
    "It's only when you stand over it, you know, when you physically stand over the bike, that then you say 'hey, I don't have much stand over height', you know"-T. Ellsworth

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  22. #22
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    Rebound damping is to slow the return spring - if it's in the tires, and you dampen the return from maximum compression, wouldn't that have an effect of really high rolling resistance? The back side of the balance point would return to shape slowly.

    I mean, people market things like "energy return wheels" or non-pneumatic tires, as being very efficient.

    Unfamiliar to the science of it, but wanting a damped tire sounds synonymous with wanting a slow tire with no additional grip.

    Nothing else to add to the other points above, I'm using a Mendon clamped Lefty fork for squish, works great.
    Disclaimer: I run Regular Cycles (as of 2016). As a profiteer of the bicycle industry, I am not to be taken very seriously.

  23. #23
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    To phrase it another way:

    Friction between an inner tube and a tire could be considered damping... right? I don't think it's outrageous to say that people experience small rolling resistance improvements when moving sequentially through these setups:

    1) Dry inner tube inside dry tire
    2) Inner tube swimming in baby powder inside a tire
    3) Tubeless or Tubular

    So I'm not sure it'd even be something you'd want.

    I'm all about low maintenance suspension concepts, so I know what you're driving at.
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    I've found that when I land from jumping my fatty or doing something that bottoms the tire, the bike is hard to control right after because of this undamped rebound. In my mind, the ideal tire would deform with very little resistance for absorbing small rocks and roots (120 tpi and tubeless) but when there is an impact that nearly bottoms out the tire, the rebound would be damped (to avoid the pogo stick effect). Damping the first part of the rebound would be the most important since that's where the tire applies the most force to decompress. I've been thinking of lining the inner half of the tire with an impact foam like the one that's found in g-form knee pads but that would most likely add a lot of weight.

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    I encourage someone to jam a couple of swimming pool foam noodles and some small tubes into their tires and report back to us. I'm just not in the mood to be a guinea pig.

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    Just having foam stuck in the tire would help with damping the compression but also damping the rebound is what I was trying to figure out.

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    This was 2 1/2" pool tube with 3/4" thick walls before I pumped it to 25 lbs. to ride on pavement. Maybe would last at 6-10 lbs. On dirt at 10lbs it felt kinda dead. Maybe need different foam. Now It protects the tube from the screw-stud heads.

  28. #28
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    Quote Originally Posted by Machinist View Post
    I encourage someone to jam a couple of swimming pool foam noodles and some small tubes into their tires and report back to us. I'm just not in the mood to be a guinea pig.
    you'd also need to set the tire up tubeless, as the beads need air pressure to seat and remain seated.

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