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Self steering FAT tires

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    Self steering FAT tires

    This came up in another thread and got some input from others so I think its worth having its own thread so more people can see it and learn from it. What I am hoping to learn from this thread is if there is anything you can identify about your bike or the tires that may indicate if self steering may be a problem. Higher TPI's were brought up as an indicator but someone else said they had not really seen that and I just checked all 3 of my tires are 120tpi so it can't be TPI alone.

    In the other thread the OP mentioned how loud his Surly Nates were and I mentioned I had the same opinion and had just switched and done a short test ride on Surly Knards and they seemed to roll easier and were much quieter. Later I took a much longer ride on them and found they really have some pretty serious self steering on my Pugsley.

    The Nates have been around a long time and in general when grip is the top priority people don't argue that the Nate is one of the best. Its only when weight and rolling resistance come in that people start looking for other options. Since I'm on an E bike weight and rolling are not that high on my list but I often ride the roads to get to the trails and I don't get super aggressive on the trails so I think I'm willing to trade some grip for a little smoother ride on the pavement.

    I had never experienced self steering before on any bike and I have put quite a few miles on this bike with 4 other tires and not had it so it was quite a shock. With the snow season just ending it really reminded me of what happens to the snow trails is they get a groove you can get stuck in and it starts to effect your balance and you really have to fight the steering to stay kinda in control. If everything is perfectly flat and smooth and you are going straight no problem and if you get more extreme turn wise no problem but anything in between you really have to put a lot of steering effort in and concentrate. Slight difference in the road surface like a crack seems to want to grab and steer the wheel. Rough surface offroad that you would just normally smush and roll over you have to fight.

    The geometry of the bike and maybe rider has to be a factor too so here are my details. 2014 Surly Pugsley, large frame which is a fully rigid steel setup. Me and the BBSHD easily 300lbs. I have a set of Surly Rabbit hole 29's that I have run 2 different tires on with no issues but those are closer to 2" widths and a different animal. For fat rims I have what came stock which is the Surly Rollin Daryl's which are 82mm wide so decently wide but not crazy. Most of last year I ran Surly 26x4.0 120tpi Nates. Over the winter I ran 45Nrth carbide studded Dillinger 4's which were 26x4 120tpi. Just recently for spring I switched to the Surly Knards 26x3.8 120tpi. Didn't notice any self steering with the Nates or Dillingers. Nates I tended to run around 10psi. Dillingers closer to 5. With the Knards I tried 5-15. Sometimes I was thinking the pressure made a difference but in the end I don't think it did.

    Hi 73eldo - "self steering", as in a resistance to turn via normal handlebar pressure? I'm guessing more, as you mentioned the tire reacting to/grabbing surface features.

    If so, I'd add the 27.5 by 3.8 Maxxis Minion FBF to the list. My Scapegoat had 'em when I first got it, and they were very noisy on the road and high turning effort. One ride and they were pulled.
    BBSHD/BBS02B builds: IGH 1 2 3 4 5 6


      I suspect it's all down to the tpi. That's a cross country thread pitch in the mountain bike world and I will assume that alomg with the large contact area it causes the tire casing to be too compliant which makes it tend to aggressively follow the path its on.
      is it a really thin tire casing?


      • 73Eldo
        73Eldo commented
        Editing a comment
        I was thinking TPI could be a factor and thought all 3 of mine were different but when I went and checked turns out they were all 120's.

      I think some of it is resistance to turning in the first place but once you start turning it seems like some gyroscope action and it wants to keep turning on its own so you have to fight it back. What got really got me is how the surface didn't seem to make that much difference. I did about 18 miles and it was a combination of smooth roads, rough roads, damp hard pack, and then where I had to give up and turn around even after lowering pressure more was basically a single track that was forming in a rut left my a typical tractor chevron tread tire on a large piece of equipment that drove through there when it was soft mud.

      The tractor track was well over a foot wide and the single bike track that was forming in it was maybe 8" and not really a groove or rut, it was just smoothing down the bumps from the tractor tread so its not like it should have really been causing steering issues. It felt to me that I was in a tight groove and had trouble holding my balance and if I did turn a bit like I was over steering and would then end up over correcting and going out the other way.

      I'm just having troubles grasping what is mechanically going on with this. I'm currently negotiating with someone on facebook for an assortment of used tires so I can try some more types. Maybe I can find some that work for me as well as having more to compare maybe zero in on what the cause may be.


        I was just looking at photos of the Maxxis Minion FBF and it looks like the knobs are pretty similar height center vs sides. That is one thing that is different about the Knards is the center knobs are not as tall as the side ones. Guessing that is what makes them roll nicer and quieter. At a glance the main casing part of the Knards seems to be more rounded than my others but its my impression that because of the lower knobs in the center the actual contact area is similar to the others that don't seem as round.


        • AZguy
          AZguy commented
          Editing a comment
          I haven't pulled out a ruler (or a durmoeter) but pretty darn sure that 4.8" FBF's (and FBR's - some do run those on the front) have taller side knobs and they are a different compound (very soft but stiff)...

        I've had fat tires (4"+) when at low pressures when you turn the bike it really wants to "fall into the turn" and requires very actively applying a pressure counter to the turn - guessing that's what we're talking about and I've certainly read about this effect on plenty of sites, particularly reviews for fat tires

        There may be some correlation to tpi however in my experience it's certainly not a great indicator of the effect - for me it's more about specific tires and the pressures I run them at. Nearly all fat tires I've run give some of this sensation if the pressure is low enough... it's just some start to feel it at 12-15psi and others I can be down below 8psi. As mentioned in the other thread I've run cheap 26tpi that had it bad at 10-12psi and much more expensive 120tpi that it's barely noticeable even as low as 6-8psi. It's more pronounced on hard surface but I suspect that's just because there's typically more forces affecting the turning forces than just turning like on level hard surface. They also tend to experience it worse when they are getting closer to their end-of-life. FWIW I've got about 9000mi on fat tires and have run likely five-six different tires and have also had the opportunity to run friends bikes with others although not really enough time on them to get a good solid feel.

        I had a friend that on his first set he complained about this, especially after he test rode my bike which was running about 50-60% the pressure he was running. He got new tires - complained about how much more they cost than the others - and has been silly happy with the new ones although he still runs a lot more pressure than I do...

        In another thread we talked about noise too and it's another one of those things were you think the high tpi super aggressive knobby tires would make all the noise but some much milder 26tpi (albeit much cheaper) are actually much worse.

        To me it's just a simple thing that all tires are not created equal - not even remotely so... and it's another one of those things that borders on religion and politics (like chain lube and maintenance) - people can get pretty passionate about "their" brand. IMO cost is a factor but not the only one... Moto forums are full of crazy discussions about tires - seems obvious bikes would too... what works best for one guy may not be the best for another and it's really hard to try a lot of them since they are relatively expensive and last a long time so we tend to figure out how to embrace what we have... OTOH I'd run the same tire twice just thinking they were plenty good - and they were better than anything I tried at that point but then took a gamble and tired something different and so glad I did and don't look back... That happened to me a lot on motos too... get complacent with something that "works" well enough that we don't want to take a chance on something else that may or may not...


          The note about seeming maybe worse after some wear is interesting. That fits with what I think I see on those Knards where the center knobs are not as tall as the side ones. Most of the wear tends to happen on the center ones so if they started out all the same it would make sense that as the center ones wear you are getting a larger contact area than you did before the wear because the side knobs would start to make more contact.

          What makes me think that isn't all it is I didn't notice as much difference with the pressure change. At higher pressures you are going to have a smaller contact area and the knobs are not going to depress as far so your only contact may be the actual knobs down the center. Lower pressure I assume the first thing that happens is the knobs tend to get depressed more so you get a little contact with the main casing but still a similar footprint. Lower the pressure more and with some tires I bet the knobs pretty much disappear and the foot print gets bigger.


            This new discovery also makes me fear for people buying new fat bikes these days. With how difficult it is for the manufactures to get parts you wonder how many fat bikes are getting shipped with tires that no one has tested. If I had not ridden my bike before these tires I would have said fat bikes are the dumbest thing ever. At least I knew the tires were the only change and was able to change back to prove it. Actually that is a lie, I did also change the hub so that is one reason I went back to the Nate just to make sure that somehow I didn't build the wheel wrong.


              Most fat tire bikes seem to ship with crap tires - certainly the cheap ones do... noisy, don't handle the low pressures well, not as much "stick" in the corners and worse handling when cornering hard overall

              Novice bike riders may not notice and if it's their first fat-tire bike may have little to compare to

              I look at my chicken strips on the different tires I've run and it's clear I corner my latest tires harder although there's clearly room for harder and they are much larger than what was on my motos... but then again I'm a lot older now and don't push things as hard although from what I can tell by measuring the tire contour against the edge of the chicken strips ~45° lean (~1.4G) is where I frequently go... funny thing I've always cornered harder to the left too although it's not as apparent on the bikes as it was on the motos

              I think the large side knobs on the aggressive MTB tires go further around than you'd ever use on hard surface (looked just shy of 55° on mine) for bite in the loose stuff - I doubt I'll use those far side knobs much on hard surface

              Was on some silly smooth hard surface this weekend with the knobs and took a turn hard enough that I could feel both tires break... just lucky I was on my game and the old moto reactions kicked and didn't go down...


              • Dshue
                Dshue commented
                Editing a comment
                The downside to many fast rolling mtb tires on smooth hard surfaces is the aggressive shoulder tread. They can be too squirmy.
                I have them on my acoustic Specialized and they tool some getting used to.. And for that reason I'm not putting them on the e bike.

              • AZguy
                AZguy commented
                Editing a comment
                I'm really surprised how well the latest set takes corners on hard surface even though the knobs are super aggressive and tall, they are clearly stiff (vs. felxi) but soft (vs. hard) at the same time if that makes sense... they are dual compound but I've had other dual compound that cornered on hard surface as well but weren't as aggressive, didn't do as well off-road, didn't like the low pressures as much and didn't last as long...

                I don't mind a little squirm on the rear, it can add some predicitability

              I just scored 3 different tires to try off facebook. Pair of Larry's, single Husker Du, and an Endomorph. Read some people run all 3 of those on the front and Knards on the back so if that works I'm set.


                Tires tested again on my 2014 Large Surly Pugsley which does not have the offset fork. All 26' fats. All at 15 psi and 7. 7 was a little worse as expected.

                Worst self steering worst to less bad:
                Surly Knard 3.8" 120tpi
                Surly Endomorph 4.0 120
                45Nrth Husker Du 4.0 33

                Slightly self steering to hardly noticeable:
                45Nrth Dillinger 4 120 w/240 carbide studs
                Surly Larry 3.8 120
                Surly Larry 3.8 33
                Surly Nate 4.0 120

                Really noisy and vibrate to pretty quiet for a non slick:
                Dillinger.... 240 studs duh.......
                Husker Du

                Can anyone tell I live in the home of Surly and 45Nrth? There was other stuff available used but I didn't know the brands as well to know if the prices were crazy or not.

                These tests were just a short pavement lap around my house so I think for a proper test I'm going to leave the Knard on the rear and try one of the Larry's up front. We had rain earlier in the week and again tomorrow so I don't think there is going to be any off road riding anytime soon but since this combo should be alright for pavement I may do a medium length ride to see how it goes.


                  I settled on the Knard on the rear and a Larry 120 on the front. Done several laps at the local park and so far am very satisfied with that combo. Have not noticed any self steering. Both tires seem to have plenty of grip both brake and climbing even over rocks. Both of those are reasonable for noise and control on pavement too which was a factor for me since I often ride pavement several miles to the trails. I'm still amazed that a tire could have had that much effect on the steering.


                    My two cents on the "self steering" fat tires..
                    From my experience as a bicycle mechanic is that it comes down to rotating mass. I feel it alot when I ride the cheaper Wal-Mart fat bikes and Motobecanes and whatnot. Much less with tubeless setups on lighter wheel / tire setups.


                      Seems logical, some gyroscope action? I would have to look up or weigh the tires I tested but I don't think there was a huge difference in the weight of the tires and they were all on the same wheel with the same tube on the same bike.


                        I got the KHS-500 new from Lunacycle. The 4" tires It came with self-steered like crazy. It was bad. Then I got Jumbo-Jims and the bike was a different animal. It went from being a poor cornering bike to a fast cornering bike. Just for swapping out the tires. It makes THAT much difference. Of course the new tires were relatively expensive at about $75 each, but the difference was huge.