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  1. #1
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    Fat tire pressures for snow.


    A good friend of mine recently got the fatbike bug, largely so that he could ride on snow, and wanted to better understand appropriate tire pressures for that surface.


    He's ridden bikes for decades and skied for even longer, but the correct range of pressures for 5" tires on soft snow is not as auto-intuitive as you might think.







    I spent a few minutes writing a detailed response, and after sending it to him it occurred that many here might benefit from it as well, if only as a resource for their new-to-fat friends.



    Without further ado...







    It takes some time to wrap your head around appropriate PSI for snow--it's probably gonna be a lot less than you think. The standard credo for tire pressure when snow riding is 'when in doubt, let air out'.







    Best way to be sure is to take a little low-pressure (0-15psi) gauge with you for the first month or so, and check pressure frequently with both the gauge and your hand to get your hand calibrated. The idea being to learn what works by feel, so that you can ditch the gauge sooner than later.







    This is a rough guideline. The absolute number is irrelevant, finding a pressure that works, and then being able to both recognize the conditions and duplicate the appropriate pressure is what matters.



    10psi and up=pavement pressure.

    6-8psi=*very* hardpacked snow.

    4-5psi=softer or less consistently packed snow.

    2-3psi=deeper snow, when more flotation is needed. If you need this kind of

    pressure, you'd probably be having more fun with skis on! But

    sometimes you start a ride on hardpack and have an ambitious

    objective, then it snows or blows and you have to dump air to keep

    riding.

    0-2psi=what I most often ride at, due to lots of light, dry snow and very little traffic.











    As temperatures and conditions change the appropriate pressure for the surface can fluctuate pretty dramatically. 1psi makes a big difference. My way of staying safe (avoiding flats or rim damage) is to lean all my body weight on the saddle, while looking down at the rear tire. Any wrinkles in the sidewall? Add psi until the wrinkles go away. That's your baseline for hardpack. The flipside of that process is that for the softest, least-packed snow (the kind where you should have chosen to ride lifts with skis on that day!) you can go as low as four or five wrinkles in the sidewall as long as you're being delicate. More than five wrinkles and you're generally just adding resistance without increasing float or traction. That said, conditions in my neck of the woods often require 5+ wrinkles just to keep pedaling, and since pedaling beats walking...











    One last bit of editorial: Not many people understand how far you can go in a short time on one of these steeds when conditions are good, but how absolutely hosed you can be if it's nuking or blowing or both on the return. Like 7-8mph when it's good, and hours per mile when it's bad. I don't take a sleeping bag with me on every ride, but I *always* have a puffy, firestarter and lighter, and some food on winter rides. Seems like about every other year I get antsy to do something epic, and conditions change halfway through the ride, leaving me out for the night and into the next day (or til a sledneck comes along and packs the track back in).






    Don't hesitate with questions!

  2. #2
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    I've heard this thing about the light dry snow a few times now. I've noticed that the light dry snow is the "easiest" to pedal through, so many inches of this and it's still possible to ride, even without crazy low pressure. It's the dense slushy snow that creates the most issues for me, the more dense and slushy, the easier your tires slip and the more traction I need. 4" of dense slushy snow can be a major PITA compared to 8" of light dry fluffy snow. That dense wet snow is where I feel a real aggressive snow tire starts to make a difference.

    The next few days usually tells the tale, as the fluffy snow packs down to less than an inch and the dense slushy stuff packs down to 2-3.

    But mostly, I just go by "feel" for pressure. I almost never look at gauges, because conditions are just too variable to refer to a chart. Snow composition changes, it packs, refreezes, surface hoar, ice, roots and rocks may become exposed, etc. The easiest way is to start out slightly overpressure and let out until it is right for the conditions.
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    One suggested addition to this well written resource that maybe fits with your comment about "absolute" pressure not being important: the effect of temp on pressure. Not a problem if you always check & adjust at ambient. But if the check is done in the nice warm basement before heading out into riding temps that often widely differ, or even more profound, sometimes check inside and other times outside, the results can mess with the pressure "learning curve" for somebody starting out.

  4. #4
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    Quote Originally Posted by cfta View Post
    One suggested addition to this well written resource that maybe fits with your comment about "absolute" pressure not being important: the effect of temp on pressure. Not a problem if you always check & adjust at ambient. But if the check is done in the nice warm basement before heading out into riding temps that often widely differ, or even more profound, sometimes check inside and other times outside, the results can mess with the pressure "learning curve" for somebody starting out.
    Absolutely correct!

    I tend to run mine by feel as well based on many many miles of personal experience. But the above suggestions are a good starting point for those new to the sport, as is this reference:

    What's The Correct Tire Pressure For My Fatbike?

  5. #5
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    Takes time and experimentation. Slight changes can make all the difference. Having a pump handy is worthy with fabikes. Some peeps are timid about letting the air out because they see "Max Pressure 30 PSI" on the tire and don't think low pressure can possibly be an improvement. Mikesee's credo is spot on.

    Pressure charts are meaningless in the real world...
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  6. #6
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    Great info Mike, and I think in general your guidelines are spot-on. One thing I might add is that sometimes on packed trails that have seen a fair bit multi-use traffic, postholes, etc. it's beneficial to run even lower psi than one might typically recommend for "hard pack" conditions, just for a smoother, less bumpy ride. I was thinking of this as I rode one of our in-town trails this afternoon that is pretty crusty right now after a few days of no snow, and has seen walkers, skiers, dogs, etc. in addition to bikes, and that even at 4psi today it was a notably rougher ride than when I rode it last night at 3psi.

    Appropriate pressure still seems to be the biggest thing I see a lot of folks struggle with. Lots of folks are still shocked when you tell them that 8-10 psi. isn't actually "low" by fat tire standards and that they will be struggling a lot less (and maybe even enjoying themselves!) by dropping more pressure than that in soft/loose conditions. I just don't think most folks accustomed to 'normal' bikes are used to paying as much attention to their psi as a fat bike requires. And while it's tempting to wish there was some magical chart to tell people what they needed to do, there are just way too many variables involved to simplify it that much, including the highly dynamic surface we ride on.

    Like a lot of the most fun things imo, there are no easy, pre-fab answers, and it just takes some experience and experimentation with one's particular setup and conditions.
    "The only way we can truly control the outcome of a ride is not going on it, which is a choice I'm unwilling to make." -K.B.

  7. #7
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    All of the suggestions that have been made thus far are good, and reinforce that local conditions are always more important than any one rule.

    Keep 'em coming.

  8. #8
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    Quote Originally Posted by mikesee View Post
    All of the suggestions that have been made thus far are good, and reinforce that local conditions are always more important than any one rule.

    Keep 'em coming.
    Great thread mikesee!! Great photography, great information and great replies. Much appreciated!

  9. #9
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    Sick pics mikesee!!!

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    I'd love to see another thread about your survival gear, and exactly how you manage when out all night in this stuff.

  11. #11
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    Quote Originally Posted by matto6 View Post
    I'd love to see another thread about your survival gear, and exactly how you manage when out all night in this stuff.
    I've got a decent sized trip coming up late Feb. Will try to remember to take some pics as we pack.

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    Great thread. Thanks for taking the time to posts it.

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    Here in the Northeast, we ride on ice a lot. This past weekend I went for a ride on "dust on crust", There was a fresh dusting on a layer of thin ice over a 2" layer of snow. I wound up running about 3 psi(checked when I got home) to flatten the tire out to increase friction. Yes, the thin ice layer had a little flexibility which helped. So sometimes there are more variables than just snow depth and quality. For the record I am running Flow and Dunder tubeless on DT swiss rims.

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    Another great thread. Thanks Mike.

    One thing I'd like to add about pressure is (IMO of course), is that I really prefer low pressures in all situations (with the exception of trying to keep up with Carbon Fiber Road Bikes on paved trails). I'm really happy with the feel of a low pressure tire pretty much everywhere. Something about the world going a little slower, and being more connected to the ground.

    So I'm around 140lbs, and ride no more than 5psi down to 4psi on roads and trails, and well below that on snow (on Nates). The wrinkle test is something I'll look at when I get back to Big Sky on snow. Leyzne HV pumps work wonders for their size, and

    http://www.amazon.com/Accugage-Press...essure+meisner
    Dash Pt. State Park (Tacoma), Big Sky Montana during Snowboard Season, Duluth Mn, a couple of times of year incl. Xmas.

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    Nice thread and wonderful pictures. Thanks.


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  16. #16
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    Those pressure guidelines are very similar to what I discovered after doing the experimentation process last winter.

    I never carried the pressure gauge with me, though. I set my pressures at home before the ride, and adjust as needed on the trail. I will re-check pressures at home in the warm basement afterwards once the bike has warmed back up, so I get a better idea of where to set the pressure before I leave for my next ride in similar conditions. I generally will start a little high, though, so I can dump air if necessary, rather than finding out that I'm too low to start, and needing to add air.

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    I can add one more equation to the puzzle is pedaling force or torque.

    At 3 psi I can pedal as hard as I can and just barely get the rim to touch without bouncing. If I spin I can go as low as 1.5 psi. Now this is all uphill and the rear tire. Front tire I gauge when doing hard turns to set my lowest, which is 1 psi and usually 1 psi lower than my back.

    I am 110 lbs female. My man is 165lbs and runs 2 psi front, 3 psi back as limit for the softest snow uphill

  18. #18
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    Quote Originally Posted by Jayem View Post
    I've heard this thing about the light dry snow a few times now. I've noticed that the light dry snow is the "easiest" to pedal through,
    You're talking about fresh snow that has a base underneath -- which is common in a normal year in Anchorage.

    I'm talking about dry snow that is feet deep, with no base whatsoever. At best it has a few millimeter thick crust that may or may not support both wheels at the same time.

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    Hardest part for me whike riding in super soft stuff is to remember I'm about 1/4 to 1/2" away from pinch flatting at all times. When I start going downhill it gets me into trouble. I tried to double a snow machine brake bump a couple weeks ago, then had a mad sprint to the car before i lost all my air.

  20. #20
    Rippin da fAt
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    What, no base under that snow?
    Get fAt, Stay fAt, Ride fAt
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  21. #21
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    What is the minimum pressure with tubes to be on the safe side?



    Enviado desde mi GT-I9506 mediante Tapatalk

  22. #22
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    Quote Originally Posted by kaire View Post
    What is the minimum pressure with tubes to be on the safe side?
    Enviado desde mi GT-I9506 mediante Tapatalk
    That depends on whether there is sufficient base between the rocks and other crap to prevent pinching. In deep base with 10" of powder I can run my tires very close to rimmed out and not think about it. Currently we have over 3' of base or more where I do my really low tire rides.
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    Quote Originally Posted by kaire View Post
    What is the minimum pressure with tubes to be on the safe side?



    Enviado desde mi GT-I9506 mediante Tapatalk
    A pinch flat occurs when the solid object you hit pinches the tube between the object and the rim. So it's totally dependent on the terrain/your weight/your speed. Without knowing any of that, it's pretty difficult. I'm a lightweight 140lbs, ran tubes for a year, and was running about 4 to 5.5 lbs and not taking any major hits at any speed. Worked for me. Get on your bike, bounce upon and down on the edge of a curb and see how close the tire comes to the rim and that should give you an idea.
    Dash Pt. State Park (Tacoma), Big Sky Montana during Snowboard Season, Duluth Mn, a couple of times of year incl. Xmas.

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    Quote Originally Posted by Bumpyride View Post
    The wrinkle test is something I'll look at
    It is a good guideline, but no more than that. Which tire you're running, on which rim, tubed vs. tubeless -- all of these factor in to how you have to interpret the visual data you're receiving.

    You can't necessarily take that data from one bike to a different setup. You have to learn them both. 3 wrinkles is sort of the quick start guide.

  25. #25
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    Damn it! Miksee's accounting for his wrinkles now?!?! O.o
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    Quote Originally Posted by BansheeRune View Post
    Damn it! Miksee's accounting for his wrinkles now?!?! O.o
    I tried Mikesee's wrinkle method today, but I kept running off the trail when I looked down to count.

  27. #27
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    Just a quick glance will resolve that prollem!
    Get fAt, Stay fAt, Ride fAt
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  28. #28
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    Not a snow rider but I ride beach sand nearly 100% save for the short road to the beach. Sand is variable. A half dozen+ types that allow for 10 mph+ down to oh, say 3 mph, nearly the limits of ride-ability, particularly if there is a 15 mph+ headwind. Then there's unrideable crap. I finally settled on 6 psi rear and 4.5 psi front due to the shear variability and as I got stronger with better tech skills (lower speeds) I tolerate a bit more pressure than going sub 4 psi. Key is regulating front pressure so it doesn't plough, makes it easier to crawl up that perpetual ridge in front and once the front tires lays down a track, the rear has an easier time. I've not measured front rear weight bias but the Blackborow I briefly rode clearly has rear bias. That, BFLs and the Bluto FS made it a sand crawling machine. FS makes it less prone to ploughing as well.

  29. #29
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    I got out for a great ride last night, surfing the leading edge of a big storm that dropped anywhere from a foot to two feet across the region, and it's still coming down.

    In the woods on this ride the trail was great -- packed by skiers and snowshoers and as such it was shoulder width and with a consistent surface. Like a ribbon of white singletrack beckoning ever onward.

    But where it left the trees and crossed meadows it was really, really wind affected. Wind affected snow has been tumbled and collided so many times in its descent that the snowflakes have no more arms -- inspect them closely and you'll see that they're closer to ball bearings. No way for them to stick together until melt-freeze season happens in a few months.

    I bring this up because while in the trees we wanted low pressures (it was a 3 wrinkle kinda ride...) to float on the ephemeral crust. But out in the open there was *no* pressure that worked, as the packed trail surface was buried beneath ~6" of ball bearings. You couldn't float on the ball bearings, nor could you dig down deep enough to access the traction of the trail surface. Pushing was the only option, period.

    I bring this up as a springboard to get people to think about the big picture of both the topography and prevailing wind direction on their rides, as these are the two main determinants of which sections of trail get scoured and which get drifted in. You can burn a lot of time and get really frustrated trying to adjust pressures up and down. Not to mention cold because you're not producing heat anymore.

    Or, put more simply, you can't always buy (or ride, or deflate) your way out of a situation -- sometimes you just have to deal with it.
    Attached Thumbnails Attached Thumbnails Fat tire pressures for snow.-8a3a6391.jpg  

    Fat tire pressures for snow.-8a3a1875.jpg  


  30. #30
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    Great advice Mike...

    Sometimes I do enjoy a good walk with my bike..

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    Apparently we all like walking our bikes

    Nice pics Mike, good pressure primer, and reminding folks that going out fast can mean coming back slow.

    At the minimum, carry a temporary bivy, layers, food, and water. Even a couple miles out can be dangerous if the weather or gear fail.

    I was hut skiing in Colorado a few years back, it was cold, zero degreed midday, we started early and still struggled to reach the hut before dark.

    After we'd been there an hour, started the stove, warmed up, this guy rolls up, so cold that we drag him in the door with his skis still on. He's not alone, there are two more behind him, one guy is soaked because his water bladder burst hours earlier and he refused to turn back.

    Smart people die from stoopid choices.

  32. #32
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    Great thread! I especially like the comments about when you'd be better off skiing rather than trying to ride your bike. I think a fatbike makes a great addition to a person's collection of winter toys. But there are times when the snow conditions are not conducive for biking but excellent for other winter toys. The best thing is it works the other way and bikes make crap conditions fun and they actually excel in them.

    ive never paid any attention to wrinkles on my tires. I'll now look for that in the future.

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    I've found fat bikes and fat tires to be very very fickle to tire pressure and front/rear weight distribution.

    Basically my rule now is that if any kind of snow is involved, keep letting air out till the side wall crinkles a little bit when you bounce on the bike. This is lower than registers on my digital guage, probably 2 psi?

    And make sure your ergos are balanced such that you have good front/rear balance. You need to get the most float out of BOTH tires.


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  34. #34
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    Quote Originally Posted by ak-rider View Post
    ive never paid any attention to wrinkles on my tires. I'll now look for that in the future.

    I noticed, paid attention to, and evolved the 'wrinkle rule' in the original Endomorph years. And those tires had stupid wimpy casings and sidewalls. These days, casing technology has evolved to the extent that the Endo's look even more like the dinosaurs that they were, and I'm not referring to the chevron tread.

    Point simply being that if you're running a 60tpi FBR 4.8 on the rear of one bike (or one wheelset), and a 127tpi JJ 4.8 on another, the wrinkles and preferred pressures are not going to match up. Are probably in fact going to be a significant distance apart, owing to the very different casing construction.

    This is a good thing -- if you're appropriately OCD -- as you can tune the ride of your bike to the Nth degree with casing options now too.

  35. #35
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    Yep, wind packed snow is even worse than artificial snow.
    Ball bearing like surface, and in addition, much harder to pedal through as the snow is packed and has lotsa resistance.
    When the fatbike boom over here (Norway) hit back in the fall of 2013, that was pretty much default conditions for the first half of the winter and many got a bad impression, trying to make progress in the wind packed snow with 4.0'' tires at 10psi.
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  36. #36
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    We've got a neighbor who's big into cycling and got curious about fatbikes. Her first and only ride was on wind blown loose snow. She had a miserable time and continues to think that fatbiking is a terrible experience. Obviously she needs to try it again in different conditions but wind blown snow can be awful. You even notice it on a snowmachine as the inconsistent firmness/softness can cause you to get stuck or unexpectedly get a harsh impact.

    My default is riding the largest tires my bike can fit. But sometimes the wind blown snow is so bad that you are better off doing something else than riding your bike.

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    Even in great conditions some new riders are put off fatbiking just because they aren't made aware of how important correct tire pressure is. I went for a ride yesterday in a local park that grooms trails with a Wildcat and also rents out fatties. The couple ahead of me headed out on the trail with their rentals, both were sinking in about 2 inches and washing out on every turn and off camber section through the woods. I figure I am at least 60lb heavier than either of them and with the correct pressure was floating along on top nicely, only leaving a tread pattern on top of the snow.
    Correct pressure is the key to having a great experience, too bad new bikes don't come with a warning label on the top tube to enlighten those new to FAT.
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  38. #38
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    Some peeps are not adventurous from the start and can't fathom the act of letting air out and riding a bike cause the tires aren't rock hard. Those little wrinkles must mean the tires is flat!

    Pfft! Fatbiking is all about adventure and sometimes we have to determine how many wrinkles are required for the current conditions.
    All in good squishy fun...
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    Thanks for bringing this back up again Mike, I have shared your original blog post on this many many times with fat bikers new and old alike.

    OE

  40. #40
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    Quote Originally Posted by mikesee View Post
    I noticed, paid attention to, and evolved the 'wrinkle rule' in the original Endomorph years. And those tires had stupid wimpy casings and sidewalls. These days, casing technology has evolved to the extent that the Endo's look even more like the dinosaurs that they were, and I'm not referring to the chevron tread.

    Point simply being that if you're running a 60tpi FBR 4.8 on the rear of one bike (or one wheelset), and a 127tpi JJ 4.8 on another, the wrinkles and preferred pressures are not going to match up. Are probably in fact going to be a significant distance apart, owing to the very different casing construction.

    This is a good thing -- if you're appropriately OCD -- as you can tune the ride of your bike to the Nth degree with casing options now too.
    This is probably a dumb question but how do you check the wrinkles? Do you to it stationary while sitting on the bike and leaning against something? I was trying to look down at my rear tire while riding very slowly in my driveway and that didn't give me a very good idea. I couldn't do it on the trail at all. Most of my ride had nothing to lean on so I was just letting air out while counting the seconds to make both tires similar. My hand isn't calibrated so I don't know what pressure I went down to but I had to have them very low to float and had I run over something hard with a little bit of speed I'd have bottomed out the tire to the rim.

  41. #41
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    Just look straight down over the stays and you'll see the tire and if it's wrinkling. The lightweight tires will wrinkle more readily than a heavier one.
    My Jumbo Jim Liteskins wrinkle at 6 psi with a 160# beanpole rolling around on em. My Bud/Lou have been ridden almost exclusively at >3psi and are so soft and supple from it that the sides wrinkle at 6-7 psi.

    The good ole squeeze gauge gives an approximate idea of what is rideable once you get accustomed to the feel of the tires at various pressures. My favorite pressure gauge is the Meiser 0-15 psi range. It gives .25 psi increments and is rather nice.

    Hmm, smart phone set where it can capture an image of you rolling along with a good view of the tires. A wee video and you can see how flat your tire is riding. Hope that you get deep enough base that you can under inflate without worry of rim damage.
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  42. #42
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    Quote Originally Posted by ak-rider View Post
    This is probably a dumb question but how do you check the wrinkles? Do you to it stationary while sitting on the bike and leaning against something? I was trying to look down at my rear tire while riding very slowly in my driveway and that didn't give me a very good idea. I couldn't do it on the trail at all. Most of my ride had nothing to lean on so I was just letting air out while counting the seconds to make both tires similar. My hand isn't calibrated so I don't know what pressure I went down to but I had to have them very low to float and had I run over something hard with a little bit of speed I'd have bottomed out the tire to the rim.
    From Mike's original post:

    "My way of staying safe (avoiding flats or rim damage) is to lean all my body weight on the saddle, while looking down at the rear tire."

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    I was skeptical at first about going below 10psi, but each week this winter I seem to be dropping 1 psi. 9 was better then 10, 8 was better then 9. Now I am down to 6psi and the traction is great on packed snow trails. My climbing has improved and haven't had any tire or tube issues. I know many run below 5, but I haven't tested that low, but I will keep going down until I experience diminished returns. I am on very technical roots, rocky trails and all the real pros in the area use tubes, so I am following the crowd and not going tubeless yet. Not sure if tubes are just popular here or there is a benefit to having them, but I know I have been on a few rides waiting for someone to patch or change a tube.

  44. #44
    turtles make me hot
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    Yesterday, I went on the softest snow ride so far. It was also my first ride with 80mm rims instead of 100 and I had brand new Bud and Lous.
    The snow was 7-8" deep. I was able to ride through it slowly. I started with 8 psi in my rear tire and 4 in the front. I ended up with about 4 psi in the rear and 2 or 3 in the front. Softest I'd ever run so far and it worked great.
    Second lap was awesome since we rode in our tracks from the first lap.
    I like turtles

  45. #45
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    Verdict on the 80s vs 100s? I ask cuz you've been pretty dedicated to the Clownshoes since go...

  46. #46
    Rippin da fAt
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    Quote Originally Posted by NYrr496 View Post
    Yesterday, I went on the softest snow ride so far. It was also my first ride with 80mm rims instead of 100 and I had brand new Bud and Lous.
    The snow was 7-8" deep. I was able to ride through it slowly. I started with 8 psi in my rear tire and 4 in the front. I ended up with about 4 psi in the rear and 2 or 3 in the front. Softest I'd ever run so far and it worked great.
    Second lap was awesome since we rode in our tracks from the first lap.
    I discovered the same during my first season on my Bud/Lou. They work very well on either 100's or 80's.
    They have more miles on em half flat than they do with 6-8 psi, now they wrinkle at 6 psi and peeps are always commenting on the rear tire needing air. I really enjoy the Bud/Lou for various ride conditions and the Jumbo Jim's are great for conditions where Bud/Lou are too much tread.
    There's never been a 4.0 on my 907 or the Mayor. Magic fatbike ride, it's similar to a magic carpet ride, but different!
    Get fAt, Stay fAt, Ride fAt
    Doctor recommended...

  47. #47
    gone walk about
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    magic carpet ride?? whatchu talkin bout willis??
    "ORANGE IS THE NEW BLACK"

  48. #48
    turtles make me hot
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    Quote Originally Posted by frozenmonkey View Post
    Verdict on the 80s vs 100s? I ask cuz you've been pretty dedicated to the Clownshoes since go...
    I hate to say it but the Other Brother Darryls make the bike feel fantastic and less like I'm trying to pedal power a track vehicle. My Clownshoes are going on my beach bike with Big Fat Larrys.
    I like turtles

  49. #49
    Rippin da fAt
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    Quote Originally Posted by nvphatty View Post
    magic carpet ride?? whatchu talkin bout willis??
    Punkin's tires aren't fat enough to qualify...

    Punkin's still invited to ride Valhalla, needless to say!
    Get fAt, Stay fAt, Ride fAt
    Doctor recommended...

  50. #50
    gone walk about
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    Quote Originally Posted by BansheeRune View Post
    Punkin's tires aren't fat enough to qualify...

    Punkin's still invited to ride Valhalla, needless to say!
    true, perhaps some day.
    "ORANGE IS THE NEW BLACK"

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