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.

 

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.

 

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...

 

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

 

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.

 

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.

 

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!

 

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.

 

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!

 

A very soft snow ride this evening -- at base pressures, which still weren't always low enough -- reminded me that it's the time of year to bump this back to the top.

 

This is still the most accessible info on fat bike tire pressures, I send others to it regularly. A lot of newbies as well as people experienced enough to know better tell me that my tires are flat just before I ride through stuff that they're pushing through. Thanks for the reminder.

 

...tell me that my tires are flat just before I ride through stuff that they're pushing through.

This exact scenario this evening is what prompted me to bump the post.

There were stretches of ~80 meters where I could hear the front tire folding on itself (because the trail had suddenly become scoured underfoot) and then we'd turn ~30* across a meadow, it'd be drifted over and in, and the tire would suddenly go silent again.

Sublime.

 

I get a kick outta peeps telling me that my tires are flat... Cause they are! The wrinkles and full tread width on the ground are perfect inflation for snow riding.

And, yup, Mike! I experience that many times with the funky conditions. First time on a ride and check to make sure it is not a real flat and find it's a snow tire thing, pedal on.

 

I quit using a gauge years ago. My ‘by feel test’ is simply how much force it takes to hit the rim when pushing down with my palm. Very firm conditions I can’t hit the rim, but is a rare pressure. Most conditions I encounter I can push down and hit it without much force. Soft snow requiring float and seeking traction, I can hold my palm on the rim.

 

I quit using a gauge years ago. My 'by feel test' is simply how much force it takes to hit the rim when pushing down with my palm. Very firm conditions I can't hit the rim, but is a rare pressure. Most conditions I encounter I can push down and hit it without much force. Soft snow requiring float and seeking traction, I can hold my palm on the rim.

As long as it's logical and repeatable, you don't need to complicate it.

 

I normally go by feel, but got out my 15psi gauge after last night's ride just to check. 3.5 front, 4.0 rear. No annoying squish going on, could have gone lower, but the 2 mile uphill dirt road at the end always has me trying to keep some pressure in the tires...

 

These are pretty normal winter running pressures with the J5's on 100's for our trails, which are groomed but not packed.

And this is pretty normal for non-groomed deeper snow.

 

I found that below 4 PSI the tire developed wrinkles (27.5 3.8 Gnarwhal) and although a plush feel, it is also more vague, less confidence inspiring when cornering. I am talking about hard pack snow.

So for me (150lbs rider) 4-5 PSI is good enough for where I ride.


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I clock in at 250lbs I assume my pressures will be higher but would think the sidewall wrinkle rule would most definitely still apply but it would occur ah higher pressures due to my Clydesdale status?! And I'll definitely be doing a lot of experimentation.

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I clock in at 250lbs I assume my pressures will be higher but would think the sidewall wrinkle rule would most definitely still apply but it would occur ah higher pressures due to my Clydesdale status?! And I'll definitely be doing a lot of experimentation.

Appropriate pressures are dependent on rider weight, yes, but also rim width, tire size relative to rim width, tire casing construction, as well as softness/firmness of the trail tread.

In short, experimenting with pressures on your bike, on your trails, is the only way to know what will work for you, and the wrinkle rule is a great place to start.

 

I run my gnarwhals at 6-7 front and 7-8 rear.

More than that on singletrack they dont turn well or have climbing traction.

Less they are a slog but this is boot packed singletrack.

This is hills that you almost need poles to climb walking hills, or decent momentum as they are pitchy.

For double track ill keep them here or go up if its quite packed for speed and go down via squeeze test if im breaking thru groomed which is rare at 6/7

Im over 200 lbs


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For me personally, the riding isn't much fun until its fairly packed snow and temps are low so I can ride fast (6-7mph avg pace rides). For my 27.5x4.0's I'm finding most often that around 6psi is my happy zone. I'm 170lbs. For comparison we had some fresh snow on top of hardpack a couple weeks ago and I did go to 4.5psi and it was better, but the conditions were more challenging overall and less fun (IMO at least).

 

the hard part is when you have changing surfaces. a 6 mile loop I do out of the house, can be pavement, sheets of ice with water on it and 6 inches of fluff, all on the same ride. it can be a pain in the ass to always be changing tire pressure.. Sometimes, I just find a psi that does non of the above good, but does all of the above.

 

Yea, this is true. Sometimes you have to just pick what works best overall. I rode last week on a trail system that was a 4 mile loop. It had hardpack, frozen dirt...smooth firm snow, then after that post-holed crunchy snow from some deer and human tracks...then back to dirt again...repeat.

 

I joined the fatty club today after checking things out and reading good stuff like this diary. When I took the bike out for a test ride the tires were obviously pumped too much. When I got back he told me 10psi.
So I was looking for some info on pressure and wound up here. Lots of good ideas.
I had the lbs set up the wheels tubeless for the wicked goat head/puncture vine thistles we have around here in southern Idahoe and am now thinking how running extremely low pressures with tubeless wheels might not work too well. Any experience with tubeless and low pressure out there or other opinion on tubeless in cold temps?

 

thinking how running extremely low pressures with tubeless wheels might not work too well. Any experience with tubeless and low pressure out there or other opinion on tubeless in cold temps?

At super low pressures, tubes will peel away from the sidewalls of the tires and create a higher pressure ridge along the tube, You can feel it from the outside of the tire.
Tubeless, with proper tubeless rims and tires is absolutely the way to go for fatbiking on snow. At -40º last year, I had no trouble with tubeless, but somewhere around there, I believe the sealant sticking your tires to the sidewalls will get stiff and that could cause problems with sidewalls leaking. Previously sealed thorn punctures could also start to leak.
So yes, there could be problems, but the problems with tubes are worse.

 

Here in New England, we frequently experience snow that goes through multiple freeze-thaw cycles, and occasional rain. Currently, the trails that have been ridden are pretty much rock hard, however untraveled snow provides barely enough support to ride. Using tires and pressures usually associated with soft, unconsolidated snow allows one to ride through trail-less terrain that is inaccessible for the rest of the year. For these conditions, I've been riding partially-studded J5s (flat-tipped studs), on 80mm rims, at 2-3 psi. We currently have enough snow cover to pick lines through open hardwood forests, without worrying about rocks, roots, or fallen limbs, and only occasionally punching through. It's fantastic!

 

I noticed that wider is not often slower. I was worried about this going from D5's to J5's, but the J5's I found can be run at higher pressures for the same float, and the wider footprint allows me to keep going when the D5 loses traction or breaks through.

 

Is it float or traction? J5's do have the tread for loose where D5's are a shallow tread more suited to sand than snow. Once one looses traction and spins, the tire drops through the surface readily.

 

Well, yeah, but you are only going 2mph, which may be faster than walking...but you sure aren't going "fast". J5s are big and slow.