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Fat tire pressures for snow.

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#22 ·
kaire said:
What is the minimum pressure with tubes to be on the safe side?
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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.
 
#23 ·
kaire said:
What is the minimum pressure with tubes to be on the safe side?

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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.
 
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Discussion starter · #24 ·
Bumpyride said:
The wrinkle test is something I'll look at
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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.
 
#28 ·
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.
 
Discussion starter · #29 ·
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.
 

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#31 ·
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 ·
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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#33 ·
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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Discussion starter · #34 ·
ak-rider said:
ive never paid any attention to wrinkles on my tires. I'll now look for that in the future.
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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 ·
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.
 
#36 ·
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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#37 ·
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.
 
#38 ·
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...
 
#40 ·
mikesee said:
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.
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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.
 
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