Mountain Bike Reviews Forum banner

1 - 20 of 76 Posts

·
This place needs an enema
Joined
·
15,681 Posts
Discussion Starter #1

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!
 

·
Elitest thrill junkie
Joined
·
35,209 Posts
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.
 

·
Registered
Joined
·
54 Posts
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.
 

·
Registered
Joined
·
71 Posts
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?
 

·
Rippin da fAt
Joined
·
8,441 Posts
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...
 

·
Ambassador of Chub
Joined
·
2,827 Posts
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.
 

·
This place needs an enema
Joined
·
15,681 Posts
Discussion Starter #7
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.
 

·
Registered
Joined
·
63 Posts
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!
 

·
Registered
Joined
·
1,095 Posts
I'd love to see another thread about your survival gear, and exactly how you manage when out all night in this stuff.
 

·
This place needs an enema
Joined
·
15,681 Posts
Discussion Starter #11
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.
 

·
Registered
Joined
·
500 Posts
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.
 

·
Registered
Joined
·
733 Posts
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-Pres...8-2-fkmr0&keywords=0-15+tire+pressure+meisner
 

·
since 4/10/2009
Joined
·
31,231 Posts
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.
 

·
Registered
Joined
·
423 Posts
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
 

·
This place needs an enema
Joined
·
15,681 Posts
Discussion Starter #18
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.
 

·
Registered
Joined
·
483 Posts
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.
 
1 - 20 of 76 Posts
Top