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Although gaining in popularity, many people still see fat bikes as a bit of a novelty. Whether it’s on the trail or outside the garage, these odd-looking contraptions attract a lot of attention. It’s unsurprising that whenever I show off my fat bike (which I do often), people’s attention usually goes straight to the tires. And for good reason. The tires are what set fat bikes apart from their other two-wheeled cousins. Once onlookers get over the initial shock of seeing such a cartoonishly-large tire, the question of fat bike tire pressure usually comes up. The answer often catches people off-guard because the pressures are so low.
Of course, there are good reasons for using such low pressures. And, while they always remain low, they can vary depending on riding conditions. This is true for both summer and winter fat bike riding. On top of that, fat bikes use pressure so low that a standard floor pump will have a hard time measuring them.
By following the basic guidelines outlined in this article you’ll be dialing-in the tire pressure on your fat bike like a pro in no time.
Sound confusing? Don’t worry, by following the basic guidelines outlined in this article you’ll be dialing-in the tire pressure on your fat bike like a pro in no time.
Why is fat bike tire pressure so low?
Many people are surprised to hear that I use tire pressures of between 4.5 and 6.5 PSI (pounds per square inch) in my fat bike tires, depending on conditions. But these numbers aren’t that far-fetched when you consider the large volume of the tire and how they are going to be used.
Note: For those who prefer to measure their tire pressure in Bar, 14.5 PSI is equal to 1 Bar.
As a comparison, let’s look at the pressures in a few different types of common tires:
- Road bike tire = 80-130 PSI
- Mountain bike tire = 20-30 PSI
- Car / Truck tire = +/- 30-35 PSI
- ATV tire = +/- 2-10 PSI
Of course, these numbers are for informational purposes only. Each of the pressures used in these different types of tires will depend to some degree on usage conditions and user preference. But when you look at them next to each other some patterns begin to emerge.
As tire volume increases, the desired pressure decreases. This is evident when comparing the road bike tire against the mountain bike tires and the car / truck tires against the ATV tires. In essence, a larger volume tire with lower pressure will have a similar feel to a lower volume tire with higher pressure.
In addition, the tire pressure is lower again in tires that require more traction on potentially uneven or soft surfaces. For example, the nature of mountain biking means a mountain bike tire will require more traction over uneven or soft surfaces than a road bike tire will.
What does this mean for fat bike tires?
What we can take away from these patterns is that fat bike tire pressure is so low because of the combined effect of large tire volume and the need to use them on soft and/or uneven surfaces. It all boils down to the larger the tire volume, the lower the pressure, and the more need for traction or float, the lower the pressure again.
The volume of the tires on your fat bike is constant—it doesn’t change. So if conditions were always the same, you could pick a tire pressure (say 5 PSI), set it and forget it. But fat bike conditions can vary widely: soft snow, ice, sand, asphalt, etc.
These conditions can change from ride to ride (and even within the same ride) and will affect how you set your ideal tire pressure. Let’s take a closer look at how and come up with some solid tire pressure numbers to use as a starting point.
Altering pressures to suit the conditions
When it comes to fat biking, soft snow conditions have different traction/float requirements than hard-packed snow, and the same is true for riding on sand vs. riding on asphalt. There are two ways you can change the traction characteristics of your fat bike tires: swap tires with different tread patterns or change the tire pressure. Here we’re concentrating on the most convenient and cost-effective of the two methods, adjusting the tire pressure.
It all comes down to hard vs. soft
When it comes to tire pressure, it doesn’t really matter whether you’re riding on soft snow or sand, asphalt or hard-packed snow and ice. It only really matters whether the surface you are riding on is hard or soft.
Of course, things like ice can throw a bit of a wrench into the works and in this case you might want to consider studded tires.
I’ve covered the pros and cons of studded fat bike tires here.
Generally, soft conditions in winter exist after a snowfall (before the trail has been groomed or packed by riders), or when the air temperature rises to the point that hard-packed trails begin to melt and soften. In snow-free conditions, soft can mean sand or wet/muddy trails (even on a fat bike it can be bad form to ride wet or muddy trails).
In either case, the goal here is to try and stay on top of the snow, sand, or mud and not get bogged down.
Some would say that simply the sheer size of a fat bike tire should keep them floating on soft surfaces. They would be right, to a degree. But float and traction can be further increased through pressure adjustments. And for soft conditions, low tire pressure is the name of the game.
Low tire pressure is ideal in soft conditions because when you sit on the bike, weight is applied to the tires and the low pressure allows them to flatten out. As they flatten out, the surface area increases. This spreads out the weight over a larger area, allowing the tires to float on top of the snow (or at least not sink as far as they would with less surface area).
At the same time, the enlarged surface area also improves traction in soft or loose conditions.
Hard-packed trail conditions usually come about in winter when a route has seen significant use and no new snow. Add some minor daytime thawing and an overnight freeze to the mix and you can end up with winter fat bike trails that are hard as a rock.
In summer, most dry singletrack would be considered hard-packed as would man-made surfaces such as asphalt.
In these conditions, float is no longer an issue but rolling resistance becomes a consideration. Very few people are looking to make their ride more difficult than it needs to be. Most of us would rather ride farther and faster than shorter and slower. To do this, we want our tires to have as low rolling resistance as possible. And this means increasing the tire pressure.
Low tire pressure increases surface contact and float, but it also adds to a tire’s rolling resistance. Increasing the tire pressure reduces the surface contact and thus the rolling resistance of the tire. This all means that you will be able to ride farther and faster with the same amount of effort just by increasing your tire pressure.
It’s great when you are confident that trail conditions are either consistently hard or soft. It makes deciding on a tire pressure easy, and you’ll know you have the right one for the job. But trail conditions aren’t always that straightforward.
Much of the time, your ride will consist of some mix of hard and soft packed conditions. What to do then? Compromise!
One option for dealing with mixed trail conditions is to change your tire pressure on the trail as conditions change. But this is time-consuming and if conditions are truly mixed, it’s impractical. You’d be spending more time off your bike adjusting pressures than riding. Instead, I would suggest simply setting your tire pressures to ones that are in-between what you would use for hard or soft conditions. This way you will retain some float when conditions are soft and minimize rolling resistance when conditions are hard.
Some cold, hard numbers
This is all great in theory, but let’s get down to some practical numbers we can actually use. Here are the tire pressures I use for the conditions discussed above:
- Soft conditions 4.5 PSI
- Mixed conditions 5.5 PSI
- Hard packed conditions 6.5 PSI
NOTE: These pressure suggestions are based on a 5-inch width fat bike tire. In order to match the performance of these pressures to a 4-inch tire, they would need to be slightly higher. Also, please keep in mind, these are just a starting point. Rider weight, rim width, and other factors will determine what pressures will work best for you. Experimentation is key!
Now, it may seem that the differences between these pressures are small, but when using pressures this low, these small numerical differences have a big practical impact.
This leads us to another issue. How to measure tire pressures when they are this low and the differences are so small.
Measuring very low tire pressures
Most floor pumps and small hand pumps won’t even register tire pressures as low as 4.5 psi, let alone be able to accurately gauge the difference between 4.5 and 5.5 psi. This is where a low pressure gauge comes in.
Of course, some riders are happy to go by feel alone, and this is certainly an option for determining your tire pressure. But if you want to be able to reproduce different and specific tire pressures time and time again, you’ll need a low pressure tire gauge.
Most low-pressure gauges aren’t attached to a pump. They are standalone devices used solely for the purpose of measuring tire pressure. They are more accurate than most floor pump gauges and in many cases will measure pressures to one-tenth PSI.
Most are small and can easily fit in a hydration pack or hip sack so you can take one with you as part of your fat bike kit.
I don’t carry one with me on rides. But I always use one at the trailhead prior to each ride to dial-in my tire pressure.
Below is an example of a small gauge made by Topeak, the D2 SmartGauge. It is capable of measuring low and high tire pressures, so it can be used on all of your bikes. It displays readings in PSI or Bar and fractions thereof.
Buy USA / Canada:
A few other things to consider when dialing-in the tire pressure on your fat bike
While trail conditions (hard, soft, or mixed) are the main factors in determining fat bike tire pressures, it’s worth considering the following points as you search for that tire pressure sweet spot.
How low can you go?
Low tire pressure means better float and traction. But taken to the extreme, low pressure can do more harm than good. You don’t want to lower your tire pressure too much as this can lead to flat tires.
If you use tires with tubes, extremely low pressure can result in pinch flats. This occurs when the tire folds too much under pressure and pinches the tube between itself and the rim. Some of the time this results in a hole in the tube and loss of air pressure.
Tubeless fat bike tires allow riders to lower the pressure without needing to worry about pinch flats; however, they can have issues of their own. The most common issue is ‘burping’ the tire. This happens when the bead of the tire momentarily separates from the rim, releasing air. Sometimes the amount that escapes is unnoticeable, but large amounts of air can escape this way, leaving the tire flat. Fixing this is simple: just refill the tire with air. A ‘burped’ tire rarely sustains any damage.
Don’t overdo the pressure
At the other end of the spectrum, it is also possible to over-inflate a tire. Many fat bike tires will come with a max psi rating imprinted on the side of the tire. For example, a 45Nrth Dillinger 5 tire calls for a maximum pressure of 30psi. It is rare that you would want to inflate a tire to, or above this rating. This can result in poor ride quality and possible injury.
Inflating a 5-inch tire such as the Dillinger 5 to 30 PSI would result in a very rough ride. Even on hard-packed surfaces, this amount of pressure is overkill; something as high as 10 psi would result in a very firm ride with minimal rolling resistance.
The only time you might want to inflate a tire to its maximum PSI rating is when attempting to seat a tubeless tire onto a rim. In this case, it is sometimes necessary to inflate the tire past the pressure you would use on a ride to make sure the bead fully pops into place on the rim. Again, this is only temporary. Once the bead is seated, the pressure can be lowered to something more comfortable for riding.
A tire should never be inflated past its maximum PSI. Doing so can result in damage to the tire and even injury.
Smooth out your ride
Just as over-inflating a tire can produce a very rough ride, low tire pressure can help smooth things out. If you’re more interested in smoothing out the bumps than about speed and low rolling resistance, using a low tire pressure can make your ride more pleasant. This is the case whether you’re on a fully rigid (no suspension) fat bike or a full suspension one.
Lower pressure allows the tire to conform to small and medium-sized bumps and objects on the trail. As a result, the tires soak up some of the impacts those bumps might have as they travel from the tire through to your body.
That’s my two cents, the rest is up to you!
As with everything else in life, there is no one-size-fits-all solution when it comes to fat bike tire pressures. Every rider is as different as the conditions of the ground they are riding on.
Think of this guide as a jumping-off point to find out what works best for you
The pressures we’ve discussed here are meant to be a starting point for you to experiment with and find what works best for you. Having said that, it is unlikely you’ll want to stray too far from the pressures outlined above. Anything significantly lower can result in flat tires and your rim coming in contact with the ground.
On the other hand, if you opt for significantly higher pressures than those discussed here you may be left feeling like the Flintstones riding on a piece of rock (I think that’s what their ‘wheels’ were made of).
Think of this guide as a jumping-off point to find out what works best for you. Get out there, have some fun and experiment!
I’d love to hear from you
If you have any questions or comments, please leave them in the comments section below, or you can contact me directly from our Contact page.
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