Tire Pressure for Fat Bikes in Snow / Cold

[MikeMN]

I wanted to say hello and post a topic.  I’ve been reading this website and listening to the podcasts for about 6 months.  I’ve been able to learn a lot from all of you, and you’ve helped me become more well-rounded in my cycling adventures (I was a road cyclist only until last Spring).  So before I get to my topic, thank you to the authors of this site, and all of you on these forums for helping a newbie get his tires dirty on a regular basis.

I picked up an SE F@E from Nashbar, after deciding a road bike and my Trek Superfly 5 hard-tail 29er were not enough bikes in the stable, back in November.  I finally got around to assembling the bike last night, and I took it out on it’s inaugural ride this morning on a trail west of where I live in Minneapolis, MN.  The trail was packed, good crunchy snow, clear skies, but the temps were at -10 F.  I was warm enough (thanks Jeff and Greg for the tip about Cross Country ski clothing making for great winter riding clothing), but the pedaling was extremely difficult due to the low tire pressure I had.  The tires say the max psi is should be 20psi, but I was wondering what all of you here normally run your fat bikes at when it’s really cold.  Are fat tires really optimized for winter riding at that low of a pressure setting?

Thanks again for any suggestions.  I apologize if this is repeat question, I couldn’t find the forum search function.

Happy trails everyone!

[Apvdh]

I’m guessing you were at Theo Wirth?? Going from a road bike and a xc bike, it doesn’t surpise me that a fat bike would seem hard to pedal. 20 psi is way too much for me on the trail in winter. I would be sliding out everywhere. It really depends on your weight to find the sweet spot. Firm enough to avoid pedal “bounce” on the back tire and soft enough to corner and maintain grip in the front. The big tires also help dampen the trails for a smooth, more controlled ride. For my rigid fatty, i run 8psi in the back and 6 in the front and i weigh 225lbs. I tend to run more in the summer time. It is “Wirth” playing around with. Start a ride with you tires pumped up and as you go let a little air out and see what happens. Topeak makes a nice digital tire gauge that makes it easy to get dialed in. Good luck!

[BrianI]

Have been riding a Fat bike for 3 winters now. Most of the guys I ride with run 5.5-7 psi in the rear, 5-7 psi in the front. Never any issues with cold weather and tires, but we usually do not ride when the temperature drops below -18C (0F). The lower pressure allows the tires to sit more square for better traction and provides some “suspension”.  Nobody has ever had a pinch flat and one guys rides with 4-5psi in the rear and he is about 190 lbs.  The bigger problem is getting the tire pressure set up right. If you keep you bike in a warm place and fill up the tires, when you ride the pressure may go down a lot. Good old high school chemistry and the Ideal Gas law. For example, if you fill up in the house at 70F to 6 psi, at a 0F ride the pressure will end up closer to 3 psi. So best to check your tire pressures when they are cold.

[Zoso]

Hmmm.  I’ll run anywhere between 1.5-4 psi depending on conditions.

1.5-2.5 = very poor traction/adventure fat biking (the best kind imo)

3-4 = groomed/packed trails.

For reference, I’m on a fully rigid bike, weigh ~230 geared up, run Bud/Lou tires (4.8″) on 100mm wide rims, and have never pinch flatted.

Pretty sure you’re just surprised how much more work a fat bike can be.  A 20 mile phatty ride is usually a pretty good ride.

[stumpyfsr ✓ supporter]

Air temperature shouldn’t affect your tire pressure. For example, riders at Arrowhead 135 race exposing their bikes (and their bodies) to much colder temperatures. It all depends on surface that you riding on and your weight. If it’s a hard pack then higher pressure is fine (20 psi is too high even for summer riding), on soft snow/sand or mud sometimes even 2 psi will be necessary.

so, as previous post said, it’s all trial and error.

[Downhill Mike]

Air temperature dramatically affects your tire pressure. If I put 10 psi in my tire at home and then go ride in minus 20 my tire pressure will easily drop by half within 15 minutes of my ride. What you are saying is very incorrect.

[stumpyfsr ✓ supporter]

It is correct, tire pressure drops at lower temperatures. What I meant is that no matter what the outside temperature tire pressure should be based on terrain you riding on. For example, if there’s no snow but -20F I would keep my tire pressure the same as if I was riding on summer Singletrack. Thank you for pointing it out.

[sissypants]

Congrats on your new bike!  I have ridden an SE F@E and an SE F@R. I think your #1 problem is running those cheap Vee Mission tires — they have an awful amount of self steer and are impossibly clumsy on pavement and snow.  Your best bet is probably the Schwalbe Jumbo Jim 26×4.0 TL EVO Liteskin tires, they are super light and fastest of all the fat tires I’ve ridden, run them around 3-5 PSI on snow. I ran my Missions on the F@E at around 5 PSI, the Bulldozers on my F@R around 2.5 PSI, and I even ran a Snowshoe 2XL in the front of my F@R for a while as low as 0.5 PSI (yup, that tire is huge). The F@E frame is also quite heavy, btw, even compared to the F@R, and that’s going to make it seem slow too. Good luck!

[Ross Lagasse]

I’m 175 lbs and usually run 7psi front/9psi back on groomed, 5/7 or lower for soft conditions/breaking trail.  I’m running a Spec Fatboy w/ 4.8″ 26″ tires (tubeless).  Here’s a guide I started with (from Stan’s), remember to include weight of gear in the body weight number.  This isn’t gospel, but its a good starting point:

Stan’s 29er Formula
Body Weight in lb/7=Starting Pressure
Subtract 1 PSI for Front Tire
Add 2 PSI for Rear Tire
Example 150lb/7=21
21-1=20 PSI for Front Tire
21+2=23PSI for Rear Tire

9:ZERO:7 Packed Snow Fat Tire Formula
Body Weight in lb/20=Starting Pressure
Subtract 0.5 PSI for Fat Front Tire
Add 0.5 PSI for Fat Rear Tire
Example 150lb/20=7.5
7.5-0.5=7 PSI for Fat Front Tire
7.5+0.5=8 PSI for Fat Rear Tire

9:ZERO:7 Soft Snow Fat Tire Formula
Body Weight in lb/25=Starting Pressure
Subtract 0.5 PSI for Fat Front Tire
Add 0.5 PSI for Fat Rear
Example 150lb/25=6
6-0.5=5.5 PSI for Fat Front Tire
6+0.5=6.5 PSI for Fat Rear Tire

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