Tire Pressure, Fat Bike - Winter (I finally dialled in some numbers)

I mentioned earlier that cold temperatures affect tire pressure.  Filling up at home and then heading out for a -15 C ride means that you will not end up with the same pressure on the trail.

For measurements, I am using the Accu Gauge 0-15 psi gauge.  It is small and accurate enough for me.

Optimum pressure is dependent on the rider weight, trail condition and temperature.  To illustrate how this plays out, I set the rear tire at 10 psi and the front at 9 psi at +22 C as I wanted to reduce the rolling resistance somewhat.  After a bit of a squirrely ride on the single tracks, I decided that I needed an adjustment.  My rear tire wanted to slide a lot when I touched the brakes and my front tire never really felt planted.

I checked the pressure on the trail and my 10 psi rear tire had reduced to 7.75 psi for the rear and the front from 9 psi to 6.75 psi.  I reduced the pressure (cold) to 7 in the rear and 6 in the front and the bike tracked much better.  In fact, it was night and day!  That is with only a 3/4 of a pound difference but represents a drop of 10%.....

For adjusting the pressure on the trail, I am using the Blackburn Outpost HV pump.  This high volume pump adds a couple of psi with 5 or 6 pumps.

There is some information about fat bike tires in cold weather on the web and you would be well served to check out the varying opinions.  I have seen people claim 5 psi and that may work for them but given the variables for todays ride, 7 rear and 6 front was a great balance between traction, control and rolling resistance.  I could not have all three in the conditions today and on single track with trees and drop-offs, lower pressure was the safest way to roll....  Experiment for yourself, there is a bit of art and science to getting the pressures right.

Some metrics to guide you:

Warm Front pressure:                              9 psi
Cold Front pressure before adjustment:  6.75 psi
Cold Front pressure after adjustment:     6 psi

Warm Rear pressure:                               10 psi
Cold Rear pressure before adjustment:   7.75 psi
Cold Rear pressure after adjustment:      7 psi

Rider weight: 186 lbs
Pack weight:    10 lbs
Fatboy weight: 32 lbs

Average ride temperature:  -14 C
Overnight temperature:      -17 C

Trail conditions at Mill Creek December 26, 2015: fairly hard packed in the wide multi use areas and packed with some soft spots in the single track areas.

Fun Factor after pressure change to 7 psi rear and 6 psi front: 10/10

UPDATE February 1, 2016: depending on conditions, between 5 and 6 PSI rear and 4 and 5 PSI front will allow for more float on the deep snow.  I have since suffered the expense of 45NRTH Dillinger studded tires (a set of the studded tires cost as much as 3 1/2 tires on my car and they were runflats!!).  Well worth it as I can now ride on ice that is too slippery to walk on!

Again, no endorsement of the brands mentioned is implied.  This is what I have and the products work well for me.