Just a Fat Bike Picture

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.

Keeping Warm - Hands (what the heck is a pogie?)

It seems that my fingers are the first to suffer when it is cold.  I have a nice pair of XC-ski gloves that are good to -15 C and thought they would be OK for fat biking in winter.  My first ride was almost unbearable so I bought some liners and my second ride was slightly less unbearable.

My riding buddies had these strange contraptions they called pogies.  Basically, a large mitten wrapped around the handlebar grips and they claimed that you could use a pair of cold weather MTB gloves and still be very warm.  Huh?

Ok, more research.  I could feel the wind through my regular gloves and it made sense as there were parts of the trail where we were cooking along at 25 - 30 mph.  Ah, wind chill was the culprit!  At that speed, and at a temperature of minus 15 C, the wind-chill at 20 kph would be -24 C and at 30 kph the wind chill would be -26 C.  The wind also managed to sneak through the seams of my gloves.  This would explain the biting pain in my fingers.  

There are a few choices such as lobster claw gloves or mittens however I opted for a pair of 45NRTH Cobrafist pogies.  In this rare case, I did not do any research, as this was the only option at Revolution Cycle at the time.  Note that I am a fan of all the local bike shops in Edmonton and at the moment do not have a favorite.

The Cobrafist pogies were easy to install and are well designed.  I did have to make a hole in the stock grips to allow for the locking plug to be installed.  I also needed to rotate my brake levers down a bit to allow for clearance for shifting and braking.  It was not a problem with the design, I just needed to make the change to allow for a more comfortable position.  Uninstalling and reinstalling takes under a minute per side.

The Cobrafists have vent zippers on the top and bottom and a mesh “pocket” in the interior for storing stuff.  The “pocket” does not close so you could lose anything you stuff in there if you take a tumble….

For my first pogie ride, I put on my cold weather MTB gloves and my hands were toasty warm the entire ride!  Mission accomplished and I have no negative comments about the Cobrafists after 3 rides.  They were a bit spendy at $200 however they are well made, easy to install and keep my hands very warm.

I do need to point out  that is anything you add to your bars will affect the handling.  In this case, the pogie adds surface area, which, if you are not precise, can get caught on objects such as trees.  I misjudged, caught a tree, and had an encounter with a second tree and the ground.  No fault of the pogie, I misjudged and will need to take more care.  I don’t see this as a big deal, it happens without a pogie but be aware that there is more surface to hang you up if you misjudge your clearance.  

Here is aftermath of a misjudgement (it was peaceful and a new perspective): 

In this rare case (I am fussy and OCD on some things!), I am 100% pleased with my purchase and I have not identified any issues.

REFERENCE

Here is Environment Canada's wind chill page http://www.ec.gc.ca/meteo-weather/default.asp?lang=En&n=5FBF816A-1#table1.

Here is a link to the 45NRTH Cobrafist http://45nrth.com/products/gloves/cobrafist.

Here are the Cobrafists installed on my Fatboy:

Tire Pressure - Cold Temperature Effects on Fat Bike Tire Pressure

Being new to the fat bike game, there have been a number of little surprises.  The first surprise was how easily the bikes roll and the second was how low the tire pressure is on a nearly 5” wide tire.  I am used to 110 psi on my road bike and 20 – 30 on my mountain bike.  Fat bikes tires need pressures hovering around 10 psi or less (I will cover my experience with various pressures in another installment)

Another revelation has been how temperature affects tire pressure as I had never ridden a bike in sub zero temperatures…  On my first ride, I felt the tires were getting softer shortly into the ride.  Sort of felt like I was getting a flat!  After checking in with a few folks who were “winter riders”, I learned that due to the low pressures, even a drop of a 1 or 2 psi would result in a significant change in the handling.

I needed to conduct my own experiment….  I filled a tire to 9 psi, set it outside at minus 15 degrees Celsius and measured the pressure after two hours.  The pressure went down to 6.75 psi, a drop of 25%.  Good to know!

I found a Botranger chart that can be used as a rough guide for various temperatures.  I say “guide” as my experiment showed less of a loss than the chart.  Tire volume is a variable.

My lesson learned?  Fill up at home, expect a couple psi drop and plan to adjust on the trail depending on temperature and conditions.

Please Stand By...... PS Merry Christmas!

On the eve of Christmas, the Blog Elves are busy writing and editing and eating and.....

Over the next couple of days, I will be adding some tips for Fat Bikes, Mountain Bikes and cycling in general.  The idea is to assist others with some of the planning and research necessary to enjoy cycling!

Merry Christmas