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The FAQS of Fat Bike


Should I go with 80mm rims or 100mm rims?

Unless you have some epic trips planned, like competing in the Iditarod Invitational or a heavy-duty “bike-packing” trip, 80’s are your best bet.  Lower weight, and lower rolling resistance make 80’s the best all around option.  That said, if your adventures require maximum floatation, there is no substitute for increasing the size of your contact patch.  Understand that making “hundies” work with 135mm offset and 170mm-spaced frames requires that you remove a cog or two from the cassette to get the chain to clear the now massively wide tires. These modifications are not required with the newer and wider 9:ZERO:7 frames.

What is the difference between 135mm off-set and 170mm centered?

In order to get the chain to clear the wide tires, the seat stays and chain stays of 135mm off-set frames are bent to the drive train side of the bike by 17.5mm.  To bring the wheel back to the centerline of the frame, the rim has spokes holes closer to one sidewall.  The design was essential in early days of fat bikes because it allows you the ability to use any standard mountain bike hub or internally geared hub.

170mm frames feature a symmetrical design, so the wheel does not require an off-set spoke pattern, creating a stronger wheel. 170mm frames take a 170mm rear hub. In the last year, there have been a large increase in variety of 170mm hubs. The centered design also provides better tire clearance for wider rim and tire combinations.

What about 170mm centered vs. the 190mm frame?


As the benefits of additional floatation became more apparent, rims and tires got bigger. Basically, 100mm rims and 4.8" tires outgrew 170mm frame designs, and a wider platform was needed. While running a 190mm rear hub increases the chainline and q-factor, this can be minimized by running a single chain ring system in the front. The SRAM 1x11 system is especially effective for the new, wider frames.


What PSI works best?


That depends on the conditions.  Follow this maxim: When in doubt, let air out.  Soft conditions will require a PSI of around 5 (0.4 BAR).  This is low, so low, in fact, that you will see the sidewall of the tire bulge out when you hit a bump.  Don’t let the rim hit the ground though. If the trail is hard, you will see the best performance with a PSI of around 10-12 (1.0 BAR).


Should I run clipless or platform pedals?


This is a debate that predates the invention of the super wide rims.  Strong arguments can be made for both options.  It is more difficult to keep your feet warm with a clipless setup; however, you gain a tremendous amount of pedaling efficiency, especially in hillier terrain.  Clipless systems can ice up, but platform pedals can seem sloppy, especially if you are used to riding clipless pedals on other bikes.   That said, we ride clipless pedals.


How do you keep your feet warm?


If you are using a platform pedal, choose a lightweight, insulated boot.  Based on our flat pedal riding experiences, the Steger Mukluk is the warmest option.   Size this boot up one or two sizes.


 For clipless pedals, the best off-the-shelf option is the Lake MXZ-303 winter cycling boot.  Consider buying the ‘wide’ version.   Buy the boot two or three sizes bigger than your normal size.  Buy some insulated booties to fit over the boot, and wear gaiters.  In very cold conditions, wear a liner sock, then a vapor barrier liner sock, and then a thicker, medium weight, insulated sock.


Why do some riders prefer Gripshift shifters?


If riding in cold weather without the aid of Pogies, large gloves or mitts will keep your hands warm.  These however, reduce the amount of finger dexterity and makes it more difficult to manipulate trigger shifters.  Furthermore, some types of trigger shifters do not work in extreme cold weather. We spec our build kits with trigger shifters that work great when it's real chilly.



Which tire works best? What does the difference in TPI mean?


The Endomorph is the original fat tire from Surly.  Tread patterns and which pattern works best is usually a source of animated discussion.  The Endomorph works great as a front or rear tire.  Many people run the chevron treads backwards in the rear, forward in the front.  The Larry seems to feel about the same as a rear tire, but works better as a front tire in most conditions.  The directional knobs of the Larry help prevent the tire from “planing” through soft conditions.


Last season, the 45North Husker Du and Surly Nate added two great options with more aggressive tread patterns. Husker Du's offer low weight and rolling resistance while increasing traction over both the Larry and Endomorph. This is a great year round option. The Surly Nate offers maximum traction. However grippy, these boys give the legs a hefty workout with high rolling resistance and weight.


There are two versions of these tires: 27 tpi or 120 tpi.  There is no standard for measuring ‘treads per inch’ in the cycling industry, so think of it as sleeping on stiff, course sheets, or soft, supple sheets.  They both work fine, but the higher tpi gives you a higher quality feel.  The 27 tpi tires are less expensive, slightly heavier, and have a stiffer feel to them.  The 120 tpi tires are more expensive, lighter, and yield a nicer, softer ride.  You would need to have both tires in front of you to actually feel the difference.


How well do fat bike tires handle on ice?


One word... Dillinger! New for model year 2013, 45North has unveiled the first dedicated studded fat bike tire. These will be offered with 27 and 120 tpi casings. With the exception of Dillingers, fat bike tires don't handle ice. Be very careful riding over ice with non-studded tires; they are optimized for riding on snow.


How do I keep my water from freezing?


We like the Arctic Innovations Heated hydration system. This will keep your water line clear. If using a conventional system, your best bet is to use a bladder under your jacket.  Keep the bite valve and hose under your clothing.  After drinking, blow the water back into the bladder to prevent the bite valve and hose from freezing.  If you forget, and the line freezes, it almost always freezes at the bite valve.  Suck on the bite valve and cross your fingers.  For shorter trips, putting the water bottle in your cage upside-down will work temporarily.


What are pogies?


They are one of the essential items for cold weather riding.  Basically an insulated cover for your handlebars, pogies will keep your hands warm in the coldest conditions, often while wearing only a lighter glove.  If you haven’t used them before, it is difficult to explain just how essential they are and how much of a difference they make.

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