Adventure Cycling Association

In the May issue of Adventure Cyclist, we reviewed Deputy Editor Dan Meyer’s personal Surly Wednesday, a Frankenstein-esque experiment in which he transformed his winter fat bike into a summer bikepacking machine with a wheel swap and a few other select parts. If Dan’s four-season, do-anything project bike piqued your interest, check out our guide below for what to expect when modifying your own fat bike.

Compatibility

Not all manufacturers advertise it, but most fat bikes are interchangeable with 29er wheels. (If you’re not sure whether your fat bike is compatible, check with your local bike shop.) Your typical fat bike wheel (26 x 4–5.0in.) has roughly the same outside diameter as a 29er.

In the case of my Surly Wednesday, I usually run 26 x 4.6in. tires in the winter. For my summer 29+ (also referred to as 29 Plus) setup, I use WTB Ranger 29 x 3.0in. tires mounted on Industry Nine Backcountry 450 rims, which have an internal width of 45mm. My 29+ wheels end up a little taller than my winter wheels, forcing me to slide the rear axle back in the dropout to make room. 

If your fat bike is limited to the narrower 4.0in. tires, and clearance at the bottom bracket junction is tight, you may not be able to fit 29+, but something like 29 x 2.4in. may work. Again, check with your local bike shop. 

Wheels

Before you start looking around for wheels, you’ll need to know your fat bike’s hub spacing. If you bought your bike in the last few years and it’s got thru-axles, this’ll be pretty easy. For front hubs, the market has settled on 150mm spacing. For rear hubs, 197mm spacing is what almost all new fat bikes are using. A few outliers (like the Surly Wednesday) use the narrower 177mm spacing. Check your bike manufacturer’s website or your local shop if you’re unsure.

There aren’t a lot of off-the-shelf options for 29er rims laced to fat bike hubs, which means your best bet might be talking to your local shop and/or wheelbuilder. If you can afford it, it’s as easy buying a set of aftermarket hubs and rims and asking your wheelbuilder to lace them up for you. This will cost a pretty penny, though, as there aren’t a lot of affordably priced fat bike hubs out there. Most of the available aftermarket hubs are from premium manufacturers like DT Swiss, Hope, and Industry Nine. (There are cheaper fat bike hubs, but I’m not sure they’re the kind you’d want to employ for long-distance travel.)

If you don’t have a local wheelbuilder, a quick Google search will take you to a number of online shops that specialize in custom-built wheels. Sugar Wheel Works, LaceMine29, and wheelbuilder.com are a few I know that are reputable. (Of course, you can always do what I did and shell out for Industry Nine wheels.) Fatback Bikes, the Alaskan fat bike brand, also sells 29+ wheels for fat bikes, but exclusively in the 197mm rear hub spacing. 

One option for keeping the price down is to buy a set of used fat bike wheels and cannibalize the hubs. Or you can cannibalize the hubs on your current fat bike wheels and then later buy another set. You can save some money if you’re willing to get creative. 

Geometry

Assuming that your new 29+ wheels end up a little taller than your stock wheels, your bike’s geometry will change. Basically, the entire bike will be a little higher off the ground than before, meaning you’ll have a higher bottom bracket (which could be a boon for fewer pedal strikes), a higher standover, and a higher stack. 

Q-factor

Before you embark on this 29+ journey, consider your fat bike’s Q-factor. (Q-factor is the distance between a bicycle’s crank arms.) If you’ve spent a lot of time on your fat bike, including long rides with a load, and you’re comfortable with the wide Q-factor, then go with god. But if you’re not sure, don’t leap into it. Halfway through a month-long bikepacking trip is not the time to decide that your knees don’t like the wide Q-factor. 

Aside from a couple of expensive carbon machines — Otso Voytek and Rocky Mountain Suzi Q — pretty much every fat bike has a wide Q-factor. And even within the fat bike category, actual Q-factors vary wildly. It is possible to narrow your Q-factor slightly, but it will involve hours of internet sleuthing, the cost of a new crank, and quite probably a bit of trial and error. I would recommend consulting your local shop, but nothing brings out the ire of a crusty bike mechanic quite like the Wild West of fat bike crank standards. 

For a while, I did not like the wide Q-factor. (For reference, the average Q-factor for a road bike is about 150mm; for a mountain bike, 170mm; for a fat bike, 200mm or more.) But I kept riding fat bikes anyway because they’re so fun! When a used Surly Wednesday fell into my lap, I bought it, Q-factor be damned. It was primarily a winter bike for the first couple of years. After longer rides, or rides with a lot of climbing, I could definitely feel the consequences of the wider Q-factor. My knees were not appreciative. But then a funny thing happened: I got used to it. Only then did I consider using my fat bike for bikepacking.