I recently became curious about the answers to the following questions with respect to my fat bike, a Surly Pugsley:
1. How would it ride with a standard, not-specially-dished 26″ rear wheel and standard mountain bike tire used in the rear?
2. Would it work to mount a standard — say, 2.0 — mountain bike tire (with a standard tube) on a Large Marge rim?
3. What would happen if an Endomorph was mounted on a standard, not-specially-dished mountain bike wheel with a Surly oversized tube, and that wheel was used on the Pugsley?
Of course, I had theories but I wanted some observations by way of confirmation. So I set out to do some experiments.
Surly Pugsley with a standard 26″ rear wheel (Crossmax ST borrowed from a Giant Trance)
Mounting a standard 26″ wheel with a standard mountain bike tire to the rear of the Pugsley worked just fine. It was certainly disconcerting to look at from the back with the incorrect dish offset, but there was plenty of clearance at the seat and chainstays. After a few pedal strokes any sensation of abnormality (if this wasn’t in fact just imagined) went away. The bottom bracket was, of course, substantially lowered and this would make a difference riding technical off-road trails. With the front end raised relative to the rear, steering should have been marginally lazier and slower, but I noticed no difference. Cornering on asphalt and dirt was well within the bounds of normal.
Incorrect offset on a Pugsley with a standard 26″ wheel.
Mounting a fairly standard 26″ 2.0 tire on a Large Marge rim was straightforward, and no more difficult than fitting an Endomorph or Larry.
A Kenda Karma 2.0 with a standard tube mounted on a Large Marge rim
Before inflating the tube, the tire just floated on the rim in an unpromising way, but once pumped up the bead seemed to seat decently enough. I pumped it up to 40 psi. As in experiment number 1, the Pugs rode pretty normally. My suspicion is that at pressures where the tire isn’t quite firm, the tire would squirm intolerably. The lowered bottom bracket remains an issue.
26″ 2.0 (Kenda Karma) mounted on Large Marge rim.
Mounting the Endormorph with the Surly 3.0-4.0 tube on to the Crossmax wheel was more work than mounting a regular tire and tube. This was because the big tube crowded the middle channel of the rim, so it was difficult to make enough room to tuck the bead in. Still, the task was not extraordinary; I have had as much trouble with some other more standard rim/tire combinations. I pumped the tire to 30psi, the max recommended on the Endomorph sidewall (it seemed obvious that traditional fat bike low pressures would end in disaster).
Endormorph with Surly oversized tube mounted on Mavic Crossmax ST, 19mm width.
The resulting ensemble was funny to look at, and I was plenty skeptical of whether it would stay seated on a rim so much narrower than typical fat bike rims.
The first discovery was that it would not turn in the Pugsley rear triangle, what with severe rub on both the drive side chain stay and seat stay (recall that this is a wheel that does not have the special offset). Since the front fork is the same 135mm width as the rear, I checked it in front. There it would turn without contacting the fork, but the clearance was minimal and was only reliable when all the bulges and hops were worked out of the tire.
Minimal fork clearance with the Endormoph mounted on a standard 26″ wheel.
* * *
A natural thing to wonder is why on Earth I would care about these ridiculous setups. It’s true that my line of work makes it so that I am not a stranger to esoteric questions where no one cares about the answers. But I do have what I regard as a defensible motive here. In spite of my earlier protests to the contrary, I’ve been thinking again about taking a long expedition tour overseas on the Pugsley. I won’t try to defend that ambition on its intrinsic merits other than to confirm that riding a fat bike gets under your skin so that it becomes the main bike you reach for no matter how many you own. (Okay, I’ll say a tiny thing: several places on my destinations list have a fair bit of sand and snow and soft conditions.)
Touring on the Pugsley in Alaska didn’t give me pause at all, since I knew that any bike shop in the state would have fat bike parts. But the most readily available tire and wheel size world-wide is the 26″ (559) mountain bike standard. That’s why when I ride in far-flung places I take a mountain bike or my 26″ wheeled Long Haul Trucker.
The above experiments were contrived as part of thinking through how I would handle it if, for instance, one of the tires on the Pugs was torn beyond any stitching, taping or booting repair. I wanted to know what it would be like if I mounted a locally available standard tire. The answer is that it would be entirely fine for continuing the tour to its end or getting to a place where a new tire could be sent (at, alas, likely great expense once a customs levy is assed and the DHL shipping is sorted, not to mention the cost of the tire itself). Or if one of the Pugsley wheels was damaged or bent beyond fixing. In that case, I see that the sensible course would be to acquire a rear wheel and a standard tire, rather than mounting the Endomorph/Larry on the narrow rim; the last setup makes me nervous. Obviously if it was the front wheel that was destroyed, I would put the intact rear one in front and the emergency replacement in back.
None of these solutions is ideal, nor would it ever make much sense to pursue them if one had access to fat bike parts. I never carry much by way of spares or elaborate repair equipment when I pedal far away places, but I do like to have a plan (and a backup one) in mind even for what are in my experience very unlikely mishaps. Now I do.