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Customizing a Fatbike

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Bruce Ingle photo
by
with comments by Crispin Miller, John Schubert, Mark Sevier, John Allen
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Introduction

My friend Bruce Ingle is an all-around cyclist, who commutes to work and runs errands by bicycle, and who also does long recreation and fitness rides, including randonneuring.

Bruce likes to customize bicycles for different kinds of riding. In 2014, he was thinking about a bicycle for Boston winters.

The photos below show the result -- a customized fatbike. The text which follows the pictures gives a running account taken from an e-mail correspondence with friends, of the challenge Bruce set for himself, the bicycle he bought, how he customized it, and how it was to ride.

This article may of interest if you would like to customize a fatbike, but also to get a look into customizing bicycles, in general.

In case you're wondering about those fenders: they're a do-it-yourself job. Fatbikes are designed for riding on the most challenging (read: soft, sandy wet, muddy, slushy, snowy) surfaces, but Bruce had to make his own fenders to keep sand, grime, mud, slush, road salt off himself and the machinery...go figure. The article will describe this customization, among others.

John Allen

fatboke-rear view Bruce on fatbike Fatbike-front view

Bruce describes the challenge

(August 12, 2014)

I've been following fatbikes as long as I've been commuting. I originally started commuting by bike in January `94 when the company I was working for discontinued its employee subsidy for not using on-site parking.  I had been spending the subsidy on a MBTA monthly pass since it could easily be reimbursed, but decided if it was on my own dime biking would be cheaper and more fun.  The snow was pretty deep that year and I've been looking for better human-powered mobility in it ever since.

Back then, Iditabike was run on bikes with 26" double-wide rims.  Several years ago, I made a double-wide wheelset by placing two 26" rims side-by-side and running spokes between opposite flanges and rims.  The rims twisted relative to each other when tensioning the spokes and they would separate from each other under significant inflation pressure, but it was enough to run some 2.5" tires I had at low pressure on snow.

Several years ago, I used the front wheel on my winter bike for the [Charles River Wheelmen, Boston, Massachusetts] New Year's Day ride; [Ride leader] Eric Ferioli and I were the only finishers of the ride that year.  Surprisingly, Eric was more mobile in certain conditions while riding 630-32 (27") smooth tires.

I have an MTB frame and parts for building up a dedicated fatbike for snow riding on my existing wheelset, but I'll basically be starting from scratch, the wheelset has the noted deficiencies and the tires aren't nearly as wide as those of true fatbikes currently on the market (26x4").  However, for as often as I'd ride in deep snow, the price is right.

I noticed a 26x4" fatbike in Walmart the other day and it got me looking into low-priced ones; all the Walmart fatbikes are Mongoose brand (Pacific). The one I looked at was a singlespeed with coaster brake for $200, which had some decent components like a 3-piece crank and alloy rims, but would be unacceptable to me for winter commuting because a 50 pound bike would need derailleur gearing to get up steep hills and accommodate variable depths of snow (and drag).  I use a fixed gear MTB for commuting in light snow and ice, but it's relatively light (25 lb) and has multiple ratios available.

http://www.walmart.com/ip/26-Mongoose-Beast-Men-s-Oversized-All-Terrain-Bike/22861845

The Mongoose Beast

There are some others...the Mongoose Dolomite is available for $250 with a 1x7 drivetrain, disc brakes and 26x4" wheels; the lowest-priced "real" bike I've seen, the Gravity Bullseye Monster, adds a double crank and some alloy parts for $500.

http://www.sears.com/mongoose-26inch-men-s-dolomite-bike/p-00670007000P

Mongoose Dolomite

http://www.bikesdirect.com/products/gravity/fat-bikes/fat-bikes-bullseye-monster.htm

Bulleeye monster unmodified

However, I was considering drive ratios this morning and figured the 26x4" size would be a real loser for drivetrain durability.  I've used a gearing range somewhere around 15-100" for riding in pavement to deep snow, and the needed range would probably be even lower with wider tires.  The larger tire diameter also requires a lower gear ratio, so I'd be looking at something like 17/36 chainrings with an 11-34 cassette.  With such small rings, the crankset would take some work to set up and the chain would be toast in less than 1000 miles.

I recalled a juvenile 20x4" fatbike from my travels and figured this would probably be a better way to go if I were to spend some money, since it solves a lot of problems:

http://www.walmart.com/ip/20-Mongoose-Boys-Massif-Black-Yellow/29741122

The Massif bicycle with 20"wheels

One other plus in this case is that it appears to use cable-actuated brakes, so I may be able to use drop levers.

Biggest drawback is the smooth tires, and I haven't seen others in the same size.  I'd probably add some sheet-metal screw studs to the front tire to make it more compatible with winter conditions -- I've done this before and it works fine, although I haven't tried it with smooth tires.  One other option may be seeing if a normal 20x2" knobby tire stays on the rim okay at low pressure, and using the widest available studded tire if it does

[Update as of March, 2016: At this point, inexpensive 20" fatbikes with knobby tires are available, e.g.,

http://www.kohls.com/product/prd-2308872/mongoose-20-in-fatbike-boys.jsp.]

mongoose boy's fatbike

I'd probably have to kludge a front derailleur to reach the chainline on the chainrings, but this appears to be a general problem on fatbikes anyway...the Gravity bike noted above uses only the inner two ring positions, presumably because the front derailleur can't reach the outside ring.  Best solution would probably be an oversized band-clamp front derailleur with a spacer block between the derailleur and seat tube.

Discs on a $200 bike may not be worth much, but probably better than a spoon brake.  ;-)

I already have plenty of other projects I've bought and haven't yet implemented, so I'm just thinking at this point.

John Schubert replied:

I also think the 20-inch bike is a non-starter.  You do not want slick tires; you'll need to cobble a giraffe seat post and handlebar stem, and you'll look dorky on it.  If you buy a bike, buy the one that's not a project.  The 20-inch one would be a project.

Ingle again:

I don't have problems with the other issues you've noted on the 20-inch bike, but you are right about the tires...I looked into tires and couldn't find anything wider than 2.35" with an appreciable tread, and Schwalbe 20" studded tires are only 42mm wide.  The only readily-available replacement tire that's close is a 4-1/4" slick for chopper bikes.  

I'm not keen on the potential fit issues of 26" oversized tires, so I guess I'll keep chipping away on the project I already have.
 
Personally, I've yet to find a bike that isn't a project or that I don't look dorky on.

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Bruce decides

January 30, 2015

[as the snowiest month in recent Boston history was about to set in]

I went for a 44 mile ride Sunday with some off-road riding in the fresh snow and decided wider tires than the 2" ones I was using would work a lot better...I was okay as long as I had some momentum and going straight, but as soon as I had to steer I'd bog down.
 
Last night, I put a wheel with a double rim and 2.5" tire on my cratemobile so I could ride to an appointment...going north from my house generally involves riding through mashed potatoes unless there's been a substantial time since the last storm.  Cushy and it sticks like a glue trap, but it has enough drag that the brakes that don't see much use.
 
I decided at that point I should go ahead and order a real fatbike rather than trying to dump time and money into trying to kludge something together from my existing equipment that wouldn't work as well.
 
I've heard that cheap disc brakes are nearly impossible to set up without drag.  Tektro brakes have always been a good value, so I expect their discs would work well.
  
Tuesday night, I put in an order for a Gravity Bullseye Monster with 20" frame in silver.  I went with the largest size with a reasonable effective top tube length and standover to minimize the need for headtube extensions and/or a riser stem, and I went with silver to match the reflective tape I normally use.
 
I expect 4" tires will offer less drag for the same pressure; we'll see.
 
I've been able to keep doing at least a mile a day on the road since October but haven't commuted to work at all this week.
 
I also started looking into 26x4" studded tires yesterday (and found them to be incredibly expensive) but remembered the zip tie trick this morning. Zip ties can be added around the tire and rim if more traction is needed, since they wouldn't interfere with disc brakes.

Crispin Miller

In light snow, fat knobbies may be useful, but I counted it a mistake one time in Allentown when we had a 6" snow and I decided to ride home on a fatbike from [a bicycle magazine's] current road-test stable.

Too much work to make a fat furrow in deep snow.  A 27x1" knifes through it and a fat tire doesn't.

There MIGHT be a crossover point so that 4" tires would offer enough flotation to begin to reduce the furrowing work -- I kinda doubt it since x-c skis have way more contact area (a contact patch 6' long) and still sink several inches.  Maybe 4"ers would float over slush, not in fresh snow I suspect.

Mark Sevier

I've seen fatbikes advertised here and there and never thought much about them (aside from: why?), but last weekend we went x-c skiing in Vermont and they had them for rent for use on the trails, so I figured I had to try one. The snow was good for skiing, and was OK on the level or downhill with the fatbike, but going uphill on the trails was somewhere between very difficult to impossible except where the snow was really hard-packed. Downhill was fun, though turning at speed was interesting / didn't instill confidence. As I thought more about it, fatbikes are a good idea for x-c ski / MTB areas in the northeast, since they can still be used on hardpack / marginal snow conditions / marginal MTB trail conditions which probably accounts for most of the year. I don't think I'd have a use for a fatbike (my MTB has gone unused for many years, and I've become a winter cycling wimp), but the Gravity bike option seems like a great deal - hope you enjoy it!

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Customization

February 9, 2015 -- fenders

I fabricated and mounted some [Coroplast] retroreflective fenders for the Monster last night.  [What is Coroplast? See Kent Peterson's article.] The rear fender line is a bit high in the middle because it only has a couple of horizontal stays, but it should be okay once I've installed a rack.

The frame has seatstay mounting points for a rack, but the only racks I have which would fit around a 4" tire are Pletschers.  I'll probably fabricate a custom mount from some steel strip.

[Update, March 2016: a rack was never installed.]

I went out for 6.5 miles very early this morning on local residential streets, modifying my route as needed to stay well clear of plows.  Most streets only had an inch or two, and where they had more I had enough traction to stay in any recently-made tire tracks.

When I got to the end of my street, the plow had left a foot-tall mound at the end, so I got a running start and dove in.  To my surprise, the front wheel floated over; the rear plowed through.  Tires were at 3.5/5.1 PSI.

The rear tire was low enough that the sidewalls would wrinkle while cruising, so I put a bit more in after the ride.  I noticed a small notation on the tire reading "inflate to 22 PSI" at that point.  I've never had them that high.

I was out about an hour, and my top speed was around 12 MPH -- the brakes didn't get used much.  Probably not much faster than a decent runner in the snow on average, but I enjoy cycling more.

A 4.7" Snowshoe XL tire on the front would probably work slightly better and it would fit, but I'll probably wait until I've worn out a tire first.

February 11 -- mudflaps

I found this morning I'll need to add mudflaps to the fenders I've installed on the Monster...the bottom bracket still gets covered with slush, and the trailer would as well.

At this point, my utility riding is more limited by etiquette and/or inferiority complex than weather and/or road conditions.  I can pretty much ride in anything and do in the early morning, but I don't want to wind up on a narrowed two-lane road with heavy traffic in both directions and a line of fuming drivers or a plow behind me.

I used the Monster to get to an appointment on Thursday and for shopping on Saturday, but between the road conditions it's best used for and the bike's (lack of) speed, I can't see using it for commuting to work at this point.  I'll probably wait until the local roads are down to pavement so I can commute on a bike with 2" wide tires.

I measured the Monster's rim width and some 2" tires last night; widths were roughly identical, so the rims could accept the tires if I wanted...but the BB would be lower by 2", so the risk of pedal strike with the wide tread would be pretty high.  I'd almost certainly be able to park the bike by putting a pedal down on a flat surface.

February 15 -- trying a narrower rear tire; wheel-truing

I put a 2.2" tire on the rear Friday for grocery shopping Saturday.  All it did was decrease traction without improving speed, so I put the 4" tire back on. I probably could've just used my normal shopping bike this week, but it's done.

While the rear wheel was off, I checked the tension, evened it out and put on an extra turn all around; the factory build was pretty lousy.  I also replaced the wheel reflector with some reflective tape on the rim (wrapped around the edges, since there's no rim brake).

The 170mm overlocknut distance is more than my Park TS-2 [truing stand] can handle (never mind 190mm on some fat bikes), so I wound up truing on the bike.

March 2: customizing handlebars and controls

I installed Sakae drop bars, Barcons, Tektro V-levers, QBP riser stem, Shimano XT rear derailer, cables and housing.  I was short a couple hours' of sleep last night getting it finished for this morning but got everything done.

I rode it in the freshly-plowed snow this morning.  The local Department of Public Works widened the local roads last week but left a couple of inches of ice where the snow had been.  The tires were sliding off the parallel ice ridge at the edge of the road until I lowered the tire pressure, but the controls worked fine and my hands were much more comfortable.

The fatbike still needs a gear chart, cyclometer and a couple more rear fender stays, but those should be relatively minor.

 I've installed mudflaps on both fenders -- front to keep the snow off the bottom bracket, rear to keep it off the trailer.

Bruce's fatbike

The fully-customized Bullseye Monster fatbike

and for comparison, the Bullseye Monster unmodified

 Bullseye Monster unmodified

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Cyclecomputer; tire widths

April 9

Cyclecomputer and gear shartI pulled the [trailer] hitch from the Monster this weekend to use it on a fair-weather beater, so I took the time to install a speedometer, true up the discs and install reflective tape on the front wheel as well.

I just used a cheap computer I'd effectively gotten for free, so it was pretty maddening to set up.  I wound up scrapping a 2GB hard drive for some more magnets and swapping out the wiring harness.  Fortunately, the supplied magnet was relatively long to help with the gap between spokes and fork.

I measured the rollout [to set the cyclecomputer] at 10 PSI at 225 cm and went for a test ride to check it against GPS.  The GPS read 1.51 miles for 1.49 miles on the computer; I corrected it to 228 cm.

I measured the Monster's rim width and some 2" tires; widths were roughly identical, so the rims could accept the tires if I wanted...but the BB would be lower by 2", so the risk of pedal strike with the wide tread would be pretty high.  I'd almost certainly be able park the bike by putting a pedal down on a flat surface.

I need to concentrate more making the corrections for future battles than past ones...my distance bikes need work as well.

Additional comments, March 2016

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Last Updated: by John Allen