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Fat Bike FAQ's

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bighit

Discussion Starter · Mar 10, 2009 (Edited by Moderator)

This thread is to address the most frequently asked questions fat bike riders get. I am no expert, but some here are and are welcome to add questions and answers.

The first comment I get all the time is, what size are the tires.

They are 26x3.7 inches wide and weigh about 1200 grams. they are made by a company called surly. http://www.surlybikes.com/
You use a tube in them and run about 5-10psi depending on the terrain.

There are some other tires available in the 26x3 inch size. they are Nokian and Arrow.
They are more of a downhill tire than a snow tire. They are often used because they fit more frames and forks.
These tires usually weigh about 1600 grams. Arrow still makes them and they are called the savage http://www.arrowracing.com/home.html
The nokians will be hard to find, because they dont make them in the 3in size anymore.

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MendonCycleSmith

· #2 · Mar 10, 2009

Tires, does Nokian still do them? The Arrows are 15lb for the pair (seriously), so bring your quads for those!

Tire pressure?
They run really low, like, 5 PSI low. More than 30 and they get scary :eekster:

"What's the bike for???"
Sand, snow, anything else you feel like riding, and making you smile from the first pedal stroke

"Are those motorcycle tires?"
No.

"Is everything special for them?"
Frame, fork, bottom bracket, tires tubes, and the need for two rear, specific rimmed Pug wheels.

All I can think of at the moment, sure others will percolate up through the fog...

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Wildfire

· #3 · Mar 10, 2009 (Edited)

Soft condition riding

I get this one a lot:

"I want to ride on really loose sand and snow, how do they work?"

Despite their ability to take you places no other bike can go, Fat Bikes do have their limitations. Even with the 3.7" tires and 65, 80, and now 100mm rims, you will probably find that they can bog down in really loose conditions like unconsolidated beach and dune sand, powder and loose granular snow, shale, and pea gravel.

Often you will be able to ride downhill and maybe even on the level in these types of conditions but climbing won't work at all and steering can get very sketchy. You can decrease tire pressure to increase the footprint of the tires and increase flotation and performance but be aware that no tire can hold up to prolonged riding at very low air pressures and I've seen a lot of failed sidewalls and delaminated tire beads from doing just that.

Oftentimes, it's possible to find an alternate line or route to hunt out those little pockets of firmer goodness and be able to ride without slowly destroying your tires. On beaches, the sand is firmer where it's still holding some moisture such as near the tide line. On snowmobile trails, the trail is loosest where the machine's track has rototilled the snow but it's often good riding if you can stay on the ski track, the proverbial "thin white line". A wonderful feature of snow is it's property of sintering, or packing down and becoming firmer after it's been disturbed so if you wait a little while after traffic, it usually gets firmer and much more ridable. Likewise, drifted snow can firm up into white slickrock dunes which make for incredible riding. If you're riding in a group, switching trail breaking duties will spread the burden out among your companions.

An ironic thing, when I first started building FatBikes, I kind of intended them as a great equalizer for bigger, heavier riders because light people floated sooo much better on the SnowCat rims which were the current state of the art. And it worked great for a while but then smaller people started getting their hands on FatBikes and now guess what, we're right back to square one. In retrospect, I should have lobbied hard to enact laws to prevent this travesty. So yeah, being lighter is often a big advantage but then there are times that being heavier helps keep you from wallowing around as much as the lighter folks.

Being able to adapt to challenging conditions is an innate part of the sport (can I call it a sport?) of Fat Biking. As you gain experience, you'll get much better at putting together micro lines to come up with a ridable route through seemingly impossible conditions and become adept at subtle weight shifts from front to rear to avoid bogging down.

When worse comes to worse, just strap a wheel to each foot, and voila, snowshoes.

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Wildfire

· #4 · Mar 11, 2009

5

All time most asked Fat Bike question:

"How come you don't put studs on those big tires for winter riding?"

Contrary to popular opinion, most snow trails have pretty good traction because the big tires put a lot of surface area in contact with the snow. And even a lot of ice has decent traction, especially if it's flat and smooth, below freezing out, and/or there's a little windblown dust on it. You just have to ride smoothly over the ice stretches and not try any abrubt maneuvers.

Most winter XC riding, at least around here in Alaska, is mostly on packed snow with short stretches of overflow or wind scoured ice. Adding studs increases rolling resisance drastically, so most riders opt to not use the studs and just be careful when crossing the occasional ice patches.

There are times, though, when studded tires are life savers: rough, uneven ice, commuting, very slick ice with water on top of it, etc. I've had really good success using the 26 X 2.25" Nokian Fredie's Revenz tires on Large Marge rims. They are slow and sound like a freight train when you're riding, but traction is great, and they're big enough to offer good rim protection when hitting rocks or logs. Or if you have a spare set of 29er wheels for your Fat Bike, Nokian now has a decent 29er studded tire on the market. There's nothing like bombing down frozen class IV whitewater rivers or highmarking on icebergs which would be almost suicidal without studded tires. Just be careful, even studded tires have their limits.

Here's some photos from the Knik Glacier. Everyone had FatBikes with studded tires.

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GrumpyOne

· #5 · Mar 12, 2009

Per bighit's request...

Fat Fork info:

The Pugsley 100mm hub fork is 447mm AtoC.
The Jones 135mm hub fork is 435mm AtoC with 55mm of rake. (Not good for suspension corrected 29er retrofits.)
The Vicious Snow fork is 450mm and they can't/won't do longer do to blade availability. (I talked to Carl at NAHBS about it.)
DeSalvo makes his snow fork at 460mm. Which is the longest "production" fork I could find. He also is limited by available blade length due to the Uni-Crown construction.
If you need a longer fork for a 29er retrofit, I think Walt can make custom lengths using his segmented fork construction. But of course it's custom ($'s) and he has a back log.

There may be other builders who can make "Fat" forks. But these are the ones I've looked into and have done Fat forks before.

jw

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Wildfire

· #6 · Mar 12, 2009

Addendum

GrumpyOne said:
Per bighit's request...

Fat Fork info:

The Pugsley 100mm hub fork is 447mm AtoC.

The Jones 135mm hub fork is 435mm AtoC with 55mm of rake. (Not good for suspension corrected 29er retrofits.)

The Vicious Snow fork is 450mm and they can't/won't do longer do to blade availability. (I talked to Carl at NAHBS about it.)

DeSalvo makes his snow fork at 460mm. Which is the longest "production" fork I could find. He also is limited by available blade length due to the Uni-Crown construction.

If you need a longer fork for a 29er retrofit, I think Walt can make custom lengths using his segmented fork construction. But of course it's custom ($'s) and he has a back log.

There may be other builders who can make "Fat" forks. But these are the ones I've looked into and have done Fat forks before.

jw

The Wildfire FatFork is 465mm A - C without having to use a blade stretcher.

fastale

· #7 · Mar 12, 2009

I'll add a question that has been on my mind, why no competition for the Endomorph? Considering the amount of bikes being built up around this tire/platform, some other tire companies must be trying to develop something, right?

Wildfire

· #8 · Mar 12, 2009

Rear triangle offset explained

I'll try to tackle this one since somebody asked it on another thread:

"What's the deal with the offset rear stays on some Fat Bikes?"

Here's how the offset came about:

-The tires and rims are much wider then a standard mountain bike. This required the use of a wider chainline so the chain wouldn't rub on the big tire and wear out the sidewall.

-In order to get the wider chainline, it was necessarry to build the frame with a wider bottom bracket shell for use with a wider bottom bracket spindle. At the time, most MTBs used a 68 or 73 mm shell with a 113mm spindle. That wasn't wide enough to clear the tire so we had to use wider bottom brackets. After a couple generations to accomodate increasingly wider rims and tires, we ended up with a 100 mm shell and a 145 mm bottom bracket spindle. So that solved that problem but led to:

-Okay, the front problem was solved but led to a dilemna on the other end of the drive train: how to carry the new wider chainline back to the rear hub? At the time, there were very few wider then normal hubs available so we had to figure out a way to move the cassette out further from the bike's centerline to match the wider front chainrings using the available 135mm wide hubs. We decided to create a "virtual wide hub" by offsetting the rear triangle 18 mm out toward the drive side which brought the cassette out in line with the front chainrings. So that problem was solved but led to:

-Now that we offset the rear stays, how do we bring the rim and tire back in line with the bike's centerline? If you were to take a standard rear mountain bike wheel and stick it in the dropouts, it would not line up with the centerline of the frame, it would be way out of line toward the drive side. That led to drilling offset spoke holes toward the drive side of the rear rim to bring the centerline of the rim and tire back into alignment with the frame's centerline. This allowed the use of equal length spokes on each side for a nice strong wheel build. Problem solved, or was it?

-Somewhere along the line, the 29er market started taking off and I realized that the FatBike geometry was almost identical to the 29er geometry. Why not build a spare set of 29er wheels to make the FatBike a versatile, year-round machine? Unfortunately, the 29er rims are skinny and do not allow much of an offset spoke drilling. I had fairly good luck using a Bontrager offset rim, but the offset spoke drilling was only a couple mms so in order to make everything line up, I had to use much shorter (3 mm) spokes on the non-drive side of the rear wheel to get everything to line up. Not ideal: the spoke tension was very tight on the nondrive side and very loose on the drive side. Some hubs had wider flange spacing and I was able to get them to work. I've been riding the same rear wheel for years with no problems, but again, it's not ideal. Which led to:

-Ditching the rear offset and using wider hubs which have recently come on the market. With a 160 mm hub everything works out nicely for chainline. Yes, they are a little heavier though the Chris King is lighter then many top 135mm hubs. And for sure, they are more expensive then most 135mm hubs but look at it this way: it allows your FatBike to be used rear round so think of how much money you'll save by not having to have two different bikes. That's why I've kept the 465mm axle to crown length on the rigid fork allowing a summer swapout to a 29er suspension fork. Losing the rear offset has the added benefit of making the framebuilder's job a lot easier: much less chainstay and seatstay bending. And of course, summer 29er wheels build up nice and strong.

So anyway, if all of the above didn't give you a massive headache to try to comprehend, that is the deal with the rear offset stays.:idea:

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Reactions: 1

coach#1

· #9 · Mar 12, 2009

Thank you for the explanation - you cleared that up nicely.

Love the look of your bikes BTW. The John Deer was my favorite.

Coach

D.F.L.

· #10 · Mar 13, 2009

What about adding images of all available snow rims with Pugsley and Arrow tires mounted on each? I think people would benefit from seeing what sort of tire profile they'll get before purchasing.

I'm crushed about no more Gazz 3.0s. I needed those.

Wildfire

· #11 · Mar 18, 2009

Rolling Resistance Q

If I had a dollar for every time I heard this one...

"With all that rotating weight, aren't fat bikes hard to pedal?"

I think this has been my biggest hurdle to get people to buy FatBikes. I encountered a ton of skepticism and naysayers when the FatBikes came out and a lot of those were very experienced winter cyclists. Even with people now routinely winning just about every winter race out there with various brands of fat bikes, I still encounter this a lot.

While it's doubtful that you will see Lance riding one in the Tour de France the things roll pretty darn good on softer surfaces. And surprisingly well on hard surfaces too (but I still swap out with 29er wheels in the summer).

First of all, the Endomorph tread is just a bigger version of a semi-slick. Back in the Nokian Gazzaloddi/Remolino 80 mm rim days, we used to spend a lot of time shaving knobs off our treads to get them to roll faster. No need for that with the Endo.

Second, rolling resistance of a bike goes up drastically when the tires are making ruts in soft stuff because the wheels are always trying to climb up out of their own tracks. The big tires make a lot shallower rut so rolling resistance is a lot less on fat tires then skinny tires. Also the big wheels track better with a lot less wallowing around in soft conditions which saves a lot of wasted energy.

There are probably other theories out there why they roll so well so techy types, feel free to chime in if you have one.

So roll on, fat bikes, roll on.:thumbsup:

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fastale

· #12 · Mar 19, 2009

fastale said:
I'll add a question that has been on my mind, why no competition for the Endomorph? Considering the amount of bikes being built up around this tire/platform, some other tire companies must be trying to develop something, right?

I'm going to bump my question because I think it's a good one.

bighit

Discussion Starter · #13 · Mar 19, 2009

fastale said:
I'm going to bump my question because I think it's a good one.

i wish there were more options. i think its because there is a small market right now.

Wildfire

· #14 · Mar 19, 2009

bighit said:
i wish there were more options. i think its because there is a small market right now.

I'm hoping there will be some more options. I've heard a couple rumors but so far nothing else comparable has appeared on the market. It's probably just a matter of time until other manufacturers respond to the growing market.

bighit

Discussion Starter · #15 · Mar 20, 2009

100mm bottom brackets

the pugsley takes a 100mm bottom bracket. the only ones i know of are,
FSA Platinum DH isis
Truvativ Gigapipe DH isis

the next question is, can you use any of the new external bottom brackets and cranks. they all list the bb shell as 68/73.

you would need a longer axle on the cranks right?

caminoloco

· #16 · Mar 21, 2009

Wildfire said:
First of all, the Endomorph tread is just a bigger version of a semi-slick. Back in the Nokian Gazzaloddi/Remolino 80 mm rim days, we used to spend a lot of time shaving knobs off our treads to get them to roll faster. No need for that with the Endo.

Second, rolling resistance of a bike goes up drastically when the tires are making ruts in soft stuff because the wheels are always trying to climb up out of their own tracks. The big tires make a lot shallower rut so rolling resistance is a lot less on fat tires then skinny tires. Also the big wheels track better with a lot less wallowing around in soft conditions which saves a lot of wasted energy.

There are probably other theories out there why they roll so well so techy types, feel free to chime in if you have one.

So roll on, fat bikes, roll on.:thumbsup:

A few years ago in Germany (where else...) some major bike mags decided to get to the bottom of rolling resistance once and for all. They kitted out several bikes with more wires than a spiderweb and went for it. I'm not going to translate all those articles (it's not my mother tongue for starters) and computer read-outs, but here's the gist:

- it's not because it's got big, fat knobs that it rolls slower. Actually, some pretty agressive treads outperformed all semislicks on the market. Construction of the carcass is crucial to rolling resistance.

- adding a tube increases rolling resistance x-fold. Friction between the tube and tire is responsible for that. Tubeless is the way to go.

- the lower the tire pressure/wider the tire, the less rolling resistance on uneven terrain. Two reasons for that.
First: a skinny, hard inflated tire presents a long, narrow footprint. A fat, underinflated tire presents a short, wide footprint. The latter has the least rolling resistance (don't ask me why, it's physics).
Second: every pebble wants to stop a tire. A hard tire bounces over it, resulting in an upward movement and deceleration. A soft tire deforms and rolls over it without vertical movement, which results in less rolling resistance.

- a heavier wheel takes more watt to accelerate, but once going pays dividends when the going gets rough. I forgot and am too lame to go look for the actual figures but I think it took like 5 extra watts to accelerate a heavy wheel vs a light one to 15 mph.
But it took 20 watts extra per 200 yards to maintain that light wheel at that speed over rough stuff vs the heavier one.

That pretty much sums up what we've all felt: a soft, fat tire is a drag on pavement but seems to accelerate when the going gets rough.
Vs a skinny tire at mega psi: great when smooth, but hits a wall when hitting rough spots.

And explains why our very fat tired bikes are faster on rough terrain than they appear at first sight.

Another reason why fat bikes are so good on rough stuff is the rotational force. If you want to experience it, grab a spinning wheel by both hub ends and try to turn it. It's difficult and it's a main reason why we stay upright on a two-wheeled contraption.
A heavy wheel generates more force than a light one and very much wants to keep in the same plane when spinning. Slippery roots or rock gardens don't impress heavy wheels as much as lighter ones.

So don't follow skinny tired folk on their terrain... try to lure them onto yours

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MendonCycleSmith

· #17 · Mar 21, 2009

bighit said:
the pugsley takes a 100mm bottom bracket. the only ones i know of are,
FSA Platinum DH isis
Truvativ Gigapipe DH isis

the next question is, can you use any of the new external bottom brackets and cranks. they all list the bb shell as 68/73.

you would need a longer axle on the cranks right?

It's beyond just ISIS at this point. I just ordered a Race Face Atlas FR with a 100 mm spindle for mine. How could I not? It's available in purple now....

The Surly Mr. Whirly is available in a 100mm option too. So yep, the external bearing BB's are a workable option too.

HardyWeinberg

· #18 · Mar 21, 2009

Phil Wood 100mm BB too, square taper

Wildfire

· #19 · Mar 21, 2009

What he said.

Great explanation which runs contrary to a lot of conventional wisdom.

"

caminoloco said:
A few years ago in Germany (where else...) some major bike mags decided to get to the bottom of rolling resistance once and for all. They kitted out several bikes with more wires than a spiderweb and went for it. I'm not going to translate all those articles (it's not my mother tongue for starters) and computer read-outs, but here's the gist:

- it's not because it's got big, fat knobs that it rolls slower. Actually, some pretty agressive treads outperformed all semislicks on the market. Construction of the carcass is crucial to rolling resistance."

Not quite convinced on this point, shaving all the knobs except the outer row on the old Nokian Gazzaloddi 3.0 tires made them noticeably faster. I agree that supple sidewalls make tires faster on soft and uneven surfaces.

"- adding a tube increases rolling resistance x-fold. Friction between the tube and tire is responsible for that. Tubeless is the way to go."

So far all the attempts I've heard about to make a winter tubeless setup for the big tires and rims at low air pressures in the cold have failed. If somebody could figure that one out it would be a big breakthrough.

"- the lower the tire pressure/wider the tire, the less rolling resistance on uneven terrain. Two reasons for that.
First: a skinny, hard inflated tire presents a long, narrow footprint. A fat, underinflated tire presents a short, wide footprint. The latter has the least rolling resistance (don't ask me why, it's physics)."

I think it has to do with how far the tire is sinking into the snow. Short and wide could be compared to a rolling pin on dough, long and skinny is more like a pizza cutter.

"Second: every pebble wants to stop a tire. A hard tire bounces over it, resulting in an upward movement and deceleration. A soft tire deforms and rolls over it without vertical movement, which results in less rolling resistance".

Amen.

"- a heavier wheel takes more watt to accelerate, but once going pays dividends when the going gets rough. I forgot and am too lame to go look for the actual figures but I think it took like 5 extra watts to accelerate a heavy wheel vs a light one to 15 mph.
But it took 20 watts extra per 200 yards to maintain that light wheel at that speed over rough stuff vs the heavier one."

That's interesting.

"That pretty much sums up what we've all felt: a soft, fat tire is a drag on pavement but seems to accelerate when the going gets rough.
Vs a skinny tire at mega psi: great when smooth, but hits a wall when hitting rough spots.

And explains why our very fat tired bikes are faster on rough terrain than they appear at first sight.

Another reason why fat bikes are so good on rough stuff is the rotational force. If you want to experience it, grab a spinning wheel by both hub ends and try to turn it. It's difficult and it's a main reason why we stay upright on a two-wheeled contraption.
A heavy wheel generates more force than a light one and very much wants to keep in the same plane when spinning. Slippery roots or rock gardens don't impress heavy wheels as much as lighter ones.

So don't follow skinny tired folk on their terrain... try to lure them onto yours

"

Thanks.

Stroganof

· #20 · Sep 17, 2009

Where?

MendonCycleSmith said:
It's beyond just ISIS at this point. I just ordered a Race Face Atlas FR with a 100 mm spindle for mine. How could I not? It's available in purple now....

Where does one order the 100mm Atlas? thx.

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