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New School Fatties (B Fat minus)

4K views 43 replies 16 participants last post by  nitrousjunky 
#1 ·
Let me first preface. This has worked for me, and my personal riding where I live in Vermont. This is my experience.

I have fully embraced the 27.5 fat. But took it to another level by mounting my 4.0s on 40mm rims. Why 40mm? Because I had them laying around after a rebuild with my Hightower to 29er wheels. So my buddy and I relaced my fat i9 hubs to my summer 27.5 x 40mm hoops.

Why did I do this? Because in Vermont we have tremendous winter trail usage, and most-importantly dedicated individuals who groom our summer singletrack. Those heroes get their SnowDogs, Rokons, and snowshoes into tight twisty single-track.

More networks around here are grooming in some aspect. Long gone are the days of bushwacking fresh deep powder, or sloppy slush. Thank god, because powering through that stuff in a granny gear kinda sucked. Every week more trails open with a firm hard base. That we can ride fast. Dare I say we could eve ride our skinny tire bikes on some of our networks.

Our networks seem to becoming less about float. Granted you still need some float so we don't bust through the hardpack, but 5 inch tires on 80-100mm rims seem unnecessary with our networks. Like I said, our days of bushwacking new singletrack appears to be slowing thanks for numerous trail networks grooming the summer trails.

Also Vermont winters the last few years have been spotty. We can get a foot of snow, pack the trails in, then get a heat wave for a week, then when the temps drops again, we have bare ground, ice, and hardpack (mixed conditions). Mixed is actually my favorite terrain.

How does the 4.0s on 40mm ride? The answer is awesome. They are super moto with a great round profile. They are damn light and spin up incredibly fast for our conditions. I have ridden: primo groomed, loose flour-type of dust, 3 inches of powder ontop of crust, crust, textured ice, and boot packed (the loosest of the bunch). The B Fat Minus did fine.

Definitely have to keep more air pressure in tires to keep from being wobbly on the rim (found that out first ride, my pressure was too low), however a shot of air and it made all the difference. Its finding the right balance for my weight and conditions (just like with fatter tires on beefier rims) just my margin of PSI is smaller.

Like I said, this is just my experience. If you are overnighting in the middle of nowhere where you are blazing your own path this is not a good set-up.

If you spend 95% of your time riding packed trails this set up works. New School Fat.

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Branch Winter Freezing Snow Sunlight
 
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#2 ·
So this is the opposite end of the skinny tires on wide rim thread spectrum. Sure, both will hold air and roll. One thing that going outside of the intended rim width does is change the profile and thus the location of the knobs. I would expect one to really have to lean a 4" tire over to get the edge knobs to engage when mounted on a 40mm rim.

For me this would be an "in a pinch you can..." solution. I don't see any benefits over more traditional tire/rim width ratios.
 
#3 ·
Yes, it does indeed change the profile for sure, no question (see pics). I have ridden every single day since I received my tires from Mikesee Friday morning. Up in the North Eastern part of the state for Winterbike on a 5.5 hour ride (higher elevation, fluffier flour snow) to my local trails today (textured ice, very hardpack) and a few other rides in-between. I really wanted to have some good saddle time in in several instances / conditions before I posted this. Yes, it was a pinch because I had the rims, and ability to rebuild.

I haven't noticed a lack of traction cornering from my Wrathchild on 80mm. The biggest adjustment was the higher BB and had to readjust my body english which took a couple rides to figure out. Today's ride was very fast with perfect traction.

My benefit with this combo is an extremely spritely fatbike. Instead of pushing loads of rotational weight around for our hardpack trail conditions.

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#8 ·
So this is Duroc 40 rims?

I've spent quite a bit of time on 27.5x3.8 on i45mm rims myself and it's a blast. I've wondered what the tires would look like on a true i40mm rim...
 
#9 ·
I guess this works fine, but certainly not ideal. You already had the rims, so no harm in giving this a go, but If starting from scratch, I think it makes sense to go wider. It's really condition dependent if this setup will provide enough float, but considering the weather in the Northeast these past years, if you can't ride today, tomorrow will bring something completely different!

When I built up a B fat setup I went pretty wide to give myself as much 'float' as possible, seeing as this is the biggest I can go on my current bike. I went with a set of 65mm Nextie carbons, which weigh 580g each according to Nextie. Running Hodags right now which work well for my limited winter riding, but I'm thinking about some Van Helgas for extra bite and size. Hopefully they fit!
 
#10 ·
I have had real struggles with this size. I built up a set of hugo's with hodags last spring. They are light and fast, but at 225 lbs I had a real hard time achiving the benefits of fat cush without dingin my rims all the time while riding dirt (or poking holes in the hodags). The volume sweet spot was very hard to obtain. I am running on a wozo with magnum fork.

Now that we have had a good winter in Colorado - I really have missed having a true fat bike. I just started building up a set of 27.5 mulefuts 80s to hopefully get back to a fat bike like ride and increase the range of the sweet spot I have had a hard time with. I have not been able to ride soft snow as well as my buddy who runs nates - even to the point of failure with the hodag on hugo where I had to turn around while nates kept chugging.

Conditions on the Front Range are similar to what you describe. My local trail gets massive amount of foot traffic within 24-48 hours after a storm - especially right before a a weekend. But the frequency of snow this year has lead to many packed-powder and loose snow conditions (not necessarly plowing fresh tracks) and the hodags have met their match. I just moved to vanhelga in the rear and it is great and kept me going, but not a great fit on the hugo - thus the mulefuts.
 
#11 ·
I have had real struggles with this size.
Honestly, it sounds like you had issues because you hadn't properly managed expectations.

It also sounds like you're on your way to solving that with the new setup.

I wasn't aware that Hugo's still existed. Perhaps the most underwhelming rim of the last decade.
 
#14 ·
This is where im at but i do find the icy boot pack mtb trails need grip for hard corners and steep hills and my 4.5 gnarwhals provide dirt like grip.

Would 3.8” gnarwhals and 50-65mm wheels provide enough? Possibly but i dont currently have the funds to find out.

Im trying to price out a second wheel set. In canada we get so ****ed over right now i can get light bicycle or nextie wheels made for as much a durocs or hugos from the states.

So then do i get a light carbon set for my gnarwhals? Or do i get 40-50mm rims for my 3.8 minions?

Decisions....




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#15 ·
Just finished another rip tonight. Set-up is solid for me, personally.

Again, this is on Vermont's singletrack that get heavily groomed (and we have a robust fatbike community that ride daily). We are not riding slop or deep snow. We are riding hard, firm singletrack. Even many A-Lines from summer. Float isn't a main concern.

Like I said, possibly a New School Fat because more and more trails are setting-up better with better maintenance. Lots of support here in VT.
 
#16 ·
I think a setup like OP suggested would work very well for Anchorage riding and the similar conditions to Vermont (albeit longer winters). I'm riding 26" D4s on 80mm wheels. This is more than enough for riding in/around Anchorage, even though many people say it's not really riding fat. I get plenty of drag and balloon effect with this set up that I sometimes wish for something a bit narrower. The larger contact patch of 27.5 would also help. It would be nice to have both the Fat Bike, and a B Fat Minus bike...n+1, I guess.
 
#18 ·
I also ride in Anchorage. I only have 26ers but I have used a couple of 40 ish mm wheel sets over the years with various tires. They work fine in summer and OK in winter except where they don't. Even hard packed trails have soft spots and skinny trails have soft edges. My experience was the narrower set up would find those soft spots where 80 mm rims or even 65's pretty much just rolled on by.
 
#23 ·
Your contact patch is directly correlated to your pressure, not your tire size. If you're running the same pressure, your contact patch will have the same area. It will be a different shape depending on width and diameter. Of course different sizes allow you to run different pressures. It's very condition dependent, but the different shapes of the contact patch between 26 and 27.5 will result in different performance for the same contact patch area.
 
#31 ·
This is the conversation I wanted to start having. Thank you everyone!

Back in the day some dudes form New Hampshire figured out a Boost Fox 34 can fit 4 inch tires on 65mm rims. No one told them it was okay. They just did it, And it works. Thanks to those cool dudes!

Back when I raced RC cars, guys used to think they needed the biggest engine, and gear their buggy for 60mph, but there was no where on our racetrack you get up to that speed.. Maybe 30mph tops. It was just a "dick contest" bigger and faster... but didn't benefit them on raceday. Same in our area with our trails... We don't need huge rotational rubber on wide-ass rims anymore. It's less efficient. But some people still claim they want the fattest tire... because they can. No one is wrong here, at least we are riding bikes in woods in the winter. I just wanted to ride a little more spritely.

Its okay to experiment beyond what the industry tells you is acceptable.
 
#32 ·
Best part of ditching my gnars and going to D4s Is riding faster! Heavy 4.5s were just slowing be down and for me going slow just isn't fun! I was over my tires braking in the straights and slowing me down. The D4s allow me to pump and hold speed in all the flow sections vs constantly peddally just to keep moving. If you're 250+ you may obviously want more tire but I think 90% of people out there dont need the width/float it just slows them down.

I'm 165-170 and the D4s are perfect. I've tried barbs gnars beists and wrathchilds to compare.

Agreed I'm just happy to be out in the woods riding bikes with my friends!
 
#33 ·
Agree, good discussion. If all you're riding is groomed snow that's set up really solid, your setup will work great and be fun and fast, as you've found out. But what happens on those days when the snow isn't setup perfectly? Then your skinny setup will punch through and leave ruts in the trail, or you'll be walking. The wider setup will be slower when the conditions are perfect, but will be MUCH faster when they aren't.

It's all a trade-off obviously, and I'm not at all saying your setup is wrong. Just different priorities I guess. I'd rather ride more, even if it's slower sometimes, than ride faster when it's perfect and not ride at all when it's not.

All that said, I currently don't have a dedicated fatbike, just can't justify the cost for the limited winter riding I do. But, when I had my trail hardtail designed, I gave it room for 27.5x4.0 tires for the winter. Currently running 27.5 Hodag on 65mm rims, although I just ordered a set of 27.5 Vanhelga tires to try to get a bit more traction and float. Hoping it fits in the back! The Hodag is a great tire, but gets overwhelmed pretty easily when the snow's not perfect.
 
#34 ·
My set up is about the same width as my friend's Husker Du's on Marge Lites (65mm). Its not "that skinny" of a set-up... My friend who weighs 280 on Bud and Lous will punch through as well...

Its all relative. Lots of factors. Different for everyone. Experiment, ride, tweak, ride, tweak again, ride, type on forums... ha.
 
#35 ·
This weekend couldn't have been better for testing.

Yesterday was low 30s bright sun and zero ice on some of our premier Snow dogged groomed signgletrack.

Conditions were hard pack. Never lost side grip on any of the corners (and I pushed it beyond my comfort).

Today Colder, with a small snow squall in morning. We rode a non-groomed old school trail that was only boot packed (no snowshoes, just a ton of dog-walkers from the neighborhood on our summer trail.

Conditions were mostly firm, very lumpy, lots of textured ice, few sections of windblown snowdrifts, and a downhill ledge section that we blazed first tracks. Trail is punchy and tight.

Both days were very different in trail set-up, and my B Fat Minus ruled in every situation. I wanted to ride today's un-manicured conditions to see if I made a terrible mistake as I knew today's trails are very different then what we normally ride the last couple of years. Today's trails get very little love - which is good.

The larger diameter, and lighter wheeleset, made getting up and through nasty trail conditions a breeze. With momentum on your side, I could kinda skim over and through chunky loose sections.

So far I have ridden 7 out of the last 9 days with this new set-up, and still waiting to find a negative. I have only experienced a ton of benefits.

Also side note: I really didn't expect the Lightly Studded Cake Eaters to grip as well as my previous Wrathchild / Dillinger set up, but I have managed to be pleasantly surprised with these as well. No bails yet, and today had nasty off camber river sections.

Old car in the middle of the woods. Mobbs Americana trail.

Bicycle tire Tire Bicycle frame Wheel Bicycle wheel
 
#36 ·
Road 27.5x3.8 minions and im over 200 lbs and man i didnt feel confident on them on very boot packed snow.

Had them at 5/6 psi at -10c and had a bit of self steer. Got down to -15 later and finally felt i could push them in the corners. Lost maybe 1/2 a psi?

Got these for summer anyways so i dont really care.

4.5 Gnarwhals for the conditions i would have ran 7/8 and they would have had gobs of traction turning and climbing. I dont find these slow on packed snow at all. Did a couple laps at our one double track with both tires. Was only 15 seconds faster over 5 minutes on minions over gnarwhals. Was just getting sick at the time with the gnarwhals too.

Still would love to try 3.8” gnarwhals, i believe they would grip the same as with 6/7-7/8 psi not much of the 4.5” tire is on the snow anyways.
 
#39 ·
How does the B Fat Minus perform on dry, summer trails? I have 29+ and B Fats on 80mm that I ride in the summer. The 29+ sometimes leaves a bit to be desired and the Fat often feels excessive. Is this option the elusive.... perfect set up? ;) I ride mostly backcountry primitive trails.
 
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