djb

recently got suckered into getting a fatbike, figured what the heck I'd try it out and got a used one, so far its a lot of fun goofing around on dirt and the first bit of snow we've had.
Got some better tires and at the same time, bought a couple of shrader downhill 3" tubes, as I had read of folks using these in 4" tires without problems. So am trying them out and so far have ridden in dirt and a bit on snow, in temps down to about -6c and pressures from 10 psi to 7.5 give or take a bit.

anyone else done this?
In changing tires and tubes, I've saved a bit over a kilo / 2.2 lbs over the two wheels, although I'm very aware that saving a few hundred grams off a full size fat tube that is made for 3.8-4.8 really isn't a big deal, certainly not if having to deal with a tube problem in the cold.
The tires were a no brainer, nicer tires and better tread for snow anyway, the stock tires are a cheap Kenda with very small and tight tread pattern, and the downhill tubes are supposed to be thicker rubber with a reinforced area near the valve, and a reasonable price, so I figured I'd experiment.

I can always put the original tubes back in, rated up to 4", and I also have a full size fat tube that goes to 4.8" , so I'm at least covered in that I have larger spares.
thoughts from those of you who have been around fatbikes for a while now?
I have bought a new 0-15psi gauge, so will be able to keep track of pressures reasonably accurately on both of our bikes.
thanks

Hypno Toad

I've been running 2.8" tubes in my 4" tires for years, works great.

Last time I was at the LBS for a tube, the let me know Surly now has a light fatbike tube option too https://www.modernbike.com/product-2126212346

djb

thanks H Toad, being new to this whole fat world, its good to hear from someone like you that its been working well. In the touring world and general biking, where I ride 28s, 32, 35, 45, 50, 55mm tires, I've sometimes used smaller tubes also and not had any real problems. Useful for. touring where smaller tubes take up less volume/weight for when travelling, which is always appreciated.
Over the decades, I seem to average about a flat per season, so what I'm doing works out ok.

found where I jotted down fatbike tube weights....stock Kenda 3.5-4" schrader 500g, Schwalbe 3.5-4.8" presta 405g, Schwalbe downhill 2.1-3" shrader 291g.
The Surly lightweight one you mention is 310g
I have to say, this whole fat thing is a real gas, I've been riding in Montreal winters for a bunch of years, so have a fair amount of snow riding experience on knobby mtb tires, 2.1 or 2.5" playing with pressures for best traction, and also on 1.75 studded winters.

have you had any issues with your 2.8 tubes being loosey goosey when running low pressures?
How low have you reliably run to?
I'm a lightweight, 135, 140 tops, so have always run lower pressures anyway, and ride light.

both my wifes and my fatbike rims are not tubeless ready, plus I don't really have an urge or need for tubeless in the rest of my riding life, so that's not on the cards for right now.

thanks again, am looking forward to having fun on trails this winter. (and not be covered in salty crap like on my daily commute--which reminds me, I need to go wash my bike, just got home)
cheers

sloppy12

I dont see much flatting with fat bike tires. I have personally came back with thorns and nails in a fat bike tire and still has air a week later just kinda noticed when topping off.

djb

I'm curious to see how with the smaller tubes at low pressures, if the tubes will move around a bit too much and angle and stress the valve area.
thats more what I meant by "loosey goosey"
guess I'll find out in the upcoming weeks

sloppy12

I think you should be fine. I tried a 26"x 2.3'" tube at one point and it seemed fine the stem did not shift. I didnt do any huge rides on that set up it was just to see how small I could go with a tube...

djb

ya, I had a spare tube rated to 2.6 that I was carrying as a spare on rides, but when I saw the 3" ones classified as downhill, I figured they would be tougher/thicker to begin with, and a bit larger anyway.
The main thing for me is that in reading fatbike posts here, I saw that hypnotoad has been riding/racing his fatbike for years, so I feel comfortable taking his opinion as reliable, and your experience just confirms that people do this and it works.

thanks again

prj71

When I used to use tubes in my fat bike, I would use Q-Tubes Superlight 26 x 2.4 - 2.7. Never had a problem.

What wheels and tires you have? You may even consider going tubeless

djb

4 inch tires 120 tpi so should be fairly supple at low pressures, rims are non tubeless compatible though.

djb

Been playing with low pressures, 7, 6, 5.5 psi with these smaller tubes and so far is been ok. Touch wood.
I have noticed that in doing the "pushing thumb firmly down" tire flex indicator, my tires go down more than my wife's tires at same pressures.
Both are 120 tpi , and while I realize that different tires have different construction and overall flexibility, main carcass and sidewalls, I do wonder if it's because my tubes are physically a lot smaller.
Both are 4inch tires, but mine are jumbo Jim's, known for lightness and rolling fast, so a more supple tire overall.

I can say that on loose snow and no tracks, I like that my admittedly narrow tires, (already narrower due to my narrow rims) have more give in loose stuff.

will get back here as I ride more and more in varying conditions and temps. Have been down to about -15c so far, 5f

Hypno Toad

Sorry for the slow reply, my December schedule is a nightmare, I'm always happy to turn the calendar over to January ... HAPPY NEW YEAR!

Here are the tubes (pic below) I've been using for the last 5 years, but going forward, I'll buy the Surly tubes. I rode my Pugsley 1,800 miles in 2021 with one flat ... and it was a slow leak that allowed me to ride 20ish miles home.

I always use tubes too, my old rims are not tubeless ready. I use these 2.4/2.75 tubes summer and winter without any issue. I'll run them down to 4 psi when riding fresh snow and they work great. Tires will make a difference on the bike getting loosey goosey at low pressures. My 45NRTH Dillingers are great at low pressure, but my Panaracer Fat B Nimble tires are awful at lower pressures.

I'll always remember a ride when I was blazing trail across a lake with the Dillingers, I dropped the pressure on my tires way down. On the return trip, I opted for a plowed trail, I didn't have a pump so I rode the low pressure without issue, including a fast downhill with a turn in the middle, the bike handled great. When I got home, I found I was running 4 psi!

djb

no problem at all, and a Happy New Year to you and the others here also.
tks for the tube shot, and frankly, nearly 3000kms without issues basically is proof it works. Thats a awful lot of mileage, going from how so far our riding is always laughably short distances in actual kms, but high up there in the fun factor (all that matters really)
Interesting on you getting down to 4psi and it working alright, although I get ya on the "specific tire" thing. The Jumbo Jims aren't particularly tready or knobby, and I'm still getting to grips with traction feel, so I really have no reference point yet as to if they are good at low pressures or reasonable. Probably reasonable, and on some quickish downhill turns with a bit of trail braking at both ends, I've had the front let go but it came back fairly well (no crashes...yet) but I am completely aware that there is no black and white answer--depends on a whole slew of factors.
Ive been riding with a large seatbag that can fit my pump, spare tube and all kinds of stuff like wallet, multitool, extra outer mitts, puffy jacket.....but I'm still only often letting air out during rides visually to get more "wrinkle" and not really paying that much attention to playing too much with pressures---really because riding with friends, its just so much fun, so dont want to stop so much--and generally Ive been getting the tires to work pretty good, so thats at least working.

thanks again for input, the weather is up and down lately like a toilet seat, so I expect that we'll be riding in a big range of temps and surfaces. Started out for a ride by car today but bailed cuz it started raining and just got heavier and heavier, so it was a bust. Will be hard again in a day (lows of -18c tomorrow night) so a good chance of ice stuff , crusty, etc going on for the next bunch of days.
Anyway, a lot of fun like I keep saying, so its all good.

Hypno Toad

OH That crusty snow ... we had a fresh snow with a hard crust of frozen ice topping, it so much work to ride through and getting into a track is dangerously difficult to handle!

For millage, I'm a DAMn fool! in 2021 I trained up for and rode The Day Across Minnesota (The DAMn) on my drop-bar Pugsley https://www.bikeforums.net/22195497-post28.html And to the point of this thread, I rode with 2.4/2.75 tubes.

djb

Eff me, 390 klicks, no wonder you had to rack up the mileage. Yup, a damn fool and completely beyond my comprehension, but pretty effing cool.
I had seen photos of your dropbar pug here in the fat bike section, I have a similar setup on my dropbar troll with Gevenalles, and love that bike to bits. Have spent months touring on that bike and the Gevenalles work great.

re crust, we got out finally but were on actually trails that lots of people had been on, so crust only off line if you went wide and then it was weird and noisy.

djb