Seldom. But you sometimes will. In my case, I’d say a handful of times each year – and I’d also warrant I’m in exactly the place where you’d notice it most.

As I’ve already said, 5″ seems to make more sense if you’ve already got something running 3-3.5″. Without that, I reckon 4″ is going to be just fine.

FWIW, despite having a B+ Pact I’m not planning a move to 5″.

Caveat; I weigh 12st ready to roll. Heavier riders will benefit from the added girth more than I do.

I have both a 4″ 170 and 5″ 190, both on 100mm bb’s and teh same size and brand of bike but running different wheels, otherwise itentical as near as makes no difference.

I had the 4″ first on Holey Rolling Daryls and Floaters, Nates (they come up at 3.8 I think), for winter. Running Tubed
Nice, nimble, quick on those floaters, less so on Nates. Never struggled anywhere eg beach, trail etc etc, only in snow when it wouldnt float as much as I hoped.

5″ bike on Chinese Carbon ICAN tubeless and Jumbo Jim, 4.8. Very light, nimble and floaty on snow. As quick or less than the 4″ bike. Also, a lot is in the tyre. I can believe the 5″ JJ would be skytey in mud, its just going to float through everything and not grip. Our trails here dont get muddy so I reckon it will be fine.
The wheels havve made a massibe difference, the rim is wider and tubless saved a lot of weight and was very easy to get up and running.

Another downside, in rainy conditions, the 4″ bike threw up a lot of spray. The 5″ is a fair bit worse and I got properly soaked, not being a fan of mudguards….

what rims, 5th?

I’ve got Bud and bulldozer on 65mm rims. I’m wondering about JJs, whether I should go small or big.

Really depends on where / what you’re planning on riding – you can always run skinnier tyres on a 5″ bike, but you can’t fit wider tyres to a 4″ bike. Just come back from the arctic where those of us on 5″ tyres could ride where 4″ tyres couldn’t. The whole chainstay length thing is a bit spurious in the real world, not bike journo land where like 1% differences in wheelbase are really noticeable? Same goes for 100mm vs 120mm BBs. I would suggest that 170mm rear bikes will become more limited, particularly now with plus-size and boost and that fatbikes will settle on 197mm rear. You can run a single-ring chainset like a Turbine Cinch on a 100mm threaded BB with clearance for wider tyres. The only case for really wide rims like 100mm is if your riding on sand or snow – been getting along fine with Dilly 5s on 65mm rims for general riding, but if I go back to the arctic, I’d prefer 90mm+ to reduce tyre squirm at low pressures which can make the difference between staying-on and riding or falling-off

I think this sums it up.

If you ride in the Artic in winter, then get 100mm rims and 5″ tyres. If you’re not then…………

Will 170mm hubs dissapear? No idea, I doubt it. Likewise 100mm BB’s. It’s not like fat bikes are big market anyway, so I’m not entertaining any sort of market forces based argument. Saying 5″ and 3″ bikes make 4″ bikes obsolete is following the same logic that 2.4″ tyres will cease to exist because you can now get 2.2 and 2.8″ tyres.

And you can’t fit a 5″ tyre in a Bluto anyway. You can get a Bud in, with an inner tube, when new. But tubeless makes tyres expand a bit, as does time, so a 12month old Bud run tubeless is 50/50 whether it’l fit (and certainly had no mud room). So unless RS release a new Bluto, 4″ is here to stay.

Wasn’t directly, but I’d heard the same argument made elsewhere.

Also, I’m not-not in favor of 5″ bikes, they open up other options. If you need 5″ tyres they’re a necessity, if you don’t need them they’re just 5″ tyres though.

And a 4″ tyre on a bike designed arorund 5″ tyres, is an inch lower too, but then most bikes designed for snow/sand will have taller BB’s for ground clearance too as that’s what their geometry is designed around, rather than handling. Horses for courses.

What’s the biggest tyre I can fit to my standard Fatty rims with carbon fork?

Apparently a Bud fits, not tried it personally though.

Rule of thumb on rim width is tyres equal tot he rim width and upto double, so the 80mm rims are fine for just about anything from 3.8’s to a hypothetical 6″ tyre. Narrow rims are better for handling (at 10psi), wider rims are better for float (at 3psi).

I wouldn’t assume for normal riding that narrower is better- I’m loving the minion 4.8 front and the 4.8 JJ is a way more useful tyre than the 4.0. More grip but I can run it at much lower pressures too.

Obviously I’m a nouveau fattist. And possibly my idea of normal riding isn’t normal. But I can’t see what 4.0s I’d swap to. Nate, possibly, but I can’t see that working as well as the minion or bud.

I have never ridden a fat bike. I have however been on a ride with a mate who has one, and I found the gigantic puddle splashes endlessly amusing 🙂

Bear in mind also the Bud grows a lot with pressure, put 10psi in and its very close which I think is where most people go wrong, you really don’t need more than 6psi in that monster.

Aye, absolutely this- Bud stretches massively, mine jams in the frame if I pump it up harder. Though is 10psi so outrageous? I had 5 or 6psi in mine, I forget, but I only weigh 10 stone. Someone with less elf blood than me would want more…

Minion is a nice compromise, just a shame they weren’t honest that it’s a 4.5 really, but twas ever thus with maxxis. It seems less stretchy too but, maybe that’s just because it’s new

Thing is, the only fat bike I really want is a Bucksaw. But would I regret not being able to run 5″?

I took my bike for a spin today.

The last two rides up my nearest hill* with 4.0 JJs 12:11 and 12:14

Today with fatty stripper tubeless 4.8 JJs (exactly a pound lighter than the 4.0s with tubes) 10:36… which is 12s of my best on a skinny bike when I was fitter.

The descent was even weirder. Felt like I was plodding. My skinny bike feels really fast and really sketchy. Second best time do date (of 28 runs). I was just 2s off by best time.

I’m amazed.

Shame the rear tyre shat itself at the end of the ride. I was running 6psi and it felt like I could go down to 5.

* 0.8 miles, 370′ of mixed rough and smooth cart track from flat to very steep

The day I get tired of exploding puddles with the front wheel may be the day I stop riding bikes. SPLOOOOSH!

Given I live in Cardiff regular snow is not much of a factor, and I’ve no great desire to ride over a beach. But anyway – is sand going to get into the bearings? The local soil is full of sand and even finer particles and it gets splashed all over my FS bikes every ride, and the bearings seem to hold up fine.

Having a wide enough selection of bikes to have the perfectly adapted bike for every single situation is sadly beyond my means!

I just worry that if we DID have loads of snow, or I happened upon the opportunity to ride in Scandinavia (more likely tbh) then I’d regret being on 4″. But given that last winter in Sweden I almost rode ok on 2.4″ then 4″ would probably be ok up there.

For the bearings or the rest of the frame?

Water of any kind in bearings is bad. Plus, I’d assume I’d be avoiding salty water as a general principle..?

I’m a Bud/Bud user. I prefer the big tyres for the extra cush when riding rough terrain, they allow more speed to be carried. The float is a side benefit for the occasional time my bike sees very soft terrain, but even on soft winter mud/cut up grassy surfaces they roll so much easier.

I know four people running Bud tubeless on 80m rims in a Bluto with no issues.

Soooooo – I have an ICT with Bud and Lou. Currently testing a Bluto and the Bud fits, even with a fender! It’s right tight but it works even in think mud.

For chunk and gnarr, the extra width and weight give the truck a brilliantly planted feel. I rode the boulder field on MacDui on it. It really is that good.

I also have a Fat Caad 1 and it is a different beast. Very quick and responsive. The Jumbo Jims lack the grip of the Surly tyres and pinch flat easily. Early days but I really like it……A LOT! 😀

Don’t get hung up on geometry. Just test ride and see which one you like best.

I’m running 4.8s on my first ever fatbike. I’ve never ridding anything smaller and I can’t really think why I would? I’m really not sure what I’d gain. If I wanted all out speed, I wouldn’t be on that bike anyway. My biggest issue to date is the downright terrifying floatiness when hitting a patch of mud. I’m sure that float is great on sand or snow at 2mph but at speed it’s just scary as hell! I doubt a 4″ tyre would be much different.