Yeah, I think 4″ is the sweet spot for a rear tyre, for non snow fatbikes.

That’s the thing though. We do get snow up here in the frozen North. In fact that’s often my biggest frustration at this time of year when some of my favourite routes have still got too much snow to be ridable in March (and even April some years).

roverpig – Member

The 4.6″ is funny though as there aren’t really 4.6″ tyres.

Suppose it depends on whose ruler you use, I reckon most 4.8 tyres would fit in a bike that fitted true 4.6s, but bike companies seem to work with the same rubber ruler as tyre companies tbh. Hard to know what’s a genuine measurement and what’s made up bullshit though.

4.6″?
http://www.leisurelakesbikes.com/p/19027/specialized-ground-control-fat-26in-tyre?variantId=89891

The problem with 4.6 is not the tyre, but the chainset. Typically you can get chainsets to clear 4″ or 5″. You can already run into problems trying to use some doubles up front and a full width cassette, so trying to fit 4.6 tyres you are probably going to have to use a 5″ chainset so may as well just go 5″ and have the choice of decent tyres.

Can someone offer sizing advice on a Fatty Trail please?

I’m 6’0 tall with monkey arms and a 34″ inside leg.
I can’t decide between the M (18″) or the L (20″).
I also ride an L (18.5″) Heckler which I like the fit of if that makes any difference.

6ft 2″ here 33 inside leg & mine was a large frame

5 ft 10 with 30 inside leg and my mucky thing is a medium

Trout….is that a standard ‘rear’ mud hugger on the front too…good idea…off to get the Dremel out.

I’m 6ft (and wear 33″ trousers), bought a large, but haven’t ridden it yet!

If it’s any help the dropped top tube is lower than it looks, the implied center to center is about 16.5″ IIRC.

After riding a fatty the fatty trail top tube felt like it was high enough to rest my chin on

There is that! The fatty must be about 12″?

Catching up with this thread after trying a Genesis Caribou and thinking I might prefer a more trail-oriented fat bike. You may have seen my other thread with (many) more thoughts on this.

One aspect of geometry I’ve become a bit fixated on is BB height, which I found limiting on the Caribou. Has anyone thought much about this?

Have compared a few specs and the majority seem to be in the 50-60mm BB drop range, whereas the only one I’ve seen much less than that is the Puffin. Anyone got numbers for any others?

BB height is 320 mm on my Scott Big Jon. offset is 60 mm

tbh the more I read about fat bikes and geometry the more puzzled I am

I got on mine and rode off without giving the geometry a second thought. It rides just like an XC trail bike. No calf rub no self-steering no clearance probs no q-factor issues in fact nothing weird at all 😕

I eventually opted for a 853 custom frame as nothing came close to what I wanted. It works for me but may not for others.

470mm fork with 55mm offset. In reality, the 470 works out at 485 as the design was based on a internal headset but it’s a external one I eventually went for.
68.5 HA
71.5 SA
142 headset with an additional 50mm UNDER the stem
617mm stack
429mm reach
422 – 438mm CS
60mm BB drop. I possibly should / could have gone a little higher to stop clattering things but a 26T chairing helps.

It works with 29 x 3.25 tyres and 26×5 tyres…both work out the same height, save for a couple of mm. It’s a hoot, stable enough at speed, nice and light front end, easy…VERY easy to pop the front end and super comfy with some carbon Jones Loops. Next stop is a Ti version although the short CS were a real headache for the builder. Thanks again Ben Cooper.

I’m with Sanny…

Just test ride a few and don’t get hung up on geometry.

I tried LOADS of different set ups & bikes before deciding on the numbers. They don’t make sense but boy does it work…for me.

don’t get hung up on geometry.

But there’s nothing else stopping me buying one! (OK, not quite true)

60mm BB drop. I possibly should / could have gone a little higher to stop clattering things but a 26T chairing helps.

It’s more pedal strikes that concern me. Short cranks would help though – any 165s around?

roverpig – Member
I wonder whether my desire for “trail geometry” is based on a misunderstanding.

I tend to think (as a lot of people do, I suspect) that a slacker head angle makes it easier to get down steep stuff, but I suspect this is not true. A slacker head angle is mainly, I think, about stability at speed. So, if you are happy to crawl down the steep stuff it’s irrelevant. It’s also about the bike being less sensitive to getting knocked off-line, but a huge tyre is going to do that anyway.

“Modern trail geometry” is marketing speak for slackening the head angle of a bike so that when suspension is fitted and the fork sags/gets into its working position, the bike then has the geometry of a rigid bike.

If you are not going to fit a suspension fork, you are better off getting geometry for a rigid bike. The fork is shorter and does not have to be so heavier to resist bending, and your headtube can be longer too.

Slack geometry is a PITA when climbing, and the reality is more time is spent climbing than descending. The important figure for stability at speed is generally accepted as being the trail figure, and regardless of HA used that tends to fall within a small set of numbers.

On a fatbike I’d sooner have a steep HA and a decent trail, because if you are going to take it the places only a fatbike can go, that is what is necessary to ensure your front wheel isn’t flapping around.

The other factor often overlooked is the CoG of your body on the bike. Slack geometry effectively places it further back in relation to the front wheel, which on descents feels better, but you can give yourself the same body position in relation to the front wheel on a steep HA bike simply by using a shorter stem and having a layback seatpost.

The real benefit from fat tyres is huge grip – anything that helps me keep pedalling is a bonus rather than having to get off and push. I bought my fatbike to go places a regular MTB can’t – if I want to go ragging around a trail centre, then I’d go for plus bike as fat is overkill.

epicyclo – Member

Slack geometry is a PITA when climbing

Not true, head angle plays only a small part in this. My Ragley Ti climbs better than my Scandal did, my Trailfox (65 degrees) better than either. My On One climbed better when I added a slackset and made it 2 degrees slacker.

epicyclo – Member

The other factor often overlooked is the CoG of your body on the bike. Slack geometry effectively places it further back in relation to the front wheel, which on descents feels better, but you can give yourself the same body position in relation to the front wheel on a steep HA bike simply by using a shorter stem and having a layback seatpost.

A layback seat should have absolutely no impact on your body position when descending, for obvious reasons. For that matter, the head angle and stem length has way less affect on COG-relative-to-bike than your body movement does. This all falls apart as soon as you move, which is all the time.

You can’t replicate the affects of a change in head angle with a change of stem or seatpost, because the important effects aren’t about COG-in-relation-to-wheel, which in any case isn’t a fixed point.

“Modern trail geometry” is marketing speak for slackening the head angle of a bike so that when suspension is fitted and the fork sags/gets into its working position, the bike then has the geometry of a rigid bike.

Technically not true – slack head angles were around long before suspension forks.
I’ve slackened the head angle on my (fully rigid) felt DD by 1.5 degrees and it now rides just as I like – think big tyred off road bmx. Its now a great fun bike for ragging around my local trails.

I should have made it clear my comments are about the geometry of a fatbike.

They are based on experiments I have done with variable HAs and offsets a few years ago. There are more factors to consider now, such as much wider tyres, better /stiffer axles. Hopefully I’ll be able to do more experimentation this year once I have escaped from the burden of new house DIY.

None of what I have done is likely be of much use to a racer or someone who rides on hardened trails because it is aimed at getting the best handling in the sorts of places I ride, ie deer tracks, boggy stuff, tussocked heather, lumpy rocky tracks etc, ie what you find on the side of a Highland mountain, including lots and lots of time spent climbing on loose surfaces.

Northwind – Member
“Slack geometry is a PITA when climbing”

Not true, head angle plays only a small part in this. My Ragley Ti climbs better than my Scandal did, my Trailfox (65 degrees) better than either. My On One climbed better when I added a slackset and made it 2 degrees slacker.

Climbing is a weight distribution balancing act.

There is less vertical displacement of the fork when it is turned with a steep HA, so when you’re climbing the tyre is less likely to leave lose contact with the ground when you’re sawing hard at the handlebars (unless you bias your weight more to the front with a slacker HA, but then you are more likely to lose rear traction. A longer wheelbase lessens the effect).

When you slackened your On One, did you use a different offset on your fork? Otherwise you increased your trail by about 15mm.

Northwind – Member
A layback seat should have absolutely no impact on your body position when descending, for obvious reasons. For that matter, the head angle and stem length has way less affect on COG-relative-to-bike than your body movement does. This all falls apart as soon as you move, which is all the time.

You can’t replicate the affects of a change in head angle with a change of stem or seatpost, because the important effects aren’t about COG-in-relation-to-wheel, which in any case isn’t a fixed point.

I agree it all changes when you get out of the saddle. I was referring to a seated position because the dynamic of a mobile body compensates for all sorts of geometry.

monkeyboyjc – Member
“”Modern trail geometry” is marketing speak for slackening the head angle of a bike so that when suspension is fitted and the fork sags/gets into its working position, the bike then has the geometry of a rigid bike.”
Technically not true – slack head angles were around long before suspension forks.
I’ve slackened the head angle on my (fully rigid) felt DD by 1.5 degrees and it now rides just as I like –

Slack angles come and go in bike fashion. There’s many reasons for that. In the early days (1890s to 1910s) this gave a long fork which helped to absorb road vibration. It also brought the steering close to the rider, but they also had long wheelbases.

If the offset on your fork hasn’t changed, then what you have effectively done is change your trail. It appears that you prefer more trail than standard.

One of the problems with discussing bike handling is one of the major factors cannot be measured. We are all different weights and body distributions, and on the bike, especially a MTB, our bodies are dynamic. In the suspension movements of a long travel dual suspension bike, the actual geometry ends up all over the place, but the rider handles it. Sufficient speed combined with skill will take just about any combination of geometry over anything.

A fatbike is likely to spend a lot of its time going very slow.

I went for the medium eventually, and glad I did.
The bigger circumference of the wheels makes it feel bigger than it is.
It’s taken a few outings to get used to it, but it now feels as chuckable and capable on the downs as the bouncy bike.

Cracking photo!

Is that your grader*?

* or other item of heavy plant

I’m liking the mondraker panzer with forward geometry

Right, following my Surly ICT demo, I’ve now modified my fatbike wish list. It could be summarised as “just like an ICT, but lighter”. Specifically, what I’m after is:

1. Must come with 4.8″ tyres or be able to run a Bub/Lou combo
2. 68 degree head angle
3. 450mm chainstays
4. Reach at least 440mm in large
5. Rigid but option to run a bluto (so 150mm front wheel axle)
6. Budget around £2K for a full bike.

So far I’m thinking either:

1. Just buy the damn ICT and stop worrying about weight
2. Canyon Dude 9.0 Unlimited : 68.5 HA, 456 CS and a reach of 455
That’s proper long (as long as my Smuggler). Too long maybe?
3. Scott Big Jon : 69 HA, 465 CS, reach 432
A bit short and steep. Also not keen on the grey frame festooned with neon stickers.

Anything else?

Buy something, anything, second hand. Ride it for a while. Decide how important those dimensions are.

not keen on the grey frame festooned with neon stickers

🙁

IMHO – Get the ICT, as complete package it just works fantastically (except I went 1×11 and with a shorter stem).

I got one after 2years on a Bluto’d Mukluk, and yes its heavier, but noticably more capable as a do everything bike.

Sorry rocketman 🙂 It’s just a personal preference thing though. I actually think it looks great in pictures, I just have some deep seated irrational objection to grey mountain bike frames. Not sure why. I don’t mind grey road bike frames. Nowt as queer as folk eh?

IMHO – Get the ICT, as complete package it just works fantastically (except I went 1×11 and with a shorter stem).

I got one after 2years on a Bluto’d Mukluk, and yes its heavier, but noticably more capable as a do everything bike.

There is a lot to be said for that approach. I tested it. I loved it, but now I’m trying to pick it apart and decide whether maybe I’d like something lighter even more. You can’t just buy a lighter ICT though. Other things have to change too. Maybe not by much, but sometimes small changes matter. Weight just seems like such a fundamental thing on a bike though.

As with any bike the build plays as much a part as the frame, and the stock ICT build is heavier than most as well as the frame, but that’s because it has full 100mm rims, big steel forks and quality tyres so looks a lot heavier than Alu frames with carbon forks and Jims.

I also moved from a Mukluk with Bluto and the only difference in the build is frame and 5″ tyres (and wider rear hub and crank axle). The weight is not that much more but the difference in ride is huge! Been doing laps of a local DH trail and its so much fun.

Weight just seems like such a fundamental thing on a bike though.

I would agree esp where fat bikes are concerned

ime a light fat bike can be quite a useful and versatile tool, much more so than the stereotypical sand/snow/swamp animal

As you know there’s only so much you can do with a leaden frame before it becomes a clothes horse of expensive bits. FWIW Big Jon with the wheels off is surprisingly light and weighs in at about 30 lbs with only a few changes

As with any bike the build plays as much a part as the frame

Yes, I’ve noticed that a lot of the lighter fatbikes are JJ on 80mm rims (often 4″ tyres too). I’m sure the Bud/Lou combo played a big part in my enjoyment of the ICT, especially tramping through swamps and riding down steep muddy sections. Stick a Bud/Lou combo on 100mm rims on some of the lighter bikes (assuming it will fit) them maybe the weight difference isn’t all that significant. I’ve been enjoying my steel Solaris for a while and prefer it to the (much lighter) Alu FF29 I had before, although I’m sure that’s more to do with geometry than anything else. Maybe that’s the point, weight matters, but not as much as geometry.

I based my own custom ti frame on ICT geometry, adjusted for a shorter, rigid fork – I’ve ridden it fully laden in the Arctic as well as racing and trail centre stuff – carbon fork and 65mm rims, 1×10 drivetrain and tubeless 4″ tyres given a 26lb summer trail shredder or a 30lb, racked-up winter expedition bike with 5″ studded tyres.

Just buy the ICT 😉 8) you know you want to!!

In my experience the quality of the schwalbe JJ light years ahead of the Surly offerings, caveat, once the mud has mostly disappeared. I’ve found it hard to get any of my Surly tyres mounted round and square on the rim, JJ’S on the other hand are a pice of cake!

Looking forward to trying out the juggernaught 120 tpi pros in a few weeks 🙂

Well I think one thing we can safely say about fatbikes is that there is no consensus! Some say forget about weight on a fatbike, including some who have switched from a lighter to a heavier bike and prefer it. Some say weight always matters. Some say the Bud/Lou tyres are great, others prefer JJs. Some say 4″ is plenty, others say 5″ is better. Some swear by a Bluto others claim rigid is the way to go.

I was going to say that the one constant was that people loved whatever fatbike they had, but there seems to be a worrying trend for folk to stick 27.5+ wheels in their fatbikes now and rave about them too. Since I’m contemplating replacing my 27.5+ with a “proper” fatike, the last thing I want is to end up back where I started ! OK, I know the plus-sized thing is only really supposed to be a summer option and you go back to full-fat in the winter, but it still makes me wonder whether I should just stick with my chubby Solaris until winter comes around again.

The only word I can offer on any of this is I genuinely regret selling my on one fatty

Hay rover pretty sure you bought your ff29 of me on here

No, pretty sure I bought the FF29 frame new. I might have sold it to you though 🙂

OK, I know the plus-sized thing is only really supposed to be a summer option and you go back to full-fat in the winter, but it still makes me wonder whether I should just stick with my chubby Solaris until winter comes around again.

This. Spend the next six months trying out more fatbikes so you have a more rounded opinion of them.

I was going to say that the one constant was that people loved whatever fatbike they had, but there seems to be a worrying trend for folk to stick 27.5+ wheels in their fatbikes now and rave about them too. Since I’m contemplating replacing my 27.5+ with a “proper” fatike

Just to add confusion 27+ is the same diameter as a 4″ tyre, so you should really use 29+ if you have a bike designed for a 5″ tyre. Ok so you can get away with either as its just a change in BB height, but if the BB is already low or you have long cranks its something to be aware of.

I have 180mm cranks on my XXL ICT so 4″ tyres gave me a little pedal strike, id planned to run 27+ for summer but going 29+ now.